5 \h'-\w'\fB\\$1\ \fP'u'\fB\\$1\ \fP\c
7 .TH rsync-backup 8 "7 October 2012" rsync-backup
16 script is a backup program of the currently popular
21 ability to create hardlinks from (apparently) similar existing local
22 trees to make incremental dumps efficient, even from remote sources.
23 Restoring files is easy because the backups created are just directories
24 full of files, exactly as they were on the source \(en and this is
29 The script does more than just running
31 It is also responsible for creating and removing snapshots of volumes to
32 be backed up, and expiring old dumps according to a user-specified
37 script should be installed and run on a central backup server with local
38 access to the backup volumes.
40 The script should be run with full (root) privileges, so that it can
41 correctly record file ownership information. The server should also be
44 to the client machines, and run processes there as root. (This is not a
45 security disaster. Remember that the backup server is, in the end,
46 responsible for the integrity of the backup data. A dishonest backup
47 server can easily compromise a client which is being restored from
49 .SS Command-line options
50 Most of the behaviour of
52 is controlled by a configuration file, described starting with the
54 .B Configuration commands
56 But a few features are controlled by command-line options.
59 Show a brief help message for the program, and exit successfully.
64 version number and some choice pieces of build-time configuration, and
70 instead of the default configuration file (shown as
77 Produce verbose progress information on standard output while the backup
78 is running. This keeps one amused while running a backup
79 interactively. In any event,
81 will report failures to standard error, and otherwise run silently, so
82 it doesn't annoy unnecessarily if run by
85 Backing up a filesystem works as follows.
87 Make a snapshot of the filesystem on the client, and ensure that the
88 snapshot is mounted. There are some `trivial' snapshot types which use
89 the existing mounted filesystem, and either prevent processes writing to
90 it during the backup, or just hope for the best. Other snapshot types
91 require the snapshot to be mounted somewhere distinct from the main
92 filesystem, so that the latter can continue being used.
96 to copy the snapshot to the backup volume \(en specifically, to
97 .IB host / fs / new \fR.
98 If this directory already exists, then it's presumed to be debris from a
99 previous attempt to dump this filesystem:
101 will update it appropriately, by adding, deleting or modifying the
102 files. This means that retrying a failed dump \(en after fixing whatever
103 caused it to go wrong, obviously! \(en is usually fairly quick.
107 on the client to generate a `digest' describing the contents of the
108 filesystem, and send this to the server as
109 .IB host / fs / new .fshash \fR.
111 Release the snapshot: we don't need it any more.
115 over the new backup; specifically, to
116 .BI tmp/fshash. host . fs . date \fR.
117 This gives us a digest for what the backup volume actually stored.
121 digests. If they differ then dump the differences to the log file and
122 report a backup failure. (Backups aren't any good if they don't
123 actually back up the right thing. And you stand a better chance of
124 fixing them if you know that they're going wrong.)
126 Commit the backup, by renaming the dump directory to
131 .IB host / fs / date .fshash \fR.
133 The backup is now complete.
134 .SS Configuration commands
135 The configuration file is simply a Bash shell fragment: configuration
136 commands are shell functions.
138 .BI "backup " "fs\fR[:\fIfsarg\fR] ..."
139 Back up the named filesystems. The corresponding
141 may be required by the snapshot type.
146 commands will back up filesystems on the named
148 To back up filesystems on the backup server itself, use its hostname:
150 will avoid inefficient and pointless messing about
153 This command clears the
157 .BI "like " "host\fR ..."
158 Declare that subsequent filesystems are `similar' to like-named
159 filesystems on the named
163 should use those trees as potential sources of hardlinkable files. Be
164 careful when using this option without
167 option: an erroneous hardlink will cause the backup to fail. (The
168 backup won't be left silently incorrect.)
170 .BI "retain " frequency " " duration
171 Define part a backup retention policy: backup trees of the
173 should be kept for the
185 which means the same); the
193 Expiry considers each existing dump against the policy lines in order:
194 the last applicable line determines the dump's fate \(en so you should
195 probably write the lines in decreasing order of duration.
197 .BI "snap " type " " \fR[\fIargs\fR...]
200 for subsequent backups. Some snapshot types require additional
201 arguments, which may be supplied here.
202 .SS Configuration variables
203 The following shell variables may be overridden by the configuration
207 The number of log files to be kept for each filesystem. Old logfiles
208 are deleted to keep the total number below this bound. The default
212 Command-line options to pass to
214 in addition to the basic set:
221 .B \-\-one-file-system
223 .BR "\-\-filter=""dir-merge .rsync-backup""" .
230 snapshots are mounted on subdirectories below the
232 .IR "on backup clients" .
237 is the backup mount directory configured at build time.
240 The volume size option to pass to
242 when creating a snapshot. The default is
244 which seems to work fairly well.
247 Where the actual backup trees should be stored. See the section on
254 is the backup mount directory configured at build time.
257 The hash function to use for verifying archive integrity. This is
262 so it must name one of the hash functions supported by your Python's
264 module. The default is
267 The configuration file may define shell functions to perform custom
268 actions at various points in the backup process.
270 .BI "backup_precommit_hook " host " " fs " " date
271 Called after a backup has been verified complete and about to be
272 committed. The backup tree is in
274 in the current directory, and the
278 A typical action would be to create a digital signature on the
281 .BI "backup_commit_hook " host " " fs " " date
282 Called during the commit procedure. The backup tree and manifest have
283 been renamed into their proper places. Typically one would use this
284 hook to rename files created by the
285 .B backup_precommit_hook
288 .BR "whine " [ \-n ] " " \fItext\fR...
289 Called to report `interesting' events when the
291 option is in force. The default action is to echo the
293 to (what was initially) standard output, followed by a newline unless
297 The following snapshot types are available.
300 A trivial snapshot type: attempts to back up a live filesystem. How
301 well this works depends on how active the filesystem is. If files
302 change while the dump is in progress then the
304 verification will likely fail. Backups using this snapshot type must
305 specify the filesystem mount point as the
309 A slightly less trivial snapshot type: make the filesystem read-only
310 while the dump is in progress. Backups using this snapshot type must
311 specify the filesystem mount point as the
315 Create snapshots using LVM. The snapshot argument is interpreted as the
316 relevant volume group. The filesystem name is interpreted as the origin
317 volume name; the snapshot will be called
320 .IB SNAPDIR / fs \fR;
321 space will be allocated to it according to the
325 .BI "rfreezefs " client " " vg
326 This gets complicated. Suppose that a server has an LVM volume group,
327 and exports (somehow) a logical volume to a client. Examples are a host
328 providing a virtual disk to a guest, or a server providing
329 network-attached storage to a client. The server can create a snapshot
330 of the volume using LVM, but must synchronize with the client to ensure
331 that the filesystem image captured in the snapshot is clean. The
333 program should be installed on the client to perform this rather
334 delicate synchronization. Declare the server using the
336 command as usual; pass the client's name as the
339 server's volume group name as the
341 snapshot arguments. Finally, backups using this snapshot type must
342 specify the filesystem mount point (or, actually, any file in the
343 filesystem) on the client, as the
346 Additional snapshot types can be defined in the configuration file. A
347 snapshot type requires two shell functions.
349 .BI snap_ type " " snapargs " " fs " " fsarg
350 Create the snapshot, and write the mountpoint (on the client host) to
351 standard output, in a form suitable as an argument to
354 .BI unsnap_ type " " snapargs " " fs " " fsarg
357 There are a number of utility functions which can be used by snapshot
358 type handlers: please see the script for details. Please send the
359 author interesting snapshot handlers for inclusion in the main
361 .SS Archive structure
362 Backup trees are stored in a fairly straightforward directory tree.
364 At the top level is one directory for each client host. There are also
365 some special entries:
367 .B \&.rsync-backup-store
368 This file must be present in order to indicate that a backup volume is
369 present (and not just an empty mount point).
372 The cache database used for improving performance of local file
373 hashing. There may be other
375 files used by SQLite for its own purposes.
378 Part of the filesystem used on the backup volume. You don't want to
382 Used to store temporary files during the backup process. (Some of them
383 want to be on the same filesystem as the rest of the backup.) When
384 things go wrong, files are left behind in the hope that they might help
385 someone debug the mess. It's always safe to delete the files in here
386 when no backup is running.
388 So don't use those names for your hosts.
390 The next layer down contains a directory for each filesystem on the given host.
392 The bottom layer contains a directory for each dump of that filesystem,
393 named with the date at which the dump was started (in ISO8601
394 .IB yyyy \(en mm \(en dd
395 format), together with associated files named
404 Mark Wooding, <mdw@distorted.org.uk>
~mdw / rsync-backup / blob