Merge branch 't/recycling'
[dss.git] / dss.ggo
1 # Copyright (C) 2008-2010 Andre Noll <maan@systemlinux.org>
2 #
3 # Licensed under the GPL v2. For licencing details see COPYING.
4
5 package "dss"
6 version "0.1.4"
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 only honored if both --run and --daemon are
82 given. Otherwise it is silently ignored and log output is
83 written to stderr.
84 "
85
86 ##################
87 section "Commands"
88 ##################
89
90 defgroup "command"
91 #=================
92 groupdesc="
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.
96
97 "
98 required
99
100 groupoption "create" C
101 #~~~~~~~~~~~~~~~~~~~~~
102 "Create a new snapshot"
103 group="command"
104 details="
105 Execute the rsync command to create a new snapshot. Note that
106 this command does not care about free disk space.
107 "
108
109 groupoption "prune" P
110 #~~~~~~~~~~~~~~~~~~~~
111 "Remove redundant and outdated snapshots"
112 group="command"
113 details="
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.
118
119 A snapshot is said to be redundant if it belongs to an
120 interval that already contains more than the desired number
121 of snapshots.
122
123 The prune command gets rid of both outdated and redundant
124 snapshots.
125 "
126
127 groupoption "ls" L
128 #~~~~~~~~~~~~~~~~~
129 "Print a list of all snapshots"
130 group="command"
131 details="
132 The list will contain all snapshots no matter of their state,
133 i. e. incomplete snapshots and snapshots being deleted will
134 also be listed.
135 "
136
137 groupoption "run" R
138 #~~~~~~~~~~~~~~~~~~
139 "Start creating and pruning snapshots"
140 group="command"
141 details="
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.
146 "
147
148 ###############################
149 section "Rsync-related options"
150 ###############################
151
152 option "remote-host" H
153 #~~~~~~~~~~~~~~~~~~~~~
154 "Remote host"
155 string typestr="hostname"
156 default="localhost"
157 optional
158 details="
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.
164 "
165
166 option "remote-user" U
167 #~~~~~~~~~~~~~~~~~~~~~
168 "Remote user name (default: current user)"
169 string typestr="username"
170 optional
171 details="
172 Set this if the user running dss is different from the
173 user at the remote host when using ssh.
174 "
175
176 option "source-dir" -
177 #~~~~~~~~~~~~~~~~~~~~
178 "The data directory"
179 string typestr="dirname"
180 required
181 details="
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.
185 "
186
187 option "dest-dir" -
188 #~~~~~~~~~~~~~~~~~~
189 "Snapshot dir"
190 string typestr="dirname"
191 required
192 details="
193 The destination directory on the local host where snapshots
194 will be written. This must be writable by the user who runs
195 dss.
196 "
197
198 option "no-resume" -
199 #~~~~~~~~~~~~~~~~~~~
200 "Do not try to resume from previous runs"
201 flag off
202 details = "
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.
208
209 The --no-resume option deactivates this feature so that a new
210 directory is always used as the rsync destination directory.
211 "
212
213 option "rsync-option" O
214 #~~~~~~~~~~~~~~~~~~~~~~
215 "Further rsync options"
216 string typestr="option"
217 optional
218 multiple
219 details="
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:
224
225 --rsync-option --exclude --rsync-option /proc
226 "
227
228 ###################
229 section "Intervals"
230 ###################
231
232 option "unit-interval" u
233 #~~~~~~~~~~~~~~~~~~~~~~~
234 "The duration of a unit interval"
235 int typestr="days"
236 default="4"
237 optional
238 details="
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
242 unit intervals.
243
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
247 interval.
248
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.
255 "
256
257 option "num-intervals" n
258 #~~~~~~~~~~~~~~~~~~~~~~~
259 "The number of unit intervals"
260 int typestr="num"
261 default="5"
262 optional
263
264 ###############
265 section "Hooks"
266 ###############
267
268 option "pre-create-hook" r
269 #~~~~~~~~~~~~~~~~~~~~~~~~~~
270 "Executed before snapshot creation"
271 string typestr="command"
272 default = "true"
273 optional
274 details="
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.
278
279 For example, one might want to execute a script that checks
280 whether all snapshot-related file systems are properly mounted.
281
282 Another possible application of this is to return non-zero
283 during office hours in order to not slow down the file systems
284 by taking snapshots.
285 "
286
287 option "post-create-hook" o
288 #~~~~~~~~~~~~~~~~~~~~~~~~~~
289 "Executed after snapshot creation"
290 string typestr="command"
291 default = "true"
292 optional
293 details="
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.
298
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.
302 "
303
304 option "pre-remove-hook" -
305 #~~~~~~~~~~~~~~~~~~~~~~~~~~
306 "Executed before snapshot removal"
307 string typestr="command"
308 default = "true"
309 optional
310 details="
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.
316
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
320 concurrently to dss.
321
322 Another possible application of this is to record disk-usage
323 patterns before and after snapshot removal.
324 "
325
326 option "post-remove-hook" -
327 #~~~~~~~~~~~~~~~~~~~~~~~~~~
328 "Executed after snapshot removal"
329 string typestr="command"
330 default = "true"
331 optional
332 details="
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.
337 "
338
339 option "exit-hook" e
340 #~~~~~~~~~~~~~~~~~~~
341 "Executed if run command exits"
342 string typestr="command"
343 default = "true"
344 optional
345 details="
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.
350
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.
354 "
355
356 ###############################
357 section "Disk space monitoring"
358 ###############################
359
360 option "min-free-mb" m
361 #~~~~~~~~~~~~~~~~~~~~~
362 "Minimal amount of free disk space"
363 int typestr="megabytes"
364 default="100"
365 optional
366 details="
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.
374
375 A value of zero deactivates this check.
376 "
377
378 option "min-free-percent" p
379 #~~~~~~~~~~~~~~~~~~~~~~~~~~
380 "Minimal percent of free disk space"
381 int typestr="percent"
382 default="2"
383 optional
384 details="
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.
388 "
389 option "min-free-percent-inodes" i
390 #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
391 "Minimal percent of free inodes"
392 int typestr="percent"
393 default="0"
394 optional
395 details="
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
399 disk space.
400
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
405 though.
406
407 A value of zero (the default) deactivates this check.
408 "
409
410 option "keep-redundant" k
411 #~~~~~~~~~~~~~~~~~~~~~~~~
412 "Prune by disk space only"
413 flag off
414 details="
415 If this flag is not given dss removes redundant and outdated
416 snapshots automatically.
417
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.
422 "