Ubuntu Manpage: rdiff-backup - local/remote mirror and incremental backup

name
synopsis
description
options
restoring
time formats
remote operation
file selection
users and groups
statistics
exit status
bugs
author
see also

NAME

       rdiff-backup - local/remote mirror and incremental backup

SYNOPSIS

       rdiff-backup [options] [[[user@]host1.foo]::source_directory] [[[user@]host2.foo]::destination_directory]

       rdiff-backup  {{  -l  |  --list-increments  } | --remove-older-than time_interval | --list-at-time time |
       --list-changed-since   time   |   --list-increment-sizes   |   --verify    |    --verify-at-time    time}
       [[[user@]host2.foo]::destination_directory]

       rdiff-backup --calculate-average statfile1 statfile2 ...

       rdiff-backup --test-server [user1]@host1.net1::path [[user2]@host2.net2::path] ...

DESCRIPTION

rdiff-backup is a script, written in python(1) that backs up one directory to another. The target
directory ends up a copy (mirror) of the source directory, but extra reverse diffs are stored in a
special subdirectory of that target directory, so you can still recover files lost some time ago. The
idea is to combine the best features of a mirror and an incremental backup. rdiff-backup also preserves
symlinks, special files, hardlinks, permissions, uid/gid ownership, and modification times.

rdiff-backup can also operate in a bandwidth efficient manner over a pipe, like rsync(1). Thus you can
use ssh and rdiff-backup to securely back a hard drive up to a remote location, and only the differences
will be transmitted. Using the default settings, rdiff-backup requires that the remote system accept ssh
connections, and that rdiff-backup is installed in the user's PATH on the remote system. For information
on other options, see the section on REMOTE OPERATION.

Note that you should not write to the mirror directory except with rdiff-backup. Many of the increments
are stored as reverse diffs, so if you delete or modify a file, you may lose the ability to restore
previous versions of that file.

Finally, this man page is intended more as a precise description of the behavior and syntax of rdiff-
backup. New users may want to check out the examples.html file included in the rdiff-backup
distribution.

OPTIONS

-b, --backup-mode
Force backup mode even if first argument appears to be an increment or mirror file.

--calculate-average
Enter calculate average mode. The arguments should be a number of statistics files. rdiff-backup
will print the average of the listed statistics files and exit.

--carbonfile
Enable backup of MacOS X carbonfile information.

--check-destination-dir
If an rdiff-backup session fails, running rdiff-backup with this option on the destination dir
will undo the failed directory. This happens automatically if you attempt to back up to a
directory and the last backup failed.

--compare
This is equivalent to '--compare-at-time now'

--compare-at-time time
Compare a directory with the backup set at the given time. This can be useful to see how archived
data differs from current data, or to check that a backup is current. This only compares
metadata, in the same way rdiff-backup decides whether a file has changed.

--compare-full
This is equivalent to '--compare-full-at-time now'

--compare-full-at-time time
Compare a directory with the backup set at the given time. To compare regular files, the
repository data will be copied in its entirety to the source side and compared byte by byte. This
is the slowest but most complete compare option.

--compare-hash
This is equivalent to '--compare-hash-at-time now'

--compare-hash-at-time time
Compare a directory with the backup set at the given time. Regular files will be compared by
computing their SHA1 digest on the source side and comparing it to the digest recorded in the
metadata.

--create-full-path
Normally only the final directory of the destination path will be created if it does not exist.
With this option, all missing directories on the destination path will be created. Use this option
with care: if there is a typo in the remote path, the remote filesystem could fill up very quickly
(by creating a duplicate backup tree). For this reason this option is primarily aimed at scripts
which automate backups.

--current-time seconds
This option is useful mainly for testing. If set, rdiff-backup will use it for the current time
instead of consulting the clock. The argument is the number of seconds since the epoch.

--exclude shell_pattern
Exclude the file or files matched by shell_pattern. If a directory is matched, then files under
that directory will also be matched. See the FILE SELECTION section for more information.

--exclude-device-files
Exclude all device files. This can be useful for security/permissions reasons or if rdiff-backup
is not handling device files correctly.

--exclude-fifos
Exclude all fifo files.

--exclude-filelist filename
Excludes the files listed in filename. If filename is handwritten you probably want --exclude-
globbing-filelist instead. See the FILE SELECTION section for more information.

--exclude-filelist-stdin
Like --exclude-filelist, but the list of files will be read from standard input. See the FILE
SELECTION section for more information.

--exclude-globbing-filelist filename
Like --exclude-filelist but each line of the filelist will be interpreted according to the same
rules as --include and --exclude.

--exclude-globbing-filelist-stdin
Like --exclude-globbing-filelist, but the list of files will be read from standard input.

--exclude-other-filesystems
Exclude files on file systems (identified by device number) other than the file system the root of
the source directory is on.

--exclude-regexp regexp
Exclude files matching the given regexp. Unlike the --exclude option, this option does not match
files in a directory it matches. See the FILE SELECTION section for more information.

--exclude-special-files
Exclude all device files, fifo files, socket files, and symbolic links.

--exclude-sockets
Exclude all socket files.

--exclude-symbolic-links
Exclude all symbolic links. This option is automatically enabled if the backup source is running
on native Windows to avoid backing-up NTFS reparse points.

--exclude-if-present filename
Exclude directories if filename is present. This option needs to come before any other include or
exclude options.

--force
Authorize a more drastic modification of a directory than usual (for instance, when overwriting of
a destination path, or when removing multiple sessions with --remove-older-than). rdiff-backup
will generally tell you if it needs this. WARNING: You can cause data loss if you mis-use this
option. Furthermore, do NOT use this option when doing a restore, as it will DELETE FILES, unless
you absolutely know what you are doing.

--group-mapping-file filename
Map group names and ids according the the group mapping file filename. See the USERS AND GROUPS
section for more information.

--include shell_pattern
Similar to --exclude but include matched files instead. Unlike --exclude, this option will also
match parent directories of matched files (although not necessarily their contents). See the FILE
SELECTION section for more information.

--include-filelist filename
Like --exclude-filelist, but include the listed files instead. If filename is handwritten you
probably want --include-globbing-filelist instead. See the FILE SELECTION section for more
information.

--include-filelist-stdin
Like --include-filelist, but read the list of included files from standard input.

--include-globbing-filelist filename
Like --include-filelist but each line of the filelist will be interpreted according to the same
rules as --include and --exclude.

--include-globbing-filelist-stdin
Like --include-globbing-filelist, but the list of files will be read from standard input.

--include-regexp regexp
Include files matching the regular expression regexp. Only files explicitly matched by regexp
will be included by this option. See the FILE SELECTION section for more information.

--include-special-files
Include all device files, fifo files, socket files, and symbolic links.

--include-symbolic-links
Include all symbolic links.

--list-at-time time
List the files in the archive that were present at the given time. If a directory in the archive
is specified, list only the files under that directory.

--list-changed-since time
List the files that have changed in the destination directory since the given time. See TIME
FORMATS for the format of time. If a directory in the archive is specified, list only the files
under that directory. This option does not read the source directory; it is used to compare the
contents of two different rdiff-backup sessions.

-l, --list-increments
List the number and date of partial incremental backups contained in the specified destination
directory. No backup or restore will take place if this option is given.

--list-increment-sizes
List the total size of all the increment and mirror files by time. This may be helpful in
deciding how many increments to keep, and when to --remove-older-than. Specifying a subdirectory
is allowable; then only the sizes of the mirror and increments pertaining to that subdirectory
will be listed.

--max-file-size size
Exclude files that are larger than the given size in bytes

--min-file-size size
Exclude files that are smaller than the given size in bytes

--never-drop-acls
Exit with error instead of dropping acls or acl entries. Normally this may happen (with a
warning) because the destination does not support them or because the relevant user/group names do
not exist on the destination side.

--no-acls
No Access Control Lists - disable backup of ACLs

--no-carbonfile
Disable backup of MacOS X carbonfile information

--no-compare-inode
This option prevents rdiff-backup from flagging a hardlinked file as changed when its device
number and/or inode changes. This option is useful in situations where the source filesystem
lacks persistent device and/or inode numbering. For example, network filesystems may have mount-
to-mount differences in their device number (but possibly stable inode numbers); USB/1394 devices
may come up at different device numbers each remount (but would generally have same inode number);
and there are filesystems which don't even have the same inode numbers from use to use. Without
the option rdiff-backup may generate unnecessary numbers of tiny diff files.

--no-compression
Disable the default gzip compression of most of the .snapshot and .diff increment files stored in
the rdiff-backup-data directory. A backup volume can contain compressed and uncompressed
increments, so using this option inconsistently is fine.

--no-compression-regexp regexp
Do not compress increments based on files whose filenames match regexp. The default includes many
common audiovisual and archive files, and may be found in Globals.py.

--no-eas
No Extended Attributes support - disable backup of EAs.

--no-file-statistics
This will disable writing to the file_statistics file in the rdiff-backup-data directory. rdiff-
backup will run slightly quicker and take up a bit less space.

--no-hard-links
Don't replicate hard links on destination side. If many hard-linked files are present, this
option can drastically decrease memory usage. This option is enabled by default if the backup
source or restore destination is running on native Windows.

--null-separator
Use nulls (\0) instead of newlines (\n) as line separators, which may help when dealing with
filenames containing newlines. This affects the expected format of the files specified by the
--{include|exclude}-filelist[-stdin] switches as well as the format of the directory statistics
file.

--parsable-output
If set, rdiff-backup's output will be tailored for easy parsing by computers, instead of
convenience for humans. Currently this only applies when listing increments using the -l or
--list-increments switches, where the time will be given in seconds since the epoch.

--override-chars-to-quote
If the filesystem to which we are backing up is not case-sensitive, automatic 'quoting' of
characters occurs. For example, a file 'Developer.doc' will be converted into ';068eveloper.doc'.
To override this behavior, you need to specify this option.

--preserve-numerical-ids
If set, rdiff-backup will preserve uids/gids instead of trying to preserve unames and gnames. See
the USERS AND GROUPS section for more information.

--print-statistics
If set, summary statistics will be printed after a successful backup. If not set, this
information will still be available from the session statistics file. See the STATISTICS section
for more information.

-r, --restore-as-of restore_time
Restore the specified directory as it was as of restore_time. See the TIME FORMATS section for
more information on the format of restore_time, and see the RESTORING section for more information
on restoring.

--remote-cmd cmd
Deprecated. Please use --remote-schema instead

--remote-schema schema
Specify an alternate method of connecting to a remote computer. This is necessary to get rdiff-
backup not to use ssh for remote backups, or if, for instance, rdiff-backup is not in the PATH on
the remote side. See the REMOTE OPERATION section for more information.

--remote-tempdir path
Adds the --tempdir option with argument path when invoking remote instances of rdiff-backup.

--remove-older-than time_spec
Remove the incremental backup information in the destination directory that has been around longer
than the given time. time_spec can be either an absolute time, like "2002-01-04", or a time
interval. The time interval is an integer followed by the character s, m, h, D, W, M, or Y,
indicating seconds, minutes, hours, days, weeks, months, or years respectively, or a number of
these concatenated. For example, 32m means 32 minutes, and 3W2D10h7s means 3 weeks, 2 days, 10
hours, and 7 seconds. In this context, a month means 30 days, a year is 365 days, and a day is
always 86400 seconds.

rdiff-backup cannot remove-older-than and back up or restore in a single session. In order to
both backup a directory and remove old files in it, you must run rdiff-backup twice.

By default, rdiff-backup will only delete information from one session at a time. To remove two
or more sessions at the same time, supply the --force option (rdiff-backup will tell you if
--force is required).

Note that snapshots of deleted files are covered by this operation. Thus if you deleted a file
two weeks ago, backed up immediately afterwards, and then ran rdiff-backup with --remove-older-
than 10D today, no trace of that file would remain. Finally, file selection options such as
--include and --exclude don't affect --remove-older-than.

--restrict path
Require that all file access be inside the given path. This switch, and the following two, are
intended to be used with the --server switch to provide a bit more protection when doing automated
remote backups. They are not intended as your only line of defense so please don't do something
silly like allow public access to an rdiff-backup server run with --restrict-read-only.

--restrict-read-only path
Like --restrict, but also reject all write requests.

--restrict-update-only path
Like --restrict, but only allow writes as part of an incremental backup. Requests for other types
of writes (for instance, deleting path) will be rejected.

--server
Enter server mode (not to be invoked directly, but instead used by another rdiff-backup process on
a remote computer).

--ssh-no-compression
When running ssh, do not use the -C option to enable compression. --ssh-no-compression is ignored
if you specify a new schema using --remote-schema.

--tempdir path
Sets the directory that rdiff-backup uses for temporary files to the given path. The environment
variables TMPDIR, TEMP, and TMP can also be used to set the temporary files directory. See the
documentation of the Python tempfile module for more information.

--terminal-verbosity [0-9]
Select which messages will be displayed to the terminal. If missing the level defaults to the
verbosity level.

--test-server
Test for the presence of a compatible rdiff-backup server as specified in the following
host::filename argument(s). The filename section will be ignored.

--user-mapping-file filename
Map user names and ids according to the user mapping file filename. See the USERS AND GROUPS
section for more information.

-v[0-9], --verbosity [0-9]
Specify verbosity level (0 is totally silent, 3 is the default, and 9 is noisiest). This
determines how much is written to the log file.

--verify
This is short for --verify-at-time now

--verify-at-time now
Check all the data in the repository at the given time by computing the SHA1 hash of all the
regular files and comparing them with the hashes stored in the metadata file.

-V, --version
Print the current version and exit

RESTORING

There are two ways to tell rdiff-backup to restore a file or directory. Firstly, you can run rdiff-
backup on a mirror file and use the -r or --restore-as-of options. Secondly, you can run it on an
increment file.

For example, suppose in the past you have run:

rdiff-backup /usr /usr.backup

to back up the /usr directory into the /usr.backup directory, and now want a copy of the /usr/local
directory the way it was 3 days ago placed at /usr/local.old.

One way to do this is to run:

rdiff-backup -r 3D /usr.backup/local /usr/local.old

where above the "3D" means 3 days (for other ways to specify the time, see the TIME FORMATS section).
The /usr.backup/local directory was selected, because that is the directory containing the current
version of /usr/local.

Note that the option to --restore-as-of always specifies an exact time. (So "3D" refers to the instant
72 hours before the present.) If there was no backup made at that time, rdiff-backup restores the state
recorded for the previous backup. For instance, in the above case, if "3D" is used, and there are only
backups from 2 days and 4 days ago, /usr/local as it was 4 days ago will be restored.

The second way to restore files involves finding the corresponding increment file. It would be in the
/backup/rdiff-backup-data/increments/usr directory, and its name would be something like
"local.2002-11-09T12:43:53-04:00.dir" where the time indicates it is from 3 days ago. Note that the
increment files all end in ".diff", ".snapshot", ".dir", or ".missing", where ".missing" just means that
the file didn't exist at that time (finally, some of these may be gzip-compressed, and have an extra
".gz" to indicate this). Then running:

rdiff-backup /backup/rdiff-backup-data/increments/usr/local.<time>.dir /usr/local.old

would also restore the file as desired.

If you are not sure exactly which version of a file you need, it is probably easiest to either restore
from the increments files as described immediately above, or to see which increments are available with
-l/--list-increments, and then specify exact times into -r/--restore-as-of.

TIME FORMATS

rdiff-backup uses time strings in two places. Firstly, all of the increment files rdiff-backup creates
will have the time in their filenames in the w3 datetime format as described in a w3 note at
http://www.w3.org/TR/NOTE-datetime. Basically they look like "2001-07-15T04:09:38-07:00", which means
what it looks like. The "-07:00" section means the time zone is 7 hours behind UTC.

Secondly, the -r, --restore-as-of, and --remove-older-than options take a time string, which can be given
in any of several formats:

1. the string "now" (refers to the current time)

2. a sequences of digits, like "123456890" (indicating the time in seconds after the epoch)

3. A string like "2002-01-25T07:00:00+02:00" in datetime format

4. An interval, which is a number followed by one of the characters s, m, h, D, W, M, or Y
(indicating seconds, minutes, hours, days, weeks, months, or years respectively), or a series of
such pairs. In this case the string refers to the time that preceded the current time by the
length of the interval. For instance, "1h78m" indicates the time that was one hour and 78 minutes
ago. The calendar here is unsophisticated: a month is always 30 days, a year is always 365 days,
and a day is always 86400 seconds.

5. A date format of the form YYYY/MM/DD, YYYY-MM-DD, MM/DD/YYYY, or MM-DD-YYYY, which indicates
midnight on the day in question, relative to the current timezone settings. For instance,
"2002/3/5", "03-05-2002", and "2002-3-05" all mean March 5th, 2002.

6. A backup session specification which is a non-negative integer followed by 'B'. For instance,
'0B' specifies the time of the current mirror, and '3B' specifies the time of the 3rd newest
increment.

REMOTE OPERATION

In order to access remote files, rdiff-backup opens up a pipe to a copy of rdiff-backup running on the
remote machine. Thus rdiff-backup must be installed on both ends. To open this pipe, rdiff-backup first
splits the filename into host_info::pathname. It then substitutes host_info into the remote schema, and
runs the resulting command, reading its input and output.

The default remote schema is 'ssh -C %s rdiff-backup --server' where host_info is substituted for '%s'.
So if the host_info is user@host.net, then rdiff-backup runs 'ssh user@host.net rdiff-backup --server'.
Using --remote-schema, rdiff-backup can invoke an arbitrary command in order to open up a remote pipe.
For instance,
rdiff-backup --remote-schema 'cd /usr; %s' foo 'rdiff-backup --server'::bar
is basically equivalent to (but slower than)
rdiff-backup foo /usr/bar

Concerning quoting, if for some reason you need to put two consecutive colons in the host_info section of
a host_info::pathname argument, or in the pathname of a local file, you can quote one of them by
prepending a backslash. So in 'a\::b::c', host_info is 'a::b' and the pathname is 'c'. Similarly, if
you want to refer to a local file whose filename contains two consecutive colons, like 'strange::file',
you'll have to quote one of the colons as in 'strange\::file'. Because the backslash is a quote
character in these circumstances, it too must be quoted to get a literal backslash, so 'foo\::\\bar'
evaluates to 'foo::\bar'. To make things more complicated, because the backslash is also a common shell
quoting character, you may need to type in '\\\\' at the shell prompt to get a literal backslash (if it
makes you feel better, I had to type in 8 backslashes to get that in this man page...). And finally, to
include a literal % in the string specified by --remote-schema, quote it with another %, as in %%.

Although ssh itself may be secure, using rdiff-backup in the default way presents some security risks.
For instance if the server is run as root, then an attacker who compromised the client could then use
rdiff-backup to overwrite arbitrary server files by "backing up" over them. Such a setup can be made
more secure by using the sshd configuration option command="rdiff-backup --server" possibly along with
the --restrict* options to rdiff-backup. For more information, see the web page, the wiki, and the
entries for the --restrict* options on this man page.

FILE SELECTION

rdiff-backup has a number of file selection options. When rdiff-backup is run, it searches through the
given source directory and backs up all the files matching the specified options. This selection system
may appear complicated, but it is supposed to be flexible and easy-to-use. If you just want to learn the
basics, first look at the selection examples in the examples.html file included in the package, or on the
web at http://rdiff-backup.nongnu.org/examples.html

rdiff-backup's selection system was originally inspired by rsync(1), but there are many differences.
(For instance, trailing backslashes have no special significance.)

The file selection system comprises a number of file selection conditions, which are set using one of the
following command line options: --exclude, --exclude-filelist, --exclude-device-files, --exclude-fifos,
--exclude-sockets, --exclude-symbolic-links, --exclude-globbing-filelist, --exclude-globbing-filelist-
stdin, --exclude-filelist-stdin, --exclude-regexp, --exclude-special-files, --include, --include-
filelist, --include-globbing-filelist, --include-globbing-filelist-stdin, --include-filelist-stdin, and
--include-regexp. Each file selection condition either matches or doesn't match a given file. A given
file is excluded by the file selection system exactly when the first matching file selection condition
specifies that the file be excluded; otherwise the file is included. When backing up, if a file is
excluded, rdiff-backup acts as if that file does not exist in the source directory. When restoring, an
excluded file is considered not to exist in either the source or target directories.

For instance,

rdiff-backup --include /usr --exclude /usr /usr /backup

is exactly the same as

rdiff-backup /usr /backup

because the include and exclude directives match exactly the same files, and the --include comes first,
giving it precedence. Similarly,

rdiff-backup --include /usr/local/bin --exclude /usr/local /usr /backup

would backup the /usr/local/bin directory (and its contents), but not /usr/local/doc.

The include, exclude, include-globbing-filelist, and exclude-globbing-filelist options accept extended
shell globbing patterns. These patterns can contain the special patterns *, **, ?, and [...]. As in a
normal shell, * can be expanded to any string of characters not containing "/", ? expands to any
character except "/", and [...] expands to a single character of those characters specified (ranges are
acceptable). The new special pattern, **, expands to any string of characters whether or not it contains
"/". Furthermore, if the pattern starts with "ignorecase:" (case insensitive), then this prefix will be
removed and any character in the string can be replaced with an upper- or lowercase version of itself.

If you need to match filenames which contain the above globbing characters, they may be escaped using a
backslash "\". The backslash will only escape the character following it so for ** you will need to use
"\*\*" to avoid escaping it to the * globbing character.

Remember that you may need to quote these characters when typing them into a shell, so the shell does not
interpret the globbing patterns before rdiff-backup sees them.

The --exclude pattern option matches a file iff:

1. pattern can be expanded into the file's filename, or

2. the file is inside a directory matched by the option.

Conversely, --include pattern matches a file iff:

1. pattern can be expanded into the file's filename,

2. the file is inside a directory matched by the option, or

3. the file is a directory which contains a file matched by the option.

For example,

--exclude /usr/local

matches /usr/local, /usr/local/lib, and /usr/local/lib/netscape. It is the same as --exclude /usr/local
--exclude '/usr/local/**'.

--include /usr/local

specifies that /usr, /usr/local, /usr/local/lib, and /usr/local/lib/netscape (but not /usr/doc) all be
backed up. Thus you don't have to worry about including parent directories to make sure that included
subdirectories have somewhere to go. Finally,

--include ignorecase:'/usr/[a-z0-9]foo/*/**.py'

would match a file like /usR/5fOO/hello/there/world.py. If it did match anything, it would also match
/usr. If there is no existing file that the given pattern can be expanded into, the option will not
match /usr.

The --include-filelist, --exclude-filelist, --include-filelist-stdin, and --exclude-filelist-stdin
options also introduce file selection conditions. They direct rdiff-backup to read in a file, each line
of which is a file specification, and to include or exclude the matching files. Lines are separated by
newlines or nulls, depending on whether the --null-separator switch was given. Each line in a filelist
is interpreted similarly to the way extended shell patterns are, with a few exceptions:

1. Globbing patterns like *, **, ?, and [...] are not expanded.

2. Include patterns do not match files in a directory that is included. So /usr/local in an include
file will not match /usr/local/doc.

3. Lines starting with "+ " are interpreted as include directives, even if found in a filelist
referenced by --exclude-filelist. Similarly, lines starting with "- " exclude files even if they
are found within an include filelist.

For example, if the file "list.txt" contains the lines:

/usr/local
- /usr/local/doc
/usr/local/bin
+ /var
- /var

then "--include-filelist list.txt" would include /usr, /usr/local, and /usr/local/bin. It would exclude
/usr/local/doc, /usr/local/doc/python, etc. It neither excludes nor includes /usr/local/man, leaving the
fate of this directory to the next specification condition. Finally, it is undefined what happens with
/var. A single file list should not contain conflicting file specifications.

The --include-globbing-filelist and --exclude-globbing-filelist options also specify filelists, but each
line in the filelist will be interpreted as a globbing pattern the way --include and --exclude options
are interpreted (although "+ " and "- " prefixing is still allowed). For instance, if the file
"globbing-list.txt" contains the lines:

dir/foo
+ dir/bar
- **

Then "--include-globbing-filelist globbing-list.txt" would be exactly the same as specifying "--include
dir/foo --include dir/bar --exclude **" on the command line.

Finally, the --include-regexp and --exclude-regexp allow files to be included and excluded if their
filenames match a python regular expression. Regular expression syntax is too complicated to explain
here, but is covered in Python's library reference. Unlike the --include and --exclude options, the
regular expression options don't match files containing or contained in matched files. So for instance

--include '[0-9]{7}(?!foo)'

matches any files whose full pathnames contain 7 consecutive digits which aren't followed by 'foo'.
However, it wouldn't match /home even if /home/ben/1234567 existed.

USERS AND GROUPS

There can be complications preserving ownership across systems. For instance the username that owns a
file on the source system may not exist on the destination. Here is how rdiff-backup maps ownership on
the source to the destination (or vice-versa, in the case of restoring):

1. If the --preserve-numerical-ids option is given, the remote files will always have the same uid
and gid, both for ownership and ACL entries. This may cause unames and gnames to change.

2. Otherwise, attempt to preserve the user and group names for ownership and in ACLs. This may
result in files having different uids and gids across systems.

3. If a name cannot be preserved (e.g. because the username does not exist), preserve the original
id, but only in cases of user and group ownership. For ACLs, omit any entry that has a bad user
or group name.

4. The --user-mapping-file and --group-mapping-file options override this behavior. If either of
these options is given, the policy described in 2 and 3 above will be followed, but with the
mapped user and group instead of the original. If you specify both --preserve-numerical-ids and
one of the mapping options, the behavior is undefined.

The user and group mapping files both have the same form:

old_name_or_id1:new_name_or_id1
old_name_or_id2:new_name_or_id2
<etc>

Each line should contain a name or id, followed by a colon ":", followed by another name or id. If a
name or id is not listed, they are treated in the default way described above.

When restoring, the above behavior is also followed, but note that the original source user/group
information will be the input, not the already mapped user/group information present in the backup
repository. For instance, suppose you have mapped all the files owned by alice in the source so that
they are owned by ben in the repository, and now you want to restore, making sure the files owned
originally by alice are still owned by alice. In this case there is no need to use any of the mapping
options. However, if you wanted to restore the files so that the files originally owned by alice on the
source are now owned by ben, you would have to use the mapping options, even though you just want the
unames of the repository's files preserved in the restored files.

STATISTICS

       Every session rdiff-backup saves various statistics into two files, the session statistics file at rdiff-
       backup-data/session_statistics.<time>.data   and   the   directory   statistics   file  at  rdiff-backup-
       data/directory_statistics.<time>.data.  They are both text files and  contain  similar  information:  how
       many  files changed, how many were deleted, the total size of increment files created, etc.  However, the
       session statistics file is intended to be very readable and only describes the session as a  whole.   The
       directory  statistics  file  is  more  compact (and slightly less readable) but describes every directory
       backed up.  It also may be compressed to save space.

       Statistics-related options include --print-statistics and --null-separator.

       Also, rdiff-backup will save various messages to the log file, which is rdiff-backup-data/backup.log  for
       backup  sessions  and  rdiff-backup-data/restore.log  for restore sessions.  Generally what is written to
       this file will coincide with the messages displayed to stdout or stderr, although  this  can  be  changed
       with the --terminal-verbosity option.

       The log file is not compressed and can become quite large if rdiff-backup is run with high verbosity.

EXIT STATUS

       If  rdiff-backup  finishes  successfully,  the  exit  status  will  be  0.   If there is an unrecoverable
       (critical) error, it will be non-zero (usually 1, but don't depend on this specific value).  When setting
       up rdiff-backup to run automatically (as from cron(8) or similar) it is probably a good idea to check the
       exit code.

BUGS

       The gzip library in versions 2.2 and earlier of python (but fixed in 2.3a1) has trouble  producing  files
       over  2GB  in  length.   This  bug  will  prevent rdiff-backup from producing large compressed increments
       (snapshots or diffs).  A workaround is to disable compression for large uncompressable files.

AUTHOR

       Ben Escoto <ben@emerose.org>

       Feel free to ask me questions or send me bug reports, but you may want to see  the  web  page,  mentioned
       below, first.