1 # Copyright (C) 2008-2010 Andre Noll <maan@systemlinux.org>
3 # Licensed under the GPL v2. For licencing details see COPYING.
7 purpose "the dyadic snapshot scheduler
9 dss creates hardlink-based snapshots of a given directory on a remote
10 or local host using rsync's link-dest feature.
13 #########################
14 section "General options"
15 #########################
17 option "config-file" c
18 #~~~~~~~~~~~~~~~~~~~~~
19 "(default='~/.dssrc')"
20 string typestr="filename"
23 Options may be given at the command line or in the
24 configuration file. As usual, if an option is given both at
25 the command line and in the configuration file, the command
26 line option takes precedence.
28 However, there is an important exception to this rule:
29 If the --run option was given (see below) then dss honors
30 SIGHUP and re-reads its configuration file whenever it
31 receives this signal. In this case the options in the config
32 file override any options that were previously given at the
33 command line. This allows to change the configuration of a
34 running dss process on the fly by sending SIGHUP.
39 "Run as background daemon"
43 Note that dss refuses to start in daemon mode if no logfile
44 was specified. This option is mostly useful in conjuction
45 with the -R option described below.
47 Note that it is not possible to change whether dss runs as
48 background daemon by sending SIGHUP.
53 "Only print what would be done"
56 This flag does not make sense for all commands. The run
57 command refuses to start if this option was given. The ls
58 command silently ignores this flag.
72 Lower values mean more verbose logging.
77 "Logfile for the dss daemon process"
78 string typestr="filename"
81 This option is only honored if both --run and --daemon are
82 given. Otherwise it is silently ignored and log output is
93 dss supports a couple of commands each of which corresponds
94 to a different command line option. Exactly one of these
95 options must be given.
100 groupoption "create" C
101 #~~~~~~~~~~~~~~~~~~~~~
102 "Create a new snapshot"
105 Execute the rsync command to create a new snapshot. Note that
106 this command does not care about free disk space.
109 groupoption "prune" P
110 #~~~~~~~~~~~~~~~~~~~~
111 "Remove redundant and outdated snapshots"
114 A snapshot is considered outdated if its interval number
115 is greater or equal than the specified number of unit
116 intervals. See the \"Intervals\" section below for the precise
117 definition of these terms.
119 A snapshot is said to be redundant if it belongs to an
120 interval that already contains more than the desired number
123 The prune command gets rid of both outdated and redundant
129 "Print a list of all snapshots"
132 The list will contain all snapshots no matter of their state,
133 i. e. incomplete snapshots and snapshots being deleted will
139 "Start creating and pruning snapshots"
142 This is the main mode of operation. Snapshots will be created
143 in an endless loop as needed and pruned automatically. The loop
144 only terminates on fatal errors or if a terminating signal was
145 received. See also the --exit-hook option.
148 ###############################
149 section "Rsync-related options"
150 ###############################
152 option "remote-host" H
153 #~~~~~~~~~~~~~~~~~~~~~
155 string typestr="hostname"
159 If this option is given and its value differs from the local
160 host, then rsync uses ssh. Make sure there is no password
161 needed for the ssh connection. To achieve that, use public key
162 authentication for ssh and, if needed, set the remote user name
163 by using the --remote-user option.
166 option "remote-user" U
167 #~~~~~~~~~~~~~~~~~~~~~
168 "Remote user name (default: current user)"
169 string typestr="username"
172 Set this if the user running dss is different from the
173 user at the remote host when using ssh.
176 option "source-dir" -
177 #~~~~~~~~~~~~~~~~~~~~
179 string typestr="dirname"
182 The directory on the remote host from which snapshots are
183 taken. Of course, the user specified as --remote-user must
184 have read access to this directory.
190 string typestr="dirname"
193 The destination directory on the local host where snapshots
194 will be written. This must be writable by the user who runs
200 "Do not try to resume from previous runs"
203 Starting from version 0.1.4, dss tries to resume from a
204 previously cancelled dss instance by default. It does so by
205 looking at the status of the most recently created snapshot. If
206 this snapshot status is incomplete, its directory is reused
207 as the destination directory for a subsequent rsync run.
209 The --no-resume option deactivates this feature so that a new
210 directory is always used as the rsync destination directory.
213 option "rsync-option" O
214 #~~~~~~~~~~~~~~~~~~~~~~
215 "Further rsync options"
216 string typestr="option"
220 This option may be given multiple times. The given argument is
221 passed verbatim to the rsync command. Note that in order to use
222 rsync options that require an argument, you have to specify the
223 option and its argument as separate --rsync-options, like this:
225 --rsync-option --exclude --rsync-option /proc
232 option "unit-interval" u
233 #~~~~~~~~~~~~~~~~~~~~~~~
234 "The duration of a unit interval"
239 dss snapshot aging is implemented in terms of intervals. There
240 are two command line options related to intervals: the
241 duration u of a \"unit\" interval and the number n of those
244 dss removes any snapshots older than n times u and tries to
245 keep 2^(n - k - 1) snapshots in interval k, where the interval
246 number k counts from zero, zero being the most recent unit
249 In other words, the oldest snapshot will at most be u * n days
250 (= 20 days if default values are used) old. Moreover, there
251 are at most 2^n - 1 snapshots in total (i. e. 31 by default).
252 Observe that you have to create at least 2^(n - 1) snapshots
253 each interval for this to work out because that is the number
254 of snapshots in interval zero.
257 option "num-intervals" n
258 #~~~~~~~~~~~~~~~~~~~~~~~
259 "The number of unit intervals"
268 option "pre-create-hook" r
269 #~~~~~~~~~~~~~~~~~~~~~~~~~~
270 "Executed before snapshot creation"
271 string typestr="command"
275 Execute this command before trying to create a new snapshot.
276 If this command returns with a non-zero exit status, no
277 snapshot is being created and the operation is retried later.
279 For example, one might want to execute a script that checks
280 whether all snapshot-related file systems are properly mounted.
282 Another possible application of this is to return non-zero
283 during office hours in order to not slow down the file systems
287 option "post-create-hook" o
288 #~~~~~~~~~~~~~~~~~~~~~~~~~~
289 "Executed after snapshot creation"
290 string typestr="command"
294 Execute this after a snapshot has successfully been
295 created. The full path of the newly created snapshot is
296 passed to the hook as the first argument. The exit code of
297 this hook is ignored.
299 For instance this hook can be used to count the number of
300 files per user and/or the disk usage patterns in order to
301 store them in a database for further analysis.
304 option "pre-remove-hook" -
305 #~~~~~~~~~~~~~~~~~~~~~~~~~~
306 "Executed before snapshot removal"
307 string typestr="command"
311 Execute this command before removing a snapshot. The full
312 path to the snapshot about to be deleted is passed to the
313 command as the first argument. If the command returns with
314 a non-zero exit status, no snapshot is being removed and the
315 operation is retried later.
317 For example, one might want to execute a script that checks
318 whether the snapshot to be deleted is currently used by
319 another process, e.g. by a tape-based backup system that runs
322 Another possible application of this is to record disk-usage
323 patterns before and after snapshot removal.
326 option "post-remove-hook" -
327 #~~~~~~~~~~~~~~~~~~~~~~~~~~
328 "Executed after snapshot removal"
329 string typestr="command"
333 Execute this after a snapshot has successfully been removed. As
334 for the pre-remove hook, the full path of the removed snapshot
335 is passed to the hook as the first argument. The exit code
336 of this hook is ignored.
341 "Executed if run command exits"
342 string typestr="command"
346 This hook is only used if the --run command was given which
347 instructs dss to run in an endless loop. The exit-hook gets
348 executed whenever this endless loop terminates. The reason
349 for terminating the loop is passed as the first argument.
351 One possible application for this hook is to send email to the
352 system administrator to let her know that no more snapshots
353 are going to be created.
356 ###############################
357 section "Disk space monitoring"
358 ###############################
360 option "min-free-mb" m
361 #~~~~~~~~~~~~~~~~~~~~~
362 "Minimal amount of free disk space"
363 int typestr="megabytes"
367 If disk space on the file system containing the destination
368 directory gets low, \"dss --run\" will suspend the currently
369 running rsync process and will start to remove snapshots in
370 order to free disk space. This option specifies the minimal
371 amount of free disk space. If less than the given number of
372 megabytes is available, snapshots are being deleted. See also
373 the --min_free_percent and the min-free-percent-inodes options.
375 A value of zero deactivates this check.
378 option "min-free-percent" p
379 #~~~~~~~~~~~~~~~~~~~~~~~~~~
380 "Minimal percent of free disk space"
381 int typestr="percent"
385 See --min-free-mb. Note that it is not recommended to set both
386 --min-free-mb and --min-free-percent to zero as this will
387 cause your file system to fill up quickly.
389 option "min-free-percent-inodes" i
390 #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
391 "Minimal percent of free inodes"
392 int typestr="percent"
396 Specify the minimum amount of free inodes on the file system
397 containing the destination dir. If less than that many inodes
398 are free, snapshot removal kicks in just as in case of low
401 Note that not every file system supports the concept of inodes.
402 Moreover it is not possible to reliably detect whether this is
403 the case. Therefore this feature is disabled by default. It's
404 safe to enable it for ext2/ext3/ext4 file systems on linux
407 A value of zero (the default) deactivates this check.
410 option "keep-redundant" k
411 #~~~~~~~~~~~~~~~~~~~~~~~~
412 "Prune by disk space only"
415 If this flag is not given dss removes redundant and outdated
416 snapshots automatically.
418 Otherwise, this feature is deactivated so that snapshots are
419 only being removed in case disk space or number of free inodes
420 becomes low. Use this flag if the file system containing the
421 destination directory is used for snapshots only.