Improve documentation of --keep-redundant.
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1 # Copyright (C) 2008-2010 Andre Noll <maan@tuebingen.mpg.de>
2 #
3 # Licensed under the GPL v2. For licencing details see COPYING.
4
5 package "dss"
6 version "0.1.6"
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 conjunction
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 groupoption "kill" K
149 #~~~~~~~~~~~~~~~~~~~
150 "Kill a running dss process"
151 group="command"
152 details="
153 This sends SIGTERM to the dss process that corresponds to the
154 given config file. If --dry-run is given, the PID of the dss
155 process is written to stdout, but no signal is sent.
156 "
157
158 groupoption "reload" -
159 #~~~~~~~~~~~~~~~~~~~~~
160 "force a running dss process to reload its config file"
161 group="command"
162 details="
163 This differs from --kill only in that SIGHUP rather than SIGTERM
164 is sent to the dss process.
165 "
166
167 ###############################
168 section "Rsync-related options"
169 ###############################
170
171 option "remote-host" H
172 #~~~~~~~~~~~~~~~~~~~~~
173 "Remote host"
174 string typestr="hostname"
175 default="localhost"
176 optional
177 details="
178 If this option is given and its value differs from the local
179 host, then rsync uses ssh. Make sure there is no password
180 needed for the ssh connection. To achieve that, use public key
181 authentication for ssh and, if needed, set the remote user name
182 by using the --remote-user option.
183 "
184
185 option "remote-user" U
186 #~~~~~~~~~~~~~~~~~~~~~
187 "Remote user name (default: current user)"
188 string typestr="username"
189 optional
190 details="
191 Set this if the user running dss is different from the
192 user at the remote host when using ssh.
193 "
194
195 option "source-dir" -
196 #~~~~~~~~~~~~~~~~~~~~
197 "The data directory"
198 string typestr="dirname"
199 required
200 details="
201 The directory on the remote host from which snapshots are
202 taken. Of course, the user specified as --remote-user must
203 have read access to this directory.
204 "
205
206 option "dest-dir" -
207 #~~~~~~~~~~~~~~~~~~
208 "Snapshot dir"
209 string typestr="dirname"
210 required
211 details="
212 The destination directory on the local host where snapshots
213 will be written. This must be writable by the user who runs
214 dss.
215 "
216
217 option "no-resume" -
218 #~~~~~~~~~~~~~~~~~~~
219 "Do not try to resume from previous runs"
220 flag off
221 details = "
222 Starting from version 0.1.4, dss tries to resume from a
223 previously cancelled dss instance by default. It does so by
224 looking at the status of the most recently created snapshot. If
225 this snapshot status is incomplete, its directory is reused
226 as the destination directory for a subsequent rsync run.
227
228 The --no-resume option deactivates this feature so that a new
229 directory is always used as the rsync destination directory.
230 "
231
232 option "rsync-option" O
233 #~~~~~~~~~~~~~~~~~~~~~~
234 "Further rsync options"
235 string typestr="option"
236 optional
237 multiple
238 details="
239 This option may be given multiple times. The given argument is
240 passed verbatim to the rsync command. Note that in order to use
241 rsync options that require an argument, you have to specify the
242 option and its argument as separate --rsync-options, like this:
243
244 --rsync-option --exclude --rsync-option /proc
245 "
246
247 option "max-rsync-errors" -
248 "Terminate after this many rsync failures"
249 int typestr="count"
250 default="10"
251 optional
252 details="
253 Only relevant when operating in --run mode (see above). If
254 the rsync process exits with a fatal error, dss restarts
255 the command in the hope that the problem is transient
256 and subsequent rsync runs succeed. After the given number
257 of consecutive rsync error exits, however, dss gives up,
258 executes the exit hook and terminates. Set this to zero if
259 dss should exit immediately on the first rsync error.
260
261 The only non-fatal error is when rsync exits with code 24. This
262 indicates a partial transfer due to vanished source files
263 and happens frequently when snapshotting a directory which
264 is concurrently being modified.
265 "
266
267 ###################
268 section "Intervals"
269 ###################
270
271 option "unit-interval" u
272 #~~~~~~~~~~~~~~~~~~~~~~~
273 "The duration of a unit interval"
274 int typestr="days"
275 default="4"
276 optional
277 details="
278 Snapshot aging is implemented in terms of intervals. There are two
279 command line options related to intervals: the duration u of a unit
280 interval and the number of unit intervals, denoted n below.
281
282 dss removes snapshots older than n times u and tries to keep 2^(n -
283 k - 1) snapshots in interval k, where the interval number k counts
284 from zero to n - 1, with zero being the most recent unit interval.
285
286 Hence the oldest snapshot will at most be u * n days old (4 days *
287 5 intervals = 20 days, if default values are used). Moreover, there
288 are at most 2^n - 1 snapshots in total (2^5 - 1 = 31 by default). Note
289 that for this to work out your system must be fast enough to create at
290 least 2^(n - 1) snapshots per unit interval (16 snapshots in 4 days =
291 one snapshot in 6 hours), because this is the number of snapshots in
292 interval zero.
293 "
294
295 option "num-intervals" n
296 #~~~~~~~~~~~~~~~~~~~~~~~
297 "The number of unit intervals"
298 int typestr="num"
299 default="5"
300 optional
301 details="
302 Note that increasing this number by one doubles the total number of
303 snapshots. See the documentation of --unit-interval above.
304 "
305
306 ###############
307 section "Hooks"
308 ###############
309
310 option "pre-create-hook" r
311 #~~~~~~~~~~~~~~~~~~~~~~~~~~
312 "Executed before snapshot creation"
313 string typestr="command"
314 default = "true"
315 optional
316 details="
317 Execute this command before trying to create a new snapshot.
318 If this command returns with a non-zero exit status, no
319 snapshot is being created and the operation is retried later.
320
321 For example, one might want to execute a script that checks
322 whether all snapshot-related file systems are properly mounted.
323
324 Another possible application of this is to return non-zero
325 during office hours in order to not slow down the file systems
326 by taking snapshots.
327 "
328
329 option "post-create-hook" o
330 #~~~~~~~~~~~~~~~~~~~~~~~~~~
331 "Executed after snapshot creation"
332 string typestr="command"
333 default = "true"
334 optional
335 details="
336 Execute this after a snapshot has successfully been
337 created. The full path of the newly created snapshot is
338 passed to the hook as the first argument. The exit code of
339 this hook is ignored.
340
341 For instance this hook can be used to count the number of
342 files per user and/or the disk usage patterns in order to
343 store them in a database for further analysis.
344 "
345
346 option "pre-remove-hook" -
347 #~~~~~~~~~~~~~~~~~~~~~~~~~~
348 "Executed before snapshot removal"
349 string typestr="command"
350 default = "true"
351 optional
352 details="
353 Execute this command before removing a snapshot. The full
354 path to the snapshot about to be deleted is passed to the
355 command as the first argument. If the command returns with
356 a non-zero exit status, no snapshot is being removed and the
357 operation is retried later.
358
359 For example, one might want to execute a script that checks
360 whether the snapshot to be deleted is currently used by
361 another process, e.g. by a tape-based backup system that runs
362 concurrently to dss.
363
364 Another possible application of this is to record disk-usage
365 patterns before and after snapshot removal.
366 "
367
368 option "post-remove-hook" -
369 #~~~~~~~~~~~~~~~~~~~~~~~~~~
370 "Executed after snapshot removal"
371 string typestr="command"
372 default = "true"
373 optional
374 details="
375 Execute this after a snapshot has successfully been removed. As
376 for the pre-remove hook, the full path of the removed snapshot
377 is passed to the hook as the first argument. The exit code
378 of this hook is ignored.
379 "
380
381 option "exit-hook" e
382 #~~~~~~~~~~~~~~~~~~~
383 "Executed if run command exits"
384 string typestr="command"
385 default = "true"
386 optional
387 details="
388 This hook is only used if the --run command was given which
389 instructs dss to run in an endless loop. The exit-hook gets
390 executed whenever this endless loop terminates. The reason
391 for terminating the loop is passed as the first argument.
392
393 One possible application for this hook is to send email to the
394 system administrator to let her know that no more snapshots
395 are going to be created.
396 "
397
398 ###############################
399 section "Disk space monitoring"
400 ###############################
401
402 option "min-free-mb" m
403 #~~~~~~~~~~~~~~~~~~~~~
404 "Minimal amount of free disk space"
405 int typestr="megabytes"
406 default="100"
407 optional
408 details="
409 If disk space on the file system containing the destination
410 directory gets low, \"dss --run\" will suspend the currently
411 running rsync process and will start to remove snapshots in
412 order to free disk space. This option specifies the minimal
413 amount of free disk space. If less than the given number of
414 megabytes is available, snapshots are being deleted. See also
415 the --min_free_percent and the min-free-percent-inodes options.
416
417 A value of zero deactivates this check.
418 "
419
420 option "min-free-percent" p
421 #~~~~~~~~~~~~~~~~~~~~~~~~~~
422 "Minimal percent of free disk space"
423 int typestr="percent"
424 default="2"
425 optional
426 details="
427 See --min-free-mb. Note that it is not recommended to set both
428 --min-free-mb and --min-free-percent to zero as this will
429 cause your file system to fill up quickly.
430 "
431 option "min-free-percent-inodes" i
432 #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
433 "Minimal percent of free inodes"
434 int typestr="percent"
435 default="0"
436 optional
437 details="
438 Specify the minimum amount of free inodes on the file system
439 containing the destination dir. If less than that many inodes
440 are free, snapshot removal kicks in just as in case of low
441 disk space.
442
443 Note that not every file system supports the concept of inodes.
444 Moreover it is not possible to reliably detect whether this is
445 the case. Therefore this feature is disabled by default. It's
446 safe to enable it for ext2/ext3/ext4 file systems on linux
447 though.
448
449 A value of zero (the default) deactivates this check.
450 "
451
452 option "keep-redundant" k
453 #~~~~~~~~~~~~~~~~~~~~~~~~
454 "Prune by disk space only"
455 flag off
456 details="
457 By default, redundant and outdated snapshots are removed automatically
458 to keep the number of snapshots in harmony with the configured
459 policy. If this flag is given, dss removes such snapshots only if
460 disk space or number of free inodes becomes low.
461 "
462
463 option "min-complete" -
464 #~~~~~~~~~~~~~~~~~~~~~~
465 "Minimal number of complete snapshots to keep"
466 int typestr = "num"
467 default = "1"
468 optional
469 details = "
470 This option is only relevant if snapshots must be deleted
471 because disk space gets low.
472
473 dss refuses to remove old snapshots if there are fewer complete
474 snapshots left than the given number. The default value of one
475 guarantees that at least one complete snapshot is available
476 at all times.
477
478 If only <num> complete snapshot are left, and there is not
479 enough disk space available for another snapshot, the program
480 terminates with a \"No space left on device\" error.
481 "