Clarify the difference between outdated and redundant snapshots.
[dss.git] / dss.ggo
1 # Copyright (C) 2008 Andre Noll <maan@systemlinux.org>
2 #
3 # Licensed under the GPL v2. For licencing details see COPYING.
4
5 package "dss"
6 version "0.0.5"
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 it belongs to an interval
114 greater than the maximum number of intervals. It is said to be
115 redundant if it belongs to an interval that already contains
116 more than the desired number of snapshots. This command gets
117 rid of such snapshots.
118 "
119
120 groupoption "ls" L
121 #~~~~~~~~~~~~~~~~~
122 "Print a list of all snapshots"
123 group="command"
124 details="
125 The list will contain all snapshots no matter of their state,
126 i. e. incomplete snapshots and snapshots being deleted will
127 also be listed.
128 "
129
130 groupoption "run" R
131 #~~~~~~~~~~~~~~~~~~
132 "Start creating and pruning snapshots"
133 group="command"
134 details="
135 This is the main mode of operation. Snapshots will be created
136 as needed and pruned automatically.
137 "
138
139 ###############################
140 section "Rsync-related options"
141 ###############################
142
143 option "remote-host" H
144 #~~~~~~~~~~~~~~~~~~~~~
145 "Remote host"
146 string typestr="hostname"
147 default="localhost"
148 optional
149 details="
150 If this option is given and its value differs from the local
151 host, then rsync uses ssh. Make sure there is no password
152 needed for the ssh connection. To achieve that, use public key
153 authentication for ssh and, if needed, set the remote user name
154 by using the --remote-user option.
155 "
156
157 option "remote-user" U
158 #~~~~~~~~~~~~~~~~~~~~~
159 "Remote user name (default: current user)"
160 string typestr="username"
161 optional
162 details="
163 Set this if the user running dss is different from the
164 user at the remote host when using ssh.
165 "
166
167 option "source-dir" -
168 #~~~~~~~~~~~~~~~~~~~~
169 "The data directory"
170 string typestr="dirname"
171 required
172 details="
173 The directory on the remote host from which snapshots are
174 taken. Of course, the user specified as --remote-user must
175 have read access to this directory.
176 "
177
178 option "dest-dir" -
179 #~~~~~~~~~~~~~~~~~~
180 "Snapshot dir"
181 string typestr="dirname"
182 required
183 details="
184 The destination directory on the local host where snapshots
185 will be written. This must be writable by the user who runs
186 dss.
187 "
188
189 option "rsync-option" O
190 #~~~~~~~~~~~~~~~~~~~~~~
191 "Further rsync options"
192 string typestr="option"
193 optional
194 multiple
195 details="
196 These option may be given multiple times. The arguments passed
197 to that option are passed verbatim to the rsync command.
198 "
199
200 ###################
201 section "Intervals"
202 ###################
203
204 option "unit-interval" u
205 #~~~~~~~~~~~~~~~~~~~~~~~
206 "The duration of a unit interval"
207 int typestr="days"
208 default="4"
209 optional
210 details="
211 dss snapshot aging is implemented in terms of intervals. There
212 are two command line options related to intervals: the
213 duration u of a \"unit\" interval and the number n of those
214 unit intervals.
215
216 dss removes any snapshots older than n times u and tries to
217 keep 2^(k-1) snapshots in interval k, where the interval number
218 k counts from zero, zero being the most recent unit interval.
219
220 In other words, the oldest snapshot will at most be u * n days
221 (= 20 days if default values are used) old. Moreover, there
222 are at most 2^n - 1 snapshots in total (i. e. 31 by default).
223 Observe that you have to create at least 2 ^ (n - 1) snapshots
224 each interval for this to work out because that is the number
225 of snapshots in interval zero.
226 "
227
228 option "num-intervals" n
229 #~~~~~~~~~~~~~~~~~~~~~~~
230 "The number of unit intervals"
231 int typestr="num"
232 default="5"
233 optional
234
235 ###############
236 section "Hooks"
237 ###############
238
239 option "pre-create-hook" r
240 #~~~~~~~~~~~~~~~~~~~~~~~~~~
241 "Executed before snapshot creation"
242 string typestr="command"
243 optional
244 details="
245 Execute this command before trying to create a new snapshot.
246 If this command returns with a non-zero exit status, no
247 snapshot is being created and the operation is retried later.
248
249 For example, one might want to execute a script that checks
250 whether all snapshot-related file systems are properly mounted.
251
252 Another possible application of this is to return non-zero
253 during office hours in order to not slow down the file systems
254 by taking snapshots.
255 "
256
257 option "post-create-hook" o
258 #~~~~~~~~~~~~~~~~~~~~~~~~~~
259 "Executed after snapshot creation"
260 string typestr="command"
261 optional
262 details="
263 Execute this after a snapshot has successfully been
264 created. The full path of the newly created snapshot is
265 passed to the hook as the first argument. The exit code of
266 this hook is ignored.
267
268 For instance this hook can be used to count the number of
269 files per user and/or the disk usage patterns in order to
270 store them in a database for further analysis.
271 "
272
273 ###############################
274 section "Disk space monitoring"
275 ###############################
276
277 option "min-free-mb" m
278 #~~~~~~~~~~~~~~~~~~~~~
279 "Minimal amount of free disk space"
280 int typestr="megabytes"
281 default="100"
282 optional
283 details="
284 If disk space on the file system containing the destination
285 directory gets low, \"dss --run\" will suspend the currently
286 running rsync process and will start to remove snapshots in
287 order to free disk space. This option specifies the minimal
288 amount of free disk space. If less than the given number of
289 megabytes is available, snapshots are being deleted. See also
290 the --min_free_percent and the min-free-percent-inodes options.
291
292 A value of zero deactivates this check.
293 "
294
295 option "min-free-percent" p
296 #~~~~~~~~~~~~~~~~~~~~~~~~~~
297 "Minimal percent of free disk space"
298 int typestr="percent"
299 default="2"
300 optional
301 details="
302 See --min-free-mb. Note that it is not recommended to set both
303 --min-free-mb and --min-free-percent to zero as this will
304 cause your file system to fill up quickly.
305 "
306 option "min-free-percent-inodes" i
307 #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
308 "Minimal percent of free inodes"
309 int typestr="percent"
310 default="0"
311 optional
312 details="
313 Specify the minimum amount of free inodes on the file system
314 containing the destination dir. If less than that many inodes
315 are free, snapshot removal kicks in just as in case of low
316 disk space.
317
318 Note that not every file system supports the concept of inodes.
319 Moreover it is not possible to reliably detect whether this is
320 the case. Therefore this feature is disabled by default. It's
321 safe to enable it for ext3 file systems on linux though.
322
323 A value of zero (the default) deactivates this check.
324 "