+# Copyright (C) 2008-2010 Andre Noll <maan@tuebingen.mpg.de>
#
+# Licensed under the GPL v2. For licencing details see COPYING.
+
package "dss"
-version "0.0.3"
+version "0.1.7"
purpose "the dyadic snapshot scheduler
dss creates hardlink-based snapshots of a given directory on a remote
#~~~~~~~~~~~~~~~~
"Run as background daemon"
flag off
-dependon="logfile"
details="
- 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.
+ This option is mostly useful in conjunction with the -R option
+ described below.
- Note that it is not possible to change whether dss runs as
- background daemon by sending SIGHUP.
+ Note that it is not possible to change whether dss runs as background
+ daemon by sending SIGHUP.
"
option "dry-run" D
"Logfile for the dss daemon process"
string typestr="filename"
optional
-details="
- This option is mostly useful for the run command if --daemon
- is also given.
+default="/dev/null"
+details = "
+ This option is only honored if both --run and --daemon are
+ given. Otherwise it is silently ignored and log output is written
+ to stderr.
+
+ The default value means that nothing will be logged in daemon mode
+ unless this option is 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.
+
"
required
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+"Remove redundant and outdated snapshots"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+ A snapshot is considered outdated if its interval number
+ is greater or equal than the specified number of unit
+ intervals. See the \"Intervals\" section below for the precise
+ definition of these terms.
+
+ A snapshot is said to be redundant if it belongs to an
+ interval that already contains more than the desired number
+ of snapshots.
+
+ The prune command gets rid of both outdated and redundant
+ 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.
+"
+
+groupoption "kill" K
+#~~~~~~~~~~~~~~~~~~~
+"Kill a running dss process"
+group="command"
+details="
+ This sends SIGTERM to the dss process that corresponds to the
+ given config file. If --dry-run is given, the PID of the dss
+ process is written to stdout, but no signal is sent.
+"
+
+groupoption "reload" -
+#~~~~~~~~~~~~~~~~~~~~~
+"force a running dss process to reload its config file"
+group="command"
+details="
+ This differs from --kill only in that SIGHUP rather than SIGTERM
+ is sent to the dss process.
"
###############################
dss.
"
+option "no-resume" -
+#~~~~~~~~~~~~~~~~~~~
+"Do not try to resume from previous runs"
+flag off
+details = "
+ Starting from version 0.1.4, dss tries to resume from a
+ previously cancelled dss instance by default. It does so by
+ looking at the status of the most recently created snapshot. If
+ this snapshot status is incomplete, its directory is reused
+ as the destination directory for a subsequent rsync run.
+
+ The --no-resume option deactivates this feature so that a new
+ directory is always used as the rsync destination directory.
+"
+
option "rsync-option" O
#~~~~~~~~~~~~~~~~~~~~~~
"Further rsync options"
optional
multiple
details="
- These option may be given multiple times. The arguments passed
- to that option are passed verbatim to the rsync command.
+ This option may be given multiple times. The given argument is
+ passed verbatim to the rsync command. Note that in order to use
+ rsync options that require an argument, you have to specify the
+ option and its argument as separate --rsync-options, like this:
+
+ --rsync-option --exclude --rsync-option /proc
"
-option "exclude-patterns" e
-#~~~~~~~~~~~~~~~~~~~~~~~~~~
-"Rsync exclude patterns"
-string typestr="path"
+option "max-rsync-errors" -
+"Terminate after this many rsync failures"
+int typestr="count"
+default="10"
optional
+details="
+ Only relevant when operating in --run mode (see above). If
+ the rsync process exits with a fatal error, dss restarts
+ the command in the hope that the problem is transient
+ and subsequent rsync runs succeed. After the given number
+ of consecutive rsync error exits, however, dss gives up,
+ executes the exit hook and terminates. Set this to zero if
+ dss should exit immediately on the first rsync error.
+
+ The only non-fatal error is when rsync exits with code 24. This
+ indicates a partial transfer due to vanished source files
+ and happens frequently when snapshotting a directory which
+ is concurrently being modified.
+"
###################
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 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^(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.
+ 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 of unit intervals, denoted n below.
+
+ dss removes 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 to n - 1, with zero being the most recent unit interval.
+
+ Hence the oldest snapshot will at most be u * n days old (4 days *
+ 5 intervals = 20 days, if default values are used). Moreover, there
+ are at most 2^n - 1 snapshots in total (2^5 - 1 = 31 by default). Note
+ that for this to work out your system must be fast enough to create at
+ least 2^(n - 1) snapshots per unit interval (16 snapshots in 4 days =
+ one snapshot in 6 hours), because this is the number of snapshots in
+ interval zero.
"
option "num-intervals" n
int typestr="num"
default="5"
optional
+details="
+ Note that increasing this number by one doubles the total number of
+ snapshots. See the documentation of --unit-interval above.
+"
###############
section "Hooks"
#~~~~~~~~~~~~~~~~~~~~~~~~~~
"Executed before snapshot creation"
string typestr="command"
+default = "true"
optional
details="
Execute this command before trying to create a new snapshot.
#~~~~~~~~~~~~~~~~~~~~~~~~~~
"Executed after snapshot creation"
string typestr="command"
+default = "true"
optional
details="
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 return value of that
- hook is ignored.
+ 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 treatment.
+ store them in a database for further analysis.
+"
+
+option "pre-remove-hook" -
+#~~~~~~~~~~~~~~~~~~~~~~~~~~
+"Executed before snapshot removal"
+string typestr="command"
+default = "true"
+optional
+details="
+ Execute this command before removing a snapshot. The full
+ path to the snapshot about to be deleted is passed to the
+ command as the first argument. If the command returns with
+ a non-zero exit status, no snapshot is being removed and the
+ operation is retried later.
+
+ For example, one might want to execute a script that checks
+ whether the snapshot to be deleted is currently used by
+ another process, e.g. by a tape-based backup system that runs
+ concurrently to dss.
+
+ Another possible application of this is to record disk-usage
+ patterns before and after snapshot removal.
+"
+
+option "post-remove-hook" -
+#~~~~~~~~~~~~~~~~~~~~~~~~~~
+"Executed after snapshot removal"
+string typestr="command"
+default = "true"
+optional
+details="
+ Execute this after a snapshot has successfully been removed. As
+ for the pre-remove hook, the full path of the removed snapshot
+ is passed to the hook as the first argument. The exit code
+ of this hook is ignored.
+"
+
+option "exit-hook" e
+#~~~~~~~~~~~~~~~~~~~
+"Executed if run command exits"
+string typestr="command"
+default = "true"
+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 ext2/ext3/ext4 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="
+ By default, redundant and outdated snapshots are removed automatically
+ to keep the number of snapshots in harmony with the configured
+ policy. If this flag is given, dss removes such snapshots only if
+ disk space or number of free inodes becomes low.
+"
+
+option "min-complete" -
+#~~~~~~~~~~~~~~~~~~~~~~
+"Minimal number of complete snapshots to keep"
+int typestr = "num"
+default = "1"
+optional
+details = "
+ This option is only relevant if snapshots must be deleted
+ because disk space gets low.
+
+ dss refuses to remove old snapshots if there are fewer complete
+ snapshots left than the given number. The default value of one
+ guarantees that at least one complete snapshot is available
+ at all times.
+
+ If only <num> complete snapshot are left, and there is not
+ enough disk space available for another snapshot, the program
+ terminates with a \"No space left on device\" error.
+"
projects / dss.git / blobdiff