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[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 "rsync-option" O
198 #~~~~~~~~~~~~~~~~~~~~~~
199 "Further rsync options"
200 string typestr="option"
201 optional
202 multiple
203 details="
204 This option may be given multiple times. The given argument is
205 passed verbatim to the rsync command. Note that in order to use
206 rsync options that require an argument, you have to specify the
207 option and its argument as separate --rsync-options, like this:
208
209 --rsync-option --exclude --rsync-option /proc
210 "
211
212 ###################
213 section "Intervals"
214 ###################
215
216 option "unit-interval" u
217 #~~~~~~~~~~~~~~~~~~~~~~~
218 "The duration of a unit interval"
219 int typestr="days"
220 default="4"
221 optional
222 details="
223 dss snapshot aging is implemented in terms of intervals. There
224 are two command line options related to intervals: the
225 duration u of a \"unit\" interval and the number n of those
226 unit intervals.
227
228 dss removes any snapshots older than n times u and tries to
229 keep 2^(n - k - 1) snapshots in interval k, where the interval
230 number k counts from zero, zero being the most recent unit
231 interval.
232
233 In other words, the oldest snapshot will at most be u * n days
234 (= 20 days if default values are used) old. Moreover, there
235 are at most 2^n - 1 snapshots in total (i. e. 31 by default).
236 Observe that you have to create at least 2^(n - 1) snapshots
237 each interval for this to work out because that is the number
238 of snapshots in interval zero.
239 "
240
241 option "num-intervals" n
242 #~~~~~~~~~~~~~~~~~~~~~~~
243 "The number of unit intervals"
244 int typestr="num"
245 default="5"
246 optional
247
248 ###############
249 section "Hooks"
250 ###############
251
252 option "pre-create-hook" r
253 #~~~~~~~~~~~~~~~~~~~~~~~~~~
254 "Executed before snapshot creation"
255 string typestr="command"
256 optional
257 details="
258 Execute this command before trying to create a new snapshot.
259 If this command returns with a non-zero exit status, no
260 snapshot is being created and the operation is retried later.
261
262 For example, one might want to execute a script that checks
263 whether all snapshot-related file systems are properly mounted.
264
265 Another possible application of this is to return non-zero
266 during office hours in order to not slow down the file systems
267 by taking snapshots.
268 "
269
270 option "post-create-hook" o
271 #~~~~~~~~~~~~~~~~~~~~~~~~~~
272 "Executed after snapshot creation"
273 string typestr="command"
274 optional
275 details="
276 Execute this after a snapshot has successfully been
277 created. The full path of the newly created snapshot is
278 passed to the hook as the first argument. The exit code of
279 this hook is ignored.
280
281 For instance this hook can be used to count the number of
282 files per user and/or the disk usage patterns in order to
283 store them in a database for further analysis.
284 "
285
286 option "pre-remove-hook" -
287 #~~~~~~~~~~~~~~~~~~~~~~~~~~
288 "Executed before snapshot removal"
289 string typestr="command"
290 optional
291 details="
292 Execute this command before removing a snapshot. The full
293 path to the snapshot about to be deleted is passed to the
294 command as the first argument. If the command returns with
295 a non-zero exit status, no snapshot is being removed and the
296 operation is retried later.
297
298 For example, one might want to execute a script that checks
299 whether the snapshot to be deleted is currently used by
300 another process, e.g. by a tape-based backup system that runs
301 concurrently to dss.
302
303 Another possible application of this is to record disk-usage
304 patterns before and after snapshot removal.
305 "
306
307 option "post-remove-hook" -
308 #~~~~~~~~~~~~~~~~~~~~~~~~~~
309 "Executed after snapshot removal"
310 string typestr="command"
311 optional
312 details="
313 Execute this after a snapshot has successfully been removed. As
314 for the pre-remove hook, the full path of the removed snapshot
315 is passed to the hook as the first argument. The exit code
316 of this hook is ignored.
317 "
318
319 option "exit-hook" e
320 #~~~~~~~~~~~~~~~~~~~
321 "Executed if run command exits"
322 string typestr="command"
323 optional
324 details="
325 This hook is only used if the --run command was given which
326 instructs dss to run in an endless loop. The exit-hook gets
327 executed whenever this endless loop terminates. The reason
328 for terminating the loop is passed as the first argument.
329
330 One possible application for this hook is to send email to the
331 system administrator to let her know that no more snapshots
332 are going to be created.
333 "
334
335 ###############################
336 section "Disk space monitoring"
337 ###############################
338
339 option "min-free-mb" m
340 #~~~~~~~~~~~~~~~~~~~~~
341 "Minimal amount of free disk space"
342 int typestr="megabytes"
343 default="100"
344 optional
345 details="
346 If disk space on the file system containing the destination
347 directory gets low, \"dss --run\" will suspend the currently
348 running rsync process and will start to remove snapshots in
349 order to free disk space. This option specifies the minimal
350 amount of free disk space. If less than the given number of
351 megabytes is available, snapshots are being deleted. See also
352 the --min_free_percent and the min-free-percent-inodes options.
353
354 A value of zero deactivates this check.
355 "
356
357 option "min-free-percent" p
358 #~~~~~~~~~~~~~~~~~~~~~~~~~~
359 "Minimal percent of free disk space"
360 int typestr="percent"
361 default="2"
362 optional
363 details="
364 See --min-free-mb. Note that it is not recommended to set both
365 --min-free-mb and --min-free-percent to zero as this will
366 cause your file system to fill up quickly.
367 "
368 option "min-free-percent-inodes" i
369 #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
370 "Minimal percent of free inodes"
371 int typestr="percent"
372 default="0"
373 optional
374 details="
375 Specify the minimum amount of free inodes on the file system
376 containing the destination dir. If less than that many inodes
377 are free, snapshot removal kicks in just as in case of low
378 disk space.
379
380 Note that not every file system supports the concept of inodes.
381 Moreover it is not possible to reliably detect whether this is
382 the case. Therefore this feature is disabled by default. It's
383 safe to enable it for ext3 file systems on linux though.
384
385 A value of zero (the default) deactivates this check.
386 "
387
388 option "keep-redundant" k
389 #~~~~~~~~~~~~~~~~~~~~~~~~
390 "Prune by disk space only"
391 flag off
392 details="
393 If this flag is not given dss removes redundant and outdated
394 snapshots automatically.
395
396 Otherwise, this feature is deactivated so that snapshots are
397 only being removed in case disk space or number of free inodes
398 becomes low. Use this flag if the file system containing the
399 destination directory is used for snapshots only.
400 "