+# Copyright (C) 2008 Andre Noll <maan@systemlinux.org>
#
+# Licensed under the GPL v2. For licencing details see COPYING.
+
package "dss"
-version "0.0.3"
+version "0.1.0"
purpose "the dyadic snapshot scheduler
dss creates hardlink-based snapshots of a given directory on a remote
file override any options that were previously given at the
command line. This allows to change the configuration of a
running dss process on the fly by sending SIGHUP.
-
- Note that it is not possible to change whether dss runs as
- background daemon by sending SIGHUP.
"
option "daemon" d
Note that dss refuses to start in daemon mode if no logfile
was specified. This option is mostly useful in conjuction
with the -R option described below.
+
+ Note that it is not possible to change whether dss runs as
+ background daemon by sending SIGHUP.
"
option "dry-run" D
default="3"
optional
details="
- Lower values mean less verbose logging.
+ Lower values mean more verbose logging.
"
option "logfile" -
is also given.
"
+##################
+section "Commands"
+##################
+
defgroup "command"
#=================
groupdesc="
- dss supports a couple of commands each of which corresponds to a different
- command line option. Exactly one of these options must be given.
+ dss supports a couple of commands each of which corresponds
+ to a different command line option. Exactly one of these
+ options must be given.
+
"
required
"Create a new snapshot"
group="command"
details="
- Execute the rsync command to create a new snapshot. Note that this
- command does not care about free disk space.
+ Execute the rsync command to create a new snapshot. Note that
+ this command does not care about free disk space.
"
+
groupoption "prune" P
#~~~~~~~~~~~~~~~~~~~~
-"Remove a redundant snapshot"
+"Remove redundant and outdated snapshots"
group="command"
details="
- A snapshot is considered redundant if it ether belongs to
- an interval greater than the maximum number of intervals,
- or if it belongs to an interval that already contains more
- than the desired number of snapshots.
+ A snapshot is considered outdated if it belongs to an interval
+ greater than the maximum number of intervals. It is said to be
+ redundant if it belongs to an interval that already contains
+ more than the desired number of snapshots. This command gets
+ rid of such snapshots.
"
groupoption "ls" L
group="command"
details="
This is the main mode of operation. Snapshots will be created
- as needed and pruned automatically.
+ in an endless loop as needed and pruned automatically. The loop
+ only terminates on fatal errors or if a terminating signal was
+ received. See also the --exit-hook option.
"
###############################
#~~~~~~~~~~~~~~~~~~~~
"The data directory"
string typestr="dirname"
-optional
+required
details="
The directory on the remote host from which snapshots are
taken. Of course, the user specified as --remote-user must
#~~~~~~~~~~~~~~~~~~
"Snapshot dir"
string typestr="dirname"
-optional
+required
details="
The destination directory on the local host where snapshots
will be written. This must be writable by the user who runs
to that option are passed verbatim to the rsync command.
"
-option "exclude-patterns" e
-#~~~~~~~~~~~~~~~~~~~~~~~~~~
-"Rsync exclude patterns"
-string typestr="path"
-optional
-
###################
section "Intervals"
###################
default="4"
optional
details="
- dss snapshot aging is implemented in terms of intervals. There are
- two command line options related to intervals: the duration of a
- \"unit\" interval and the number of those unit intervals.
-
- dss removes any snapshots older than the given number of intervals
- times the duration of a unit interval and tries to keep the following
- number of snapshots per interval:
-
- interval number number of snapshots
- ===============================================
- 0 2 ^ (num-intervals - 1)
- 1 2 ^ (num-intervals - 2)
- 2 2 ^ (num-intervals - 3)
- ...
- num-intervals - 2 2
- num-intervals - 1 1
- num-intervals 0
-
- In other words, the oldest snapshot will at most be unit_interval *
- num_intervals old (= 5 days * 4 = 20 days if default values are used).
- Moreover, there are at most 2^num_intervals - 1 snapshots in total
- (i. e. 31 by default). Observe that you have to create at least
- 2 ^ (num_intervals - 1) snapshots each interval for this to work out.
+ dss snapshot aging is implemented in terms of intervals. There
+ are two command line options related to intervals: the
+ duration u of a \"unit\" interval and the number n of those
+ unit intervals.
+
+ dss removes any snapshots older than n times u and tries to
+ keep 2^(n - k - 1) snapshots in interval k, where the interval
+ number k counts from zero, zero being the most recent unit
+ interval.
+
+ In other words, the oldest snapshot will at most be u * n days
+ (= 20 days if default values are used) old. Moreover, there
+ are at most 2^n - 1 snapshots in total (i. e. 31 by default).
+ Observe that you have to create at least 2^(n - 1) snapshots
+ each interval for this to work out because that is the number
+ of snapshots in interval zero.
"
option "num-intervals" n
#~~~~~~~~~~~~~~~~~~~~~~~~~~
"Executed before snapshot creation"
string typestr="command"
-default="/bin/true"
optional
details="
Execute this command before trying to create a new snapshot.
- If this command returns with a non-zero exit status, do not
- perform the backup. One possible application of this is to
- return non-zero during office hours in order to not slow down
- the file systems by taking snapshots.
-"
+ If this command returns with a non-zero exit status, no
+ snapshot is being created and the operation is retried later.
+ For example, one might want to execute a script that checks
+ whether all snapshot-related file systems are properly mounted.
+
+ Another possible application of this is to return non-zero
+ during office hours in order to not slow down the file systems
+ by taking snapshots.
+"
option "post-create-hook" o
#~~~~~~~~~~~~~~~~~~~~~~~~~~
"Executed after snapshot creation"
string typestr="command"
-default="/bin/true"
optional
details="
- Execute this after a snapshot has successfully been created
- The return value on the command is ignored. For instance one
- could count the number of files per user and/or the disk
- usage patterns in order to store them in a database for
- further treatment.
+ Execute this after a snapshot has successfully been
+ created. The full path of the newly created snapshot is
+ passed to the hook as the first argument. The exit code of
+ this hook is ignored.
+
+ For instance this hook can be used to count the number of
+ files per user and/or the disk usage patterns in order to
+ store them in a database for further analysis.
+"
+
+option "exit-hook" e
+#~~~~~~~~~~~~~~~~~~~
+"Executed if run command exits"
+string typestr="command"
+optional
+details="
+ This hook is only used if the --run command was given which
+ instructs dss to run in an endless loop. The exit-hook gets
+ executed whenever this endless loop terminates. The reason
+ for terminating the loop is passed as the first argument.
+
+ One possible application for this hook is to send email to the
+ system administrator to let her know that no more snapshots
+ are going to be created.
"
###############################
default="100"
optional
details="
- If less than this many megabytes of space is available on
- the file system containing the destination directory, \"dss
- --run\" will suspend the currently running rsync process and will
- start to remove snapshots, starting from the oldest snapshot,
- until the free disk space exceeds this value. See also the
- --min_free_percent option.
+ If disk space on the file system containing the destination
+ directory gets low, \"dss --run\" will suspend the currently
+ running rsync process and will start to remove snapshots in
+ order to free disk space. This option specifies the minimal
+ amount of free disk space. If less than the given number of
+ megabytes is available, snapshots are being deleted. See also
+ the --min_free_percent and the min-free-percent-inodes options.
A value of zero deactivates this check.
-
"
option "min-free-percent" p
default="2"
optional
details="
- See --min-free-mb. Note that it is not recommended to set both
+ See --min-free-mb. Note that it is not recommended to set both
--min-free-mb and --min-free-percent to zero as this will
cause your file system to fill up quickly.
"
+option "min-free-percent-inodes" i
+#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+"Minimal percent of free inodes"
+int typestr="percent"
+default="0"
+optional
+details="
+ Specify the minimum amount of free inodes on the file system
+ containing the destination dir. If less than that many inodes
+ are free, snapshot removal kicks in just as in case of low
+ disk space.
+
+ Note that not every file system supports the concept of inodes.
+ Moreover it is not possible to reliably detect whether this is
+ the case. Therefore this feature is disabled by default. It's
+ safe to enable it for ext3 file systems on linux though.
+
+ A value of zero (the default) deactivates this check.
+"
+
+option "keep-redundant" k
+#~~~~~~~~~~~~~~~~~~~~~~~~
+"Prune by disk space only"
+flag off
+details="
+ If this flag is not given dss removes redundant and outdated
+ snapshots automatically.
+
+ Otherwise, this feature is deactivated so that snapshots
+ are only being removed in case disk space or inode ratio
+ becomes low. Use this flag if the file system containing the
+ destination directory is used for snapshots only.
+"
projects / dss.git / blobdiff