Ubuntu Manpage: This documentation describes BackupPC version 4.4.0, released on 20 Jun 2020.

Provided by: backuppc_4.4.0-5ubuntu2_amd64

BackupPC Introduction

This documentation describes BackupPC version 4.4.0, released on 20 Jun 2020.

Overview
BackupPC is a high-performance, enterprise-grade system for backing up Unix, Linux, WinXX,
and MacOSX PCs, desktops and laptops to a server's disk. BackupPC is highly configurable
and easy to install and maintain.

Given the ever decreasing cost of disks and raid systems, it is now practical and cost
effective to backup a large number of machines onto a server's local disk or network
storage. For some sites this might be the complete backup solution. For other sites
additional permanent archives could be created by periodically backing up the server to
tape.

Features include:

• A clever pooling scheme minimizes disk storage and disk I/O. Identical files across
multiple backups of the same or different PC are stored only once, resulting in
substantial savings in disk storage and disk writes.

• Compression provides additional reductions in storage, depending on the type of data
being backed up. The CPU impact of compression is low since only new files (those not
already in the pool) need to be compressed.

• A powerful http/cgi user interface allows administrators to view the current status,
edit configuration, add/delete hosts, view log files, and allows users to initiate and
cancel backups and browse and restore files from backups.

• The http/cgi user interface has internationalization (i18n) support, currently
providing English, French, German, Spanish, Italian, Dutch, Polish, Portuguese-
Brazilian, Chinese, Polish, Czech, Japanese, Ukrainian, and Russian.

• No client-side software is needed. On WinXX the standard smb protocol is used to
extract backup data. On linux, unix or MacOSX clients, rsync, tar (over ssh/rsh/nfs)
or ftp is used to extract backup data. Alternatively, rsync can also be used on WinXX
(using cygwin), since rsync provides for efficient transfers and allows incremental
backups to detect almost all changes.

• Flexible restore options. Single files can be downloaded from any backup directly
from the CGI interface. Zip or Tar archives for selected files or directories from
any backup can also be downloaded from the CGI interface. Finally, direct restore to
the client machine (using smb or tar) for selected files or directories is also
supported from the CGI interface.

• BackupPC supports mobile environments where laptops are only intermittently connected
to the network and have dynamic IP addresses (DHCP). Configuration settings allow
machines connected via slower WAN connections (eg: dial up, DSL, cable) to not be
backed up, even if they use the same fixed or dynamic IP address as when they are
connected directly to the LAN.

• Flexible configuration parameters allow multiple backups to be performed in parallel,
specification of which shares to backup, which directories to backup or not backup,
various schedules for full and incremental backups, schedules for email reminders to
users and so on. Configuration parameters can be set system-wide or also on a per-PC
basis.

• Users are sent periodic email reminders if their PC has not recently been backed up.
Email content, timing and policies are configurable.

• BackupPC is Open Source software hosted by GitHub.

BackupPC 4.0
This is the first release of 4.0, which is a significant rewrite of BackupPC. This
section provides a short overview of the changes and features in 4.0.

Here's a short summary of what has changed in V4:

• No use of hardlinks (except temporarily to do atomic renames). Reference counting is
handled at the application level in a batch manner (hardlinks will still remain for
any legacy V3 backups).

• Backups are stored as "reverse deltas" - the most recent backup is always filled and
older backups are reconstituted by merging all the deltas starting with the nearest
future filled backup and working backwards.

This is the opposite of V3 where incrementals are stored as "forward deltas" to a
prior backup (typically the last full backup or prior lower-level incremental backup,
or the last full in the case of rsync).

• Since the most recent backup is filled, viewing/restoring that backup (which is the
most common backup used) doesn't require merging any deltas from other backups.

• The concepts of incr/full backups and unfilled/filled storage are decoupled. The most
recent backup is always filled. By default, for the remaining backups, full backups
are filled and incremental backups are unfilled, but that is configurable.

• Uses full-file MD5 digests, which are stored in the directory attrib files. Each
backup directory only contains an empty attrib file whose name includes its own MD5
digest, which is used to look up the attrib file's contents in the pool. In turn,
that file contains the metadata for every file in that directory, including each
files's MD5 digest.

• The Pool layout still supports chains to handle md5 collisions. While collisions can
be constructed and are now well-known, they are highly unlikely in the wild. Pool
files are never renamed or moved, unlike V3.

• Any backup can be deleted (deltas are merged into next older backup if it is not
filled).

• The reverse deltas allow "infinite incrementals" - no need for a full backup if you
are willing to trade speed for the risk that a file change will not be detected if the
metadata (eg, mtime or size) doesn't change.

• An rsync "full" backup now uses --checksum (instead of --ignore-times), which is much
more efficient on the server side - the server just needs to check the full-file
checksum computed by the client, together with the mtime, nlinks, size attributes, to
see if the file has changed. If you want a more conservative approach, you can change
it back to --ignore-times, which requires the server to send block checksums to the
client.

• The use of rsync --checksum allows BackupPC to guess a potential match anywhere in the
pool, even on a first-time backup. In that case, the usual rsync block checksums are
still exchanged to make sure the complete file is identical.

• Uses a modified rsync called rsync_bpc (currently based on rsync-3.0.9) on the server
side (in place of File::RsyncP), with a C code interface to the BackupPC storage. So
the whole data path for rsync is now in compiled C code, which is much faster than
perl.

• Due to the use of rsync-3.X, acls and xattrs are supported, and many other useful
options (but not all) are supported. Rsync protocol 30 supports the efficient
incremental file list, which significantly improves memory usage and startup time. It
also supports MD5 full-file checksums, which match BackupPC's new digest. That allows
a full-file digest to be checked as easily as an mtime on the server side.

• Significant portions of the BackupPC code are now compiled C code in a new module
called BackupPC::XS that is dynamically linked to perl.

Here is a more detailed discussion:

• Completely new backup storage. No hardlinks! Backups are stored as reverse deltas,
with the most recent backup always filled. Prior backup "n" contains the changes
relative to prior backup "n+1".

• Since every backup is based on the last filled backup, the concept of incremental
levels is removed.

• Example: let's assume backup #4 is the most recent, and therefore filled, and backups
#0..3 are not filled.

Backups #0..3 store just the necessary reverse changes needed to reconstruct those
backups, relative to the next backup.

- To view/restore backup #4, all the information is stored in backup #4.
- To view/restore backup #3, backup #4 (the filled one), is merged with the deltas in #3.
- To view/restore backup #2, backup #4 (the filled one), is merged with the deltas in #3 and #2
- etc.

When a new backup is started (#5), we begin by renaming backup #4 to #5. At that
instant, backup #4 storage is now empty (which means backups #4 and #5 are currently
identical). As the backup runs, changes are made to #5 with the changed/new files in
place, and the opposite changes are added to backup #4, to keep the "view" of backup
#4 unchanged.

After the backup is done, #5 is now the filled version of the latest backup, and #4
contains the changes necessary to turn #5 back into the state when backup #4 was done.
If there are no changes detected in the new backup, the storage tree for #4 will be
empty. If just one file changed, the new file will be below #5, and the prior file
will be below #4 (well, technically not quite true, since files aren't stored below
the backup trees; more correctly, the attrib file in #5 will point to the new pool
file, and the attrib file in #4 will point to the old pool file).

• The concepts of incr/full backups and unfilled/filled storage are now decoupled. The
most recent backup is always filled (whether or not the last backup was a full or
incr). Certain older backups can be filled for convenience to make restoring old
backups faster (because fewer backups need to be merged), and are used to specify
expiry schedules.

• When a backup starts, there are several different cases that determine how the backups
are stored and whether prior deltas are stored:

1. No existing backups: create a new backup #0 and do a full backup in place (ie: no
prior deltas are stored).

2. V3 backups exist, but no V4 backups. The last V3 backup is duplicated into V4
format, and a full backup is done in place (ie: no prior deltas are stored).

3. Last V4 backup is a full, or more than $Conf{FillCycle} since last filled backup.
The last backup is duplicated to create a new filled backup, and the new backup is
done in place (ie: no prior deltas are stored).

4. There are V4 backups and it's less than $Conf{FillCycle} since last one is filled.
Renumber the last backup to #n+1, and put the reverse deltas in initially empty
backup tree #n.

5. CompressLevel has toggled on/off between backups. This isn't well tested and it's
very hard to support efficiently. We treat this as a brand new (empty) backup in
place, that is therefore filled. That way we won't need to merge between backups
with compress on/off.

6. Last backup was a V4 partial. If prior V4 backup is filled (and not partial),
then just do another in-place backup. Otherwise, treat as case 4. When complete
(whether successful or another partial), delete the prior deltas in #n, which
merges the cumulative changes into #n-1.

• The treatment of a "Partial" backup has changed. Unlike in V3 where partials are
removed prior to the next backup, in V4 partials are kept and are used as the starting
point for the next backup. See case 6 above. If the new backup fails, if no files
have been backed up, the empty backup #n is removed.

• Backups are stored as mangled directory trees, but each directory only contains an
"attrib" file. The attrib file is zero-length, and its name includes the MD5 digest
so the contents can be looked up in the pool.

The attrib contents in the pool contains the directory contents: for each file, that
means the metadata, xattrs and the MD5 digest of the file contents.

• A modified rsync called rsync_bpc, based on rsync 3.0.9, is used on the server side,
with a C code layer that emulates all the file-system OS calls to be compatible with
the BackupPC store. That means for rsync, the data path is now fully in compiled C,
which should mean a significant speedup. It also means many (but not all) of the
rsync options are supported natively.

• Significant parts of the BackupPC storage and pooling code have been written in C (the
same code is used in the server rsync_bpc). BackupPC::FileZIO, BackupPC::PoolWrite,
BackupPC::Attrib, BackupPC::AttribCache and BackupPC::PoolRefCnt (reference counting
and storage) are all replaced with BackupPC::XS, a C-code perl extension.

• Extended attributes (xattr) are supported. Rsync is configured to "store acls using
xattr", meaning both acls and xattrs are supported.

• infinite incrementals with rsync are supported. The most recent backup is always
filled, so an incremental will still leave the most recent backup filled.

• any V4 backup can be deleted - dependencies are merged into the next older backup if
it isn't already filled.

• file digests are full-file MD5. Collisions are much more unlikely than V3, but still
possible. Duplicates are implemented with an extension to the 16 byte MD5 digest (ie:
16 bytes for plain file, 17 bytes for next 255 duplicates etc).

• V4 pool files are stored in a new hierarchy, two levels deep, with 7 bits at each
level (ie: 128 directories at top-level, and each with 128 directories at next level).

• V4 pool files are never moved or renamed.

• Inodes for hardlinked files are stored in each backup tree. This makes backing up
hardlinks accurate, compared to V3, and provides for consistent inode numbering across
backups.

• zero-sized files or empty attribute files don't get written or pooled.

• the elimination of hardlinks means that reference counting has to be maintained by the
BackupPC code. This is one of the riskiest area in terms of development and testing.
Reference counts are maintained per-backup, per-host, and for the whole pool.

Each operation that changes reference counts (eg: doing a new backup, deleting a
backup, or duplicating (filling) a backup) creates one or more poolRefDelta files in
that client's backup directory (ie: TopDir/pc/HOST/NNN). These files are lists of MD5
digests, and corresponding counts deltas.

Each night, BackupPC_nightly runs BackupPC_refCountUpdate, which, for each host,
updates the per-host reference count database with the new deltas. It then combines
all the per-host reference count files to create the global pool reference count
database.

BackupPC_refCountUpdate can run concurrently with backups. If you still have V3
backups and pool, BackupPC_nightly still needs to run and check for old V3 pool files
that can be deleted. But since there are no new V3 backups happening,
BackupPC_nightly can run concurrently with backups.

• There is a new utility BackupPC_fsck that can check/fix the per-host and global
reference counts. The per-host reference count database is verified by parsing all
the attrib files in each backup tree. The global reference count database is verified
by combing all the per-host reference count databases and comparing them.

BackupPC_fsck cannot run when BackupPC is.

• When BackupPC_refCountUpdate updates the overall reference counts, it removes pool
files that have a reference count of zero. To avoid race conditions, it uses a two-
phase process. It first flags files that have zero reference counts using one of the
file attributes. The next time it runs (typically 24 hours later), any flagged files
that still have zero reference count are then removed. The rest of the code knows not
to use flagged pool files to avoid race conditions.

• Progress indication: a simple status that shows the number of files processed so far.
It's hard to convert that to a percentage, since the total isn't known until the end
of the backup. But knowing the number of files is quite helpful, since you can get an
idea of the expected total based on the prior backups, or knowing what configuration
you have changed (ie: adding a large new tree).

• BackupPC_link is removed since it is no longer used.

• Since files are no longer stored in backup trees, browsing the backup trees is even
harder than V3 (where you just had to deal with mangling). A new utility BackupPC_ls
acts like "ls -l", showing accurate directory listings of files, together with the MD5
digests.

BackupPC_ls can be given either an explicit hostname, number, and unmangled path, or
can be given the full (mangled) path, which makes it easier to use directory
completion. It should be possible to configure tcsh and bash, together with some new
hooks in BackupPC_ls, to give a more natural file/directory completion.

BackupPC_zcat also can take just the MD5 digest (which you can paste from
BackupPC_ls). Currently BackupPC_zcat doesn't support the tree parsing that
BackupPC_ls does (it can only zcat actual files), but that should be easy to rectify.

• Configuration for expiry: since full/incr are decoupled from filled/unfilled, expiry
is a bit trickier.

The convention for expiry parameters is "FullKeepPeriod/FullKeepCnt" etc refer to
Filled backups, and "IncrKeepPeriod/IncrKeepCnt" refer to Unfilled backups.

• V3 migration: nothing specific is needed. V4 can browse/view/restore V3 backups.
When you install V4, no changes are made to any V3 backups. If you are upgrading from
V3, be sure to set $Conf{PoolV3Enabled} to 1 so the old V3 pool is searched for
matching files.

• When you install V4, it will notice that the V3 pool exists. Running configure.pl
should set $Conf{PoolV3Enabled} to 1 in that case, but you should be sure to check
that.

• When a V4 backup is first done, BackupPC_backupDuplicate is run to duplicate the
most recent V3 backup to create a new V4 backup. A "filled" view of the most
recent V3 backup is used to create a "filled" V4 backup tree.

This step could be time consuming, since every file needs to be read (as a V3
file) and written as a V4 file. However, the V4 pooling code knows about the V3
pool, so it will move the V3 pool file into the V4 pool. So this duplication
process doesn't burn a lot of pool storage space, but every file still needs to be
read (to compute the MD5 digest) and "written" (really just matching/linking).

• Expiry: all the V3 + V4 backups are considered on a combined basis for expiry
checking.

• On a clean new V4 install, the steps of computing and checking V3 digests is
eliminated.

• Downgrading V4->V3: Not tested and not recommended. In theory you can remove any
new V4 backups, remove the V4 pool itself, and you should be able to re-install V3
and still have access to your original full working V3 store (except for any V3
backups that V4 might have routinely removed based on normal backup expiry
configuration).

However, any V3 pool files moved to V4 will no longer be in the V3 pool. So
subsequent V3 backups will burn more storage as files get re-added to the old V3
pool.

Hopefully downgrading isn't necessary...

• Optimizations: the C code implementation should give a significant performance
advantage, as well as the more flexible.

Potential V4 optimizations that are planned, but not yet implemented, include:

• rsync-bpc doesn't support checksum caching.

• rsync-bpc with --ignore-times actually reads each unchanged file three times, and
writes it once (normal rsync reads twice and writes once; the extra one is due to
compression). Some careful optimization can eliminate two reads and the write.
The final read can be eliminated with checksum caching.

• BackupPC_refCountUpdate, BackupPC_fsck, BackupPC_backupDuplicate,
BackupPC_backupDelete are all single-threaded.

Backup basics
Full Backup
A full backup is a complete backup of a share. BackupPC can be configured to do a full
backup at a regular interval (typically weekly). BackupPC can be configured to keep a
certain number of full backups. Exponential expiry is also supported, allowing full
backups with various vintages to be kept (for example, a settable number of most
recent weekly fulls, plus a settable number of older fulls that are 2, 4, 8, or 16
weeks apart).

Incremental Backup
An incremental backup is a backup of files that have changed since the last successful
backup.

Rsync is the best option for BackupPC. Any files whose attributes have changed (ie:
uid, gid, mtime, modes, size) since the last full are backed up. Deleted, new files
and renamed files are detected by rsync incrementals.

For SMB and tar, BackupPC uses the modification time (mtime) to determine which files
have changed since the last backup. That means SMB and tar incrementals are not able
to detect deleted files, renamed files or new files whose modification time is prior
to the last lower-level backup.

BackupPC can also be configured to keep a certain number of incremental backups, and
to keep a smaller number of very old incremental backups.

BackupPC "fills-in" incremental backups when browsing or restoring, based on the
levels of each backup, giving every backup a "full" appearance. This makes browsing
and restoring backups much easier: you can restore from any one backup independent of
whether it was an incremental or full.

Partial Backup
When a full or incremental backup fails or is canceled, the most recent backup is
labeled "partial". Prior to V4, that backup was incomplete, and would be deleted when
the next backup completed.

In V4 a partial backup denotes that the last backup is incomplete. However, since V4
does backup updating in place, it represents the best and latest backup. A partial
backup can be browsed or used to restore files just like a successful full or
incremental backup. And it will be used as the starting point for the next backup
attempt.

Identical Files
BackupPC pools identical files. By "identical files" we mean files with identical
contents, not necessary the same permissions, ownership or modification time. Two
files might have different permissions, ownership, or modification time but will still
be pooled whenever the contents are identical. This is possible since BackupPC stores
the file metadata (permissions, ownership, and modification time) separately from the
file contents.

Prior to V4, identical files were stored using hardlinks. In V4+, hardlinks are
eliminated (except for temporary atomic renames), and reference counting is done at
the application level.

Backup Policy
Based on your site's requirements you need to decide what your backup policy is.
BackupPC is not designed to provide exact re-imaging of failed disks. See "Some
Limitations" for more information. However, with rsync and tar transports for
linux/unix clients, plus full support for special file types, extended attributes etc,
likely means an exact image of a linux/unix file system can be made.

BackupPC saves backups onto disk. Because of pooling you can relatively economically
keep several weeks or months of old backups.

At some sites the disk-based backup will be adequate, without a secondary offsite
cloud, disk or tape backup. This system is robust to any single failure: if a client
disk fails or loses files, the BackupPC server can be used to restore files. If the
server disk fails, BackupPC can be restarted on a fresh file system, and create new
backups from the clients. The chance of the server disk failing can be made very small
by spending more money on increasingly better RAID systems. However, there is still
the risk of catastrophic events like fires or earthquakes that can destroy both the
BackupPC server and the clients it is backing up if they are physically nearby.

Some sites might choose to do periodic backups to tape or cd/dvd. This backup can be
done perhaps weekly using the archive function of BackupPC.

Other users have reported success with removable disks to rotate the BackupPC data
drives, or using rsync to mirror the BackupPC data pool offsite.

In V4, since hardlinks are not used permanently, duplicating a V4 pool is much easier,
allowing remote copying of the pool.

Resources
BackupPC home page
The BackupPC project page is at:

https://backuppc.github.io/backuppc

This page has links to the current documentation, github project source and general
information.

Github
BackupPC development is hosted on github:

https://github.com/backuppc

Releases for BackupPC and the required packages BackupPC-XS and rsync-bpc are
available at:

https://github.com/backuppc/backuppc/releases
https://github.com/backuppc/backuppc-xs/releases
https://github.com/backuppc/rsync-bpc/releases

BackupPC Wiki
BackupPC has a Wiki at <https://github.com/backuppc/backuppc/wiki>. Everyone is
encouraged to contribute to the Wiki. Anyone with a Github account can edit the Wiki.

Mailing lists
Three BackupPC mailing lists exist for announcements (backuppc-announce), developers
(backuppc-devel), and a general user list for support, asking questions or any other
topic relevant to BackupPC (backuppc-users).

The lists are archived on SourceForge:

https://sourceforge.net/p/backuppc/mailman/backuppc-users/

You can subscribe to these lists by visiting:

http://lists.sourceforge.net/lists/listinfo/backuppc-announce
http://lists.sourceforge.net/lists/listinfo/backuppc-users
http://lists.sourceforge.net/lists/listinfo/backuppc-devel

The backuppc-announce list is moderated and is used only for important announcements
(eg: new versions). It is low traffic. You only need to subscribe to one of
backuppc-announce and backuppc-users: backuppc-users also receives any messages on
backuppc-announce.

The backuppc-devel list is only for developers who are working on BackupPC. Do not
post questions or support requests there. But detailed technical discussions should
happen on this list.

To post a message to the backuppc-users list, send an email to

backuppc-users@lists.sourceforge.net

Do not send subscription requests to this address!

Other Programs of Interest
If you want to mirror linux or unix files or directories to a remote server you should
use rsync, <http://rsync.samba.org>. BackupPC uses rsync as a transport mechanism; if
you are already an rsync user you can think of BackupPC as adding efficient storage
(compression and pooling) and a convenient user interface to rsync.

Two popular open source packages that do tape backup are Amanda
(<http://www.amanda.org>) and Bacula (<http://www.bacula.org>). These packages can be
used as complete solutions, or also as back ends to BackupPC to backup the BackupPC
server data to tape.

Avery Pennarun's bup (<https://github.com/bup/bup>) uses the git packfile format to do
efficient incrementals and deduplication. Various programs and scripts use rsync to
provide hardlinked backups. See, for example, Mike Rubel's site
(<http://www.mikerubel.org/computers/rsync_snapshots>), JW Schultz's dirvish
(<http://www.dirvish.org/>), Ben Escoto's rdiff-backup
(<http://www.nongnu.org/rdiff-backup>), and John Bowman's rlbackup
(<http://www.math.ualberta.ca/imaging/rlbackup>).

BackupPC provides many additional features, such as compressed storage, deduplicating
any matching files (rather than just files with the same name), and storing special
files without root privileges. But these other programs provide simple, effective and
fast solutions and are definitely worthy of consideration.

Road map
The new features planned for future releases of BackupPC are on the Wiki at
<https://github.com/backuppc/backuppc/wiki>.

Comments and suggestions are welcome.

You can help
BackupPC is free. I work on BackupPC because I enjoy doing it and I like to contribute to
the open source community.

BackupPC already has more than enough features for my own needs. The main compensation
for continuing to work on BackupPC is knowing that more and more people find it useful.
So feedback is certainly appreciated, both positive and negative.

Also, everyone is encouraged to contribute patches, bug reports, feature and design
suggestions, new code, Wiki additions (you can do those directly) and documentation
corrections or improvements. Answering questions on the mailing list is a big help too.

Installing BackupPC

Requirements
BackupPC requires:

• A linux, solaris, or unix based server with a substantial amount of free disk space
(see the next section for what that means). The CPU and disk performance on this
server will determine how many simultaneous backups you can run. You should be able to
run 4-8 simultaneous backups on a moderately configured server.

It is also recommended you consider either an LVM or RAID setup so that you can expand
the file system as necessary.

• Perl version 5.8.0 or later. If you don't have perl, please see
<http://www.cpan.org>.

• The perl modules BackupPC::XS (version >= 0.50) is required, and several others,
File::Listing, Archive::Zip, XML::RSS, JSON::XS, Net::FTP, Net::FTP::RetrHandle,
Net::FTP::AutoReconnect are recommended.

Try "perldoc BackupPC::XS" and "perldoc Archive::Zip" to see if you have these
modules. If not, fetch them from <http://www.cpan.org> and see the instructions below
for how to build and install them.

The CGI Perl module is required for the http/cgi user interface. CGI was a core
module, but from version 5.22 Perl no longer ships with it.

• If you are using rsync to backup linux/unix machines you should have rsync on each
client machine. Version 3+ is strongly recommended, but earlier versions will work
too. See <http://rsync.samba.org>. Use "rsync --version" to check your version.

For BackupPC to use Rsync you will also need to install rsync-bpc on the server.

• If you are using smb to backup WinXX machines you need smbclient and nmblookup from
the samba package. You will also need nmblookup if you are backing up linux/unix DHCP
machines. See <http://www.samba.org>.

See <http://www.samba.org> for source and binaries. It's pretty easy to fetch and
compile samba, and just grab smbclient and nmblookup, without doing the installation.
Alternatively, <http://www.samba.org> has binary distributions for most platforms.

• If you are using tar to backup linux/unix machines, those machines should have version
1.13.20 or higher recommended. Use "tar --version" to check your version. Various
GNU mirrors have the newest versions of tar; see <http://www.gnu.org/software/tar/>.

• The Apache web server, see <http://www.apache.org>, preferably built with mod_perl
support.

• If rrdtool is installed on the BackupPC server, graphs of the pool usage will be
maintained and displayed. To enable the graphs, point $Conf{RrdToolPath} to the
rrdtool executable.

What type of storage space do I need?
Starting with 4.0.0, BackupPC no longer uses hardlinks for storage of deduplicated files.
However, hardlinks are still used temporarily in a few places for doing atomic renames,
with a fallback doing a file copy if the hardlink fails, and files are moved (renamed)
across various paths that turn into expensive file copies if they span multiple file
systems.

So ideally BackupPC's data store (__TOPDIR__) is a single file system that supports
hardlinks. It is ok to use a single symbolic link at the top-level directory (__TOPDIR__)
to point the entire data store somewhere else). You can of course use any kind of RAID
system or logical volume manager that combines the capacity of multiple disks into a
single, larger, file system. Such approaches have the advantage that the file system can
be expanded without having to copy it.

Any standard linux or unix file system supports hardlinks. NFS mounted file systems work
too (provided the underlying file system supports hardlinks). But windows based FAT and
NTFS file systems will not work.

In BackupPC 3.x, hardlinks are fundamental to deduplication, so a startup check is done
ensure that the file system can support hardlinks, since this is a common area of
configuration problems in v3. In 4.x, that check is only done if the pool still contains
v3 backups and pool files.

How much disk space do I need?
Here's one real example (circa 2002) for an environment that is backing up 65 laptops with
compression off. Each full backup averages 3.2GB. Each incremental backup averages about
0.2GB. Storing one full backup and two incremental backups per laptop is around 240GB of
raw data. But because of the pooling of identical files, only 87GB is used. This is
without compression.

Another example, with compression on: backing up 95 laptops, where each backup averages
3.6GB and each incremental averages about 0.3GB. Keeping three weekly full backups, and
six incrementals is around 1200GB of raw data. Because of pooling and compression, only
150GB is needed.

Here's a rule of thumb. Add up the disk usage of all the machines you want to backup
(210GB in the first example above). This is a rough minimum space estimate that should
allow a couple of full backups and at least half a dozen incremental backups per machine.
If compression is on you can reduce the storage requirements by maybe 30-40%. Add some
margin in case you add more machines or decide to keep more old backups.

Your actual mileage will depend upon the types of clients, operating systems and
applications you have. The more uniform the clients and applications the bigger the
benefit from pooling common files.

In addition to total disk space, you should make sure you have plenty of inodes on your
BackupPC data partition. Some users have reported running out of inodes on their BackupPC
data partition. So even if you have plenty of disk space, BackupPC will report failures
when the inodes are exhausted. This is a particular problem with ext2/ext3 file systems
that have a fixed number of inodes when the file system is built. Use "df -i" to see your
inode usage.

Step 1: Getting BackupPC
Many linux distributions now include BackupPC, so installing BackupPC via your package
manager is the best approach.

For example, for Debian, supported by Ludovic Drolez, can be found at
<http://packages.debian.org/backuppc> and is included in the current stable Debian
release. On Debian, BackupPC can be installed with the command:

apt-get install backuppc

You should also install rsync-bpc; the BackupPC package might include it already, but if
not:

apt-get install rsync-bpc

If those commands work, you can skip to Step 3.

Alternatively, manually fetching and installing BackupPC is easy. Start by downloading
the latest version from

https://github.com/backuppc/backuppc/releases

Step 2: Installing the distribution
Note: most information in this step is only relevant if you build and install BackupPC
yourself. If you use a package provided by a distribution, the package management system
should take of installing any needed dependencies.

First off, there are several perl modules you should install. The first one,
BackupPC::XS, is required. The others are optional but highly recommended. Use either
your linux package manager, or the cpan command, or follow the instructions in the README
files to install these packages:

BackupPC::XS
Significant portions of BackupPC are implemented in C code contained in this module.
You can run "perldoc BackupPC::XS" to see if this module is installed. You need to
have version >= 0.50. BackupPC::XS is available from:

https://github.com/backuppc/backuppc-xs/releases

and also CPAN.

Archive::Zip
To support restore via Zip archives you will need to install Archive::Zip, also from
<http://www.cpan.org>. You can run "perldoc Archive::Zip" to see if this module is
installed.

XML::RSS
To support the RSS feature you will need to install XML::RSS, also from
<http://www.cpan.org>. There is not need to install this module if you don't plan on
using RSS. You can run "perldoc XML::RSS" to see if this module is installed.

JSON::XS
To support the JSON formatted metrics you will need to install JSON::XS, also from
<http://www.cpan.org>. There is not need to install this module if you don't plan on
using JSON formatted metrics. You can run "perldoc JSON::XS" to see if this module is
installed.

CGI The CGI Perl module is required for the http/cgi user interface. CGI was a core
module, but from version 5.22 Perl no longer ships with it so you'll need to install
it if you are using a recent version of perl.

SCGI
The SCGI Perl module is required to use the S/CGI protocol for the http/cgi user
interface.

File::Listing, Net::FTP, Net::FTP::RetrHandle, Net::FTP::AutoReconnect
To use ftp with BackupPC you will need four libraries, but actually need to install
only File::Listing from <http://www.cpan.org>. You can run "perldoc File::Listing" to
see if this module is installed. Net::FTP is a standard module. Net::FTP::RetrHandle
and Net::FTP::AutoReconnect included in BackupPC distribution.

To build and install these packages you should use the cpan command. At the prompt, type

install BackupPC::XS

Alternatively, if you want to install these manually, you can fetch the tarball from
<http://www.cpan.org> and then run these commands:

tar zxvf BackupPC-XS-0.50.tar.gz
cd BackupPC-XS-0.50
perl Makefile.PL
make
make test
make install

The same sequence of commands can be used for each module.

Next, you should install rsync_bpc if you want to use rsync to backup clients (which is
the recommended approach for all client types). If you don't use your package manager,
fetch the release from:

https://github.com/backuppc/rsync-bpc/releases

Then run these commands (updating the version number as appropriate):

tar zxf rsync-bpc-3.0.9.5.tar.gz
cd rsync-bpc-3.0.9.5
./configure
make
make install

Now let's move onto BackupPC itself. After fetching BackupPC-4.4.0.tar.gz, run these
commands as root:

tar zxf BackupPC-4.4.0.tar.gz
cd BackupPC-4.4.0
perl configure.pl

The configure.pl script also accepts command-line options if you wish to run it in a non-
interactive manner. It has self-contained documentation for all the command-line options,
which you can read with perldoc:

perldoc configure.pl

Starting with BackupPC 3.0.0, the configure.pl script by default complies with the file
system hierarchy (FHS) conventions. The major difference compared to earlier versions is
that by default configuration files will be stored in /etc/BackupPC rather than below the
data directory, __TOPDIR__/conf, and the log files will be stored in /var/log/BackupPC
rather than below the data directory, __TOPDIR__/log.

Note that distributions may choose to use different locations for BackupPC files than
these defaults.

If you are upgrading from an earlier version the configure.pl script will keep the
configuration files and log files in their original location.

When you run configure.pl you will be prompted for the full paths of various executables,
and you will be prompted for the following information.

BackupPC User
It is best if BackupPC runs as a special user, eg backuppc, that has limited
privileges. It is preferred that backuppc belongs to a system administrator group so
that sysadmin members can browse BackupPC files, edit the configuration files and so
on. Although configurable, the default settings leave group read permission on pool
files, so make sure the BackupPC user's group is chosen restrictively.

On this installation, this is __BACKUPPCUSER__.

For security purposes you might choose to configure the BackupPC user with the shell
set to /bin/false. Since you might need to run some BackupPC programs as the BackupPC
user for testing purposes, you can use the -s option to su to explicitly run a shell,
eg:

su -s /bin/bash __BACKUPPCUSER__

Depending upon your configuration you might also need the -l option.

If the -s option is not available on your operating system, you can specify the -m
option to use your login shell as invoked shell:

su -m __BACKUPPCUSER__

Data Directory
You need to decide where to put the data directory, below which all the BackupPC data
is stored. This needs to be a big file system.

On this installation, this is __TOPDIR__.

Install Directory
You should decide where the BackupPC scripts, libraries and documentation should be
installed, eg: /usr/local/BackupPC.

On this installation, this is __INSTALLDIR__.

CGI bin Directory
You should decide where the BackupPC CGI script resides. This will usually be below
Apache's cgi-bin directory.

It is also possible to use a different directory and use Apache's ``<Directory>''
directive to specify that location. See the Apache HTTP Server documentation for
additional information.

On this installation, this is __CGIDIR__.

Apache image Directory
A directory where BackupPC's images are stored so that Apache can serve them. You
should ensure this directory is readable by Apache and create a symlink to this
directory from the BackupPC CGI bin Directory.

Config and Log Directories
In this installation the configuration and log directories are located in the
following locations:

__CONFDIR__/config.pl main config file
__CONFDIR__/hosts hosts file
__CONFDIR__/pc/HOST.pl per-pc config file
__LOGDIR__/BackupPC log files, pid, status

The configure.pl script doesn't prompt for these locations but they can be set for new
installations using command-line options.

Step 3: Setting up config.pl
After running configure.pl, browse through the config file, __CONFDIR__/config.pl, and
make sure all the default settings are correct. In particular, you will need to decide
whether to use smb, tar,or rsync or ftp transport (or whether to set it on a per-PC basis)
and set the relevant parameters for that transport method. See the section "Step 5: Client
Setup" for more details.

Step 4: Setting up the hosts file
The file __CONFDIR__/hosts contains the list of clients to backup. BackupPC reads this
file in three cases:

• Upon startup.

• When BackupPC is sent a HUP (-1) signal. Assuming you installed the init.d script,
you can also do this with "/etc/init.d/backuppc reload".

• When the modification time of the hosts file changes. BackupPC checks the
modification time once during each regular wakeup.

Whenever you change the hosts file (to add or remove a host) you can either do a kill -HUP
BackupPC_pid or simply wait until the next regular wakeup period.

Each line in the hosts file contains three fields, separated by whitespace:

Host name
This is typically the hostname or NetBios name of the client machine and should be in
lowercase. The hostname can contain spaces (escape with a backslash), but it is not
recommended.

Please read the section "How BackupPC Finds Hosts".

In certain cases you might want several distinct clients to refer to the same physical
machine. For example, you might have a database you want to backup, and you want to
bracket the backup of the database with shutdown/restart using $Conf{DumpPreUserCmd}
and $Conf{DumpPostUserCmd}. But you also want to backup the rest of the machine while
the database is still running. In the case you can specify two different clients in
the host file, using any mnemonic name (eg: myhost_mysql and myhost), and use
$Conf{ClientNameAlias} in myhost_mysql's config.pl to specify the real hostname of the
machine.

DHCP flag
Starting with v2.0.0 the way hosts are discovered has changed and now in most cases
you should specify 0 for the DHCP flag, even if the host has a dynamically assigned IP
address. Please read the section "How BackupPC Finds Hosts" to understand whether you
need to set the DHCP flag.

You only need to set DHCP to 1 if your client machine doesn't respond to the NetBios
multicast request:

nmblookup myHost

but does respond to a request directed to its IP address:

nmblookup -A W.X.Y.Z

If you do set DHCP to 1 on any client you will need to specify the range of DHCP
addresses to search is specified in $Conf{DHCPAddressRanges}.

Note also that the $Conf{ClientNameAlias} feature does not work for clients with DHCP
set to 1.

User name
This should be the unix login/email name of the user who "owns" or uses this machine.
This is the user who will be sent email about this machine, and this user will have
permission to stop/start/browse/restore backups for this host. Leave this blank if no
specific person should receive email or be allowed to stop/start/browse/restore
backups for this host. Administrators will still have full permissions.

More users
Additional usernames, separated by commas and with no whitespace, can be specified.
These users will also have full permission in the CGI interface to
stop/start/browse/restore backups for this host. These users will not be sent email
about this host.

The first non-comment line of the hosts file is special: it contains the names of the
columns and should not be edited.

Here's a simple example of a hosts file:

host dhcp user moreUsers
farside 0 craig jim,dave
larson 1 gary andy

Step 5: Client Setup
Four methods for getting backup data from a client are supported: smb, tar, rsync and ftp.
Smb or rsync are the preferred methods for WinXX clients and rsync or tar are the
preferred methods for linux/unix/MacOSX clients.

The transfer method is set using the $Conf{XferMethod} configuration setting. If you have
a mixed environment (ie: you will use smb for some clients and tar for others), you will
need to pick the most common choice for $Conf{XferMethod} for the main config.pl file, and
then override it in the per-PC config file for those hosts that will use the other method.
(Or you could run two completely separate instances of BackupPC, with different data
directories, one for WinXX and the other for linux/unix, but then common files between the
different machine types will duplicated.)

Here are some brief client setup notes:

WinXX
One setup for WinXX clients is to set $Conf{XferMethod} to "smb". Actually, rsyncd is
the better method for WinXX if you are prepared to run rsync/cygwin on your WinXX
client.

If you want to use rsyncd for WinXX clients you can find a pre-packaged exe installer
on <https://github.com/backuppc/cygwin-rsyncd/releases>. The package is called
cygwin-rsync. It contains rsync.exe, template setup files and the minimal set of
cygwin libraries for everything to run. The README file contains instructions for
running rsync as a service, so it starts automatically every time you boot your
machine. If you use rsync to backup WinXX machines, be sure to set
$Conf{ClientCharset} correctly (eg: 'cp1252') so that the WinXX filename encoding is
correctly converted to utf8.

Otherwise, to use SMB, you can either create shares for the data you want to backup or
your can use the existing C$ share. To create a new share, open "My Computer", right
click on the drive (eg: C), and select "Sharing..." (or select "Properties" and select
the "Sharing" tab). In this dialog box you can enable sharing, select the share name
and permissions.

All Windows NT based OS (NT, 2000, XP Pro), are configured by default to share the
entire C drive as C$. This is a special share used for various administration
functions, one of which is to grant access to backup operators. All you need to do is
create a new domain user, specifically for backup. Then add the new backup user to the
built in "Backup Operators" group. You now have backup capability for any directory on
any computer in the domain in one easy step. This avoids using administrator accounts
and only grants permission to do exactly what you want for the given user, i.e.:
backup. Also, for additional security, you may wish to deny the ability for this user
to logon to computers in the default domain policy.

The relevant configuration settings are $Conf{SmbShareName}, $Conf{SmbShareUserName},
$Conf{SmbSharePasswd}, $Conf{SmbClientPath}, $Conf{SmbClientFullCmd},
$Conf{SmbClientIncrCmd} and $Conf{SmbClientRestoreCmd}.

BackupPC needs to know the smb share username and password for a client machine that
uses smb. The username is specified in $Conf{SmbShareUserName}. There are four ways
to tell BackupPC the smb share password:

• As an environment variable BPC_SMB_PASSWD set before BackupPC starts. If you
start BackupPC manually the BPC_SMB_PASSWD variable must be set manually first.
For backward compatibility for v1.5.0 and prior, the environment variable PASSWD
can be used if BPC_SMB_PASSWD is not set. Warning: on some systems it is possible
to see environment variables of running processes.

• Alternatively the BPC_SMB_PASSWD setting can be included in /etc/init.d/backuppc,
in which case you must make sure this file is not world (other) readable.

• As a configuration variable $Conf{SmbSharePasswd} in __CONFDIR__/config.pl. If
you put the password here you must make sure this file is not world (other)
readable.

• As a configuration variable $Conf{SmbSharePasswd} in the per-PC configuration file
(__CONFDIR__/pc/$host.pl or __TOPDIR__/pc/$host/config.pl in non-FHS versions of
BackupPC). You will have to use this option if the smb share password is
different for each host. If you put the password here you must make sure this file
is not world (other) readable.

Placement and protection of the smb share password is a significant security issue, so
please double-check the file and directory permissions. In a future version there
might be support for encryption of this password, but a private key will still have to
be stored in a protected place. Suggestions are welcome.

As an alternative to setting $Conf{XferMethod} to "smb" (using smbclient) for WinXX
clients, you can use an smb network filesystem (eg: ksmbfs or similar) on your
linux/unix server to mount the share, and then set $Conf{XferMethod} to "tar" (use tar
on the network mounted file system).

Also, to make sure that filenames with special characters are correctly transferred by
smbclient you should make sure that the smb.conf file has (for samba 3.x):

[global]
unix charset = UTF8

UTF8 is the default setting, so if the parameter is missing then it is ok. With this
setting $Conf{ClientCharset} should be empty, since smbclient has already converted
the filenames to utf8.

Linux/Unix
The preferred setup for linux/unix clients is to set $Conf{XferMethod} to "rsync",
"rsyncd" or "tar".

You can use either rsync, smb, or tar for linux/unix machines. Smb requires that the
Samba server (smbd) be run to provide the shares. Since the smb protocol can't
represent special files like symbolic links and fifos, tar and rsync are the better
transport methods for linux/unix machines. (In fact, by default samba makes symbolic
links look like the file or directory that they point to, so you could get an infinite
loop if a symbolic link points to the current or parent directory. If you really need
to use Samba shares for linux/unix backups you should turn off the "follow symlinks"
samba config setting. See the smb.conf manual page.)

Important note: many linux systems use sparse files for /var/log/lastlog, and have
large special files below /proc and /run. Make sure you exclude those directories and
files when you configure your client.

The requirements for each Xfer Method are:

rsync
To use rsync, you need rsync-bpc installed on the BackupPC server.

On the client, you should have at least rsync 3.x. Rsync is run on the remote
client via ssh.

The relevant configuration settings are $Conf{RsyncClientPath},
$Conf{RsyncSshArgs}, $Conf{RsyncShareName}, $Conf{RsyncArgs},
$Conf{RsyncArgsExtra}, $Conf{RsyncFullArgsExtra}, and $Conf{RsyncRestoreArgs}.

rsyncd
To use rsync, you need rsync-bpc installed on the BackupPC server.

On the client, you should have at least rsync 3.x. In this case the rsync daemon
should be running on the client machine and BackupPC connects directly to it.

The relevant configuration settings are $Conf{RsyncBackupPCPath},
$Conf{RsyncdClientPort}, $Conf{RsyncdUserName}, $Conf{RsyncdPasswd},
$Conf{RsyncShareName}, $Conf{RsyncArgs}, $Conf{RsyncArgsExtra}, and
$Conf{RsyncRestoreArgs}. $Conf{RsyncShareName} is the name of an rsync module (ie:
the thing in square brackets in rsyncd's conf file -- see rsyncd.conf), not a file
system path.

Be aware that rsyncd will remove the leading '/' from path names in symbolic links
if you specify "use chroot = no" in the rsynd.conf file. See the rsyncd.conf
manual page for more information.

tar You must have GNU tar on the client machine. Use "tar --version" or "gtar
--version" to verify. The version should be at least 1.13.20. Tar is run on the
client machine via rsh or ssh.

The relevant configuration settings are $Conf{TarClientPath}, $Conf{TarShareName},
$Conf{TarClientCmd}, $Conf{TarFullArgs}, $Conf{TarIncrArgs}, and
$Conf{TarClientRestoreCmd}.

ftp FTP Xfer Method is supported in V4 but not recommended since it only handles
minimal metadata, it doesn't support hardlinks or special files, and can only
restore regular files (not symbolic links etc).

You need to be running an ftp server on the client machine. The relevant
configuration settings are $Conf{FtpShareName}, $Conf{FtpUserName},
$Conf{FtpPasswd}, $Conf{FtpBlockSize}, $Conf{FtpPort}, $Conf{FtpTimeout}, and
$Conf{FtpFollowSymlinks}.

You need to set $Conf{ClientCharset} to the client's charset so that filenames are
correctly converted to utf8. Use "locale charmap" on the client to see its charset.
Note, however, that modern versions of smbclient and rsync handle this conversion
automatically, so in most cases you won't need to set $Conf{ClientCharset}.

For linux/unix machines you should not backup "/proc". This directory contains a
variety of files that look like regular files but they are special files that don't
need to be backed up (eg: /proc/kcore is a regular file that contains physical
memory). See $Conf{BackupFilesExclude}. It is safe to backup /dev since it contains
mostly character-special and block-special files, which are correctly handed by
BackupPC (eg: backing up /dev/hda5 just saves the block-special file information, not
the contents of the disk). Similarly, on many linux systems, /var/log/lastlog is a
sparse file, with a very large apparent size, so you should exclude that too.

Alternatively, rather than backup all the file systems as a single share ("/"), it is
easier to restore a single file system if you backup each file system separately. To
do this you should list each file system mount point in $Conf{TarShareName} or
$Conf{RsyncShareName}, and add the --one-file-system option to $Conf{TarClientCmd} or
$Conf{RsyncArgs}. In this case there is no need to exclude /proc explicitly since it
looks like a different file system.

Ssh allows BackupPC to run as a privileged user on the client (eg: root), since it
needs sufficient permissions to read all the backup files. Ssh is setup so that
BackupPC on the server (an otherwise low privileged user) can ssh as root on the
client, without being prompted for a password. However, directly enabled ssh root
logins is not good practice. A better approach is the ssh as a regular user, and then
configure sudo to allow just rsync to be executed.

There are two common versions of ssh: v1 and v2. Here are some instructions for one
way to setup ssh. (Check which version of SSH you have by typing "ssh" or "man ssh".)

MacOSX
In general this should be similar to Linux/Unix machines. In versions 10.4 and later,
the native MacOSX tar works, and also supports resource forks. xtar is another
option, and rsync works too (although the MacOSX-supplied rsync has an extension for
extended attributes that is not compatible with standard rsync).

SSH Setup
SSH is a secure way to run tar or rsync on a backup client to extract the data. SSH
provides strong authentication and encryption of the network data.

Note that if you run rsyncd (rsync daemon), ssh is not used. In this case, rsyncd
provides its own authentication, but there is no encryption of network data. If you
want encryption of network data you can use ssh to create a tunnel, or use a program
like stunnel.

Setup instructions for ssh can be found on the Wiki at
<https://github.com/backuppc/backuppc/wiki>.

Clients that use DHCP
If a client machine uses DHCP BackupPC needs some way to find the IP address given the
hostname. One alternative is to set dhcp to 1 in the hosts file, and BackupPC will
search a pool of IP addresses looking for hosts. More efficiently, it is better to
set dhcp = 0 and provide a mechanism for BackupPC to find the IP address given the
hostname.

For WinXX machines BackupPC uses the NetBios name server to determine the IP address
given the hostname. For unix machines you can run nmbd (the NetBios name server) from
the Samba distribution so that the machine responds to a NetBios name request. See the
manual page and Samba documentation for more information.

Alternatively, you can set $Conf{NmbLookupFindHostCmd} to any command that returns the
IP address given the hostname.

Please read the section "How BackupPC Finds Hosts" for more details.

Step 6: Running BackupPC
The installation contains an init.d backuppc script that can be copied to /etc/init.d so
that BackupPC can auto-start on boot. See init.d/README for further instructions.

BackupPC should be ready to start. If you installed the init.d script, then you should be
able to run BackupPC with:

/etc/init.d/backuppc start

(This script can also be invoked with "stop" to stop BackupPC and "reload" to tell
BackupPC to reload config.pl and the hosts file.)

Otherwise, just run

__INSTALLDIR__/bin/BackupPC -d

as user __BACKUPPCUSER__. The -d option tells BackupPC to run as a daemon (ie: it does an
additional fork).

Any immediate errors will be printed to stderr and BackupPC will quit. Otherwise, look in
__LOGDIR__/LOG and verify that BackupPC reports it has started and all is ok.

Step 7: Talking to BackupPC
You should verify that BackupPC is running by using BackupPC_serverMesg. This sends a
message to BackupPC via the unix (or TCP) socket and prints the response. Like all
BackupPC programs, BackupPC_serverMesg should be run as the BackupPC user
(__BACKUPPCUSER__), so you should

su __BACKUPPCUSER__

before running BackupPC_serverMesg. If the BackupPC user is configured with /bin/false as
the shell, you can use the -s option to su to explicitly run a shell, eg:

su -s /bin/bash __BACKUPPCUSER__

Depending upon your configuration you might also need the -l option.

If the -s option is not available on your operating system, you can specify the -m option
to use your login shell as invoked shell:

su -m __BACKUPPCUSER__

You can request status information and start and stop backups using this interface. This
socket interface is mainly provided for the CGI interface (and some of the BackupPC
subprograms use it too). But right now we just want to make sure BackupPC is happy. Each
of these commands should produce some status output:

__INSTALLDIR__/bin/BackupPC_serverMesg status info
__INSTALLDIR__/bin/BackupPC_serverMesg status jobs
__INSTALLDIR__/bin/BackupPC_serverMesg status hosts

The output should be some hashes printed with Data::Dumper. If it looks cryptic and
confusing, and doesn't look like an error message, then all is ok.

The hosts status should produce a list of every host you have listed in __CONFDIR__/hosts
as part of a big cryptic output line.

You can also request that all hosts be queued:

__INSTALLDIR__/bin/BackupPC_serverMesg backup all

At this point you should make sure the CGI interface works since it will be much easier to
see what is going on. We'll get to that shortly.

Step 8: Checking email delivery
The script BackupPC_sendEmail sends status and error emails to the administrator and
users. It is usually run each night by BackupPC_nightly.

To verify that it can run sendmail and deliver email correctly you should ask it to send a
test email to you:

su __BACKUPPCUSER__
__INSTALLDIR__/bin/BackupPC_sendEmail -u MYNAME@MYDOMAIN.COM

BackupPC_sendEmail also takes a -c option that checks if BackupPC is running, and it sends
an email to $Conf{EMailAdminUserName} if it is not. That can be used as a keep-alive
check by adding

__INSTALLDIR__/bin/BackupPC_sendEmail -c

to __BACKUPPCUSER__'s cron.

The -t option to BackupPC_sendEmail causes it to print the email message instead of
invoking sendmail to deliver the message.

Step 9: CGI interface
The CGI interface script, BackupPC_Admin, is a powerful and flexible way to see and
control what BackupPC is doing. It is written for an Apache server. If you don't have
Apache, see <http://www.apache.org>.

There are three options for setting up the CGI interface:

SCGI
New to 4.x, SCGI uses the SCGI interface to Apache, which requires the mod_scgi.so
module to be installed and loaded by Apache. This allows Apache to run as any
unprivileged user. The actual SCGI server runs as the as the BackupPC user
(__BACKUPPCUSER__), and handles the requests from Apache via a TCP socket.

mod_perl
Mod_perl required the mod_perl module to be loaded by Apache. This allows
BackupPC_Admin to be run from inside Apache. Unlike SCGI, using mod_perl with
BackupPC_Admin requires a dedicated Apache to be run as the BackupPC user
(__BACKUPPCUSER__). This is because BackupPC_Admin needs permission to access various
files in BackupPC's data directories.

standard
The standard mode, which is significantly slower than SCGI or mod_perl, is where
Apache runs BackupPC_Admin as a separate process for every request. This adds
significant startup overhead for every request, and also requires that BackupPC_Admin
be run as setuid to the BackupPC user (__BACKUPPCUSER__), if Apache isn't being run as
that user. Setuid scripts are discouraged, so the preference is to use SCGI or
mod_perl.

Here are some specifics for each setup:

SCGI Setup
First you need to install mod_scgi. If you can't find a pre-built package, the source
is available at <http://python.ca/scgi>. The release has subdirectories for apache1
and apache2. Pick your matching version (nowadays most likely apache2). You'll need
apxs, the Apache Extension Tool, installed to build from source. Once compiled, the
module mod_scgi.so should be installed via the Makefile.

To enable the SCGI server, set $Conf{SCGIServerPort} to an available non-privileged
TCP port number, eg: 10268. The matching port number has to appear in the Apache
configuration file. Typical Apache configuration entries will look like this:

LoadModule scgi_module modules/mod_scgi.so
SCGIMount /BackupPC_Admin 127.0.0.1:10268
<Location /BackupPC_Admin>
AuthUserFile /etc/httpd/conf/passwd
AuthType basic
AuthName "access"
require valid-user
</Location>

Or a typical Nginx configuration file:

server {
listen 80;
server_name yourBackupPCServerHost;

root /var/www/backuppc;

access_log /var/log/nginx/backuppc.access.log;
error_log /var/log/nginx/backuppc.error.log;

location /BackupPC_Admin {
auth_basic "BackupPC";
auth_basic_user_file conf.d/backuppc.users;

include scgi_params;
scgi_pass 127.0.0.1:10268;
scgi_param REMOTE_USER $remote_user;
scgi_param SCRIPT_NAME $document_uri;
}
}

This allows the SCGI interface to be accessed with a URL:

http://yourBackupPCServerHost/BackupPC_Admin

You can use a different path or name if you prefer a different URL. Unlike
traditional CGI, there is no need to specify a valid path to a CGI script.

Important security warning!! The SCGIServerPort must not be accessible by anyone
untrusted. That means you can't allow untrusted users access to the BackupPC server,
and you should block the SCGIServerPort TCP port on the BackupPC server. If you don't
understand what that means, or can't confirm you have configured SCGI securely, then
don't enable SCGI - use one of the following two methods!!

Mod_perl Setup
The advantage of the mod_perl setup is that no setuid script is needed (like in the
standard method below), and there is a significant performance advantage. Not only
does all the perl code need to be parsed just once, the config.pl and hosts files,
plus the connection to the BackupPC server are cached between requests. The typical
speedup is around 10-15x.

To use mod_perl you need to run Apache as user __BACKUPPCUSER__. If you need to run
multiple Apaches for different services then you need to create multiple top-level
Apache directories, each with their own config file. You can make copies of
/etc/init.d/httpd and use the -d option to httpd to point each http to a different
top-level directory. Or you can use the -f option to explicitly point to the config
file. Multiple Apache's will run on different Ports (eg: 80 is standard, 8080 is a
typical alternative port accessed via http://yourhost.com:8080).

Inside BackupPC's Apache http.conf file you should check the settings for ServerRoot,
DocumentRoot, User, Group, and Port. See
<http://httpd.apache.org/docs/server-wide.html> for more details.

For mod_perl, BackupPC_Admin should not have setuid permission, so you should turn it
off:

chmod u-s __CGIDIR__/BackupPC_Admin

To tell Apache to use mod_perl to execute BackupPC_Admin, add this to Apache's 1.x
httpd.conf file:

<IfModule mod_perl.c>
PerlModule Apache::Registry
PerlTaintCheck On
<Location /cgi-bin/BackupPC/BackupPC_Admin> # <--- change path as needed
SetHandler perl-script
PerlHandler Apache::Registry
Options ExecCGI
PerlSendHeader On
</Location>
</IfModule>

Apache 2.0.44 with Perl 5.8.0 on RedHat 7.1, Don Silvia reports that this works (with
tweaks from Michael Tuzi):

LoadModule perl_module modules/mod_perl.so
PerlModule Apache2

<Directory /path/to/cgi/>
SetHandler perl-script
PerlResponseHandler ModPerl::Registry
PerlOptions +ParseHeaders
Options +ExecCGI
Order deny,allow
Deny from all
Allow from 192.168.0
AuthName "Backup Admin"
AuthType Basic
AuthUserFile /path/to/user_file
Require valid-user
</Directory>

There are other optimizations and options with mod_perl. For example, you can tell
mod_perl to preload various perl modules, which saves memory compared to loading
separate copies in every Apache process after they are forked. See Stas's definitive
mod_perl guide at <http://perl.apache.org/guide>.

Standard Setup
The CGI interface should have been installed by the configure.pl script in
__CGIDIR__/BackupPC_Admin. BackupPC_Admin should have been installed as setuid to the
BackupPC user (__BACKUPPCUSER__), in addition to user and group execute permission.

You should be very careful about permissions on BackupPC_Admin and the directory
__CGIDIR__: it is important that normal users cannot directly execute or change
BackupPC_Admin, otherwise they can access backup files for any PC. You might need to
change the group ownership of BackupPC_Admin to a group that Apache belongs to so that
Apache can execute it (don't add "other" execute permission!). The permissions should
look like this:

ls -l __CGIDIR__/BackupPC_Admin
-swxr-x--- 1 __BACKUPPCUSER__ web 82406 Jun 17 22:58 __CGIDIR__/BackupPC_Admin

The setuid script won't work unless perl on your machine was installed with setuid
emulation. This is likely the problem if you get an error saying such as "Wrong user:
my userid is 25, instead of 150", meaning the script is running as the httpd user, not
the BackupPC user. This is because setuid scripts are disabled by the kernel in most
flavors of unix and linux.

To see if your perl has setuid emulation, see if there is a program called sperl5.8.0
(or sperl5.8.2 etc, based on your perl version) in the place where perl is installed.
If you can't find this program, then you have two options: rebuild and reinstall perl
with the setuid emulation turned on (answer "y" to the question "Do you want to do
setuid/setgid emulation?" when you run perl's configure script), or switch to the
mod_perl alternative for the CGI script (which doesn't need setuid to work).

BackupPC_Admin requires that users are authenticated by Apache. Specifically, it expects
that Apache sets the REMOTE_USER environment variable when it runs. There are several
ways to do this. One way is to create a .htaccess file in the cgi-bin directory that
looks like:

AuthGroupFile /etc/httpd/conf/group # <--- change path as needed
AuthUserFile /etc/http/conf/passwd # <--- change path as needed
AuthType basic
AuthName "access"
require valid-user

You will also need "AllowOverride Indexes AuthConfig" in the Apache httpd.conf file to
enable the .htaccess file. Alternatively, everything can go in the Apache httpd.conf file
inside a Location directive. The list of users and password file above can be extracted
from the NIS passwd file.

One alternative is to use LDAP. In Apache's http.conf add these lines:

LoadModule auth_ldap_module modules/auth_ldap.so
AddModule auth_ldap.c

# cgi-bin - auth via LDAP (for BackupPC)
<Location /cgi-bin/BackupPC/BackupPC_Admin> # <--- change path as needed
AuthType Basic
AuthName "BackupPC login"
# replace MYDOMAIN, PORT, ORG and CO as needed
AuthLDAPURL ldap://ldap.MYDOMAIN.com:PORT/o=ORG,c=CO?uid?sub?(objectClass=*)
require valid-user
</Location>

If you want to disable the user authentication you can set $Conf{CgiAdminUsers} to '*',
which allows any user to have full access to all hosts and backups. In this case the
REMOTE_USER environment variable does not have to be set by Apache.

Alternatively, you can force a particular username by getting Apache to set REMOTE_USER,
eg, to hard code the user to www you could add this to Apache's httpd.conf:

Finally, you should also edit the config.pl file and adjust, as necessary, the CGI-
specific settings. They're near the end of the config file. In particular, you should
specify which users or groups have administrator (privileged) access: see the config
settings $Conf{CgiAdminUserGroup} and $Conf{CgiAdminUsers}. Also, the configure.pl script
placed various images into $Conf{CgiImageDir} that BackupPC_Admin needs to serve up. You
should make sure that $Conf{CgiImageDirURL} is the correct URL for the image directory.

See the section "Fixing installation problems" for suggestions on debugging the Apache
authentication setup.

How BackupPC Finds Hosts
Starting with v2.0.0 the way hosts are discovered has changed. In most cases you should
specify 0 for the DHCP flag in the conf/hosts file, even if the host has a dynamically
assigned IP address.

BackupPC (starting with v2.0.0) looks up hosts with DHCP = 0 in this manner:

• First DNS is used to lookup the IP address given the client's name using perl's
gethostbyname() function. This should succeed for machines that have fixed IP
addresses that are known via DNS. You can manually see whether a given host have a
DNS entry according to perl's gethostbyname function with this command:

perl -e 'print(gethostbyname("myhost") ? "ok\n" : "not found\n");'

• If gethostbyname() fails, BackupPC then attempts a NetBios multicast to find the host.
Provided your client machine is configured properly, it should respond to this NetBios
multicast request. Specifically, BackupPC runs a command of this form:

nmblookup myhost

If this fails you will see output like:

querying myhost on 10.10.255.255
name_query failed to find name myhost

If it is successful you will see output like:

querying myhost on 10.10.255.255
10.10.1.73 myhost<00>

Depending on your netmask you might need to specify the -B option to nmblookup. For
example:

nmblookup -B 10.10.1.255 myhost

If necessary, experiment with the nmblookup command which will return the IP address
of the client given its name. Then update $Conf{NmbLookupFindHostCmd} with any
necessary options to nmblookup.

For hosts that have the DHCP flag set to 1, these machines are discovered as follows:

• A DHCP address pool ($Conf{DHCPAddressRanges}) needs to be specified. BackupPC will
check the NetBIOS name of each machine in the range using a command of the form:

nmblookup -A W.X.Y.Z

where W.X.Y.Z is each candidate address from $Conf{DHCPAddressRanges}. Any host that
has a valid NetBIOS name returned by this command (ie: matching an entry in the hosts
file) will be backed up. You can modify the specific nmblookup command if necessary
via $Conf{NmbLookupCmd}.

• You only need to use this DHCP feature if your client machine doesn't respond to the
NetBios multicast request:

nmblookup myHost

but does respond to a request directed to its IP address:

nmblookup -A W.X.Y.Z

Other installation topics
Removing a client
If there is a machine that no longer needs to be backed up (eg: a retired machine) you
have two choices. First, you can keep the backups accessible and browsable, but
disable all new backups. Alternatively, you can completely remove the client and all
its backups.

To disable backups for a client $Conf{BackupsDisable} can be set to two different
values in that client's per-PC config.pl file:

1. Don't do any regular backups on this machine. Manually requested backups (via the
CGI interface) will still occur.

2. Don't do any backups on this machine. Manually requested backups (via the CGI
interface) will be ignored.

This will still allow the client's old backups to be browsable and restorable.

To completely remove a client and all its backups, you should remove its entry in the
conf/hosts file, and then delete the __TOPDIR__/pc/$host directory. Whenever you
change the hosts file, you should send BackupPC a HUP (-1) signal so that it re-reads
the hosts file. If you don't do this, BackupPC will automatically re-read the hosts
file at the next regular wakeup.

Note that when you remove a client's backups you won't initially recover much disk
space. That's because the client's files are still in the pool. Overnight, when
BackupPC_nightly next runs, all the unused pool files will be deleted and this will
recover the disk space used by the client's backups.

Copying the pool
If the pool disk requirements grow you might need to copy the entire data directory to
a new (bigger) file system. Hopefully you are lucky enough to avoid this by having
the data directory on a RAID file system or LVM that allows the capacity to be grown
in place by adding disks.

Backups prior to V4 make extensive use of hardlinks. So unless you have a virgin V4
installation, your file system will contain large numbers of hardlinks. This makes it
hard to copy.

Prior to V4 (or a V4 upgrade to a V3 installation), the backup data directories
contain large numbers of hardlinks. If you try to copy the pool the target directory
will occupy a lot more space if the hardlinks aren't re-established.

Unless you have a pure V4 installation, the best way to copy a pool file system, if
possible, is by copying the raw device at the block level (eg: using dd). Application
level programs that understand hardlinks include the GNU cp program with the -a option
and rsync -H. However, the large number of hardlinks in the pool will make the memory
usage large and the copy very slow. Don't forget to stop BackupPC while the copy
runs.

If you have a pure V4 installation, copying the pool and PC backup directories should
be quite easy. Rsync 3.x should work well.

Fixing installation problems
If you find a solution to your problem that could help other users please add it to the
Wiki at <https://github.com/backuppc/backuppc/wiki>.

Restore functions

BackupPC supports several different methods for restoring files. The most convenient
restore options are provided via the CGI interface. Alternatively, backup files can be
restored using manual commands.

CGI restore options
By selecting a host in the CGI interface, a list of all the backups for that machine will
be displayed. By selecting the backup number you can navigate the shares and directory
tree for that backup.

BackupPC's CGI interface automatically fills incremental backups with the corresponding
full backup, which means each backup has a filled appearance. Therefore, there is no need
to do multiple restores from the incremental and full backups: BackupPC does all the hard
work for you. You simply select the files and directories you want from the correct
backup vintage in one step.

You can download a single backup file at any time simply by selecting it. Your browser
should prompt you with the filename and ask you whether to open the file or save it to
disk.

Alternatively, you can select one or more files or directories in the currently selected
directory and select "Restore selected files". (If you need to restore selected files and
directories from several different parent directories you will need to do that in multiple
steps.)

If you select all the files in a directory, BackupPC will replace the list of files with
the parent directory. You will be presented with a screen that has three options:

Option 1: Direct Restore
With this option the selected files and directories are restored directly back onto
the host, by default in their original location. Any old files with the same name
will be overwritten, so use caution. You can optionally change the target hostname,
target share name, and target path prefix for the restore, allowing you to restore the
files to a different location.

Once you select "Start Restore" you will be prompted one last time with a summary of
the exact source and target files and directories before you commit. When you give
the final go ahead the restore operation will be queued like a normal backup job,
meaning that it will be deferred if there is a backup currently running for that host.
When the restore job is run, smbclient, tar, rsync or rsyncd is used (depending upon
$Conf{XferMethod}) to actually restore the files. Sorry, there is currently no option
to cancel a restore that has been started. Currently ftp restores are not fully
implemented.

A record of the restore request, including the result and list of files and
directories, is kept. It can be browsed from the host's home page.
$Conf{RestoreInfoKeepCnt} specifies how many old restore status files to keep.

Note that for direct restore to work, the $Conf{XferMethod} must be able to write to
the client. For example, that means an SMB share for smbclient needs to be writable,
and the rsyncd module needs "read only" set to "false". This creates additional
security risks. If you only create read-only SMB shares (which is a good idea), then
the direct restore will fail. You can disable the direct restore option by setting
$Conf{SmbClientRestoreCmd}, $Conf{TarClientRestoreCmd} and $Conf{RsyncRestoreArgs} to
undef.

Option 2: Download Zip archive
With this option a zip file containing the selected files and directories is
downloaded. The zip file can then be unpacked or individual files extracted as
necessary on the host machine. The compression level can be specified. A value of 0
turns off compression.

When you select "Download Zip File" you should be prompted where to save the
restore.zip file.

BackupPC does not consider downloading a zip file as an actual restore operation, so
the details are not saved for later browsing as in the first case. However, a mention
that a zip file was downloaded by a particular user, and a list of the files, does
appear in BackupPC's log file.

Option 3: Download Tar archive
This is identical to the previous option, except a tar file is downloaded rather than
a zip file (and there is currently no compression option).

Command-line restore options
Apart from the CGI interface, BackupPC allows you to restore files and directories from
the command line. The following programs can be used:

BackupPC_zcat
For each filename argument it inflates (uncompresses) the file and writes it to
stdout. To use BackupPC_zcat you could give it the full filename, eg:

__INSTALLDIR__/bin/BackupPC_zcat __TOPDIR__/pc/host/5/fc/fcraig/fexample.txt > example.txt

It's your responsibility to make sure the file is really compressed: BackupPC_zcat
doesn't check which backup the requested file is from. BackupPC_zcat returns a
nonzero status if it fails to uncompress a file.

In V4, BackupPC_zcat can be invoked in several other ways:

BackupPC_zcat file...
BackupPC_zcat MD5_digest...
BackupPC_zcat $TopDir/pc/host/num/share/mangledPath...
BackupPC_zcat [-h host] [-n num] [-s share] clientPath...

For example, you can do this:

BackupPC_zcat d73955e08410dfc5ea8069b05d2f43b2

That digest can be pasted from the output of BackupPC_ls.

The last form uses unmangled paths, so you can do this:

BackupPC_zcat -h HOST -n 10 -s / /home/craig/file

You can also mix real paths with unmangled paths. Both of these versions work:

BackupPC_zcat /data/BackupPC/pc/HOST/10/fhome/fcraig/ffile
BackupPC_zcat /data/BackupPC/pc/HOST/10/home/craig/file

BackupPC_tarCreate
BackupPC_tarCreate creates a tar file for any files or directories in a particular
backup. Merging of incrementals is done automatically, so you don't need to worry
about whether certain files appear in the incremental or full backup.

The usage is:

BackupPC_tarCreate [options] files/directories...
Required options:
-h host host from which the tar archive is created
-n dumpNum dump number from which the tar archive is created
A negative number means relative to the end (eg -1
means the most recent dump, -2 2nd most recent etc).
-s shareName share name from which the tar archive is created;
can be "*" to mean all shares.

Other options:
-t print summary totals
-r pathRemove path prefix that will be replaced with pathAdd
-p pathAdd new path prefix
-b BLOCKS BLOCKS x 512 bytes per record (default 20; same as tar)
-w writeBufSz write buffer size (default 1048576 = 1MB)
-e charset charset for encoding filenames (default: value of
$Conf{ClientCharset} when backup was done)
-l just print a file listing; don't generate an archive
-L just print a detailed file listing; don't generate an archive

The command-line files and directories are relative to the specified shareName. The
tar file is written to stdout.

The -h, -n and -s options specify which dump is used to generate the tar archive. The
-r and -p options can be used to relocate the paths in the tar archive so extracted
files can be placed in a location different from their original location.

BackupPC_zipCreate
BackupPC_zipCreate creates a zip file for any files or directories in a particular
backup. Merging of incrementals is done automatically, so you don't need to worry
about whether certain files appear in the incremental or full backup.

The usage is:

BackupPC_zipCreate [options] files/directories...
Required options:
-h host host from which the zip archive is created
-n dumpNum dump number from which the tar archive is created
A negative number means relative to the end (eg -1
means the most recent dump, -2 2nd most recent etc).
-s shareName share name from which the zip archive is created

Other options:
-t print summary totals
-r pathRemove path prefix that will be replaced with pathAdd
-p pathAdd new path prefix
-c level compression level (default is 0, no compression)
-e charset charset for encoding filenames (default: utf8)

The command-line files and directories are relative to the specified shareName. The
zip file is written to stdout. The -h, -n and -s options specify which dump is used to
generate the zip archive. The -r and -p options can be used to relocate the paths in
the zip archive so extracted files can be placed in a location different from their
original location.

BackupPC_ls
In V3, a full (or filled) backup tree contains all the files, albeit with "mangled"
names, and the file contents are compressed. Some users found it convenient to
directly navigate a PC's backup tree to check for files.

In V4 that is not possible, since only a single attrib file is stored per directory in
the PC backup tree, so the directory contents aren't visible without looking in the
attrib file.

A new utility BackupPC_ls (like "ls") can be used to view PC backup trees. It shows
file digests, which can be pasted to BackupPC_zcat if you want to view the file
contents. The arguments are similar to BackupPC_zcat. The usage is:

BackupPC_ls [-iR] [-h host] [-n bkupNum] [-s shareName] dirs/files...

The -i option will show inodes (inode number and number of links). The -R option
recurses into directories.

If you don't specify -h, -n and -s, then you can specify the real file system path
instead. For example, the following three commands are equivalent:

BackupPC_ls -h HOST -n 10 -s cDrive /home/craig/file
BackupPC_ls /data/BackupPC/pc/HOST/10/fcDrive/fhome/fcraig/ffile
BackupPC_ls /data/BackupPC/pc/HOST/10/cDrive/home/craig/file

As you can see, the portion of the full path after the backup number can be either
mangled or not. Note that using the mangled form allows directory-name completion via
the shell, since those directories actually exist.

It would be great if someone would like to volunteer to add features to BackupPC_ls to
make file and directory completion work with unmangled names via the shell. In tcsh
you can specify a completion program to run - BackupPC_ls could be given special
arguments to spit out the potential (unmangled) completions. I'm not sure how bash
does this.

Each of these programs reside in __INSTALLDIR__/bin.

Archive functions

BackupPC supports archiving to removable media. For users that require offsite backups,
BackupPC can create archives that stream to tape devices, or create files of specified
sizes to fit onto cd or dvd media.

Each archive type is specified by a BackupPC host with its XferMethod set to 'archive'.
This allows for multiple configurations at sites where there might be a combination of
tape and cd/dvd backups being made.

BackupPC provides a menu that allows one or more hosts to be archived. The most recent
backup of each host is archived using BackupPC_tarCreate, and the output is optionally
compressed and split into fixed-sized files (eg: 650MB).

The archive for each host is done by default using
__INSTALLDIR__/bin/BackupPC_archiveHost. This script can be copied and customized as
needed.

Configuring an Archive Host
To create an Archive Host, add it to the hosts file just as any other host and call it a
name that best describes the type of archive, e.g. ArchiveDLT

To tell BackupPC that the Host is for Archives, create a config.pl file in the Archive
Hosts's pc directory, adding the following line:

$Conf{XferMethod} = 'archive';

To further customise the archive's parameters you can add the changed parameters in the
host's config.pl file. The parameters are explained in the config.pl file. Parameters may
be fixed or the user can be allowed to change them (eg: output device).

The per-host archive command is $Conf{ArchiveClientCmd}. By default this invokes

__INSTALLDIR__/bin/BackupPC_archiveHost

which you can copy and customize as necessary.

Starting an Archive
In the web interface, click on the Archive Host you wish to use. You will see a list of
previous archives and a summary on each. By clicking the "Start Archive" button you are
presented with the list of hosts and the approximate backup size (note this is raw size,
not projected compressed size) Select the hosts you wish to archive and press the "Archive
Selected Hosts" button.

The next screen allows you to adjust the parameters for this archive run. Press the
"Start the Archive" to start archiving the selected hosts with the parameters displayed.

Starting an Archive from the command line
The script BackupPC_archiveStart can be used to start an archive from the command line (or
cron etc). The usage is:

BackupPC_archiveStart archiveHost userName hosts...

This creates an archive of the most recent backup of each of the specified hosts. The
first two arguments are the archive host and the username making the request.

Other Command Line Utilities

       These utilities are automatically run by BackupPC when needed.  You don't need to manually
       run these utilities.

       BackupPC_attribPrint
           BackupPC_attribPrint prints the contents of an attrib file.  Usage:

                   BackupPC_attribPrint attribPath
                   BackupPC_attribPrint inodePath/inodeNum

       BackupPC_backupDelete
           BackupPC_backupDelete deletes an entire backup, or a directory path within a backup.
           Usage:

               BackupPC_backupDelete -h host -n num [-p] [-l] [-r] [-s shareName [dirs...]]
               Options:
                  -h host         hostname
                  -n num          backup number to delete
                  -s shareName    don't delete the backup; delete just this share
                                  (or only dirs below this share if specified)
                  -p              don't print progress information
                  -l              don't remove XferLOG files
                  -r              do a ref count update (default: none)
               If a shareName is specified, just that share (or share/dirs) are deleted.
               The backup itself is not deleted, nor is the log file removed.

       BackupPC_backupDuplicate
           BackupPC_backupDuplicate duplicates the last backup, which is used to create a filled
           backup copy, and also to convert a V3 backup to a new V4 starting point.  Usage:

               BackupPC_backupDuplicate -h host [-p]
               Options:
                  -h host         hostname
                  -p              don't print progress information

       BackupPC_fixupBackupSummary
           BackupPC_fixupBackupSummary is used to re-create the backups file for all the hosts if
           it is damaged or deleted.  Usage:

               BackupPC_fixupBackupSummary [-l]
               Options:
                 -l    legacy mode: try to reconstruct backups from LOG
                       files for backups prior to BackupPC v3.0.

       BackupPC_fsck
           BackupPC_fsck can only be run manually, and only while BackupPC isn't running.  It
           updates the host reference counts, the overall pool reference counts and stats.
           Usage:

               BackupPC_fsck [options]
               Options:
                  -f              force regeneration of per-host reference counts
                  -n              don't remove zero count pool files - print only
                  -s              recompute pool stats

       BackupPC_migrateV3toV4
           If you upgraded an existing 3.x installation, BackupPC 4.x is backward compatible with
           3.x backups: it can browse, view and restore files.  However, the existing 3.x backups
           will still use hardlinks for storage, and until those 3.x backups eventually expire,
           hardlinks will still be used for 3.x backups.

           BackupPC_migrateV3toV4 is an optional utility that can migrate existing 3.x backups to
           4.x stoage format, eliminating hardlinks.  This allows you to eliminate the old V3
           pool and you can then set $Conf{PoolV3Enabled} to 0.

               BackupPC_migrateV3toV4 -a [-m] [-p] [-v]
               BackupPC_migrateV3toV4 -h host [-n V3backupNum] [-m] [-p] [-v]
               Options:
                  -a              migrate all hosts and all backups
                  -h host         migrate just a specific host
                  -n V3backupNum  migrate specific host backup; does all V3 backups
                                  for that host if not specified
                  -m              don't migrate anything; just print what would be done
                  -p              don't print progress information
                  -v              verbose

           The BackupPC server should not be running when you run BackupPC_migrateV3toV4.  It
           will check and exit if the BackupPC server is running.

           If you want to test BackupPC_migrateV3toV4, a cautious approach is to make backup
           copies of the V3 backups, allowing you to restore them if there is any issue.  For
           example, if exampleHost has three 3.x backups numbered 5, 6, 7, you can use cp -prl
           (preserving hardlinks) to make copies:

               cd /data/BackupPC/pc/exampleHost
               mv 5 5.orig ; cp -prl 5.orig 5
               mv 6 6.orig ; cp -prl 6.orig 6
               mv 7 7.orig ; cp -prl 7.orig 7
               cp backups backups.save

               BackupPC_migrateV3toV4 -h exampleHost -n 5
               BackupPC_migrateV3toV4 -h exampleHost -n 6
               BackupPC_migrateV3toV4 -h exampleHost -n 7

           If you want to put things back the way they were:

               rm -rf 5 ; mv 5.orig 5
               rm -rf 6 ; mv 6.orig 6
               rm -rf 7 ; mv 7.orig 7
               # copy the [567] lines from backups.save into backups;
               # only do "cp backups.save backups" if you are sure no
               # new backups have been done

           Two important things to note with BackupPC_migrateV3toV4.  First, V4 storage does use
           more filesystem inodes than V3 (that's the small cost of getting rid of hardlinks).
           In particular, each directory in a backup tree uses two inodes in V4 (one for the
           directory, and one for the (empty) attrib file), and only one inode in V3 (one for the
           directory, and the attrib and all other files are hardlinked to the pool).  So before
           you run BackupPC_migrateV3toV4, make sure you have enough inodes in __TOPDIR__; use df
           -i to make sure you are under 45% inode usage.

           Secondly, if you run BackupPC_migrateV3toV4 on all your backups, the old V3 pool
           should be empty, except for old-style attrib files, which should all have only one
           link since no backups should reference them any longer.  Before you turn off the V3
           pool by setting $Conf{PoolV3Enabled} to 0, make sure BackupPC_nightly has run enough
           times (specifically, $Conf{PoolSizeNightlyUpdatePeriod} times) so that the V3 pool can
           be emptied.  You could do this manually, but only if you are very careful to check
           that the remaining files only have one link.

       BackupPC_poolCntPrint
           BackupPC_poolCntPrint is used to print reference count information, either per-backup,
           per-host or for the entire pool depending on the file path you use.

           If you provide a hex md5 digest, the entire pool count for that digest is printed.
           Usage:

               BackupPC_poolCntPrint [poolCntFilePath|hexDigest]...

       BackupPC_refCountUpdate
           BackupPC_refCountUpdate is used to either update the per-backup and per-host reference
           counts, or the system-wide reference counts. It is used by BackupPC_dump,
           BackupPC_nightly, BackupPC_backupDelete, BackupPC_backupDuplicate and BackupPC_fsck.
           Usage:

               BackupPC_refCountUpdate -h HOST [-c] [-f] [-F] [-o N] [-p] [-v]
                   With no other args, updates count db on backups with poolCntDelta files
                   and computers the host's total reference counts.  Also builds refCnt for
                   any >=4.0 backups without refCnts.
                     -f     - do an fsck on this HOST, which involves a rebuild of the
                              last two backup refCnts.  poolCntDelta files are ignored.
                              Also forces fsck if requested by needFsck flag files
                              in TopDir/pc/HOST/refCnt.  Equivalent to -o 2.
                     -F     - rebuild all the >=4.0 per-backup refCnt files for this
                              host.  Equivalent to -o 3.
                     -c     - compare current count db to new db before replacing
                     -o N   - override $Conf{RefCntFsck}.
                     -p     - don't show progress
                     -v     - verbose
                 Notes: in case there are legacy (ie: <=4.0.0alpha3) unapplied poolCntDelta
                 files in TopDir/pc/HOST/refCnt then the -f flag is turned on.

               BackupPC_refCountUpdate -m [-f] [-p] [-c] [-r N-M] [-s] [-v] [-P phase]
                     -m       Updates main count db, based on each HOST
                     -f     - do an fsck on all the hosts, ignoring poolCntDelta files,
                              and replacing each host's count db.  Will wait for backups
                              to finish if any are running.
                     -F     - rebuild all the >=4.0 per-backup refCnt files.
                     -p     - don't show progress
                     -c     - clean pool files
                     -r N-M - process a subset of the main count db, 0 <= N <= M <= 255
                     -s     - prints stats
                     -v     - verbose
                     -P phase Phase from 0..15 each time we run BackupPC_nightly.  Used
                              to compute exact pool size for portions of the pool based
                              on the phase and $Conf{PoolSizeNightlyUpdatePeriod}.

Other CGI Functions

Configuration and Host Editor
The CGI interface has a complete configuration and host editor. Only the administrator
can edit the main configuration settings and hosts. The edit links are in the left
navigation bar.

When changes are made to any parameter a "Save" button appears at the top of the page. If
you are editing a text box you will need to click outside of the text box to make the Save
button appear. If you don't select Save then the changes won't be saved.

The host-specific configuration can be edited from the host summary page using the link in
the left navigation bar. The administrator can edit any of the host-specific
configuration settings.

When editing the host-specific configuration, each parameter has an "override" setting
that denotes the value is host-specific, meaning that it overrides the setting in the main
configuration. If you deselect "override" then the setting is removed from the host-
specific configuration, and the main configuration file is displayed.

User's can edit their host-specific configuration if enabled via
$Conf{CgiUserConfigEditEnable}. The specific subset of configuration settings that a user
can edit is specified with $Conf{CgiUserConfigEdit}. It is recommended to make this list
short as possible (you probably don't want your users saving dozens of backups) and it is
essential that they can't edit any of the Cmd configuration settings, otherwise they can
specify an arbitrary command that will be executed as the BackupPC user.

Metrics
BackupPC supports a metrics endpoint that expose common information in a digest format.
Allowed metrics formats are "json" (default), "prometheus" and "rss". Format should be
specified using "format" query parameter, a URL similar to this will provide metrics
information:

http://localhost/cgi-bin/BackupPC/BackupPC_Admin?action=metrics
http://localhost/cgi-bin/BackupPC/BackupPC_Admin?action=metrics?format=json
http://localhost/cgi-bin/BackupPC/BackupPC_Admin?action=metrics?format=prometheus
http://localhost/cgi-bin/BackupPC/BackupPC_Admin?action=metrics?format=rss

JSON format requires the JSON::XS module to be installed. RSS format requires the
XML::RSS module to be installed.

This feature is experimental. The information included will probably change.

RSS
The RSS feed has been merged in the metrics endpoint (see section above). Please use the
metrics endpoint to access the RSS feed, as the old endpoint will be deprecated.

BackupPC supports a very basic RSS feed. Provided you have the XML::RSS perl module
installed, a URL similar to this will provide RSS information:

http://localhost/cgi-bin/BackupPC/BackupPC_Admin?action=rss

This feature is experimental. The information included will probably change.

BackupPC Design

Some design issues
Pooling common files
To see if a file is already in the pool, an MD5 digest of the file contents is used.
This can't guarantee a file is identical: it just reduces the search to often a single
file or handful of files.

Depending on the Xfer method and settings, a complete file comparison is done to
verify if two files are really the same.

Prior to V4, identical files on multiples backups are represented by hard links.
Hardlinks are used so that identical files all refer to the same physical file on the
server's disk. Also, hard links maintain reference counts so that BackupPC knows when
to delete unused files from the pool.

In V4+, hardlinks are not used and reference counting is done at the application
level. It is done in a batch manner, which simplifies the implementation.

For the computer-science majors among you, you can think of the pooling system used by
BackupPC as just a chained hash table stored on a (big) file system.

The hashing function
In V4+, the file digest is the MD5 digest of the complete file. While MD5 collisions
are now well known, and can be easily constructed, in real use collisions will be
extremely unlikely.

Prior to V4, just a portion of all but the smallest files was used for the digest.
That decision was made long ago when CPUs were a lot slower. For files less than
256K, the digest is the MD5 digest of the file size and the full file. For files up
to 1MB, the first and last 128K of the file, and for over 1MB, the first and eighth
128K chunks are used, together with the file size.

Compression
BackupPC supports compression. It uses the deflate and inflate methods in the
Compress::Zlib module, which is based on the zlib compression library (see
<http://www.gzip.org/zlib/>).

The $Conf{CompressLevel} setting specifies the compression level to use. Zero (0)
means no compression. Compression levels can be from 1 (least cpu time, slightly worse
compression) to 9 (most cpu time, slightly better compression). The recommended value
is 3. Changing it to 5, for example, will take maybe 20% more cpu time and will get
another 2-3% additional compression. Diminishing returns set in above 5. See the
zlib documentation for more information about compression levels.

BackupPC implements compression with minimal CPU load. Rather than compressing every
incoming backup file and then trying to match it against the pool, BackupPC computes
the MD5 digest based on the uncompressed file, and matches against the candidate pool
files by comparing each uncompressed pool file against the incoming backup file.
Since inflating a file takes roughly a factor of 10 less CPU time than deflating there
is a big saving in CPU time.

The combination of pooling common files and compression can yield a factor of 8 or
more overall saving in backup storage.

Note that you should not turn compression on and off are you have started running
BackupPC. It will result in double the storage needs, since all the files will be
stored in both the compressed and uncompressed pools.

BackupPC operation
BackupPC reads the configuration information from __CONFDIR__/config.pl. It then runs and
manages all the backup activity. It maintains queues of pending backup requests, user
backup requests and administrative commands. Based on the configuration various requests
will be executed simultaneously.

As specified by $Conf{WakeupSchedule}, BackupPC wakes up periodically to queue backups on
all the PCs. This is a four step process:

1. For each host and DHCP address backup requests are queued on the background command
queue.

2. For each PC, BackupPC_dump is forked. Several of these may be run in parallel, based
on the configuration. First a ping is done to see if the machine is alive. If this is
a DHCP address, nmblookup is run to get the netbios name, which is used as the
hostname. If DNS lookup fails, $Conf{NmbLookupFindHostCmd} is run to find the IP
address from the hostname. The file __TOPDIR__/pc/$host/backups is read to decide
whether a full or incremental backup needs to be run. If no backup is scheduled, or
the ping to $host fails, then BackupPC_dump exits.

The backup is done using the specified XferMethod. Either samba's smbclient or tar
over ssh/rsh/nfs piped into BackupPC_tarExtract, or rsync over ssh/rsh is run, or
rsyncd is connected to, with the incoming data extracted to __TOPDIR__/pc/$host/new.
The XferMethod output is put into __TOPDIR__/pc/$host/XferLOG.

The letter in the XferLOG file shows the type of object, similar to the first letter
of the modes displayed by ls -l:

d -> directory
l -> symbolic link
b -> block special file
c -> character special file
p -> pipe file (fifo)
nothing -> regular file

The words mean:

create
new for this backup (ie: directory or file not in pool)

pool
found a match in the pool

same
file is identical to previous backup (contents were checksummed and verified
during full dump).

skip
file skipped in incremental because attributes are the same (only displayed if
$Conf{XferLogLevel} >= 2).

As BackupPC_tarExtract extracts the files from smbclient or tar, or as rsync or ftp
runs, it checks each file in the backup to see if it is identical to an existing file
from any previous backup of any PC. It does this without needed to write the file to
disk. If the file matches an existing file, a hardlink is created to the existing file
in the pool. If the file does not match any existing files, the file is written to
disk and inserted into the pool.

BackupPC_tarExtract and rsync can handle arbitrarily large files and multiple
candidate matching files without needing to write the file to disk in the case of a
match. This significantly reduces disk writes (and also reads, since the pool file
comparison is done disk to memory, rather than disk to disk).

Based on the configuration settings, BackupPC_dump checks each old backup to see if
any should be removed.

3. Once each night, BackupPC_nightly is run to complete some additional administrative
tasks, such as cleaning the pool. This involves removing any files in the pool that
only have a single hard link (meaning no backups are using that file).

If BackupPC_nightly takes too long to run, the settings $Conf{MaxBackupPCNightlyJobs}
and $Conf{BackupPCNightlyPeriod} can be used to run several BackupPC_nightly processes
in parallel, and to split its job over several nights.

BackupPC also listens for TCP connections on $Conf{ServerPort}, which is used by the CGI
script BackupPC_Admin for status reporting and user-initiated backup or backup cancel
requests.

Storage layout
BackupPC resides in several directories:

__INSTALLDIR__
Perl scripts comprising BackupPC reside in __INSTALLDIR__/bin, libraries are in
__INSTALLDIR__/lib and documentation is in __INSTALLDIR__/doc.

__CGIDIR__
The CGI script BackupPC_Admin resides in this cgi binary directory.

__CONFDIR__
All the configuration information resides below __CONFDIR__. This directory contains:

The directory __CONFDIR__ contains:

config.pl
Configuration file. See "Configuration File" below for more details.

hosts
Hosts file, which lists all the PCs to backup.

pc The directory __CONFDIR__/pc contains per-client configuration files that override
settings in the main configuration file. Each file is named
__CONFDIR__/pc/HOST.pl, where HOST is the hostname.

In pre-FHS versions of BackupPC these files were located in
__TOPDIR__/pc/HOST/config.pl.

__LOGDIR__
The directory __LOGDIR__ (__TOPDIR__/log on pre-FHS versions of BackupPC) contains:

LOG Current (today's) log file output from BackupPC.

LOG.0 or LOG.0.z
Yesterday's log file output. Log files are aged daily and compressed (if
compression is enabled), and old LOG files are deleted.

status.pl
A summary of BackupPC's status written periodically by BackupPC so that certain
state information can be maintained if BackupPC is restarted. Should not be
edited.

UserEmailInfo.pl
A summary of what email was last sent to each user, and when the last email was
sent. Should not be edited.

__RUNDIR__
The directory __RUNDIR__ (__TOPDIR__/log on pre-FHS versions of BackupPC) contains:

BackupPC.pid
Contains BackupPC's process id.

BackupPC.sock
A unix domain socket for communicating to the BackupPC server.

__TOPDIR__
All of BackupPC's data (PC backup images, logs, configuration information) is stored
below this directory.

Below __TOPDIR__ are several directories:

__TOPDIR__/pool
All uncompressed files from PC backups are stored below __TOPDIR__/pool. Each
file's name is based on the MD5 hex digest of the file contents.

For V4+, the digest is the MD5 digest of the full file contents (the length is not
used). For V4+ the pool files are stored in a 2 level tree, using 7 bits from the
top of the first two bytes of the digest. So there are 128 directories are each
level, numbered evenly in hex from 0x00, 0x02, to 0xfe.

For example, if a file has an MD5 digest of 123456789abcdef0123456789abcdef0, the
uncompressed file is stored in
__TOPDIR__/pool/12/34/123456789abcdef0123456789abcdef0.

Duplicates digest are represented with one (or more) hex byte extensions. So
three colliding files would be stored as

__TOPDIR__/pool/12/34/123456789abcdef0123456789abcdef0
__TOPDIR__/pool/12/34/123456789abcdef0123456789abcdef000
__TOPDIR__/pool/12/34/123456789abcdef0123456789abcdef001

The rest of this section describes the old pool layout. Note that both V3 and V4
pools can exist together, since they use different names for their directory
trees.

As exampled earlier, prior to V4 the digest is computed as follows. For files
less than 256K, the file length and the entire file is used. For files up to 1MB,
the file length and the first and last 128K are used. Finally, for files longer
than 1MB, the file length, and the first and eighth 128K chunks for the file are
used.

Both BackupPC_dump (actually, BackupPC_tarExtract or rsync_bpc) are responsible
for checking newly backed up files against the pool. For each file, the MD5 digest
is used to generate a filename in the pool directory.

If the file exists in the pool, the contents are compared. If there is no match,
additional files in the chain are checked (if any). (Actually, multiple candidate
files are compared in parallel.)

If $Conf{PoolV3Enabled} is set, then the V3 pool is checked if there are no
matches in the V4 pool. If a V3 file matches, it is simply moved (renamed) the
the V4 pool with it's new filename based on the V4 digest. That still allows the
V3 backups to be browsed etc, since those backups are still based on hardlinks.

If the file contents exactly match, a reference count is incremented. Otherwise,
the file is added to the pool by using an atomic link operation, followed by
unlinking the temporary file.

One other issue: zero length files are not pooled, since there are a lot of these
files and on most file systems it doesn't save any disk space to turn these files
into hard links.

Prior to V4, each pool file is stored in a subdirectory X/Y/Z, where X, Y, Z are
the first 3 hex digits of the MD5 digest.

For example, if a file has an MD5 digest of 123456789abcdef0123456789abcdef0, the
file is stored in __TOPDIR__/pool/1/2/3/123456789abcdef0123456789abcdef0.

The MD5 digest might not be unique (especially since not all the file's contents
are used for files bigger than 256K). Different files that have the same MD5
digest are stored with a trailing suffix "_n" where n is an incrementing number
starting at 0. So, for example, if two additional files were identical to the
first, except the last byte was different, and assuming the file was larger than
1MB (so the MD5 digests are the same but the files are actually different), the
three files would be stored as:

__TOPDIR__/pool/1/2/3/123456789abcdef0123456789abcdef0
__TOPDIR__/pool/1/2/3/123456789abcdef0123456789abcdef0_0
__TOPDIR__/pool/1/2/3/123456789abcdef0123456789abcdef0_1

__TOPDIR__/cpool
All compressed files from PC backups are stored below __TOPDIR__/cpool. Its
layout is the same as __TOPDIR__/pool, and the hashing function is the same (and,
importantly, based on the uncompressed file, not the compressed file).

__TOPDIR__/pc/$host
For each PC $host, all the backups for that PC are stored below the directory
__TOPDIR__/pc/$host. This directory contains the following files:

LOG Current log file for this PC from BackupPC_dump.

LOG.MMYYYY or LOG.MMYYYY.z
Last month's log file. Log files are aged monthly and compressed (if
compression is enabled), and old LOG files are deleted. In earlier versions
of BackupPC these files used to have a suffix of 0, 1, ....

XferERR or XferERR.z
Output from the transport program (ie: smbclient, tar, rsync or ftp) for the
most recent failed backup.

XferLOG or XferLOG.z
Output from the transport program (ie: smbclient, tar, rsync or ftp) for the
current backup.

nnn (an integer)
Backups are in directories numbered sequentially starting at 0. Below each
backup directory are the inodes (in nnn/inode) and the reference counts for
this backup are in nnn/refCnt.

refCnt
The host's reference count database is stored below the refCnt directory.

XferLOG.nnn or XferLOG.nnn.z
Output from the transport program (ie: smbclient, tar, rsync or ftp)
corresponding to backup number nnn.

RestoreInfo.nnn
Information about restore request #nnn including who, what, when, and why.
This file is in Data::Dumper format. (Note that the restore numbers are not
related to the backup number.)

RestoreLOG.nnn.z
Output from smbclient, tar or rsync during restore #nnn. (Note that the
restore numbers are not related to the backup number.)

ArchiveInfo.nnn
Information about archive request #nnn including who, what, when, and why.
This file is in Data::Dumper format. (Note that the archive numbers are not
related to the restore or backup number.)

ArchiveLOG.nnn.z
Output from archive #nnn. (Note that the archive numbers are not related to
the backup or restore number.)

config.pl
Old location of optional configuration settings specific to this host.
Settings in this file override the main configuration file. In new versions
of BackupPC the per-host configuration files are stored in
__CONFDIR__/pc/HOST.pl.

backups
A tab-delimited ascii table listing information about each successful backup,
one per row. The columns are:

num The backup number, an integer that starts at 0 and increments for each
successive backup. The corresponding backup is stored in the directory
num (eg: if this field is 5, then the backup is stored in
__TOPDIR__/pc/$host/5).

type
Set to "full" or "incr" for full or incremental backup.

startTime
Start time of the backup in unix seconds.

endTime
Stop time of the backup in unix seconds.

nFiles
Number of files backed up (as reported by smbclient, tar, rsync or ftp).

size
Total file size backed up (as reported by smbclient, tar, rsync or ftp).

nFilesExist
Number of files that were already in the pool (as determined by
BackupPC_dump).

sizeExist
Total size of files that were already in the pool (as determined by
BackupPC_dump).

nFilesNew
Number of files that were not in the pool (as determined by
BackupPC_dump).

sizeNew
Total size of files that were not in the pool (as determined by
BackupPC_dump).

xferErrs
Number of errors or warnings from smbclient, tar, rsync or ftp.

xferBadFile
Number of errors from smbclient that were bad file errors (zero
otherwise).

xferBadShare
Number of errors from smbclient that were bad share errors (zero
otherwise).

tarErrs
Number of errors from BackupPC_tarExtract.

compress
The compression level used on this backup. Zero or empty means no
compression.

sizeExistComp
Total compressed size of files that were already in the pool (as
determined by BackupPC_dump).

sizeNewComp
Total compressed size of files that were not in the pool (as determined by
BackupPC_dump).

noFill
Set if this backup has not been filled - it just includes the deltas from
the next backup necessary to reconstruct this backup.

fillFromNum
If this backup was filled (ie: noFill is 0) then this is the number of the
backup that it was filled from

mangle
Set if this backup has mangled filenames and attributes. Always true for
backups in v1.4.0 and above. False for all backups prior to v1.4.0.

xferMethod
Set to the value of $Conf{XferMethod} when this dump was done.

level
The level of this dump. A full dump is level 0. Currently incrementals
are 1. In V4+ multi-level incrementals are no longer supported, so this
is just a 0 or 1.

charset
The client charset when this backup was made.

version
The BackupPC version when this backup was made.

inodeLast
The last inode number used in this backup.

keep
If set this backup won't be deleted.

share2path
Saves the value of $Conf{ClientShareName2Path} via Data::Dumper (with some
tabs, newlines and % characters replaced with %xx) so that the actual
client path for each share can be displayed when browsing.

restores
A tab-delimited ascii table listing information about each requested restore,
one per row. The columns are:

num Restore number (matches the suffix of the RestoreInfo.nnn and
RestoreLOG.nnn.z file), unrelated to the backup number.

startTime
Start time of the restore in unix seconds.

endTime
End time of the restore in unix seconds.

result
Result (ok or failed).

errorMsg
Error message if restore failed.

nFiles
Number of files restored.

size
Size in bytes of the restored files.

tarCreateErrs
Number of errors from BackupPC_tarCreate during restore.

xferErrs
Number of errors from smbclient, tar, rsync or ftp during restore.

archives
A tab-delimited ascii table listing information about each requested archive,
one per row. The columns are:

num Archive number (matches the suffix of the ArchiveInfo.nnn and
ArchiveLOG.nnn.z file), unrelated to the backup or restore number.

startTime
Start time of the restore in unix seconds.

endTime
End time of the restore in unix seconds.

result
Result (ok or failed).

errorMsg
Error message if archive failed.

Compressed file format
The compressed file format is as generated by Compress::Zlib::deflate with one minor, but
important, tweak. Since Compress::Zlib::inflate fully inflates its argument in memory, it
could take large amounts of memory if it was inflating a highly compressed file. For
example, a 200MB file of 0x0 bytes compresses to around 200K bytes. If
Compress::Zlib::inflate was called with this single 200K buffer, it would need to allocate
200MB of memory to return the result.

BackupPC watches how efficiently a file is compressing. If a big file has very high
compression (meaning it will use too much memory when it is inflated), BackupPC calls the
flush() method, which gracefully completes the current compression. BackupPC then starts
another deflate and simply appends the output file. So the BackupPC compressed file
format is one or more concatenated deflations/flushes. The specific ratios that BackupPC
uses is that if a 6MB chunk compresses to less than 64K then a flush will be done.

Back to the example of the 200MB file of 0x0 bytes. Adding flushes every 6MB adds only
200 or so bytes to the 200K output. So the storage cost of flushing is negligible.

To easily decompress a BackupPC compressed file, the script BackupPC_zcat can be found in
__INSTALLDIR__/bin. For each filename argument it inflates the file and writes it to
stdout.

Rsync checksum caching
Rsync checksum caching is not implemented in V4. That's because a full backup with rsync
in V4 uses client-side whole-file checksums during a full backup, meaning that the server
doesn't need to send block-level digests on every full backup.

The rest of this section applies to V3.

An incremental backup with rsync compares attributes on the client with the last full
backup. Any files with identical attributes are skipped. In V3, a full backup with rsync
sets the --ignore-times option, which causes every file to be examined independent of
attributes.

Each file is examined by generating block checksums (default 2K blocks) on the receiving
side (that's the BackupPC side), sending those checksums to the client, where the remote
rsync matches those checksums with the corresponding file. The matching blocks and new
data is sent back, allowing the client file to be reassembled. A checksum for the entire
file is sent to as an extra check the the reconstructed file is correct.

This results in significant disk IO and computation for BackupPC: every file in a full
backup, or any file with non-matching attributes in an incremental backup, needs to be
uncompressed, block checksums computed and sent. Then the receiving side reassembles the
file and has to verify the whole-file checksum. Even if the file is identical, prior to
2.1.0, BackupPC had to read and uncompress the file twice, once to compute the block
checksums and later to verify the whole-file checksum.

Filename mangling
Backup filenames are stored in "mangled" form. Each node of a path is preceded by "f"
(mnemonic: file), and special characters (\n, \r, % and /) are URI-encoded as "%xx", where
xx is the ascii character's hex value. So c:/craig/example.txt is now stored as
fc/fcraig/fexample.txt.

This was done mainly so metadata could be stored alongside the backup files without name
collisions. In particular, the attributes for the files in a directory are stored in a
file called "attrib", and mangling avoids filename collisions (I discarded the idea of
having a duplicate directory tree for every backup just to store the attributes). Other
metadata (eg: rsync checksums) could be stored in filenames preceded by, eg, "c". There
are two other benefits to mangling: the share name might contain "/" (eg: "/home/craig"
for tar transport), and I wanted that represented as a single level in the storage tree.

The CGI script undoes the mangling, so it is invisible to the user.

Special files
Linux/unix file systems support several special file types: symbolic links, character and
block device files, fifos (pipes) and unix-domain sockets. All except unix-domain sockets
are supported by BackupPC (there's no point in backing up or restoring unix-domain sockets
since they only have meaning after a process creates them). Symbolic links are stored as a
plain file whose contents are the contents of the link (not the file it points to). This
file is compressed and pooled like any normal file. Character and block device files are
also stored as plain files, whose contents are two integers separated by a comma; the
numbers are the major and minor device number. These files are compressed and pooled like
any normal file. Fifo files are stored as empty plain files (which are not pooled since
they have zero size). In all cases, the original file type is stored in the attrib file so
it can be correctly restored.

Hardlinks are supported. In V4, file metadata include an inode number and a link count.
Any file with more than one link points at the inode information stored below the backup
directory in the inode directory. That directory contains a tree of up to 16K attrib
files based on bits 10-23 of the inode number. In particular, the directory name uses
bits 17-23, and the attrib filename includes bits 10-16. The key (index) in the attrib
file is the hex inode number. The original file metadata's link count might not be
accurate; it's more a flag (>1) for when to look up the inode information. The correct
link count is stored in the inode.

In V3, hardlinks are stored in a similar manner to symlinks. When GNU tar first
encounters a file with more than one link (ie: hardlinks) it dumps it as a regular file.
When it sees the second and subsequent hardlinks to the same file, it dumps just the
hardlink information. BackupPC correctly recognizes these hardlinks and stores them just
like symlinks: a regular text file whose contents is the path of the file linked to. The
CGI script will download the original file when you click on a hardlink.

Also, BackupPC_tarCreate has enough magic to re-create the hardlinks dynamically based on
whether or not the original file and hardlinks are both included in the tar file. For
example, imagine a/b/x is a hardlink to a/c/y. If you use BackupPC_tarCreate to restore
directory a, then the tar file will include a/b/x as the original file and a/c/y will be a
hardlink to a/b/x. If, instead you restore a/c, then the tar file will include a/c/y as
the original file, not a hardlink.

Attribute file format
V4 attrib files
The attribute file format is new in V4. Every backup directory contains an attrib
file, which is zero length and its name includes the MD5 pool digest, eg:

attrib_33fe8f9ae2f5cedbea63b9d3ea767ac0

The digest is used to look up the contents in the V4 cpool, eg:

__TOPDIR__/cpool/32/fe/33fe8f9ae2f5cedbea63b9d3ea767ac0

For inode attrib files, bits 17-23 (XX in hex) of the inode number are used for the
directory name, and the attrib filename includes bits 10-16 (YY in hex), so relative
to the backup directory:

inode/XX/attribYY_33fe8f9ae2f5cedbea63b9d3ea767ac0

An empty attrib file has the name "attrib_0" (or "attribYY_0" for inodes).

The attrib file starts with a magic number, followed by the concatenation of the
following information for each file (all integers are stored in perl's pack "w" format
(variable length base 128)):

• Filename length, followed by the filename

• Count of extended attributes

• The unix file type, mtime, mode, uid, gid, size, inode number, compress, number of
links

• MD5 digest length, followed by the digest contents

• Each extended attribute (length of xattr name, length of xattr value, name, value)

V3 attrib files
The unix attributes for the contents of a directory (all the files and directories in
that directory) are stored in a file called attrib. There is a single attrib file for
each directory in a backup. For example, if c:/craig contains a single file
c:/craig/example.txt, that file would be stored as fc/fcraig/fexample.txt and there
would be an attribute file in fc/fcraig/attrib (and also fc/attrib and ./attrib). The
file fc/fcraig/attrib would contain a single entry containing the attributes for
fc/fcraig/fexample.txt.

The attrib file starts with a magic number, followed by the concatenation of the
following information for each file:

• Filename length in perl's pack "w" format (variable length base 128).

• Filename.

• The unix file type, mode, uid, gid and file size divided by 4GB and file size
modulo 4GB (type mode uid gid sizeDiv4GB sizeMod4GB), in perl's pack "w" format
(variable length base 128).

• The unix mtime (unix seconds) in perl's pack "N" format (32 bit integer).

The attrib file is also compressed if compression is enabled. See the
lib/BackupPC/Attrib.pm module for full details.

Attribute files are pooled just like normal backup files. This saves space if all the
files in a directory have the same attributes across multiple backups, which is
common.

Optimizations
BackupPC doesn't care about the access time of files in the pool since it saves attribute
metadata separate from the files. Since BackupPC mostly does reads from disk, maintaining
the access time of files generates a lot of unnecessary disk writes. So, provided
BackupPC has a dedicated data disk, you should consider mounting BackupPC's data directory
with the noatime (or, with Linux kernels >=2.6.20, relatime) attribute (see mount(1)).

Some Limitations
BackupPC isn't perfect (but it is getting better). Please see
<http://backuppc.sourceforge.net/faq/limitations.html> for a discussion of some of
BackupPC's limitations. (Note, this is old and we should move this to the Github Wiki.)

Security issues
Please see <http://backuppc.sourceforge.net/faq/security.html> for a discussion of some of
various security issues. (Note, this is old and we should move this to the Github Wiki.)

Configuration File

The BackupPC configuration file resides in __CONFDIR__/config.pl. Optional per-PC
configuration files reside in __CONFDIR__/pc/$host.pl (or __TOPDIR__/pc/$host/config.pl in
non-FHS versions of BackupPC). This file can be used to override settings just for a
particular PC.

Modifying the main configuration file
The configuration file is a perl script that is executed by BackupPC, so you should be
careful to preserve the file syntax (punctuation, quotes etc) when you edit it.
Specifically, preserving quotes means you should never use undef for configuration
parameters that expect string values. An empty string ('') should be used in this case.
It is recommended that you use CVS, RCS or some other method of source control for
changing config.pl.

BackupPC reads or re-reads the main configuration file and the hosts file in three cases:

• Upon startup.

• When BackupPC is sent a HUP (-1) signal. Assuming you installed the init.d script,
you can also do this with "/etc/init.d/backuppc reload".

• When the modification time of config.pl file changes. BackupPC checks the
modification time once during each regular wakeup.

Whenever you change the configuration file you can either do a kill -HUP BackupPC_pid or
simply wait until the next regular wakeup period.

Each time the configuration file is re-read a message is reported in the LOG file, so you
can tail it (or view it via the CGI interface) to make sure your kill -HUP worked. Errors
in parsing the configuration file are also reported in the LOG file.

The optional per-PC configuration file (__CONFDIR__/pc/$host.pl or
__TOPDIR__/pc/$host/config.pl in non-FHS versions of BackupPC) is read whenever it is
needed by BackupPC_dump, BackupPC_restore and others.

Configuration Parameters

       The configuration parameters are divided into five general groups.  The first group
       (general server configuration) provides general configuration for BackupPC.  The next two
       groups describe what to backup, when to do it, and how long to keep it.  The fourth group
       are settings for email reminders, and the final group contains settings for the CGI
       interface.

       All configuration settings in the second through fifth groups can be overridden by the
       per-PC config.pl file.

   General server configuration
       $Conf{ServerHost} = '';
           Host name on which the BackupPC server is running.

       $Conf{ServerPort} = -1;
           TCP port number on which the BackupPC server listens for and accepts connections.
           Normally this should be disabled (set to -1).  The TCP port is only needed if apache
           runs on a different machine from BackupPC.  In that case, set this to any spare port
           number over 1024 (eg: 2359).  If you enable the TCP port, make sure you set
           $Conf{ServerMesgSecret} too!

       $Conf{ServerMesgSecret} = '';
           Shared secret to make the TCP port secure.  Set this to a hard to guess string if you
           enable the TCP port (ie: $Conf{ServerPort} > 0).

           To avoid possible attacks via the TCP socket interface, every client message is
           protected by an MD5 digest. The MD5 digest includes four items:
             - a seed that is sent to the client when the connection opens
             - a sequence number that increments for each message
             - a shared secret that is stored in $Conf{ServerMesgSecret}
             - the message itself.

           The message is sent in plain text preceded by the MD5 digest.  A snooper can see the
           plain-text seed sent by BackupPC and plain-text message from the client, but cannot
           construct a valid MD5 digest since the secret $Conf{ServerMesgSecret} is unknown.  A
           replay attack is not possible since the seed changes on a per-connection and per-
           message basis.

       $Conf{MyPath} = '/bin';
           PATH setting for BackupPC.  An explicit value is necessary for taint mode.  Value
           shouldn't matter too much since all execs use explicit paths.  However, taint mode in
           perl will complain if this directory is world writable.

       $Conf{UmaskMode} = 027;
           Permission mask for directories and files created by BackupPC.  Default value prevents
           any access from group other, and prevents group write.

       $Conf{WakeupSchedule} = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18,
       19, 20, 21, 22, 23];
           Times at which we wake up, check all the PCs, and schedule necessary backups.  Times
           are measured in hours since midnight local time.  Can be fractional if necessary (eg:
           4.25 means 4:15am).

           If the hosts you are backing up are always connected to the network you might have
           only one or two wakeups each night.  This will keep the backup activity after hours.
           On the other hand, if you are backing up laptops that are only intermittently
           connected to the network you will want to have frequent wakeups (eg: hourly) to
           maximize the chance that each laptop is backed up.

           Examples:

               $Conf{WakeupSchedule} = [22.5];         # once per day at 10:30 pm.
               $Conf{WakeupSchedule} = [2,4,6,8,10,12,14,16,18,20,22];  # every 2 hours

           The default value is every hour except midnight.

           The first entry of $Conf{WakeupSchedule} is when BackupPC_nightly is run.  You might
           want to re-arrange the entries in $Conf{WakeupSchedule} (they don't have to be
           ascending) so that the first entry is when you want BackupPC_nightly to run (eg: when
           you don't expect a lot of regular backups to run).

       $Conf{PoolV3Enabled} = 0;
           If a V3 pool exists (ie: an upgrade) set this to 1.  This causes the V3 pool to be
           checked for matches if there are no matches in the V4 pool.

           For new installations, this should be set to 0.

       $Conf{MaxBackups} = 4;
           Maximum number of simultaneous backups to run.  If there are no user backup requests
           then this is the maximum number of simultaneous backups.

       $Conf{MaxUserBackups} = 4;
           Additional number of simultaneous backups that users can run.  As many as
           $Conf{MaxBackups} + $Conf{MaxUserBackups} requests can run at the same time.

       $Conf{MaxPendingCmds} = 15;
           Maximum number of pending link commands. New backups will only be started if there are
           no more than $Conf{MaxPendingCmds} plus $Conf{MaxBackups} number of pending link
           commands, plus running jobs.  This limit is to make sure BackupPC doesn't fall too far
           behind in running BackupPC_link commands.

       $Conf{CmdQueueNice} = 10;
           Nice level at which CmdQueue commands (eg: BackupPC_link and BackupPC_nightly) are run
           at.

       $Conf{MaxBackupPCNightlyJobs} = 2;
           How many BackupPC_nightly processes to run in parallel.

           Each night, at the first wakeup listed in $Conf{WakeupSchedule}, BackupPC_nightly is
           run.  Its job is to remove unneeded files in the pool, ie: files that only have one
           link.  To avoid race conditions, BackupPC_nightly and BackupPC_link cannot run at the
           same time.  Starting in v3.0.0, BackupPC_nightly can run concurrently with backups
           (BackupPC_dump).

           So to reduce the elapsed time, you might want to increase this setting to run several
           BackupPC_nightly processes in parallel (eg: 4, or even 8).

       $Conf{BackupPCNightlyPeriod} = 1;
           How many days (runs) it takes BackupPC_nightly to traverse the entire pool.  Normally
           this is 1, which means every night it runs, it does traverse the entire pool removing
           unused pool files.

           Other valid values are 2, 4, 8, 16.  This causes BackupPC_nightly to traverse 1/2,
           1/4, 1/8 or 1/16th of the pool each night, meaning it takes 2, 4, 8 or 16 days to
           completely traverse the pool.  The advantage is that each night the running time of
           BackupPC_nightly is reduced roughly in proportion, since the total job is split over
           multiple days.  The disadvantage is that unused pool files take longer to get deleted,
           which will slightly increase disk usage.

           Note that even when $Conf{BackupPCNightlyPeriod} > 1, BackupPC_nightly still runs
           every night.  It just does less work each time it runs.

           Examples:

              $Conf{BackupPCNightlyPeriod} = 1;   # entire pool is checked every night

              $Conf{BackupPCNightlyPeriod} = 2;   # two days to complete pool check
                                                  # (different half each night)

              $Conf{BackupPCNightlyPeriod} = 4;   # four days to complete pool check
                                                  # (different quarter each night)

       $Conf{PoolSizeNightlyUpdatePeriod} = 16;
           The total size of the files in the new V4 pool is updated every night when
           BackupPC_nightly runs BackupPC_refCountUpdate.  Instead of adding up the size of every
           pool file, it just updates the pool size total when files are added to or removed from
           the pool.

           To make sure these cumulative pool file sizes stay accurate, we recompute the V4 pool
           size for a portion of the pool each night from scratch, ie: by checking every file in
           that portion of the pool.

           $Conf{PoolSizeNightlyUpdatePeriod} sets how many nights it takes to completely update
           the V4 pool size.  It can be set to:
             0:  never do a full refresh; simply maintain the cumulative sizes
                 when files are added or deleted (fastest option)
             1:  recompute all  the V4 pool size every night (slowest option)
             2:  recompute 1/2  the V4 pool size every night
             4:  recompute 1/4  the V4 pool size every night
             8:  recompute 1/8  the V4 pool size every night
             16: recompute 1/16 the V4 pool size every night
                 (2nd fastest option; ensures the pool files sizes
                  stay accurate after a few day, in case the relative
                  upgrades miss a file)

       $Conf{PoolNightlyDigestCheckPercent} = 1;
           Integrity check the pool files by confirming the md5 digest of the contents matches
           their file name.  Because the pool is very large, only check a small random percentage
           of the pool files each night.

           This is check if there has been any server file system corruption.

           The default value of 1% means approximately 30% of the pool files will be checked each
           month, although the actual number will be a bit less since some files might be checked
           more than once in that time. If BackupPC_nightly takes too long, you could reduce this
           value.

       $Conf{RefCntFsck} = 1;
           Reference counts of pool files are computed per backup by accumulating the relative
           changes.  That means, however, that any error will never be corrected.  To be more
           conservative, we do a periodic full-redo of the backup reference counts (called an
           "fsck").  $Conf{RefCntFsck} controls how often this is done:

             0: no additional fsck
             1: do an fsck on the last backup if it is from a full backup
             2: do an fsck on the last two backups always
             3: do a full fsck on all the backups

           $Conf{RefCntFsck} = 1 is the recommended setting.

       $Conf{MaxOldLogFiles} = 14;
           Maximum number of log files we keep around in log directory.  These files are aged
           nightly.  A setting of 14 means the log directory will contain about 2 weeks of old
           log files, in particular at most the files LOG, LOG.0, LOG.1, ... LOG.13 (except
           today's LOG, these files will have a .z extension if compression is on).

           If you decrease this number after BackupPC has been running for a while you will have
           to manually remove the older log files.

       $Conf{DfPath} = '';
           Full path to the df command.  Security caution: normal users should not allowed to
           write to this file or directory.

       $Conf{DfCmd} = '$dfPath $topDir';
           Command to run df.  The following variables are substituted at run-time:

             $dfPath      path to df ($Conf{DfPath})
             $topDir      top-level BackupPC data directory

           Note: all Cmds are executed directly without a shell, so the prog name needs to be a
           full path and you can't include shell syntax like redirection and pipes; put that in a
           script if you need it.

       $Conf{DfInodeUsageCmd} = '$dfPath -i $topDir';
           Command to run df to get inode % usage.  The following variables are substituted at
           run-time:

             $dfPath      path to df ($Conf{DfPath})
             $topDir      top-level BackupPC data directory

           Note: all Cmds are executed directly without a shell, so the prog name needs to be a
           full path and you can't include shell syntax like redirection and pipes; put that in a
           script if you need it.

       $Conf{SplitPath} = '';
       $Conf{ParPath} = '';
       $Conf{CatPath} = '';
       $Conf{GzipPath} = '';
       $Conf{Bzip2Path} = '';
           Full path to various commands for archiving

       $Conf{DfMaxUsagePct} = 95;
           Maximum threshold for disk utilization on the __TOPDIR__ filesystem.  If the output
           from $Conf{DfCmd} reports a percentage larger than this number then no new regularly
           scheduled backups will be run.  However, user requested backups (which are usually
           incremental and tend to be small) are still performed, independent of disk usage.
           Also, currently running backups will not be terminated when the disk usage exceeds
           this number.

       $Conf{DfMaxInodeUsagePct} = 95;
           Maximum threshold for inode utilization on the __TOPDIR__ filesystem.  If the output
           from $Conf{DfInodeUsageCmd} reports a percentage larger than this number then no new
           regularly scheduled backups will be run.  However, user requested backups (which are
           usually incremental and tend to be small) are still performed, independent of disk
           usage.  Also, currently running backups will not be terminated when the disk inode
           usage exceeds this number.

       $Conf{DHCPAddressRanges} = [];
           List of DHCP address ranges we search looking for PCs to backup.  This is an array of
           hashes for each class C address range.  This is only needed if hosts in the conf/hosts
           file have the dhcp flag set.

           Examples:

              # to specify 192.10.10.20 to 192.10.10.250 as the DHCP address pool
              $Conf{DHCPAddressRanges} = [
                  {
                      ipAddrBase => '192.10.10',
                      first => 20,
                      last  => 250,
                  },
              ];
              # to specify two pools (192.10.10.20-250 and 192.10.11.10-50)
              $Conf{DHCPAddressRanges} = [
                  {
                      ipAddrBase => '192.10.10',
                      first => 20,
                      last  => 250,
                  },
                  {
                      ipAddrBase => '192.10.11',
                      first => 10,
                      last  => 50,
                  },
              ];

       $Conf{BackupPCUser} = '';
           The BackupPC user.

       $Conf{TopDir} = '';
       $Conf{ConfDir} = '';
       $Conf{LogDir} = '';
       $Conf{RunDir} = '';
       $Conf{InstallDir} = '';
       $Conf{CgiDir} = '';
           Important installation directories:

             TopDir     - where all the backup data is stored
             ConfDir    - where the main config and hosts files resides
             LogDir     - where log files and other transient information resides
             RunDir     - where pid and sock files reside
             InstallDir - where the bin, lib and doc installation dirs reside.
                          Note: you cannot change this value since all the
                          perl scripts include this path.  You must reinstall
                          with configure.pl to change InstallDir.
             CgiDir     - Apache CGI directory for BackupPC_Admin

           Note: it is STRONGLY recommended that you don't change the values here.  These are set
           at installation time and are here for reference and are used during upgrades.

           Instead of changing TopDir here it is recommended that you use a symbolic link to the
           new location, or mount the new BackupPC store at the existing $Conf{TopDir} setting.

       $Conf{BackupPCUserVerify} = 1;
           Whether BackupPC and the CGI script BackupPC_Admin verify that they are really running
           as user $Conf{BackupPCUser}.  If this flag is set and the effective user id (euid)
           differs from $Conf{BackupPCUser} then both scripts exit with an error.  This catches
           cases where BackupPC might be accidentally started as root or the wrong user, or if
           the CGI script is not installed correctly.

       $Conf{HardLinkMax} = 31999;
           Maximum number of hardlinks supported by the $TopDir file system that BackupPC uses.
           Most linux or unix file systems should support at least 32000 hardlinks per file, or
           64000 in other cases.  If a pool file already has this number of hardlinks, a new pool
           file is created so that new hardlinks can be accommodated.  This limit will only be
           hit if an identical file appears at least this number of times across all the backups.

       $Conf{PerlModuleLoad} = undef;
           Advanced option for asking BackupPC to load additional perl modules.  Can be a list
           (arrayref) of module names to load at startup.

       $Conf{ServerInitdPath} = '';
       $Conf{ServerInitdStartCmd} = '';
           Path to init.d script and command to use that script to start the server from the CGI
           interface.  The following variables are substituted at run-time:

             $sshPath           path to ssh ($Conf{SshPath})
             $serverHost        same as $Conf{ServerHost}
             $serverInitdPath   path to init.d script ($Conf{ServerInitdPath})

           Example:

           $Conf{ServerInitdPath}     = '/etc/init.d/backuppc'; $Conf{ServerInitdStartCmd} =
           '$sshPath -q -x -l root $serverHost'
                                      . ' $serverInitdPath start'
                                      . ' < /dev/null >& /dev/null';

           Note: all Cmds are executed directly without a shell, so the prog name needs to be a
           full path and you can't include shell syntax like redirection and pipes; put that in a
           script if you need it.

   What to backup and when to do it
       $Conf{FullPeriod} = 6.97;
           Minimum period in days between full backups. A full dump will only be done if at least
           this much time has elapsed since the last full dump, and at least $Conf{IncrPeriod}
           days has elapsed since the last successful dump.

           Typically this is set slightly less than an integer number of days. The time taken for
           the backup, plus the granularity of $Conf{WakeupSchedule} will make the actual backup
           interval a bit longer.

       $Conf{IncrPeriod} = 0.97;
           Minimum period in days between incremental backups (a user requested incremental
           backup will be done anytime on demand).

           Typically this is set slightly less than an integer number of days. The time taken for
           the backup, plus the granularity of $Conf{WakeupSchedule} will make the actual backup
           interval a bit longer.

       $Conf{FillCycle} = 0;
           In V4+, full/incremental backups are decoupled from whether the stored backup is
           filled/unfilled.

           To mimic V3 behaviour, if $Conf{FillCycle} is set to zero then fill/unfilled will
           continue to match full/incremental: full backups will remained filled, and incremental
           backups will be unfilled.  (However, the most recent backup is always filled, whether
           it is full or incremental.)  This is the recommended setting to keep things simple:
           since the backup expiry is actually done based on filled/unfilled (not
           full/incremental), keeping them synched makes it easier to understand the expiry
           settings.

           If you plan to do incremental-only backups (ie: set FullPeriod to a very large value),
           then you should set $Conf{FillCycle} to how often you want a stored backup to be
           filled.  For example, if $Conf{FillCycle} is set to 7, then every 7th backup will be
           filled (whether or not the corresponding backup was a full or not).

           There are two reasons you will want a non-zero $Conf{FillCycle} setting when you are
           only doing incrementals:

             - a filled backup is a starting point for merging deltas when you restore
               or view backups.  So having periodic filled backups makes it more
               efficient to view or restore older backups.

             - more importantly, in V4+, deleting backups is done based on Fill/Unfilled,
               not whether the original backup was full/incremental.  If there aren't any
               filled backups (other than the most recent), then the $Conf{FullKeepCnt}
               and related settings won't have any effect.

       $Conf{FullKeepCnt} = 1;
           Number of filled backups to keep.  Must be >= 1.

           The most recent backup (which is always filled) doesn't count when checking
           $Conf{FullKeepCnt}.  So if you specify $Conf{FullKeepCnt} = 1 then that means keep one
           full backup in addition to the most recent backup (which might be a filled incr or
           full).

           Note: Starting in V4+, deleting backups is done based on Fill/Unfilled, not whether
           the original backup was full/incremental. For backward compatibility, these parameters
           continue to be called FullKeepCnt, rather than FilledKeepCnt.  If $Conf{FillCycle} is
           0, then full backups continue to be filled, so the terms are interchangeable.  For V3
           backups, the expiry settings have their original meanings.

           In the steady state, each time a full backup completes successfully the oldest one is
           removed.  If this number is decreased, the extra old backups will be removed.

           Exponential backup expiry is also supported.  This allows you to specify:

             - num fulls to keep at intervals of 1 * $Conf{FillCycle}, followed by
             - num fulls to keep at intervals of 2 * $Conf{FillCycle},
             - num fulls to keep at intervals of 4 * $Conf{FillCycle},
             - num fulls to keep at intervals of 8 * $Conf{FillCycle},
             - num fulls to keep at intervals of 16 * $Conf{FillCycle},

           and so on.  This works by deleting every other full as each expiry boundary is
           crossed.  Note: if $Conf{FillCycle} is 0, then $Conf{FullPeriod} is used instead in
           these calculations.

           Exponential expiry is specified using an array for $Conf{FullKeepCnt}:

             $Conf{FullKeepCnt} = [4, 2, 3];

           Entry #n specifies how many fulls to keep at an interval of 2^n * $Conf{FillCycle}
           (ie: 1, 2, 4, 8, 16, 32, ...).

           The example above specifies keeping 4 of the most recent full backups (1 week
           interval) two full backups at 2 week intervals, and 3 full backups at 4 week
           intervals, eg:

              full 0 19 weeks old   \
              full 1 15 weeks old    >---  3 backups at 4 * $Conf{FillCycle}
              full 2 11 weeks old   /
              full 3  7 weeks old   \____  2 backups at 2 * $Conf{FillCycle}
              full 4  5 weeks old   /
              full 5  3 weeks old   \
              full 6  2 weeks old    \___  4 backups at 1 * $Conf{FillCycle}
              full 7  1 week old     /
              full 8  current       /

           On a given week the spacing might be less than shown as each backup ages through each
           expiry period.  For example, one week later, a new full is completed and the oldest is
           deleted, giving:

              full 0 16 weeks old   \
              full 1 12 weeks old    >---  3 backups at 4 * $Conf{FillCycle}
              full 2  8 weeks old   /
              full 3  6 weeks old   \____  2 backups at 2 * $Conf{FillCycle}
              full 4  4 weeks old   /
              full 5  3 weeks old   \
              full 6  2 weeks old    \___  4 backups at 1 * $Conf{FillCycle}
              full 7  1 week old     /
              full 8  current       /

           You can specify 0 as a count (except in the first entry), and the array can be as long
           as you wish.  For example:

             $Conf{FullKeepCnt} = [4, 0, 4, 0, 0, 2];

           This will keep 10 full dumps, 4 most recent at 1 * $Conf{FillCycle}, followed by 4 at
           an interval of 4 * $Conf{FillCycle} (approx 1 month apart), and then 2 at an interval
           of 32 * $Conf{FillCycle} (approx 7-8 months apart).

           Example: these two settings are equivalent and both keep just the four most recent
           full dumps:

              $Conf{FullKeepCnt} = 4;
              $Conf{FullKeepCnt} = [4];

       $Conf{FullKeepCntMin} = 1;
       $Conf{FullAgeMax} = 180;
           Very old full backups are removed after $Conf{FullAgeMax} days.  However, we keep at
           least $Conf{FullKeepCntMin} full backups no matter how old they are.

           Note that $Conf{FullAgeMax} will be increased to $Conf{FullKeepCnt} times
           $Conf{FillCycle} if $Conf{FullKeepCnt} specifies enough full backups to exceed
           $Conf{FullAgeMax}.

       $Conf{IncrKeepCnt} = 6;
           Number of incremental backups to keep.  Must be >= 1.

           Note: Starting in V4+, deleting backups is done based on Fill/Unfilled, not whether
           the original backup was full/incremental.  For historical reasons these parameters
           continue to be called IncrKeepCnt, rather than UnfilledKeepCnt.  If $Conf{FillCycle}
           is 0, then incremental backups continue to be unfilled, so the terms are
           interchangeable.  For V3 backups, the expiry settings have their original meanings.

           In the steady state, each time an incr backup completes successfully the oldest one is
           removed.  If this number is decreased, the extra old backups will be removed.

       $Conf{IncrKeepCntMin} = 1;
       $Conf{IncrAgeMax} = 30;
           Very old incremental backups are removed after $Conf{IncrAgeMax} days.  However, we
           keep at least $Conf{IncrKeepCntMin} incremental backups no matter how old they are.

       $Conf{BackupsDisable} = 0;
           Disable all full and incremental backups.  These settings are useful for a client that
           is no longer being backed up (eg: a retired machine), but you wish to keep the last
           backups available for browsing or restoring to other machines.

           There are three values for $Conf{BackupsDisable}:

             0    Backups are enabled.

             1    Don't do any regular backups on this client.  Manually
                  requested backups (via the CGI interface) will still occur.

             2    Don't do any backups on this client.  Manually requested
                  backups (via the CGI interface) will be ignored.

           In versions prior to 3.0 Backups were disabled by setting $Conf{FullPeriod} to -1 or
           -2.

       $Conf{RestoreInfoKeepCnt} = 10;
           Number of restore logs to keep.  BackupPC remembers information about each restore
           request.  This number per client will be kept around before the oldest ones are
           pruned.

           Note: files/dirs delivered via Zip or Tar downloads don't count as restores.  Only the
           first restore option (where the files and dirs are written to the host) count as
           restores that are logged.

       $Conf{ArchiveInfoKeepCnt} = 10;
           Number of archive logs to keep.  BackupPC remembers information about each archive
           request.  This number per archive client will be kept around before the oldest ones
           are pruned.

       $Conf{BackupFilesOnly} = undef;
           List of directories or files to backup.  If this is defined, only these directories or
           files will be backed up.

           For Smb, only one of $Conf{BackupFilesExclude} and $Conf{BackupFilesOnly} can be
           specified per share. If both are set for a particular share, then
           $Conf{BackupFilesOnly} takes precedence and $Conf{BackupFilesExclude} is ignored.

           This can be set to a string, an array of strings, or, in the case of multiple shares,
           a hash of strings or arrays.  A hash is used to give a list of directories or files to
           backup for each share (the share name is the key).  If this is set to just a string or
           array, and $Conf{SmbShareName} contains multiple share names, then the setting is
           assumed to apply all shares.

           If a hash is used, a special key "*" means it applies to all shares that don't have a
           specific entry.

           Examples:

              $Conf{BackupFilesOnly} = '/myFiles';
              $Conf{BackupFilesOnly} = ['/myFiles'];     # same as first example
              $Conf{BackupFilesOnly} = ['/myFiles', '/important'];
              $Conf{BackupFilesOnly} = {
                 'c' => ['/myFiles', '/important'],      # these are for 'c' share
                 'd' => ['/moreFiles', '/archive'],      # these are for 'd' share
              };
              $Conf{BackupFilesOnly} = {
                 'c' => ['/myFiles', '/important'],      # these are for 'c' share
                 '*' => ['/myFiles', '/important'],      # these are other shares
              };

       $Conf{BackupFilesExclude} = undef;
           List of directories or files to exclude from the backup.  For Smb, only one of
           $Conf{BackupFilesExclude} and $Conf{BackupFilesOnly} can be specified per share.  If
           both are set for a particular share, then $Conf{BackupFilesOnly} takes precedence and
           $Conf{BackupFilesExclude} is ignored.

           This can be set to a string, an array of strings, or, in the case of multiple shares,
           a hash of strings or arrays.  A hash is used to give a list of directories or files to
           exclude for each share (the share name is the key).  If this is set to just a string
           or array, and $Conf{SmbShareName} contains multiple share names, then the setting is
           assumed to apply to all shares.

           The exact behavior is determined by the underlying transport program, smbclient or
           tar.  For smbclient the exclude file list is passed into the X option.  Simple shell
           wild-cards using "*" or "?" are allowed.

           For tar, if the exclude file contains a "/" it is assumed to be anchored at the start
           of the string.  Since all the tar paths start with "./", BackupPC prepends a "." if
           the exclude file starts with a "/".  Note that GNU tar version >= 1.13.7 is required
           for the exclude option to work correctly.  For linux or unix machines you should add
           "/proc" to $Conf{BackupFilesExclude} unless you have specified --one-file-system in
           $Conf{TarClientCmd} or --one-file-system in $Conf{RsyncArgs}.  Also, for tar, do not
           use a trailing "/" in the directory name: a trailing "/" causes the name to not match
           and the directory will not be excluded.

           Users report that for smbclient you should specify a directory followed by "/*", eg:
           "/proc/*", instead of just "/proc".

           FTP servers are traversed recursively so excluding directories will also exclude its
           contents.  You can use the wildcard characters "*" and "?" to define files for
           inclusion and exclusion.  Both attributes $Conf{BackupFilesOnly} and
           $Conf{BackupFilesExclude} can be defined for the same share.

           If a hash is used, a special key "*" means it applies to all shares that don't have a
           specific entry.

           Examples:

              $Conf{BackupFilesExclude} = '/temp';
              $Conf{BackupFilesExclude} = ['/temp'];     # same as first example
              $Conf{BackupFilesExclude} = ['/temp', '/winnt/tmp'];
              $Conf{BackupFilesExclude} = {
                 'c' => ['/temp', '/winnt/tmp'],         # these are for 'c' share
                 'd' => ['/junk', '/dont_back_this_up'], # these are for 'd' share
              };
              $Conf{BackupFilesExclude} = {
                 'c' => ['/temp', '/winnt/tmp'],         # these are for 'c' share
                 '*' => ['/junk', '/dont_back_this_up'], # these are for other shares
              };

       $Conf{BlackoutBadPingLimit} = 3;
       $Conf{BlackoutGoodCnt} = 7;
           PCs that are always or often on the network can be backed up after hours, to reduce
           PC, network and server load during working hours. For each PC a count of consecutive
           good pings is maintained. Once a PC has at least $Conf{BlackoutGoodCnt} consecutive
           good pings it is subject to "blackout" and not backed up during hours and days
           specified by $Conf{BlackoutPeriods}.

           To allow for periodic rebooting of a PC or other brief periods when a PC is not on the
           network, a number of consecutive bad pings is allowed before the good ping count is
           reset. This parameter is $Conf{BlackoutBadPingLimit}.

           Note that bad and good pings don't occur with the same interval. If a machine is
           always on the network, it will only be pinged roughly once every $Conf{IncrPeriod}
           (eg: once per day). So a setting for $Conf{BlackoutGoodCnt} of 7 means it will take
           around 7 days for a machine to be subject to blackout. On the other hand, if a ping is
           failed, it will be retried roughly every time BackupPC wakes up, eg, every one or two
           hours. So a setting for $Conf{BlackoutBadPingLimit} of 3 means that the PC will lose
           its blackout status after 3-6 hours of unavailability.

           To disable the blackout feature set $Conf{BlackoutGoodCnt} to a negative value.  A
           value of 0 will make all machines subject to blackout.  But if you don't want to do
           any backups during the day it would be easier to just set $Conf{WakeupSchedule} to a
           restricted schedule.

       $Conf{BlackoutPeriods} = [ ... ];
           One or more blackout periods can be specified.  If a client is subject to blackout
           then no regular (non-manual) backups will be started during any of these periods.
           hourBegin and hourEnd specify hours from midnight and weekDays is a list of days of
           the week where 0 is Sunday, 1 is Monday etc.

           For example:

              $Conf{BlackoutPeriods} = [
                   {
                       hourBegin =>  7.0,
                       hourEnd   => 19.5,
                       weekDays  => [1, 2, 3, 4, 5],
                   },
              ];

           specifies one blackout period from 7:00am to 7:30pm local time on Mon-Fri.

           The blackout period can also span midnight by setting hourBegin > hourEnd, eg:

              $Conf{BlackoutPeriods} = [
                   {
                       hourBegin =>  7.0,
                       hourEnd   => 19.5,
                       weekDays  => [1, 2, 3, 4, 5],
                   },
                   {
                       hourBegin => 23,
                       hourEnd   =>  5,
                       weekDays  => [5, 6],
                   },
              ];

           This specifies one blackout period from 7:00am to 7:30pm local time on Mon-Fri, and a
           second period from 11pm to 5am on Friday and Saturday night.

       $Conf{BackupZeroFilesIsFatal} = 1;
           A backup of a share that has zero files is considered fatal. This is used to catch
           miscellaneous Xfer errors that result in no files being backed up.  If you have shares
           that might be empty (and therefore an empty backup is valid) you should set this flag
           to 0.

   How to backup a client
       $Conf{XferMethod} = 'smb';
           What transport method to use to backup each host.  If you have a mixed set of WinXX
           and linux/unix hosts you will need to override this in the per-PC config.pl.

           The valid values are:

             - 'smb':     backup and restore via smbclient and the SMB protocol.
                          Easiest choice for WinXX.

             - 'rsync':   backup and restore via rsync (via rsh or ssh).
                          Best choice for linux/unix.  Good choice also for WinXX.

             - 'rsyncd':  backup and restore via rsync daemon on the client.
                          Best choice for linux/unix if you have rsyncd running on
                          the client.  Good choice also for WinXX.

             - 'tar':    backup and restore via tar, tar over ssh, rsh or nfs.
                         Good choice for linux/unix.

             - 'archive': host is a special archive host.  Backups are not done.
                          An archive host is used to archive other host's backups
                          to permanent media, such as tape, CDR or DVD.

       $Conf{XferLogLevel} = 1;
           Level of verbosity in Xfer log files.  0 means be quiet, 1 will give one line per
           file, 2 will also show skipped files on incrementals, higher values give more output.

       $Conf{ClientCharset} = '';
           Filename charset encoding on the client.  BackupPC uses utf8 on the server for
           filename encoding.  If this is empty, then utf8 is assumed and client filenames will
           not be modified.  If set to a different encoding then filenames will converted to/from
           utf8 automatically during backup and restore.

           If the filenames displayed in the browser (eg: accents or special characters) don't
           look right then it is likely you haven't set $Conf{ClientCharset} correctly.

           If you are using smbclient on a WinXX machine, smbclient will convert to the "unix
           charset" setting in smb.conf.  The default is utf8, in which case leave
           $Conf{ClientCharset} empty since smbclient does the right conversion.

           If you are using rsync on a WinXX machine then it does no conversion.  A typical WinXX
           encoding for latin1/western europe is 'cp1252', so in this case set
           $Conf{ClientCharset} to 'cp1252'.

           On a linux or unix client, run "locale charmap" to see the client's charset.  Set
           $Conf{ClientCharset} to this value.  A typical value for english/US is 'ISO-8859-1'.

           Do "perldoc Encode::Supported" to see the list of possible charset values.  The FAQ at
           http://www.cl.cam.ac.uk/~mgk25/unicode.html is excellent, and
           http://czyborra.com/charsets/iso8859.html provides more information on the iso-8859
           charsets.

       $Conf{ClientCharsetLegacy} = 'iso-8859-1';
           Prior to 3.x no charset conversion was done by BackupPC.  Backups were stored in
           whatever charset the XferMethod provided - typically utf8 for smbclient and the
           client's locale settings for rsync and tar (eg: cp1252 for rsync on WinXX and perhaps
           iso-8859-1 with rsync on linux).  This setting tells BackupPC the charset that was
           used to store filenames in old backups taken with BackupPC 2.x, so that non-ascii
           filenames in old backups can be viewed and restored.

       $Conf{ClientShareName2Path} = {};
           Optionally map the share name to a different path on the client when the xfer program
           is run. This can be used if you create a snapshot on the client, which has a different
           path to the real share name.  Or you could use simpler names for the share instead of
           a path (eg: root, home, usr) and map them to the real paths here.

           This should be a hash whose key is the share name used in $Conf{SmbShareName},
           $Conf{TarShareName}, $Conf{RsyncShareName}, $Conf{FtpShareName}, and the value is the
           string path name on the client.  When a backup or restore is done, if there is no
           matching entry in $Conf{ClientShareName2Path}, or the entry is empty, then the share
           name is not modified (so the default behavior is unchanged).

           If you are using the rsyncd xfer method, then there is no need to use this
           configuration setting (since rsyncd already supports mapping of share names to paths
           in the client's rsyncd.conf).

   Samba Configuration
       $Conf{SmbShareName} = 'C$';
           Name of the host share that is backed up when using SMB.  This can be a string or an
           array of strings if there are multiple shares per host.  Examples:

             $Conf{SmbShareName} = 'c';          # backup 'c' share
             $Conf{SmbShareName} = ['c', 'd'];   # backup 'c' and 'd' shares

           This setting only matters if $Conf{XferMethod} = 'smb'.

       $Conf{SmbShareUserName} = '';
           Smbclient share username.  This is passed to smbclient's -U argument.

           This setting only matters if $Conf{XferMethod} = 'smb'.

       $Conf{SmbSharePasswd} = '';
           Smbclient share password.  This is passed to smbclient via its PASSWD environment
           variable.  There are several ways you can tell BackupPC the smb share password.  In
           each case you should be very careful about security.  If you put the password here,
           make sure that this file is not readable by regular users!  See the "Setting up
           config.pl" section in the documentation for more information.

           This setting only matters if $Conf{XferMethod} = 'smb'.

       $Conf{SmbClientPath} = '';
           Full path for smbclient. Security caution: normal users should not allowed to write to
           this file or directory.

           smbclient is from the Samba distribution. smbclient is used to actually extract the
           incremental or full dump of the share filesystem from the PC.

           This setting only matters if $Conf{XferMethod} = 'smb'.

       $Conf{SmbClientFullCmd} = ...
           Command to run smbclient for a full dump.  This setting only matters if
           $Conf{XferMethod} = 'smb'.

           The following variables are substituted at run-time:

              $smbClientPath   same as $Conf{SmbClientPath}
              $host            host to backup/restore
              $hostIP          host IP address
              $shareName       share name
              $userName        username
              $fileList        list of files to backup (based on exclude/include)
              $I_option        optional -I option to smbclient
              $X_option        exclude option (if $fileList is an exclude list)
              $timeStampFile   start time for incremental dump

           Note: all Cmds are executed directly without a shell, so the prog name needs to be a
           full path and you can't include shell syntax like redirection and pipes; put that in a
           script if you need it.

       $Conf{SmbClientIncrCmd} = ...
           Command to run smbclient for an incremental dump.  This setting only matters if
           $Conf{XferMethod} = 'smb'.

           Same variable substitutions are applied as $Conf{SmbClientFullCmd}.

           Note: all Cmds are executed directly without a shell, so the prog name needs to be a
           full path and you can't include shell syntax like redirection and pipes; put that in a
           script if you need it.

       $Conf{SmbClientRestoreCmd} = ...
           Command to run smbclient for a restore.  This setting only matters if
           $Conf{XferMethod} = 'smb'.

           Same variable substitutions are applied as $Conf{SmbClientFullCmd}.

           If your smb share is read-only then direct restores will fail.  You should set
           $Conf{SmbClientRestoreCmd} to undef and the corresponding CGI restore option will be
           removed.

           Note: all Cmds are executed directly without a shell, so the prog name needs to be a
           full path and you can't include shell syntax like redirection and pipes; put that in a
           script if you need it.

   Tar Configuration
       $Conf{TarShareName} = '/';
           Which host directories to backup when using tar transport.  This can be a string or an
           array of strings if there are multiple directories to backup per host.  Examples:

             $Conf{TarShareName} = '/';                    # backup everything
             $Conf{TarShareName} = '/home';                # only backup /home
             $Conf{TarShareName} = ['/home', '/src'];      # backup /home and /src

           The fact this parameter is called 'TarShareName' is for historical consistency with
           the Smb transport options.  You can use any valid directory on the client: there is no
           need for it to correspond to any Smb share or device mount point.

           Note also that you can also use $Conf{BackupFilesOnly} to specify a specific list of
           directories to backup.  It's more efficient to use this option instead of
           $Conf{TarShareName} since a new tar is run for each entry in $Conf{TarShareName}.

           On the other hand, if you add --one-file-system to $Conf{TarClientCmd} you can backup
           each file system separately, which makes restoring one bad file system easier.  In
           this case you would list all of the mount points here, since you can't get the same
           result with $Conf{BackupFilesOnly}:

               $Conf{TarShareName} = ['/', '/var', '/data', '/boot'];

           This setting only matters if $Conf{XferMethod} = 'tar'.

       $Conf{TarClientCmd} = '$sshPath -q -x -n -l root $host env LC_ALL=C $tarPath -c -v -f - -C
       $shareName+ --totals';
           Command to run tar on the client.  GNU tar is required.  You will need to fill in the
           correct paths for ssh2 on the local host (server) and GNU tar on the client.  Security
           caution: normal users should not allowed to write to these executable files or
           directories.

           $Conf{TarClientCmd} is appended with with either $Conf{TarFullArgs} or
           $Conf{TarIncrArgs} to create the final command that is run.

           See the documentation for more information about setting up ssh2 keys.

           If you plan to use NFS then tar just runs locally and ssh2 is not needed.  For
           example, assuming the client filesystem is mounted below /mnt/hostName, you could use
           something like:

              $Conf{TarClientCmd} = '$tarPath -c -v -f - -C /mnt/$host/$shareName'
                                  . ' --totals';

           In the case of NFS or rsh you need to make sure BackupPC's privileges are sufficient
           to read all the files you want to backup.  Also, you will probably want to add "/proc"
           to $Conf{BackupFilesExclude}.

           The following variables are substituted at run-time:

             $host        hostname
             $hostIP      host's IP address
             $incrDate    newer-than date for incremental backups
             $shareName   share name to backup (ie: top-level directory path)
             $fileList    specific files to backup or exclude
             $tarPath     same as $Conf{TarClientPath}
             $sshPath     same as $Conf{SshPath}

           If a variable is followed by a "+" it is shell escaped.  This is necessary for the
           command part of ssh or rsh, since it ends up getting passed through the shell.

           This setting only matters if $Conf{XferMethod} = 'tar'.

           Note: all Cmds are executed directly without a shell, so the prog name needs to be a
           full path and you can't include shell syntax like redirection and pipes; put that in a
           script if you need it.

       $Conf{TarFullArgs} = '$fileList+';
           Extra tar arguments for full backups.  Several variables are substituted at run-time.
           See $Conf{TarClientCmd} for the list of variable substitutions.

           If you are running tar locally (ie: without rsh or ssh) then remove the "+" so that
           the argument is no longer shell escaped.

           This setting only matters if $Conf{XferMethod} = 'tar'.

       $Conf{TarIncrArgs} = '--newer=$incrDate+ $fileList+';
           Extra tar arguments for incr backups.  Several variables are substituted at run-time.
           See $Conf{TarClientCmd} for the list of variable substitutions.

           Note that GNU tar has several methods for specifying incremental backups, including:

             --newer-mtime $incrDate+
                    This causes a file to be included if the modification time is
                    later than $incrDate (meaning its contents might have changed).
                    But changes in the ownership or modes will not qualify the
                    file to be included in an incremental.

             --newer=$incrDate+
                    This causes the file to be included if any attribute of the
                    file is later than $incrDate, meaning either attributes or
                    the modification time.  This is the default method.  Do
                    not use --atime-preserve in $Conf{TarClientCmd} above,
                    otherwise resetting the atime (access time) counts as an
                    attribute change, meaning the file will always be included
                    in each new incremental dump.

           If you are running tar locally (ie: without rsh or ssh) then remove the "+" so that
           the argument is no longer shell escaped.

           This setting only matters if $Conf{XferMethod} = 'tar'.

       $Conf{TarClientRestoreCmd} = ...
           Full command to run tar for restore on the client.  GNU tar is required.  This can be
           the same as $Conf{TarClientCmd}, with tar's -c replaced by -x and ssh's -n removed.

           See $Conf{TarClientCmd} for full details.

           This setting only matters if $Conf{XferMethod} = "tar".

           If you want to disable direct restores using tar, you should set
           $Conf{TarClientRestoreCmd} to undef and the corresponding CGI restore option will be
           removed.

           Note: all Cmds are executed directly without a shell, so the prog name needs to be a
           full path and you can't include shell syntax like redirection and pipes; put that in a
           script if you need it.

       $Conf{TarClientPath} = '';
           Full path for tar on the client. Security caution: normal users should not allowed to
           write to this file or directory.

           This setting only matters if $Conf{XferMethod} = 'tar'.

   Rsync/Rsyncd Configuration
       $Conf{RsyncClientPath} = '';
           Path to rsync executable on the client.  If it is set, it is passed to to rsync_bpc
           using the --rsync-path option.  You can also add sudo, for example:

                 $Conf{RsyncClientPath} = 'sudo /usr/bin/rsync';

           For OSX laptop clients, you can use caffeinate to make sure the laptop stays awake
           during the backup, eg:

                 $Conf{RsyncClientPath} = '/usr/bin/sudo /usr/bin/caffeinate -ism /usr/bin/rsync';

           This setting only matters if $Conf{XferMethod} = 'rsync'.

       $Conf{RsyncBackupPCPath} = "";
           Full path to rsync_bpc on the server.  Rsync_bpc is the customized version of rsync
           that is used on the server for rsync and rsyncd transfers.

       $Conf{RsyncSshArgs} = ['-e', '$sshPath -l root'];
           Ssh arguments for rsync to run ssh to connect to the client.  Rather than permit root
           ssh on the client, it is more secure to just allow ssh via a low-privileged user, and
           use sudo in $Conf{RsyncClientPath}.

           The setting should only have two entries: "-e" and everything else; don't add
           additional array elements.

           This setting only matters if $Conf{XferMethod} = 'rsync'.

       $Conf{RsyncShareName} = '/';
           Share name to backup.  For $Conf{XferMethod} = "rsync" this should be a file system
           path, eg '/' or '/home'.

           For $Conf{XferMethod} = "rsyncd" this should be the name of the module to backup (ie:
           the name from /etc/rsynd.conf).

           This can also be a list of multiple file system paths or modules.  For example, by
           adding --one-file-system to $Conf{RsyncArgs} you can backup each file system
           separately, which makes restoring one bad file system easier.  In this case you would
           list all of the mount points:

               $Conf{RsyncShareName} = ['/', '/var', '/data', '/boot'];

       $Conf{RsyncdClientPort} = 873;
           Rsync daemon port on the client, for $Conf{XferMethod} = "rsyncd".

       $Conf{RsyncdUserName} = '';
           Rsync daemon username on client, for $Conf{XferMethod} = "rsyncd".  The username and
           password are stored on the client in whatever file the "secrets file" parameter in
           rsyncd.conf points to (eg: /etc/rsyncd.secrets).

       $Conf{RsyncdPasswd} = '';
           Rsync daemon username on client, for $Conf{XferMethod} = "rsyncd".  The username and
           password are stored on the client in whatever file the "secrets file" parameter in
           rsyncd.conf points to (eg: /etc/rsyncd.secrets).

       $Conf{RsyncArgs} = [ ... ];
           Arguments to rsync for backup.  Do not edit the first set unless you have a good
           understanding of rsync options.

       $Conf{RsyncArgsExtra} = [];
           Additional arguments added to RsyncArgs.  This can be used in combination with
           $Conf{RsyncArgs} to allow customization of the rsync arguments on a part-client basis.
           The standard arguments go in $Conf{RsyncArgs} and $Conf{RsyncArgsExtra} can be set on
           a per-client basis.

           Examples of additional arguments that should work are --exclude/--include, eg:

               $Conf{RsyncArgsExtra} = [
                     '--exclude', '/proc',
                     '--exclude', '*.tmp',
                     '--acls',
                     '--xattrs',
               ];

           Both $Conf{RsyncArgs} and $Conf{RsyncArgsExtra} are subject to the following variable
           substitutions:

                  $client       client name being backed up
                  $host         hostname (could be different from client name if
                                           $Conf{ClientNameAlias} is set)
                  $hostIP       IP address of host
                  $confDir      configuration directory path
                  $shareName    share name being backed up

           This allows settings of the form:

               $Conf{RsyncArgsExtra} = [
                       '--exclude-from=$confDir/pc/$host.exclude',
               ];

       $Conf{RsyncFullArgsExtra} = ['--checksum'];
           Additional arguments for a full rsync or rsyncd backup.

           The --checksum argument causes the client to send full-file checksum for every file
           (meaning the client reads every file and computes the checksum, which is sent with the
           file list).  On the server, rsync_bpc will skip any files that have a matching full-
           file checksum, and size, mtime and number of hardlinks.  Any file that has different
           attributes will be updating using the block rsync algorithm.

           In V3, full backups applied the block rsync algorithm to every file, which is a lot
           slower but a bit more conservative.  To get that behavior, replace --checksum with
           --ignore-times.

       $Conf{RsyncIncrArgsExtra} = [];
           Additional arguments for an incremental rsync or rsyncd backup.

       $Conf{RsyncRestoreArgs} = [ ... ];
           Arguments to rsync for restore.  Do not edit the first set unless you have a thorough
           understanding of how File::RsyncP works.

           If you want to disable direct restores using rsync (eg: is the module is read-only),
           you should set $Conf{RsyncRestoreArgs} to undef and the corresponding CGI restore
           option will be removed.

           $Conf{RsyncRestoreArgs} is subject to the following variable substitutions:

                  $client       client name being backed up
                  $host         hostname (could be different from client name if
                                           $Conf{ClientNameAlias} is set)
                  $hostIP       IP address of host
                  $confDir      configuration directory path

           Note: $Conf{RsyncArgsExtra} doesn't apply to $Conf{RsyncRestoreArgs}.

       $Conf{RsyncRestoreArgsExtra} = [];
           Additional arguments for an rsync or rsyncd restore.

           This makes it easy to have per-client arguments.

   FTP Configuration
       $Conf{FtpShareName} = '';
           Which host directories to backup when using FTP.  This can be a string or an array of
           strings if there are multiple shares per host.

           This value must be specified in one of two ways: either as a subdirectory of the
           'share root' on the server, or as the absolute path of the directory.

           In the following example, if the directory /home/username is the root share of the ftp
           server with the given username, the following two values will back up the same
           directory:

              $Conf{FtpShareName} = 'www';                # www directory
              $Conf{FtpShareName} = '/home/username/www'; # same directory

           Path resolution is not supported; i.e.; you may not have an ftp share path defined as
           '../otheruser' or '~/games'.

            Multiple shares may also be specified, as with other protocols:

              $Conf{FtpShareName} = [ 'www',
                                      'bin',
                                      'config' ];

           Note also that you can also use $Conf{BackupFilesOnly} to specify a specific list of
           directories to backup.  It's more efficient to use this option instead of
           $Conf{FtpShareName} since a new tar is run for each entry in $Conf{FtpShareName}.

           This setting only matters if $Conf{XferMethod} = 'ftp'.

       $Conf{FtpUserName} = '';
           FTP username.  This is used to log into the server.

           This setting is used only if $Conf{XferMethod} = 'ftp'.

       $Conf{FtpPasswd} = '';
           FTP user password.  This is used to log into the server.

           This setting is used only if $Conf{XferMethod} = 'ftp'.

       $Conf{FtpPassive} = 1;
           Whether passive mode is used.  The correct setting depends upon whether local or
           remote ports are accessible from the other machine, which is affected by any firewall
           or routers between the FTP server on the client and the BackupPC server.

           This setting is used only if $Conf{XferMethod} = 'ftp'.

       $Conf{FtpBlockSize} = 10240;
           Transfer block size. This sets the size of the amounts of data in each frame. While
           undefined, this value takes the default value.

           This setting is used only if $Conf{XferMethod} = 'ftp'.

       $Conf{FtpPort} = 21;
           The port of the ftp server.  If undefined, 21 is used.

           This setting is used only if $Conf{XferMethod} = 'ftp'.

       $Conf{FtpTimeout} = 120;
           Connection timeout for FTP.  When undefined, the default is 120 seconds.

           This setting is used only if $Conf{XferMethod} = 'ftp'.

       $Conf{FtpFollowSymlinks} = 0;
           Behaviour when BackupPC encounters symlinks on the FTP share.

           Symlinks cannot be restored via FTP, so the desired behaviour will be different
           depending on the setup of the share. The default for this behavior is 1.  Directory
           shares with more complicated directory structures should consider other protocols.

   Archive Configuration
       $Conf{ArchiveDest} = '/tmp';
           Archive Destination

           The Destination of the archive e.g. /tmp for file archive or /dev/nst0 for device
           archive

       $Conf{ArchiveComp} = 'gzip';
           Archive Compression type

           The valid values are:

             - 'none':  No Compression

             - 'gzip':  Medium Compression. Recommended.

             - 'bzip2': High Compression but takes longer.

       $Conf{ArchivePar} = 0;
           Archive Parity Files

           The amount of Parity data to generate, as a percentage of the archive size.  Uses the
           command line par2 (par2cmdline) available from http://parchive.sourceforge.net

           Only useful for file dumps.

           Set to 0 to disable this feature.

       $Conf{ArchiveSplit} = 0;
           Archive Size Split

           Only for file archives. Splits the output into the specified size * 1,000,000.  e.g.
           to split into 650,000,000 bytes, specify 650 below.

           If the value is 0, or if $Conf{ArchiveDest} is an existing file or device (e.g. a
           streaming tape drive), this feature is disabled.

       $Conf{ArchiveClientCmd} = ...
           Archive Command

           This is the command that is called to actually run the archive process for each host.
           The following variables are substituted at run-time:

             $Installdir    The installation directory of BackupPC
             $tarCreatePath The path to BackupPC_tarCreate
             $splitpath     The path to the split program
             $parpath       The path to the par2 program
             $host          The host to archive
             $backupnumber  The backup number of the host to archive
             $compression   The path to the compression program
             $compext       The extension assigned to the compression type
             $splitsize     The number of bytes to split archives into
             $archiveloc    The location to put the archive
             $parfile       The amount of parity data to create (percentage)

           Note: all Cmds are executed directly without a shell, so the prog name needs to be a
           full path and you can't include shell syntax like redirection and pipes; put that in a
           script if you need it.

       $Conf{SshPath} = '';
           Full path for ssh. Security caution: normal users should not allowed to write to this
           file or directory.

       $Conf{NmbLookupPath} = '';
           Full path for nmblookup. Security caution: normal users should not allowed to write to
           this file or directory.

           nmblookup is from the Samba distribution. nmblookup is used to get the netbios name,
           necessary for DHCP hosts.

       $Conf{NmbLookupCmd} = '$nmbLookupPath -A $host';
           NmbLookup command.  Given an IP address, does an nmblookup on that IP address.  The
           following variables are substituted at run-time:

             $nmbLookupPath      path to nmblookup ($Conf{NmbLookupPath})
             $host               IP address

           This command is only used for DHCP hosts: given an IP address, this command should try
           to find its NetBios name.

           Note: all Cmds are executed directly without a shell, so the prog name needs to be a
           full path and you can't include shell syntax like redirection and pipes; put that in a
           script if you need it.

       $Conf{NmbLookupFindHostCmd} = '$nmbLookupPath $host';
           NmbLookup command.  Given a netbios name, finds that host by doing a NetBios lookup.
           Several variables are substituted at run-time:

             $nmbLookupPath      path to nmblookup ($Conf{NmbLookupPath})
             $host               NetBios name

           In some cases you might need to change the broadcast address, for example if nmblookup
           uses 192.168.255.255 by default and you find that doesn't work, try 192.168.1.255 (or
           your equivalent class C address) using the -B option:

              $Conf{NmbLookupFindHostCmd} = '$nmbLookupPath -B 192.168.1.255 $host';

           If you use a WINS server and your machines don't respond to multicast NetBios requests
           you can use this (replace 1.2.3.4 with the IP address of your WINS server):

              $Conf{NmbLookupFindHostCmd} = '$nmbLookupPath -R -U 1.2.3.4 $host';

           This is preferred over multicast since it minimizes network traffic.

           Experiment manually for your site to see what form of nmblookup command works.

           Note: all Cmds are executed directly without a shell, so the prog name needs to be a
           full path and you can't include shell syntax like redirection and pipes; put that in a
           script if you need it.

       $Conf{FixedIPNetBiosNameCheck} = 0;
           For fixed IP address hosts, BackupPC_dump can also verify the netbios name to ensure
           it matches the hostname.  An error is generated if they do not match.  Typically this
           flag is off.  But if you are going to transition a bunch of machines from fixed host
           addresses to DHCP, setting this flag is a great way to verify that the machines have
           their netbios name set correctly before turning on DHCP.

       $Conf{PingPath} = '';
           Full path to the ping command.  Security caution: normal users should not be allowed
           to write to this file or directory.

           If you want to disable ping checking, set this to some program that exits with 0
           status, eg:

               $Conf{PingPath} = '/bin/echo';

       $Conf{Ping6Path} = '';
           Like PingPath, but for IPv6.  Security caution: normal users should not be allowed to
           write to this file or directory.  In some environments, this is something like
           '/usr/bin/ping6'.  In modern environments, the regular ping command can handle both
           IPv4 and IPv6. In the latter case, just set it to $Conf{PingPath}

           If you want to disable ping checking for IPv6 hosts, set this to some program that
           exits with 0 status, eg:

               $Conf{Ping6Path} = '/bin/echo';

       $Conf{PingCmd} = '$pingPath -c 1 $host';
           Ping command.  The following variables are substituted at run-time:

             $pingPath      path to ping ($Conf{PingPath} or $Conf{Ping6Path})
                            depending on the address type of $host.
             $host          hostname

           Wade Brown reports that on solaris 2.6 and 2.7 ping -s returns the wrong exit status
           (0 even on failure).  Replace with "ping $host 1", which gets the correct exit status
           but we don't get the round-trip time.

           Note: all Cmds are executed directly without a shell, so the prog name needs to be a
           full path and you can't include shell syntax like redirection and pipes; put that in a
           script if you need it.

       $Conf{PingMaxMsec} = 20;
           Maximum round-trip ping time in milliseconds.  This threshold is set to avoid backing
           up PCs that are remotely connected through WAN or dialup connections.  The output from
           ping -s (assuming it is supported on your system) is used to check the round-trip
           packet time.  On your local LAN round-trip times should be much less than 20msec.  On
           most WAN or dialup connections the round-trip time will be typically more than 20msec.
           Tune if necessary.

       $Conf{CompressLevel} = 3;
           Compression level to use on files.  0 means no compression.  Compression levels can be
           from 1 (least cpu time, slightly worse compression) to 9 (most cpu time, slightly
           better compression).  The recommended value is 3.  Changing to 5, for example, will
           take maybe 20% more cpu time and will get another 2-3% additional compression. See the
           zlib documentation for more information about compression levels.

           Changing compression on or off after backups have already been done will require both
           compressed and uncompressed pool files to be stored.  This will increase the pool
           storage requirements, at least until all the old backups expire and are deleted.

           It is ok to change the compression value (from one non-zero value to another non-zero
           value) after dumps are already done.  Since BackupPC matches pool files by comparing
           the uncompressed versions, it will still correctly match new incoming files against
           existing pool files.  The new compression level will take effect only for new files
           that are newly compressed and added to the pool.

           If compression was off and you are enabling compression for the first time you can use
           the BackupPC_compressPool utility to compress the pool.  This avoids having the pool
           grow to accommodate both compressed and uncompressed backups.  See the documentation
           for more information.

       $Conf{ClientTimeout} = 72000;
           Timeout in seconds when listening for the transport program's (smbclient, tar etc)
           stdout. If no output is received during this time, then it is assumed that something
           has wedged during a backup, and the backup is terminated.

           Note that stdout buffering combined with huge files being backed up could cause
           longish delays in the output from smbclient that BackupPC_dump sees, so in some cases
           you might want to increase this value.

           For rsync, this is passed onto rsync_bpc using the --timeout argument, which is based
           on any I/O, so you could likely reduce this value.

       $Conf{MaxOldPerPCLogFiles} = 12;
           Maximum number of log files we keep around in each PC's directory (ie: pc/$host).
           These files are aged monthly.  A setting of 12 means there will be at most the files
           LOG, LOG.0, LOG.1, ... LOG.11 in the pc/$host directory (ie: about a year's worth).
           (Except this month's LOG, these files will have a .z extension if compression is on).

           If you decrease this number after BackupPC has been running for a while you will have
           to manually remove the older log files.

       $Conf{DumpPreUserCmd} = undef;
       $Conf{DumpPostUserCmd} = undef;
       $Conf{DumpPreShareCmd} = undef;
       $Conf{DumpPostShareCmd} = undef;
       $Conf{RestorePreUserCmd} = undef;
       $Conf{RestorePostUserCmd} = undef;
       $Conf{ArchivePreUserCmd} = undef;
       $Conf{ArchivePostUserCmd} = undef;
           Optional commands to run before and after dumps and restores, and also before and
           after each share of a dump.

           Stdout from these commands will be written to the Xfer (or Restore) log file.  One
           example of using these commands would be to shut down and restart a database server,
           dump a database to files for backup, or doing a snapshot of a share prior to a backup.
           Example:

              $Conf{DumpPreUserCmd} = '$sshPath -q -x -l root $host /usr/bin/dumpMysql';

           The following variable substitutions are made at run time for $Conf{DumpPreUserCmd},
           $Conf{DumpPostUserCmd}, $Conf{DumpPreShareCmd} and $Conf{DumpPostShareCmd}:

                  $type         type of dump (incr or full)
                  $xferOK       1 if the dump succeeded, 0 if it didn't
                  $client       client name being backed up
                  $host         hostname (could be different from client name if
                                           $Conf{ClientNameAlias} is set)
                  $hostIP       IP address of host
                  $user         username from the hosts file
                  $moreUsers    list of additional users from the hosts file
                  $share        the first share name (or current share for
                                  $Conf{DumpPreShareCmd} and $Conf{DumpPostShareCmd})
                  $shares       list of all the share names
                  $XferMethod   value of $Conf{XferMethod} (eg: tar, rsync, smb)
                  $sshPath      value of $Conf{SshPath},
                  $cmdType      set to DumpPreUserCmd or DumpPostUserCmd

           The following variable substitutions are made at run time for $Conf{RestorePreUserCmd}
           and $Conf{RestorePostUserCmd}:

                  $client       client name being backed up
                  $xferOK       1 if the restore succeeded, 0 if it didn't
                  $host         hostname (could be different from client name if
                                           $Conf{ClientNameAlias} is set)
                  $hostIP       IP address of host
                  $user         username from the hosts file
                  $moreUsers    list of additional users from the hosts file
                  $share        the first share name
                  $XferMethod   value of $Conf{XferMethod} (eg: tar, rsync, smb)
                  $sshPath      value of $Conf{SshPath},
                  $type         set to "restore"
                  $bkupSrcHost  hostname of the restore source
                  $bkupSrcShare share name of the restore source
                  $bkupSrcNum   backup number of the restore source
                  $pathHdrSrc   common starting path of restore source
                  $pathHdrDest  common starting path of destination
                  $fileList     list of files being restored
                  $cmdType      set to RestorePreUserCmd or RestorePostUserCmd

           The following variable substitutions are made at run time for $Conf{ArchivePreUserCmd}
           and $Conf{ArchivePostUserCmd}:

                  $client       client name being backed up
                  $xferOK       1 if the archive succeeded, 0 if it didn't
                  $host         Name of the archive host
                  $user         username from the hosts file
                  $share        the first share name
                  $XferMethod   value of $Conf{XferMethod} (eg: tar, rsync, smb)
                  $HostList     list of hosts being archived
                  $BackupList   list of backup numbers for the hosts being archived
                  $archiveloc   location where the archive is sent to
                  $parfile      amount of parity data being generated (percentage)
                  $compression  compression program being used (eg: cat, gzip, bzip2)
                  $compext      extension used for compression type (eg: raw, gz, bz2)
                  $splitsize    size of the files that the archive creates
                  $sshPath      value of $Conf{SshPath},
                  $type         set to "archive"
                  $cmdType      set to ArchivePreUserCmd or ArchivePostUserCmd

           Note: all Cmds are executed directly without a shell, so the prog name needs to be a
           full path and you can't include shell syntax like redirection and pipes; put that in a
           script if you need it.

       $Conf{UserCmdCheckStatus} = 0;
           Whether the exit status of each PreUserCmd and PostUserCmd is checked.

           If set and the Dump/Restore/Archive Pre/Post UserCmd returns a non-zero exit status
           then the dump/restore/archive is aborted.  To maintain backward compatibility (where
           the exit status in early versions was always ignored), this flag defaults to 0.

           If this flag is set and the Dump/Restore/Archive PreUserCmd fails then the matching
           Dump/Restore/Archive PostUserCmd is not executed.  If DumpPreShareCmd returns a non-
           exit status, then DumpPostShareCmd is not executed, but the DumpPostUserCmd is still
           run (since DumpPreUserCmd must have previously succeeded).

           An example of a DumpPreUserCmd that might fail is a script that snapshots or dumps a
           database which fails because of some database error.

       $Conf{ClientNameAlias} = undef;
           Override the client's hostname.  This allows multiple clients to all refer to the same
           physical host.  This should only be set in the per-PC config file and is only used by
           BackupPC at the last moment prior to checking the host is alive, and generating the
           command used to backup # that machine (ie: the value of $Conf{ClientNameAlias} is
           invisible everywhere else in BackupPC).  The setting can be a hostname or IP address,
           eg:

                   $Conf{ClientNameAlias} = 'realHostName';
                   $Conf{ClientNameAlias} = '192.1.1.15';

           which will cause the relevant smb/tar/rsync backup/restore commands to be directed to
           realHostName or the IP address, not the client name.

           It can also be an array, to allow checking (in order) of several host names or IP
           addresses that refer to the same host.  For example, if your client has a wired and
           wireless connection you could set:

                   $Conf{ClientNameAlias} = ['hostname-lan', 'hostname-wifi'];

           If hostname-lan is alive, it will be used for the backup/restore.  If not, the next
           name (hostname-wifi) is tested.

           Note: this setting doesn't work for hosts with DHCP set to 1.

       $Conf{ClientComment} = undef;
           A user-settable comment string that is displayed in this host's status.  The value is
           otherwise ignored by BackupPC.

   Email reminders, status and messages
       $Conf{SendmailPath} = '';
           Full path to the sendmail command.  Security caution: normal users should not allowed
           to write to this file or directory.

       $Conf{EMailNotifyMinDays} = 2.5;
           Minimum period between consecutive emails to a single user.  This tries to keep
           annoying email to users to a reasonable level.  Email checks are done nightly, so this
           number is effectively rounded up (ie: 2.5 means a user will never receive email more
           than once every 3 days).

       $Conf{EMailFromUserName} = '';
           Name to use as the "from" name for email.  Depending upon your mail handler this is
           either a plain name (eg: "admin") or a fully-qualified name (eg:
           "admin@mydomain.com").

       $Conf{EMailAdminUserName} = '';
           Destination address to an administrative user who will receive a nightly email with
           warnings and errors.  If there are no warnings or errors then no email will be sent.
           Depending upon your mail handler this is either a plain name (eg: "admin") or a fully-
           qualified name (eg: "admin@mydomain.com").

       $Conf{EMailAdminSubject} = '';
           Subject for admin emails.  If empty, defaults to pre-4.2.2 values.

       $Conf{EMailUserDestDomain} = '';
           Destination domain name for email sent to users.  By default this is empty, meaning
           email is sent to plain, unqualified addresses.  Otherwise, set it to the destination
           domain, eg:

              $Cong{EMailUserDestDomain} = '@mydomain.com';

           With this setting user email will be set to 'user@mydomain.com'.

       $Conf{EMailNoBackupEverSubj} = undef;
       $Conf{EMailNoBackupEverMesg} = undef;
           This subject and message is sent to a user if their PC has never been backed up.

           These values are language-dependent.  The default versions can be found in the
           language file (eg: lib/BackupPC/Lang/en.pm).  If you need to change the message, copy
           it here and edit it, eg:

             $Conf{EMailNoBackupEverMesg} = <<'EOF';
             To: $user$domain
             cc:
             Subject: $subj

             Dear $userName,

             This is a site-specific email message.
             EOF

       $Conf{EMailNotifyOldBackupDays} = 7.0;
           How old the most recent backup has to be before notifying user.  When there have been
           no backups in this number of days the user is sent an email.

       $Conf{EMailNoBackupRecentSubj} = undef;
       $Conf{EMailNoBackupRecentMesg} = undef;
           This subject and message is sent to a user if their PC has not recently been backed up
           (ie: more than $Conf{EMailNotifyOldBackupDays} days ago).

           These values are language-dependent.  The default versions can be found in the
           language file (eg: lib/BackupPC/Lang/en.pm).  If you need to change the message, copy
           it here and edit it, eg:

             $Conf{EMailNoBackupRecentMesg} = <<'EOF';
             To: $user$domain
             cc:
             Subject: $subj

             Dear $userName,

             This is a site-specific email message.
             EOF

       $Conf{EMailNotifyOldOutlookDays} = 5.0;
           How old the most recent backup of Outlook files has to be before notifying user.

       $Conf{EMailOutlookBackupSubj} = undef;
       $Conf{EMailOutlookBackupMesg} = undef;
           This subject and message is sent to a user if their Outlook files have not recently
           been backed up (ie: more than $Conf{EMailNotifyOldOutlookDays} days ago).

           These values are language-dependent.  The default versions can be found in the
           language file (eg: lib/BackupPC/Lang/en.pm).  If you need to change the message, copy
           it here and edit it, eg:

             $Conf{EMailOutlookBackupMesg} = <<'EOF';
             To: $user$domain
             cc:
             Subject: $subj

             Dear $userName,

             This is a site-specific email message.
             EOF

       $Conf{EMailHeaders} = <<EOF;
           Additional email headers.  This sets to charset to utf8.

   CGI user interface configuration settings
       $Conf{CgiAdminUserGroup} = '';
       $Conf{CgiAdminUsers} = '';
           Normal users can only access information specific to their host.  They can
           start/stop/browse/restore backups.

           Administrative users have full access to all hosts, plus overall status and log
           information.

           The administrative users are the union of the list of unix/linux groups, separated by
           spaces, in $Conf{CgiAdminUserGroup} and the list of users, separated by spaces, in
           $Conf{CgiAdminUsers}. If you don't want a list of groups or users set the
           corresponding configuration setting to undef or an empty string.

           If you want every user to have admin privileges (careful!), set $Conf{CgiAdminUsers} =
           '*'.

           Examples:

              $Conf{CgiAdminUserGroup} = 'admin wheel';
              $Conf{CgiAdminUsers}     = 'craig celia';
              --> administrative users are the union of groups admin and wheel, plus
                craig and celia.

              $Conf{CgiAdminUserGroup} = '';
              $Conf{CgiAdminUsers}     = 'craig celia';
              --> administrative users are only craig and celia'.

       $Conf{SCGIServerPort} = -1;
           TCP port number of the SCGI server.  A negative value disables the SCGI server.  Set
           to any available unprivileged TCP port number, eg: 10268.  Apache needs the mod_scgi
           module installed, and you will need to set the same port number in the Apache
           configuration. Here are some typical settings you'll need in Apache's httpd.conf:

              LoadModule scgi_module modules/mod_scgi.so
              SCGIMount /BackupPC_Admin 127.0.0.1:10268
              <Location /BackupPC_Admin>
                  AuthUserFile /etc/httpd/conf/passwd
                  AuthType basic
                  AuthName "access"
                  require valid-user
              </Location>

           Important security warning!!  The SCGIServerPort must not be accessible by anyone
           untrusted.  That means you can't allow untrusted users access to the BackupPC server,
           and you should block the SCGIServerPort TCP port on the BackupPC server.  If you don't
           understand what that means, or can't confirm you have configured SCGI securely, then
           don't enable it!!

       $Conf{CgiURL} = '';
           Full URL of the BackupPC_Admin CGI script, or the configured path for SCGI.  Used for
           links in email messages.

       $Conf{RrdToolPath} = '';
           Full path to the rrdtool command.  If available, graphs of pool usage will be
           generated.  If empty, then the graphs will be skipped.

           Security caution: normal users should not allowed to write to this file or directory.

       $Conf{Language} = 'en';
           Language to use.  See lib/BackupPC/Lang for the list of supported languages, which
           include English (en), French (fr), Spanish (es), German (de), Italian (it), Dutch
           (nl), Polish (pl), Portuguese Brazilian (pt_br) and Chinese (zh_CN).

           Currently the Language setting applies to the CGI interface and email messages sent to
           users.  Log files and other text are still in English.

       $Conf{CgiUserHomePageCheck} = '';
       $Conf{CgiUserUrlCreate} = 'mailto:%s';
           User names that are rendered by the CGI interface can be turned into links into their
           home page or other information about the user.  To set this up you need to create two
           sprintf() strings, that each contain a single '%s' that will be replaced by the user
           name.  The default is a mailto: link.

           $Conf{CgiUserHomePageCheck} should be an absolute file path that is used to check (via
           "-f") that the user has a valid home page.  Set this to undef or an empty string to
           turn off this check.

           $Conf{CgiUserUrlCreate} should be a full URL that points to the user's home page.  Set
           this to undef or an empty string to turn off generation of URLs for usernames.

           Example:

              $Conf{CgiUserHomePageCheck} = '/var/www/html/users/%s.html';
              $Conf{CgiUserUrlCreate}     = 'http://myhost/users/%s.html';
              --> if /var/www/html/users/craig.html exists, then 'craig' will
                be rendered as a link to http://myhost/users/craig.html.

       $Conf{CgiDateFormatMMDD} = 2;
           Date display format for CGI interface.  A value of 1 uses US-style dates (MM/DD), a
           value of 2 uses full YYYY-MM-DD format, and zero for international dates (DD/MM).

       $Conf{CgiNavBarAdminAllHosts} = 1;
           If set, the complete list of hosts appears in the left navigation bar pull-down for
           administrators.  Otherwise, just the hosts for which the user is listed in the host
           file (as either the user or in moreUsers) are displayed.

       $Conf{CgiSearchBoxEnable} = 1;
           Enable/disable the search box in the navigation bar.

       $Conf{CgiNavBarLinks} = [ ... ];
           Additional navigation bar links.  These appear for both regular users and
           administrators.  This is a list of hashes giving the link (URL) and the text (name)
           for the link.  Specifying lname instead of name uses the language specific string (ie:
           $Lang->{lname}) instead of just literally displaying name.

       $Conf{CgiStatusHilightColor} = { ...
           Highlight colors based on status that are used in the PC summary page.

       $Conf{CgiHeaders} = '<meta http-equiv="pragma" content="no-cache">';
           Additional CGI header text.

       $Conf{CgiImageDir} = '';
           Directory where images are stored.  This directory should be below Apache's
           DocumentRoot.  This value isn't used by BackupPC but is used by configure.pl when you
           upgrade BackupPC.

           Example:

               $Conf{CgiImageDir} = '/var/www/htdocs/BackupPC';

       $Conf{CgiExt2ContentType} = {};
           Additional mappings of filename extensions to Content-Type for individual file
           restore.  See $Ext2ContentType in BackupPC_Admin for the default setting.  You can add
           additional settings here, or override any default settings.  Example:

               $Conf{CgiExt2ContentType} = {
                           'pl'  => 'text/plain',
                    };

       $Conf{CgiImageDirURL} = '';
           URL (without the leading http://host) for BackupPC's image directory.  The CGI script
           uses this value to serve up image files.

           Example:

               $Conf{CgiImageDirURL} = '/BackupPC';

       $Conf{CgiCSSFile} = 'BackupPC_stnd.css';
           CSS stylesheet "skin" for the CGI interface.  It is stored in the $Conf{CgiImageDir}
           directory and accessed via the $Conf{CgiImageDirURL} URL.

           For BackupPC v3 and v2 the prior css versions are available as BackupPC_retro_v3.css
           and BackupPC_retro_v2.css

       $Conf{CgiUserDeleteBackupEnable} = 0;
           Whether the user is allowed to delete backups. If set to a positive value, the user
           will have a delete button for each backup on any host they have permission to access.
           If set to 0, only administrators have access to the backup delete feature.  If set to
           a negative value, even admins will not be able to use the delete feature.

       $Conf{CgiUserConfigEditEnable} = 1;
           Whether the user is allowed to edit their per-PC config.

       $Conf{CgiUserConfigEdit} = { ...
           Which per-host config variables a non-admin user is allowed to edit.  Admin users can
           edit all per-host config variables, even if disabled in this list.

           SECURITY WARNING: Do not let users edit any of the Cmd config variables!  That's
           because a user could set a Cmd to a shell script of their choice and it will be run as
           the BackupPC user.  That script could do all sorts of bad things.

Version Numbers

       BackupPC uses a X.Y.Z version numbering system.  The first digit is for major new
       releases, the middle digit is for significant feature releases and improvements (most of
       the releases have been in this category).

Author

       Craig Barratt  <cbarratt@users.sourceforge.net>

       See <https://backuppc.github.io/backuppc/BackupPC.html>.

Copyright

       Copyright (C) 2001-2020 Craig Barratt

Credits

Ryan Kucera contributed the directory navigation code and images for v1.5.0. He
contributed the first skeleton of BackupPC_restore. He also added a significant revision
to the CGI interface, including CSS tags, in v2.1.0, and designed the BackupPC logo.

Xavier Nicollet, with additions from Guillaume Filion, added the internationalization
(i18n) support to the CGI interface for v2.0.0. Xavier provided the French translation
fr.pm, with additions from Guillaume.

Guillaume Filion wrote BackupPC_zipCreate and added the CGI support for zip download, in
addition to some CGI cleanup, for v1.5.0. Guillaume continues to support fr.pm updates
for each new version.

Josh Marshall implemented the Archive feature in v2.1.0.

Ludovic Drolez supports the BackupPC Debian package.

Javier Gonzalez provided the Spanish translation, es.pm for v2.0.0.

Manfred Herrmann provided the German translation, de.pm for v2.0.0. Manfred continues to
support de.pm updates for each new version, together with some help from Ralph Passgang.

Lorenzo Cappelletti provided the Italian translation, it.pm for v2.1.0. Giuseppe Iuculano
and Vittorio Macchi updated it for 3.0.0.

Lieven Bridts provided the Dutch translation, nl.pm, for v2.1.0, with some tweaks from
Guus Houtzager, and updates for 3.0.0.

Reginaldo Ferreira provided the Portuguese Brazilian translation pt_br.pm for v2.2.0.

Rich Duzenbury provided the RSS feed option to the CGI interface.

Jono Woodhouse from CapeSoft Software (www.capesoft.com) provided a new CSS skin for 3.0.0
with several layout improvements. Sean Cameron (also from CapeSoft) designed new and more
compact file icons for 3.0.0.

Youlin Feng provided the Chinese translation for 3.1.0.

Karol 'Semper' Stelmaczonek provided the Polish translation for 3.1.0.

Jeremy Tietsort provided the host summary table sorting feature for 3.1.0.

Paul Mantz contributed the ftp Xfer method for 3.2.0.

Petr Pokorny provided the Czech translation for 3.2.1.

Rikiya Yamamoto provided the Japanese translation for 3.3.0.

Yakim provided the Ukrainian translation for 3.3.0.

Sergei Butakov provided the Russian translation for 3.3.0.

Alexander Moisseev provided the rrdtool graphing code in 4.0.0 and has provided many fixes
and improvements in 3.x and 4.x.

Many people have provided user support on the mail lists, reported bugs, made useful
suggestions, and helped with testing; see the ChangeLog and the mailing lists.

Your name could appear here in the next version!

License

       This program is free software: you can redistribute it and/or modify it under the terms of
       the GNU General Public License as published by the Free Software Foundation, either
       version 3 of the License, or (at your option) any later version.

       This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
       without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
       See the GNU General Public License for more details.

       You should have received a copy of the GNU General Public License along with this program.
       If not, see <http://www.gnu.org/licenses/>.