5 \h'-\w'\fB\\$1\ \fP'u'\fB\\$1\ \fP\c
7 .TH rsync-backup 8 "7 October 2012" rsync-backup
9 rsync-backup \- back up files using rsync
18 script is a backup program of the currently popular
23 ability to create hardlinks from (apparently) similar existing local
24 trees to make incremental dumps efficient, even from remote sources.
25 Restoring files is easy because the backups created are just directories
26 full of files, exactly as they were on the source \(en and this is
31 The script does more than just running
33 It is also responsible for creating and removing snapshots of volumes to
34 be backed up, and expiring old dumps according to a user-specified
39 script should be installed and run on a central backup server with local
40 access to the backup volumes.
42 The script should be run with full (root) privileges, so that it can
43 correctly record file ownership information. The server should also be
46 to the client machines, and run processes there as root. (This is not a
47 security disaster. Remember that the backup server is, in the end,
48 responsible for the integrity of the backup data. A dishonest backup
49 server can easily compromise a client which is being restored from
51 .SS Command-line options
52 Most of the behaviour of
54 is controlled by a configuration file, described starting with the
56 .B Configuration commands
58 But a few features are controlled by command-line options.
61 Show a brief help message for the program, and exit successfully.
66 version number and some choice pieces of build-time configuration, and
72 instead of the default configuration file (shown as
79 Don't actually take a backup, or write proper logs: instead, write a
80 description of what would be done to standard error.
83 Produce verbose progress information on standard output while the backup
84 is running. This keeps one amused while running a backup
85 interactively. In any event,
87 will report failures to standard error, and otherwise run silently, so
88 it doesn't annoy unnecessarily if run by
91 Backing up a filesystem works as follows.
93 Make a snapshot of the filesystem on the client, and ensure that the
94 snapshot is mounted. There are some `trivial' snapshot types which use
95 the existing mounted filesystem, and either prevent processes writing to
96 it during the backup, or just hope for the best. Other snapshot types
97 require the snapshot to be mounted somewhere distinct from the main
98 filesystem, so that the latter can continue being used.
102 to copy the snapshot to the backup volume \(en specifically, to
103 .IB host / fs / new \fR.
104 If this directory already exists, then it's presumed to be debris from a
105 previous attempt to dump this filesystem:
107 will update it appropriately, by adding, deleting or modifying the
108 files. This means that retrying a failed dump \(en after fixing whatever
109 caused it to go wrong, obviously! \(en is usually fairly quick.
113 on the client to generate a `digest' describing the contents of the
114 filesystem, and send this to the server as
115 .IB host / fs / new .fshash \fR.
117 Release the snapshot: we don't need it any more.
121 over the new backup; specifically, to
122 .BI tmp/fshash. host . fs . date \fR.
123 This gives us a digest for what the backup volume actually stored.
127 digests. If they differ then dump the differences to the log file and
128 report a backup failure. (Backups aren't any good if they don't
129 actually back up the right thing. And you stand a better chance of
130 fixing them if you know that they're going wrong.)
132 Commit the backup, by renaming the dump directory to
137 .IB host / fs / date .fshash \fR.
139 The backup is now complete.
140 .SS Configuration commands
141 The configuration file is simply a Bash shell fragment: configuration
142 commands are shell functions.
144 .BI "backup " "fs\fR[:\fIfsarg\fR] ..."
145 Back up the named filesystems. The corresponding
147 may be required by the snapshot type.
152 commands will back up filesystems on the named
154 To back up filesystems on the backup server itself, use its hostname:
156 will avoid inefficient and pointless messing about
159 This command clears the
161 list, and resets the retention policy to its default (i.e., the to
162 policy defined prior to the first
166 .BI "like " "host\fR ..."
167 Declare that subsequent filesystems are `similar' to like-named
168 filesystems on the named
172 should use those trees as potential sources of hardlinkable files. Be
173 careful when using this option without
176 option: an erroneous hardlink will cause the backup to fail. (The
177 backup won't be left silently incorrect.)
179 .BI "retain " frequency " " duration
180 Define part a backup retention policy: backup trees of the
182 should be kept for the
194 which means the same); the
202 Expiry considers each existing dump against the policy lines in order:
203 the last applicable line determines the dump's fate \(en so you should
204 probably write the lines in decreasing order of duration.
213 commands collectively define a retention policy. Once a policy is
216 operations use the policy. The first
222 command clears the policy and starts defining a new one. The policy
223 defined before the first
227 policy: at the start of each
229 stanza, the policy is reset to the default.
235 snapshot type (see below) doesn't prevent a filesystem from being
236 modified while it's being backed up. If this happens, the
238 pass will detect the difference and fail. If the filesystem in question
239 is relatively quiescent, then maybe retrying the backup will result in a
240 successful consistent copy. Following this command, a backup which
243 mismatch will be retried up to
245 times before being declared a failure.
247 .BI "snap " type " " \fR[\fIargs\fR...]
250 for subsequent backups. Some snapshot types require additional
251 arguments, which may be supplied here. This command clears the
254 .SS Configuration variables
255 The following shell variables may be overridden by the configuration
259 The hash function to use for verifying archive integrity. This is
264 so it must name one of the hash functions supported by your Python's
271 The name of a SQLite database initialized by
272 .BR update-bkp-index (8)
273 in which an index is maintained of which dumps are on which backup
274 volumes. If the file doesn't exist, then no index is maintained. The
276 .IB localstatedir /lib/bkp/index.db
279 is the state directory configured at build time.
282 The number of log files to be kept for each filesystem. Old logfiles
283 are deleted to keep the total number below this bound. The default
287 The metadata directory for the currently mounted backup volume.
292 is the backup mount directory configured at build time.
295 Command-line options to pass to
297 in addition to the basic set:
304 .B \-\-one-file-system
306 .BR "\-\-filter=""dir-merge .rsync-backup""" .
313 snapshots are mounted on subdirectories below the
315 .IR "on backup clients" .
320 is the backup mount directory configured at build time.
323 The volume size option to pass to
325 when creating a snapshot. The default is
327 which seems to work fairly well.
330 Where the actual backup trees should be stored. See the section on
337 is the backup mount directory configured at build time.
340 The name of the current volume. If this is left unset, the volume name
341 is read from the file
343 once at the start of the backup run.
345 The configuration file may define shell functions to perform custom
346 actions at various points in the backup process.
348 .BI "backup_precommit_hook " host " " fs " " date
349 Called after a backup has been verified complete and about to be
350 committed. The backup tree is in
352 in the current directory, and the
356 A typical action would be to create a digital signature on the
359 .BI "backup_commit_hook " host " " fs " " date
360 Called during the commit procedure. The backup tree and manifest have
361 been renamed into their proper places. Typically one would use this
362 hook to rename files created by the
363 .B backup_precommit_hook
366 .BR "whine " [ \-n ] " " \fItext\fR...
367 Called to report `interesting' events when the
369 option is in force. The default action is to echo the
371 to (what was initially) standard output, followed by a newline unless
375 The following snapshot types are available.
378 A trivial snapshot type: attempts to back up a live filesystem. How
379 well this works depends on how active the filesystem is. If files
380 change while the dump is in progress then the
382 verification will likely fail. Backups using this snapshot type must
383 specify the filesystem mount point as the
387 A slightly less trivial snapshot type: make the filesystem read-only
388 while the dump is in progress. Backups using this snapshot type must
389 specify the filesystem mount point as the
393 Create snapshots using LVM. The snapshot argument is interpreted as the
394 relevant volume group. The filesystem name is interpreted as the origin
395 volume name; the snapshot will be called
398 .IB SNAPDIR / fs \fR;
399 space will be allocated to it according to the
403 .BI "rfreezefs " client " " vg
404 This gets complicated. Suppose that a server has an LVM volume group,
405 and exports (somehow) a logical volume to a client. Examples are a host
406 providing a virtual disk to a guest, or a server providing
407 network-attached storage to a client. The server can create a snapshot
408 of the volume using LVM, but must synchronize with the client to ensure
409 that the filesystem image captured in the snapshot is clean. The
411 program should be installed on the client to perform this rather
412 delicate synchronization. Declare the server using the
414 command as usual; pass the client's name as the
417 server's volume group name as the
419 snapshot arguments. Finally, backups using this snapshot type must
420 specify the filesystem mount point (or, actually, any file in the
421 filesystem) on the client, as the
424 Additional snapshot types can be defined in the configuration file. A
425 snapshot type requires two shell functions.
427 .BI snap_ type " " snapargs " " fs " " fsarg
428 Create the snapshot, and write the mountpoint (on the client host) to
429 standard output, in a form suitable as an argument to
432 .BI unsnap_ type " " snapargs " " fs " " fsarg
435 There are a number of utility functions which can be used by snapshot
436 type handlers: please see the script for details. Please send the
437 author interesting snapshot handlers for inclusion in the main
439 .SS Archive structure
440 Backup trees are stored in a fairly straightforward directory tree.
442 At the top level is one directory for each client host. There are also
443 some special entries:
445 .B \&.rsync-backup-store
446 This file must be present in order to indicate that a backup volume is
447 present (and not just an empty mount point).
450 The cache database used for improving performance of local file
451 hashing. There may be other
453 files used by SQLite for its own purposes.
456 Part of the filesystem used on the backup volume. You don't want to
460 Used to store temporary files during the backup process. (Some of them
461 want to be on the same filesystem as the rest of the backup.) When
462 things go wrong, files are left behind in the hope that they might help
463 someone debug the mess. It's always safe to delete the files in here
464 when no backup is running.
466 So don't use those names for your hosts.
468 The next layer down contains a directory for each filesystem on the given host.
470 The bottom layer contains a directory for each dump of that filesystem,
471 named with the date at which the dump was started (in ISO8601
472 .IB yyyy \(en mm \(en dd
473 format), together with associated files named
475 There is also a symbolic link
477 referring to the most recent backup of the filesystem.
484 .BR update-bkp-index (8).
486 Mark Wooding, <mdw@distorted.org.uk>
~mdw / rsync-backup / blob