Make all hooks default to /bin/true.
[dss.git] / dss.ggo
1 # Copyright (C) 2008-2009 Andre Noll <maan@systemlinux.org>
2 #
3 # Licensed under the GPL v2. For licencing details see COPYING.
4
5 package "dss"
6 version "0.1.3"
7 purpose "the dyadic snapshot scheduler
8
9 dss creates hardlink-based snapshots of a given directory on a remote
10 or local host using rsync's link-dest feature.
11 "
12
13 #########################
14 section "General options"
15 #########################
16
17 option "config-file" c
18 #~~~~~~~~~~~~~~~~~~~~~
19 "(default='~/.dssrc')"
20 string typestr="filename"
21 optional
22 details="
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.
27
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.
35 "
36
37 option "daemon" d
38 #~~~~~~~~~~~~~~~~
39 "Run as background daemon"
40 flag off
41 dependon="logfile"
42 details="
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.
46
47 Note that it is not possible to change whether dss runs as
48 background daemon by sending SIGHUP.
49 "
50
51 option "dry-run" D
52 #~~~~~~~~~~~~~~~~~
53 "Only print what would be done"
54 flag off
55 details="
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.
59 "
60
61 #################
62 section "Logging"
63 #################
64
65 option "loglevel" l
66 #~~~~~~~~~~~~~~~~~~
67 "Set loglevel (0-6)"
68 int typestr="level"
69 default="3"
70 optional
71 details="
72 Lower values mean more verbose logging.
73 "
74
75 option "logfile" -
76 #~~~~~~~~~~~~~~~~~
77 "Logfile for the dss daemon process"
78 string typestr="filename"
79 optional
80 details="
81 This option is mostly useful for the run command if --daemon
82 is also given.
83 "
84
85 ##################
86 section "Commands"
87 ##################
88
89 defgroup "command"
90 #=================
91 groupdesc="
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.
95
96 "
97 required
98
99 groupoption "create" C
100 #~~~~~~~~~~~~~~~~~~~~~
101 "Create a new snapshot"
102 group="command"
103 details="
104 Execute the rsync command to create a new snapshot. Note that
105 this command does not care about free disk space.
106 "
107
108 groupoption "prune" P
109 #~~~~~~~~~~~~~~~~~~~~
110 "Remove redundant and outdated snapshots"
111 group="command"
112 details="
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.
117
118 A snapshot is said to be redundant if it belongs to an
119 interval that already contains more than the desired number
120 of snapshots.
121
122 The prune command gets rid of both outdated and redundant
123 snapshots.
124 "
125
126 groupoption "ls" L
127 #~~~~~~~~~~~~~~~~~
128 "Print a list of all snapshots"
129 group="command"
130 details="
131 The list will contain all snapshots no matter of their state,
132 i. e. incomplete snapshots and snapshots being deleted will
133 also be listed.
134 "
135
136 groupoption "run" R
137 #~~~~~~~~~~~~~~~~~~
138 "Start creating and pruning snapshots"
139 group="command"
140 details="
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.
145 "
146
147 ###############################
148 section "Rsync-related options"
149 ###############################
150
151 option "remote-host" H
152 #~~~~~~~~~~~~~~~~~~~~~
153 "Remote host"
154 string typestr="hostname"
155 default="localhost"
156 optional
157 details="
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.
163 "
164
165 option "remote-user" U
166 #~~~~~~~~~~~~~~~~~~~~~
167 "Remote user name (default: current user)"
168 string typestr="username"
169 optional
170 details="
171 Set this if the user running dss is different from the
172 user at the remote host when using ssh.
173 "
174
175 option "source-dir" -
176 #~~~~~~~~~~~~~~~~~~~~
177 "The data directory"
178 string typestr="dirname"
179 required
180 details="
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.
184 "
185
186 option "dest-dir" -
187 #~~~~~~~~~~~~~~~~~~
188 "Snapshot dir"
189 string typestr="dirname"
190 required
191 details="
192 The destination directory on the local host where snapshots
193 will be written. This must be writable by the user who runs
194 dss.
195 "
196
197 option "no-resume" -
198 #~~~~~~~~~~~~~~~~~~~
199 "Do not try to resume from previous runs"
200 flag off
201 details = "
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.
207
208 The --no-resume option deactivates this feature so that a new
209 directory is always used as the rsync destination directory.
210 "
211
212 option "rsync-option" O
213 #~~~~~~~~~~~~~~~~~~~~~~
214 "Further rsync options"
215 string typestr="option"
216 optional
217 multiple
218 details="
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:
223
224 --rsync-option --exclude --rsync-option /proc
225 "
226
227 ###################
228 section "Intervals"
229 ###################
230
231 option "unit-interval" u
232 #~~~~~~~~~~~~~~~~~~~~~~~
233 "The duration of a unit interval"
234 int typestr="days"
235 default="4"
236 optional
237 details="
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
241 unit intervals.
242
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
246 interval.
247
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.
254 "
255
256 option "num-intervals" n
257 #~~~~~~~~~~~~~~~~~~~~~~~
258 "The number of unit intervals"
259 int typestr="num"
260 default="5"
261 optional
262
263 ###############
264 section "Hooks"
265 ###############
266
267 option "pre-create-hook" r
268 #~~~~~~~~~~~~~~~~~~~~~~~~~~
269 "Executed before snapshot creation"
270 string typestr="command"
271 default = "/bin/true"
272 optional
273 details="
274 Execute this command before trying to create a new snapshot.
275 If this command returns with a non-zero exit status, no
276 snapshot is being created and the operation is retried later.
277
278 For example, one might want to execute a script that checks
279 whether all snapshot-related file systems are properly mounted.
280
281 Another possible application of this is to return non-zero
282 during office hours in order to not slow down the file systems
283 by taking snapshots.
284 "
285
286 option "post-create-hook" o
287 #~~~~~~~~~~~~~~~~~~~~~~~~~~
288 "Executed after snapshot creation"
289 string typestr="command"
290 default = "/bin/true"
291 optional
292 details="
293 Execute this after a snapshot has successfully been
294 created. The full path of the newly created snapshot is
295 passed to the hook as the first argument. The exit code of
296 this hook is ignored.
297
298 For instance this hook can be used to count the number of
299 files per user and/or the disk usage patterns in order to
300 store them in a database for further analysis.
301 "
302
303 option "pre-remove-hook" -
304 #~~~~~~~~~~~~~~~~~~~~~~~~~~
305 "Executed before snapshot removal"
306 string typestr="command"
307 default = "/bin/true"
308 optional
309 details="
310 Execute this command before removing a snapshot. The full
311 path to the snapshot about to be deleted is passed to the
312 command as the first argument. If the command returns with
313 a non-zero exit status, no snapshot is being removed and the
314 operation is retried later.
315
316 For example, one might want to execute a script that checks
317 whether the snapshot to be deleted is currently used by
318 another process, e.g. by a tape-based backup system that runs
319 concurrently to dss.
320
321 Another possible application of this is to record disk-usage
322 patterns before and after snapshot removal.
323 "
324
325 option "post-remove-hook" -
326 #~~~~~~~~~~~~~~~~~~~~~~~~~~
327 "Executed after snapshot removal"
328 string typestr="command"
329 default = "/bin/true"
330 optional
331 details="
332 Execute this after a snapshot has successfully been removed. As
333 for the pre-remove hook, the full path of the removed snapshot
334 is passed to the hook as the first argument. The exit code
335 of this hook is ignored.
336 "
337
338 option "exit-hook" e
339 #~~~~~~~~~~~~~~~~~~~
340 "Executed if run command exits"
341 string typestr="command"
342 default = "/bin/true"
343 optional
344 details="
345 This hook is only used if the --run command was given which
346 instructs dss to run in an endless loop. The exit-hook gets
347 executed whenever this endless loop terminates. The reason
348 for terminating the loop is passed as the first argument.
349
350 One possible application for this hook is to send email to the
351 system administrator to let her know that no more snapshots
352 are going to be created.
353 "
354
355 ###############################
356 section "Disk space monitoring"
357 ###############################
358
359 option "min-free-mb" m
360 #~~~~~~~~~~~~~~~~~~~~~
361 "Minimal amount of free disk space"
362 int typestr="megabytes"
363 default="100"
364 optional
365 details="
366 If disk space on the file system containing the destination
367 directory gets low, \"dss --run\" will suspend the currently
368 running rsync process and will start to remove snapshots in
369 order to free disk space. This option specifies the minimal
370 amount of free disk space. If less than the given number of
371 megabytes is available, snapshots are being deleted. See also
372 the --min_free_percent and the min-free-percent-inodes options.
373
374 A value of zero deactivates this check.
375 "
376
377 option "min-free-percent" p
378 #~~~~~~~~~~~~~~~~~~~~~~~~~~
379 "Minimal percent of free disk space"
380 int typestr="percent"
381 default="2"
382 optional
383 details="
384 See --min-free-mb. Note that it is not recommended to set both
385 --min-free-mb and --min-free-percent to zero as this will
386 cause your file system to fill up quickly.
387 "
388 option "min-free-percent-inodes" i
389 #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
390 "Minimal percent of free inodes"
391 int typestr="percent"
392 default="0"
393 optional
394 details="
395 Specify the minimum amount of free inodes on the file system
396 containing the destination dir. If less than that many inodes
397 are free, snapshot removal kicks in just as in case of low
398 disk space.
399
400 Note that not every file system supports the concept of inodes.
401 Moreover it is not possible to reliably detect whether this is
402 the case. Therefore this feature is disabled by default. It's
403 safe to enable it for ext3 file systems on linux though.
404
405 A value of zero (the default) deactivates this check.
406 "
407
408 option "keep-redundant" k
409 #~~~~~~~~~~~~~~~~~~~~~~~~
410 "Prune by disk space only"
411 flag off
412 details="
413 If this flag is not given dss removes redundant and outdated
414 snapshots automatically.
415
416 Otherwise, this feature is deactivated so that snapshots are
417 only being removed in case disk space or number of free inodes
418 becomes low. Use this flag if the file system containing the
419 destination directory is used for snapshots only.
420 "