Ubuntu Manpage: This documentation describes BackupPC version 3.3.1, released on 11 Jan 2015.

Provided by: backuppc_3.3.1-4ubuntu1_amd64

BackupPC Introduction

This documentation describes BackupPC version 3.3.1, released on 11 Jan 2015.

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 (using hard links), resulting in substantial savings
in disk storage and disk writes.

• Optional compression provides additional reductions in storage (around 40%). 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 and Chinese

• 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), and Samba could be installed on
the linux or unix client to provide smb shares).

• 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 SourceForge.

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 full or
incremental backup. Starting in BackupPC 3.0 multi-level incrementals are supported. A full backup
has level 0. A new incremental of level N will backup all files that have changed since the most
recent backup of a lower level. $Conf{IncrLevels} is used to specify the level of each successive
incremental. The default value is all level 1, which makes the behavior the same as earlier versions
of BackupPC: each incremental will back up all the files that changed since the last full (level 0).

For SMB and tar, BackupPC uses the modification time (mtime) to determine which files have changed
since the last lower-level 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.

Rsync is more clever: 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.

BackupPC can also be configured to keep a certain number of incremental backups, and to keep a
smaller number of very old incremental backups. If multi-level incrementals are specified then it is
likely that more incrementals will need to be kept since lower-level incrementals (and the full
backup) are needed to reconstruct a higher-level incremental.

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 backup fails or is canceled, and some files have already been backed up, BackupPC keeps a
partial backup containing just the files that were backed up successfully. The partial backup is
removed when the next successful backup completes, or if another full backup fails resulting in a
newer partial backup. A failed full backup that has not backed up any files, or any failed
incremental backup, is removed; no partial backup is saved in these cases.

The partial backup may be browsed or used to restore files just like a successful full or incremental
backup.

With the rsync transfer method the partial backup is used to resume the next full backup, avoiding
the need to retransfer the file data already in the partial backup.

Identical Files
BackupPC pools identical files using hardlinks. 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 meta-data (permissions, ownership,
and modification time) separately from the file contents.

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, the addition of tar transport for linux/unix clients, plus full support for special file
types and unix attributes in v1.4.0 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 of old backups.

At some sites the disk-based backup will be adequate, without a secondary 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.

Resources
BackupPC home page
The BackupPC Open Source project is hosted on SourceForge. The home page can be found at:

http://backuppc.sourceforge.net

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

SourceForge project
The SourceForge project page is at:

http://sourceforge.net/projects/backuppc

This page has links to the current releases of BackupPC.

BackupPC Wiki
BackupPC has a Wiki at <http://backuppc.wiki.sourceforge.net>. Everyone is encouraged to contribute
to the Wiki. Anyone with a SourceForge account can edit the Wiki.

The old FAQ is at <http://backuppc.sourceforge.net/faq>, but is deprecated in favor of 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 and Gmane. The SourceForge lists are not always up to date and
the searching is limited, so Gmane is a good alternative. See:

http://news.gmane.org/index.php?prefix=gmane.comp.sysutils.backup.backuppc
http://sourceforge.net/mailarchive/forum.php?forum=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.

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>).

Unison is a utility that can do two-way, interactive, synchronization. See
<http://freshmeat.net/projects/unison>. An external wrapper around rsync that maintains transfer
data to enable two-way synchronization is drsync; see <http://freshmeat.net/projects/drsync>.

BackupPC provides many additional features, such as compressed storage, hardlinking 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
<http://backuppc.wiki.sourceforge.net>.

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.

Beyond being a satisfied user and telling other people about it, everyone is encouraged to add links to
<http://backuppc.sourceforge.net> (I'll see them via Google) or otherwise publicize BackupPC. Unlike the
commercial products in this space, I have a zero budget (in both time and money) for marketing, PR and
advertising, so it's up to all of you! Feel free to vote for BackupPC at
<http://freshmeat.net/projects/backuppc>.

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.

Several users have reported significantly better performance using reiserfs compared to ext3 for the
BackupPC data file system. It is also recommended you consider either an LVM or RAID setup (either
in HW or SW; eg: 3Ware RAID10 or RAID5) so that you can expand the file system as necessary.

When BackupPC starts with an empty pool, all the backup data will be written to the pool on disk.
After more backups are done, a higher percentage of incoming files will already be in the pool.
BackupPC is able to avoid writing to disk new files that are already in the pool. So over time disk
writes will reduce significantly (by perhaps a factor of 20 or more), since eventually 95% or more of
incoming backup files are typically in the pool. Disk reads from the pool are still needed to do file
compares to verify files are an exact match. So, with a mature pool, if a relatively fast client
generates data at say 1MB/sec, and you run 4 simultaneous backups, there will be an average server
disk load of about 4MB/sec reads and 0.2MB/sec writes (assuming 95% of the incoming files are in the
pool). These rates will be perhaps 40% lower if compression is on.

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

• Perl modules Compress::Zlib, Archive::Zip and File::RsyncP. Try "perldoc Compress::Zlib" 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 File::RsyncP module is available from <http://perlrsync.sourceforge.net> or CPAN. You'll need to
install the File::RsyncP module if you want to use Rsync as a transport method.

• 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>. Samba versions 3.x are stable and now recommended instead of 2.x.

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 1.13.7 at a
minimum, with 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/>.

• If you are using rsync to backup linux/unix machines you should have version 2.6.3 or higher on each
client machine. See <http://rsync.samba.org>. Use "rsync --version" to check your version.

For BackupPC to use Rsync you will also need to install the perl File::RsyncP module, which is
available from <http://perlrsync.sourceforge.net>. Version 0.68 or later is required.

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

What type of storage space do I need?
BackupPC uses hardlinks to pool files common to different backups. Therefore BackupPC's data store
(__TOPDIR__) must point to a single file system that supports hardlinks. You cannot split this file
system with multiple mount points or using symbolic links to point a sub-directory to a different file
system (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.

Starting with BackupPC 3.1.0, run-time checks are done at startup and at the start of each backup to
ensure that the file system can support hardlinks, since this is a common area of configuration problems.

How much disk space do I need?
Here's one real example 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.

For example, the Eudora email tool stores each mail folder in a separate file, and attachments are
extracted as separate files. So in the sadly common case of a large attachment emailed to many
recipients, Eudora will extract the attachment into a new file. When these machines are backed up, only
one copy of the file will be stored on the server, even though the file appears in many different full or
incremental backups. In this sense Eudora is a "friendly" application from the point of view of backup
storage requirements.

An example at the other end of the spectrum is Outlook. Everything (email bodies, attachments, calendar,
contact lists) is stored in a single file, which often becomes huge. Any change to this file requires a
separate copy of the file to be saved during backup. Outlook is even more troublesome, since it keeps
this file locked all the time, so it cannot be read by smbclient whenever Outlook is running. See the
"Some Limitations" section for more discussion of this problem.

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
Some linux distributions now include BackupPC. The Debian distribution, 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

In the future there might be packages for Gentoo and other linux flavors. If the packaged version is
older than the released version then you may want to install the latest version as described below.

Otherwise, manually fetching and installing BackupPC is easy. Start by downloading the latest version
from <http://backuppc.sourceforge.net>. Hit the "Code" button, then select the "backuppc" or "backuppc-
beta" package and download the latest version.

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 five perl modules you should install. These are all optional, but highly
recommended:

Compress::Zlib
To enable compression, you will need to install Compress::Zlib from <http://www.cpan.org>. You can
run "perldoc Compress::Zlib" to see if this module is installed.

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.

File::RsyncP
To use rsync and rsyncd with BackupPC you will need to install File::RsyncP. You can run "perldoc
File::RsyncP" to see if this module is installed. File::RsyncP is available from
<http://perlrsync.sourceforge.net>. Version 0.68 or later is required.

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 program. Alternatively, you can fetch the
tar.gz file from <http://www.cpan.org> and then run these commands:

tar zxvf Archive-Zip-1.26.tar.gz
cd Archive-Zip-1.26
perl Makefile.PL
make
make test
make install

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

Now let's move onto BackupPC itself. After fetching BackupPC-3.3.1.tar.gz, run these commands as root:

tar zxf BackupPC-3.3.1.tar.gz
cd BackupPC-3.3.1
perl configure.pl

In the future this release might also have patches available on the SourceForge site. These patch files
are text files, with a name of the form

BackupPC-3.3.1plN.diff

where N is the patch level, eg: pl2 is patch-level 2. These patch files are cumulative: you only need
apply the last patch file, not all the earlier patch files. If a patch file is available, eg:
BackupPC-3.3.1pl2.diff, you should apply the patch after extracting the tar file:

# fetch BackupPC-3.3.1.tar.gz
# fetch BackupPC-3.3.1pl2.diff
tar zxf BackupPC-3.3.1.tar.gz
cd BackupPC-3.3.1
patch -p0 < ../BackupPC-3.3.1pl2.diff
perl configure.pl

A patch file includes comments that describe that bug fixes and changes. Feel free to review it before
you apply the patch.

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 sys admin 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.

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
specifiy 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 white space:

Host name
This is typically the host name or NetBios name of the client machine and should be in lower case.
The host name 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 host name 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 user names, separate by commas and with no white space, 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 zip file on
<http://backuppc.sourceforge.net>. 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 everytime 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 file name 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 user name and password for a client machine that uses smb. The
user name 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 possible security risk, 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 file names 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 emtpy, since smbclient has already converted the file names 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.)

The requirements for each Xfer Method are:

tar You must have GNU tar on the client machine. Use "tar --version" or "gtar --version" to verify.
The version should be at least 1.13.7, and 1.13.20 or greater is recommended. 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}.

rsync
You should have at least rsync 2.6.3, and the latest version is recommended. Rsync is run on the
remote client via rsh or ssh.

The relevant configuration settings are $Conf{RsyncClientPath}, $Conf{RsyncClientCmd},
$Conf{RsyncClientRestoreCmd}, $Conf{RsyncShareName}, $Conf{RsyncArgs}, and
$Conf{RsyncRestoreArgs}.

rsyncd
You should have at least rsync 2.6.3, and the latest version is recommended. 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{RsyncdClientPort}, $Conf{RsyncdUserName},
$Conf{RsyncdPasswd}, $Conf{RsyncdAuthRequired}, $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.

ftp 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 file names are correctly
converted to utf8. Use "locale charmap" on the client to see its charset.

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 back up /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).

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.

Next you should decide whether to run tar over ssh, rsh or nfs. Ssh is the preferred method. Rsh is
not secure and therefore not recommended. Nfs will work, but you need to make sure that the BackupPC
user (running on the server) has sufficient permissions to read all the files below the nfs mount.

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. 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 at <http://backuppc.sourceforge.net/faq/ssh.html> or on the
Wiki.

Clients that use DHCP
If a client machine uses DHCP BackupPC needs some way to find the IP address given the host name.
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 host name.

For WinXX machines BackupPC uses the NetBios name server to determine the IP address given the host
name. 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 host name.

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.

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 sub-programs 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 jobs status should initially show just BackupPC_trashClean. 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. That's our next subject.

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 two options for setting up the CGI interface: standard mode and using mod_perl. Mod_perl
provides much higher performance (around 15x) and is the best choice if your Apache was built with
mod_perl support. To see if your apache was built with mod_perl run this command:

httpd -l | egrep mod_perl

If this prints mod_perl.c then your Apache supports mod_perl.

Note: on some distributions (like Debian) the command is not ``httpd'', but ``apache'' or ``apache2''.
Those distributions will generally also use ``apache'' for the Apache user account and configuration
files.

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. In contrast, the standard installation (without mod_perl) solves this
problem by having BackupPC_Admin installed as setuid to the BackupPC user, so that BackupPC_Admin runs as
the BackupPC user.

Here are some specifics for each setup:

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).

Mod_perl Setup
The advantage of the mod_perl setup is that no setuid script is needed, and there is a huge
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 15 times.

To use mod_perl you need to run Apache as user __BACKUPPCUSER__. If you need to run multiple
Apache's 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>.

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-binBackupPC/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 user name by getting Apache to set REMOTE_USER, eg, to hardcode
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.

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.

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.

Starting in 3.0.0 a new script bin/BackupPC_tarPCCopy can be used to assist the copy process. Given
one or more pc paths (eg: TOPDIR/pc/HOST or TOPDIR/pc/HOST/nnn), BackupPC_tarPCCopy creates a tar
archive with all the hardlinks pointing to ../cpool/.... Any files not hardlinked (eg: backups, LOG
etc) are included verbatim.

You will need to specify the -P option to tar when you extract the archive generated by
BackupPC_tarPCCopy since the hardlink targets are outside of the directory being extracted.

To copy a complete store (ie: __TOPDIR__) using BackupPC_tarPCCopy you should:

• stop BackupPC so that the store is static.

• copy the cpool, conf and log directory trees using any technique (like cp, rsync or tar) without
the need to preserve hardlinks.

• copy the pc directory using BackupPC_tarPCCopy:

su __BACKUPPCUSER__
cd NEW_TOPDIR
mkdir pc
cd pc
__INSTALLDIR__/bin/BackupPC_tarPCCopy __TOPDIR__/pc | tar xvPf -

Fixing installation problems
Please see the Wiki at <http://backuppc.wiki.sourceforge.net> for debugging suggestions. If you find a
solution to your problem that could help other users please add it to the 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 file name 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 host name, 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 file name argument it inflates (uncompresses) the file and writes it to stdout. To use
BackupPC_zcat you could give it the full file name, 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 non-zero status if it fails to
uncompress a 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

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 file names (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 file names (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.

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 adding 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 user name making the request.

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 unselect
"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.

RSS
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 quickly see if a file is already in the pool, an MD5 digest of the file length and contents is
used as the file name in the pool. This can't guarantee a file is identical: it just reduces the
search to often a single file or handful of files. A complete file comparison is always done to
verify if two files are really the same.

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.

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
There is a tradeoff between how much of file is used for the MD5 digest and the time taken comparing
all the files that have the same hash.

Using the file length and just the first 4096 bytes of the file for the MD5 digest produces some
repetitions. One example: with 900,000 unique files in the pool, this hash gives about 7,000
repeated files, and in the worst case 500 files have the same hash. That's not bad: we only have to
do a single file compare 99.2% of the time. But in the worst case we have to compare as many as 500
files checking for a match.

With a modest increase in CPU time, if we use the file length and the first 256K of the file we now
only have 500 repeated files and in the worst case around 20 files have the same hash. Furthermore,
if we instead use the first and last 128K of the file (more specifically, the first and eighth 128K
chunks for files larger than 1MB) we get only 300 repeated files and in the worst case around 20
files have the same hash.

Based on this experimentation, this is the hash function used by BackupPC. It is important that you
don't change the hash function after files are already in the pool. Otherwise your pool will grow to
twice the size until all the old backups (and all the old files with old hashes) eventually expire.

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.

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 host name. If DNS lookup fails,
$Conf{NmbLookupFindHostCmd} is run to find the IP address from the host name. The file
__TOPDIR__/pc/$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 the file name is saved in __TOPDIR__/pc/$host/NewFileList for later
processing by BackupPC_link. 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. Any expired backups are moved to __TOPDIR__/trash for later removal by BackupPC_trashClean.

3. For each complete, good, backup, BackupPC_link is run. To avoid race conditions as new files are
linked into the pool area, only a single BackupPC_link program runs at a time and the rest are
queued.

BackupPC_link reads the NewFileList written by BackupPC_dump and inspects each new file in the
backup. It re-checks if there is a matching file in the pool (another BackupPC_link could have added
the file since BackupPC_dump checked). If so, the file is removed and replaced by a hard link to the
existing file. If the file is new, a hard link to the file is made in the pool area, so that this
file is available for checking against each new file and new backup.

Then, if $Conf{IncrFill} is set (note that the default setting is off), for each incremental backup,
hard links are made in the new backup to all files that were not extracted during the incremental
backups. The means the incremental backup looks like a complete image of the PC (with the exception
that files that were removed on the PC since the last full backup will still appear in the backup
directory tree).

The CGI interface knows how to merge unfilled incremental backups will the most recent prior filled
(full) backup, giving the incremental backups a filled appearance. The default for $Conf{IncrFill}
is off, since there is no need to fill incremental backups. This saves some level of disk activity,
since lots of extra hardlinks are no longer needed (and don't have to be deleted when the backup
expires).

4. BackupPC_trashClean is always run in the background to remove any expired backups. Every 5 minutes it
wakes up and removes all the files in __TOPDIR__/trash.

Also, 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). Again, to avoid race conditions, BackupPC_nightly is only
run when there are no BackupPC_link processes running. When BackupPC_nightly is run no new
BackupPC_link jobs are started. 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 host
name.

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.

BackupPC.pid
Contains BackupPC's process id.

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.

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

Below __TOPDIR__ are several directories:

__TOPDIR__/trash
Any directories and files below this directory are periodically deleted whenever
BackupPC_trashClean checks. When a backup is aborted or when an old backup expires, BackupPC_dump
simply moves the directory to __TOPDIR__/trash for later removal by BackupPC_trashClean.

__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. Specifically, 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.

Each 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 123456789abcdef0, the file is stored in
__TOPDIR__/pool/1/2/3/123456789abcdef0.

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/1/2/3/123456789abcdef0
__TOPDIR__/pool/1/2/3/123456789abcdef0_0
__TOPDIR__/pool/1/2/3/123456789abcdef0_1

Both BackupPC_dump (actually, BackupPC_tarExtract) and BackupPC_link are responsible for checking
newly backed up files against the pool. For each file, the MD5 digest is used to generate a file
name in the pool directory. If the file exists in the pool, the contents are compared. If there
is no match, additional files ending in "_n" are checked. (Actually, BackupPC_tarExtract
compares multiple candidate files in parallel.) If the file contents exactly match, the file is
created by simply making a hard link to the pool file (this is done by BackupPC_tarExtract as the
backup proceeds). Otherwise, BackupPC_tarExtract writes the new file to disk and a new hard link
is made in the pool to the file (this is done later by BackupPC_link).

Therefore, every file in the pool will have at least 2 hard links (one for the pool file and one
for the backup file below __TOPDIR__/pc). Identical files from different backups or PCs will all
be linked to the same file. When old backups are deleted, some files in the pool might only have
one link. BackupPC_nightly checks the entire pool and removes all files that have only a single
link, thereby recovering the storage for that 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.

__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.DDMMYYYY or LOG.DDMMYYYY.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.

new Subdirectory in which the current backup is stored. This directory is renamed if the backup
succeeds.

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

nnn (an integer)
Successful backups are in directories numbered sequentially starting at 0.

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 and
BackupPC_link).

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

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

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

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 and BackupPC_link).

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

noFill
Set if this backup has not been filled in with the most recent previous filled or full
backup. See $Conf{IncrFill}.

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 file names 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. But when
multi-level incrementals are supported this will reflect each dump's incremental level.

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 file name argument it inflates the file and writes it to stdout.

Rsync checksum caching
An incremental backup with rsync compares attributes on the client with the last full backup. Any files
with identical attributes are skipped. 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.

Starting in 2.1.0, BackupPC supports optional checksum caching, which means the block and file checksums
only need to be computed once for each file. This results in a significant performance improvement.
This only works for compressed pool files. It is enabled by adding

'--checksum-seed=32761',

to $Conf{RsyncArgs} and $Conf{RsyncRestoreArgs}.

Rsync versions prior to and including rsync-2.6.2 need a small patch to add support for the
--checksum-seed option. This patch is available in the cygwin-rsyncd package at
<http://backuppc.sourceforge.net>. This patch is already included in rsync CVS, so it will be standard
in future versions of rsync.

When this option is present, BackupPC will add block and file checksums to the compressed pool file the
next time a pool file is used and it doesn't already have cached checksums. The first time a new file is
written to the pool, the checksums are not appended. The next time checksums are needed for a file, they
are computed and added. So the full performance benefit of checksum caching won't be noticed until the
third time a pool file is used (eg: the third full backup).

With checksum caching enabled, there is a risk that should a file's contents in the pool be corrupted due
to a disk problem, but the cached checksums are still correct, the corruption will not be detected by a
full backup, since the file contents are no longer read and compared. To reduce the chance that this
remains undetected, BackupPC can recheck cached checksums for a fraction of the files. This fraction is
set with the $Conf{RsyncCsumCacheVerifyProb} setting. The default value of 0.01 means that 1% of the
time a file's checksums are read, the checksums are verified. This reduces performance slightly, but,
over time, ensures that files contents are in sync with the cached checksums.

The format of the cached checksum data can be discovered by looking at the code. Basically, the first
byte of the compressed file is changed to denote that checksums are appended. The block and file
checksum data, plus some other information and magic word, are appended to the compressed file. This
allows the cache update to be done in-place.

File name mangling
Backup file names 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 meta-data 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 file name collisions (I discarded the idea of having a duplicate directory tree for every
backup just to store the attributes). Other meta-data (eg: rsync checksums) could be stored in file names
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.
Secondly, as files are written to NewFileList for later processing by BackupPC_link, embedded newlines in
the file's path will cause problems which are avoided by mangling.

The CGI script undoes the mangling, so it is invisible to the user. Old (unmangled) backups are still
supported by the CGI interface.

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 also supported. 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
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:

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

• File name.

• 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 meta-data
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.

Security issues
Please see <http://backuppc.sourceforge.net/faq/security.html> for a discussion of some of various
security issues.

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. 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_link 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.  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{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{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{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{DfPath} 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{TrashCleanSleepSec} = 300;
           How long BackupPC_trashClean sleeps in seconds between each check of the trash directory.  Once every
           5 minutes should be reasonable.

       $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{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
             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
           accidently 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 (array ref) 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{FullKeepCnt} = 1;
           Number of full backups to keep.  Must be >= 1.

           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.

           If  filling  of incremental dumps is off the oldest backup always has to be a full (ie: filled) dump.
           This might mean one or two extra full dumps are kept until the oldest incremental backups expire.

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

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

           and so on.  This works by deleting every other full as each expiry boundary is crossed.

           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{FullPeriod} (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{FullPeriod}
              full 2 11 weeks old   /
              full 3  7 weeks old   \____  2 backups at 2 * $Conf{FullPeriod}
              full 4  5 weeks old   /
              full 5  3 weeks old   \
              full 6  2 weeks old    \___  4 backups at 1 * $Conf{FullPeriod}
              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{FullPeriod}
              full 2  8 weeks old   /
              full 3  6 weeks old   \____  2 backups at 2 * $Conf{FullPeriod}
              full 4  4 weeks old   /
              full 5  3 weeks old   \
              full 6  2 weeks old    \___  4 backups at 1 * $Conf{FullPeriod}
              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{FullPeriod}, followed by 4 at an interval of
           4 * $Conf{FullPeriod} (approx 1 month apart), and then 2 at an interval  of  32  *  $Conf{FullPeriod}
           (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} = 90;
           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{FullPeriod}  if
           $Conf{FullKeepCnt} specifies enough full backups to exceed $Conf{FullAgeMax}.

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

           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{IncrLevels} = [1];
           Level  of  each incremental.  "Level" follows the terminology of dump(1).  A full backup has level 0.
           A new incremental of level N will backup all files that have changed since the most recent backup  of
           a lower level.

           The entries of $Conf{IncrLevels} apply in order to each incremental after each full backup.  It wraps
           around until the next full backup.  For example, these two settings have the same effect:

                 $Conf{IncrLevels} = [1, 2, 3];
                 $Conf{IncrLevels} = [1, 2, 3, 1, 2, 3];

           This  means  the 1st and 4th incrementals (level 1) go all the way back to the full.  The 2nd and 3rd
           (and 5th and 6th) backups just go back to the immediate preceeding incremental.

           Specifying a sequence of multi-level incrementals will  usually  mean  more  than  $Conf{IncrKeepCnt}
           incrementals will need to be kept, since lower level incrementals are needed to merge a complete view
           of a backup.  For example, with

                 $Conf{FullPeriod}  = 7;
                 $Conf{IncrPeriod}  = 1;
                 $Conf{IncrKeepCnt} = 6;
                 $Conf{IncrLevels}  = [1, 2, 3, 4, 5, 6];

           there will be up to 11 incrementals in this case:

                 backup #0  (full, level 0, oldest)
                 backup #1  (incr, level 1)
                 backup #2  (incr, level 2)
                 backup #3  (incr, level 3)
                 backup #4  (incr, level 4)
                 backup #5  (incr, level 5)
                 backup #6  (incr, level 6)
                 backup #7  (full, level 0)
                 backup #8  (incr, level 1)
                 backup #9  (incr, level 2)
                 backup #10 (incr, level 3)
                 backup #11 (incr, level 4)
                 backup #12 (incr, level 5, newest)

           Backup #1 (the oldest level 1 incremental) can't be deleted since backups 2..6 depend on it.  Those 6
           incrementals  can't all be deleted since that would only leave 5 (#8..12).  When the next incremental
           happens (level 6), the complete set of 6 older incrementals  (#1..6)  will  be  deleted,  since  that
           maintains the required number ($Conf{IncrKeepCnt}) of incrementals.  This situation is reduced if you
           set shorter chains of multi-level incrementals, eg:

                 $Conf{IncrLevels}  = [1, 2, 3];

           would only have up to 2 extra incremenals before all 3 are deleted.

           BackupPC  as  usual merges the full and the sequence of incrementals together so each incremental can
           be browsed and restored as though it  is  a  complete  backup.   If  you  specify  a  long  chain  of
           incrementals  then  more  backups need to be merged when browsing, restoring, or getting the starting
           point for rsync backups.  In the example above (levels 1..6), browing backup #6 requires 7  different
           backups (#0..6) to be merged.

           Because  of this merging and the additional incrementals that need to be kept, it is recommended that
           some level 1 incrementals be included in $Conf{IncrLevels}.

           Prior to version 3.0 incrementals were always level 1, meaning each incremental  backed  up  all  the
           files that changed since the last full.

       $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{PartialAgeMax} = 3;
           A failed full backup is saved as a partial backup.  The rsync XferMethod can take  advantage  of  the
           partial full when the next backup is run. This parameter sets the age of the partial full in days: if
           the  partial  backup  is older than this number of days, then rsync will ignore (not use) the partial
           full when the next backup is run.  If you set this to a negative  value  then  no  partials  will  be
           saved.  If you set this to 0, partials will be saved, but will not be used by the next backup.

           The  default  setting  of 3 days means that a partial older than 3 days is ignored when the next full
           backup is done.

       $Conf{IncrFill} = 0;
           Whether incremental backups are filled.  "Filling" means that the most recent full (or  filled)  dump
           is  merged into the new incremental dump using hardlinks.  This makes an incremental dump look like a
           full dump.  Prior to v1.03 all incremental backups were filled.  In v1.4.0 and later the  default  is
           off.

           BackupPC,  and  the cgi interface in particular, do the right thing on un-filled incremental backups.
           It will correctly display the merged incremental backup with the most recent  filled  backup,  giving
           the  un-filled  incremental backups a filled appearance.  That means it invisible to the user whether
           incremental dumps are filled or not.

           Filling backups takes a little extra disk space, and it  does  cost  some  extra  disk  activity  for
           filling, and later removal.  Filling is no longer useful, since file mangling and compression doesn't
           make  a  filled  backup  very  useful.  It's  likely  the  filling option will be removed from future
           versions: filling will be delegated to the display and extraction of backup data.

           If filling is off, BackupPC makes sure that the oldest backup is  a  full,  otherwise  the  following
           incremental  backups  will  be incomplete.  This might mean an extra full backup has to be kept until
           the following incremental backups expire.

           The default is off.  You can turn this on or off at any time without affecting existing backups.

       $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.

           When editing from the web interface, you should add a valid ShareName (based  on  $Conf{XferMethod}),
           and  then  enter  the  directories  specific  to that ShareName.  A special ShareName "*" matches any
           ShareName that doesn't have an explicit entry.

           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.

           When editing from the web interface, you should add a valid ShareName (based  on  $Conf{XferMethod}),
           and  then enter the directories or files specific to that ShareName.  A special ShareName "*" matches
           any ShareName that doesn't have an explicit entry.

           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 exlclude 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 fro 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 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 file names 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  what  ever  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 file names in old backups taken  with  BackupPC  2.x,  so
           that non-ascii file names in old backups can be viewed and restored.

   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 user name.  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'.

       $Conf{SmbClientFullCmd} = '$smbClientPath \\\\$host\\$shareName' ...
           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        user name
              $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.

       $Conf{SmbClientIncrCmd} = '$smbClientPath \\\\$host\\$shareName' ...
           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.

       $Conf{SmbClientRestoreCmd} = '$smbClientPath \\\\$host\\$shareName' ...
           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' ...
           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        host name
             $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'.

       $Conf{TarClientRestoreCmd} = '$sshPath -q -x -l root $host' ...
           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

       $Conf{RsyncClientCmd} = '$sshPath -q -x -l root $host $rsyncPath $argList+';
           Full command to run rsync on the client machine.  The following variables  are  substituted  at  run-
           time:

                  $host           host name being backed up
                  $hostIP         host's IP address
                  $shareName      share name to backup (ie: top-level directory path)
                  $rsyncPath      same as $Conf{RsyncClientPath}
                  $sshPath        same as $Conf{SshPath}
                  $argList        argument list, built from $Conf{RsyncArgs},
                                  $shareName, $Conf{BackupFilesExclude} and
                                  $Conf{BackupFilesOnly}

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

       $Conf{RsyncClientRestoreCmd} = '$sshPath -q -x -l root $host $rsyncPath $argList+';
           Full command to run rsync for restore on the client.  The following variables are substituted at run-
           time:

                  $host           host name being backed up
                  $hostIP         host's IP address
                  $shareName      share name to backup (ie: top-level directory path)
                  $rsyncPath      same as $Conf{RsyncClientPath}
                  $sshPath        same as $Conf{SshPath}
                  $argList        argument list, built from $Conf{RsyncArgs},
                                  $shareName, $Conf{BackupFilesExclude} and
                                  $Conf{BackupFilesOnly}

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

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

       $Conf{RsyncdAuthRequired} = 1;
           Whether authentication is mandatory when connecting to the client's rsyncd.  By default this  is  on,
           ensuring  that  BackupPC  will  refuse  to  connect  to  an rsyncd on the client that is not password
           protected.  Turn off at your own risk.

       $Conf{RsyncCsumCacheVerifyProb} = 0.01;
           When  rsync  checksum  caching  is  enabled  (by   adding   the   --checksum-seed=32761   option   to
           $Conf{RsyncArgs}),  the  cached checksums can be occasionally verified to make sure the file contents
           matches the cached checksums.  This is to avoid the risk that disk problems might cause the pool file
           contents to get corrupted, but the cached checksums would make BackupPC think  that  the  file  still
           matches the client.

           This  setting  is  the  probability (0 means never and 1 means always) that a file will be rechecked.
           Setting it to 0 means the checksums will not be rechecked  (unless  there  is  a  phase  0  failure).
           Setting it to 1 (ie: 100%) means all files will be checked, but that is not a desirable setting since
           you are better off simply turning caching off (ie: remove the --checksum-seed option).

           The  default  of  0.01 means 1% (on average) of the files during a full backup will have their cached
           checksum re-checked.

           This setting has no effect unless checksum caching is turned on.

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

       $Conf{RsyncArgsExtra} = [];
           Additional arguments added to RsyncArgs.  This can be used in conbination  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',
               ];

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

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

           This allows settings of the form:

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

       $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         host name (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}.

   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 user name.  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 behavor 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  commandline
           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.

       $Conf{ArchiveClientCmd} = '$Installdir/bin/BackupPC_archiveHost' ...
           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
           host  name.  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 DCHP.

       $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';

       $Conf{PingCmd} = '$pingPath -c 1 $host';
           Ping command.  The following variables are substituted at run-time:

             $pingPath      path to ping ($Conf{PingPath})
             $host          host name

           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} = 0;
           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.

           Note:  compression  needs  the  Compress::Zlib  perl library.  If the Compress::Zlib library can't be
           found then $Conf{CompressLevel} is forced to 0 (compression off).

       $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 rare cases  you  might  want  to  increase  this
           value.

           Despite the name, this parameter sets the timeout for all transport methods (tar, smb etc).

       $Conf{MaxOldPerPCLogFiles} = 12;
           Maximum  number  of  log files we keep around in each PC's directory (ie: pc/$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 years 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         host name (could be different from client name if
                                           $Conf{ClientNameAlias} is set)
                  $hostIP       IP address of host
                  $user         user name 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         host name (could be different from client name if
                                           $Conf{ClientNameAlias} is set)
                  $hostIP       IP address of host
                  $user         user name 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  host name 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         user name 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  host  name.   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   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 host name  or
           IP address, eg:

                   $Conf{ClientNameAlias} = 'realHostName';
                   $Conf{ClientNameAlias} = '192.1.1.15';

           will cause the relevant smb/tar/rsync backup/restore commands to be directed to realHostName, not the
           client name.

           Note: this setting doesn't work for hosts with DHCP set to 1.

   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{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 destintation 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  unix/linux  group  $Conf{CgiAdminUserGroup}  and  the
           manual  list  of  users,  separated  by spaces, in $Conf{CgiAdminUsers}. If you don't want a group or
           manual list of 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';
              $Conf{CgiAdminUsers}     = 'craig celia';
              --> administrative users are the union of group admin, plus
                craig and celia.

              $Conf{CgiAdminUserGroup} = '';
              $Conf{CgiAdminUsers}     = 'craig celia';
              --> administrative users are only craig and celia'.

       $Conf{CgiURL} = undef;
           URL of the BackupPC_Admin CGI script.  Used for email messages.

       $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
           Brazillian (pt_br) and Chinese (zh_CH).

           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 user names.

           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} = 1;
           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} = { ...
           Hilight 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  file  name  extenions  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.x  several  color, layout and font changes were made.  The previous v2.x version is
           available  as  BackupPC_stnd_orig.css,  so  if  you   prefer   the   old   skin,   change   this   to
           BackupPC_stnd_orig.css.

       $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

       Starting  with v1.4.0 BackupPC uses a X.Y.Z version numbering system, instead of X.0Y. 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), and the last digit is for bug fixes. You should think of the
       old 1.00, 1.01, 1.02 and 1.03 as 1.0.0, 1.1.0, 1.2.0 and 1.3.0.

       Additionally, patches might be made available.  A patched version number is of  the  form  X.Y.ZplN  (eg:
       2.1.0pl2), where N is the patch level.

Author

       Craig Barratt  <cbarratt@users.sourceforge.net>

       See <http://backuppc.sourceforge.net>.

Copyright

       Copyright (C) 2001-2015 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 Brazillian 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.

Many people have 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 2 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 in the LICENSE file along with this
       program; if not, write to the Free Software Foundation, Inc., 59 Temple  Place,  Suite  330,  Boston,  MA
       02111-1307 USA.

perl v5.24.1                                       2016-12-14                                        BACKUPPC(8)