1 # Copyright (C) 2008-2009 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 mostly useful for the run command if --daemon
92 dss supports a couple of commands each of which corresponds
93 to a different command line option. Exactly one of these
94 options must be given.
99 groupoption "create" C
100 #~~~~~~~~~~~~~~~~~~~~~
101 "Create a new snapshot"
104 Execute the rsync command to create a new snapshot. Note that
105 this command does not care about free disk space.
108 groupoption "prune" P
109 #~~~~~~~~~~~~~~~~~~~~
110 "Remove redundant and outdated snapshots"
113 A snapshot is considered outdated if its interval number
114 is greater or equal than the specified number of unit
115 intervals. See the \"Intervals\" section below for the precise
116 definition of these terms.
118 A snapshot is said to be redundant if it belongs to an
119 interval that already contains more than the desired number
122 The prune command gets rid of both outdated and redundant
128 "Print a list of all snapshots"
131 The list will contain all snapshots no matter of their state,
132 i. e. incomplete snapshots and snapshots being deleted will
138 "Start creating and pruning snapshots"
141 This is the main mode of operation. Snapshots will be created
142 in an endless loop as needed and pruned automatically. The loop
143 only terminates on fatal errors or if a terminating signal was
144 received. See also the --exit-hook option.
147 ###############################
148 section "Rsync-related options"
149 ###############################
151 option "remote-host" H
152 #~~~~~~~~~~~~~~~~~~~~~
154 string typestr="hostname"
158 If this option is given and its value differs from the local
159 host, then rsync uses ssh. Make sure there is no password
160 needed for the ssh connection. To achieve that, use public key
161 authentication for ssh and, if needed, set the remote user name
162 by using the --remote-user option.
165 option "remote-user" U
166 #~~~~~~~~~~~~~~~~~~~~~
167 "Remote user name (default: current user)"
168 string typestr="username"
171 Set this if the user running dss is different from the
172 user at the remote host when using ssh.
175 option "source-dir" -
176 #~~~~~~~~~~~~~~~~~~~~
178 string typestr="dirname"
181 The directory on the remote host from which snapshots are
182 taken. Of course, the user specified as --remote-user must
183 have read access to this directory.
189 string typestr="dirname"
192 The destination directory on the local host where snapshots
193 will be written. This must be writable by the user who runs
199 "Do not try to resume from previous runs"
202 Starting from version 0.1.4, dss tries to resume from a
203 previously cancelled dss instance by default. It does so by
204 looking at the status of the most recently created snapshot. If
205 this snapshot status is incomplete, its directory is reused
206 as the destination directory for a subsequent rsync run.
208 The --no-resume option deactivates this feature so that a new
209 directory is always used as the rsync destination directory.
212 option "rsync-option" O
213 #~~~~~~~~~~~~~~~~~~~~~~
214 "Further rsync options"
215 string typestr="option"
219 This option may be given multiple times. The given argument is
220 passed verbatim to the rsync command. Note that in order to use
221 rsync options that require an argument, you have to specify the
222 option and its argument as separate --rsync-options, like this:
224 --rsync-option --exclude --rsync-option /proc
231 option "unit-interval" u
232 #~~~~~~~~~~~~~~~~~~~~~~~
233 "The duration of a unit interval"
238 dss snapshot aging is implemented in terms of intervals. There
239 are two command line options related to intervals: the
240 duration u of a \"unit\" interval and the number n of those
243 dss removes any snapshots older than n times u and tries to
244 keep 2^(n - k - 1) snapshots in interval k, where the interval
245 number k counts from zero, zero being the most recent unit
248 In other words, the oldest snapshot will at most be u * n days
249 (= 20 days if default values are used) old. Moreover, there
250 are at most 2^n - 1 snapshots in total (i. e. 31 by default).
251 Observe that you have to create at least 2^(n - 1) snapshots
252 each interval for this to work out because that is the number
253 of snapshots in interval zero.
256 option "num-intervals" n
257 #~~~~~~~~~~~~~~~~~~~~~~~
258 "The number of unit intervals"
267 option "pre-create-hook" r
268 #~~~~~~~~~~~~~~~~~~~~~~~~~~
269 "Executed before snapshot creation"
270 string typestr="command"
273 Execute this command before trying to create a new snapshot.
274 If this command returns with a non-zero exit status, no
275 snapshot is being created and the operation is retried later.
277 For example, one might want to execute a script that checks
278 whether all snapshot-related file systems are properly mounted.
280 Another possible application of this is to return non-zero
281 during office hours in order to not slow down the file systems
285 option "post-create-hook" o
286 #~~~~~~~~~~~~~~~~~~~~~~~~~~
287 "Executed after snapshot creation"
288 string typestr="command"
291 Execute this after a snapshot has successfully been
292 created. The full path of the newly created snapshot is
293 passed to the hook as the first argument. The exit code of
294 this hook is ignored.
296 For instance this hook can be used to count the number of
297 files per user and/or the disk usage patterns in order to
298 store them in a database for further analysis.
301 option "pre-remove-hook" -
302 #~~~~~~~~~~~~~~~~~~~~~~~~~~
303 "Executed before snapshot removal"
304 string typestr="command"
307 Execute this command before removing a snapshot. The full
308 path to the snapshot about to be deleted is passed to the
309 command as the first argument. If the command returns with
310 a non-zero exit status, no snapshot is being removed and the
311 operation is retried later.
313 For example, one might want to execute a script that checks
314 whether the snapshot to be deleted is currently used by
315 another process, e.g. by a tape-based backup system that runs
318 Another possible application of this is to record disk-usage
319 patterns before and after snapshot removal.
322 option "post-remove-hook" -
323 #~~~~~~~~~~~~~~~~~~~~~~~~~~
324 "Executed after snapshot removal"
325 string typestr="command"
328 Execute this after a snapshot has successfully been removed. As
329 for the pre-remove hook, the full path of the removed snapshot
330 is passed to the hook as the first argument. The exit code
331 of this hook is ignored.
336 "Executed if run command exits"
337 string typestr="command"
340 This hook is only used if the --run command was given which
341 instructs dss to run in an endless loop. The exit-hook gets
342 executed whenever this endless loop terminates. The reason
343 for terminating the loop is passed as the first argument.
345 One possible application for this hook is to send email to the
346 system administrator to let her know that no more snapshots
347 are going to be created.
350 ###############################
351 section "Disk space monitoring"
352 ###############################
354 option "min-free-mb" m
355 #~~~~~~~~~~~~~~~~~~~~~
356 "Minimal amount of free disk space"
357 int typestr="megabytes"
361 If disk space on the file system containing the destination
362 directory gets low, \"dss --run\" will suspend the currently
363 running rsync process and will start to remove snapshots in
364 order to free disk space. This option specifies the minimal
365 amount of free disk space. If less than the given number of
366 megabytes is available, snapshots are being deleted. See also
367 the --min_free_percent and the min-free-percent-inodes options.
369 A value of zero deactivates this check.
372 option "min-free-percent" p
373 #~~~~~~~~~~~~~~~~~~~~~~~~~~
374 "Minimal percent of free disk space"
375 int typestr="percent"
379 See --min-free-mb. Note that it is not recommended to set both
380 --min-free-mb and --min-free-percent to zero as this will
381 cause your file system to fill up quickly.
383 option "min-free-percent-inodes" i
384 #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
385 "Minimal percent of free inodes"
386 int typestr="percent"
390 Specify the minimum amount of free inodes on the file system
391 containing the destination dir. If less than that many inodes
392 are free, snapshot removal kicks in just as in case of low
395 Note that not every file system supports the concept of inodes.
396 Moreover it is not possible to reliably detect whether this is
397 the case. Therefore this feature is disabled by default. It's
398 safe to enable it for ext3 file systems on linux though.
400 A value of zero (the default) deactivates this check.
403 option "keep-redundant" k
404 #~~~~~~~~~~~~~~~~~~~~~~~~
405 "Prune by disk space only"
408 If this flag is not given dss removes redundant and outdated
409 snapshots automatically.
411 Otherwise, this feature is deactivated so that snapshots are
412 only being removed in case disk space or number of free inodes
413 becomes low. Use this flag if the file system containing the
414 destination directory is used for snapshots only.