# Copyright (C) 2008-2010 Andre Noll # # Licensed under the GPL v2. For licencing details see COPYING. package "dss" version "0.1.4" purpose "the dyadic snapshot scheduler dss creates hardlink-based snapshots of a given directory on a remote or local host using rsync's link-dest feature. " ######################### section "General options" ######################### option "config-file" c #~~~~~~~~~~~~~~~~~~~~~ "(default='~/.dssrc')" string typestr="filename" optional details=" Options may be given at the command line or in the configuration file. As usual, if an option is given both at the command line and in the configuration file, the command line option takes precedence. However, there is an important exception to this rule: If the --run option was given (see below) then dss honors SIGHUP and re-reads its configuration file whenever it receives this signal. In this case the options in the config 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. " option "daemon" d #~~~~~~~~~~~~~~~~ "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. Note that it is not possible to change whether dss runs as background daemon by sending SIGHUP. " option "dry-run" D #~~~~~~~~~~~~~~~~~ "Only print what would be done" flag off details=" This flag does not make sense for all commands. The run command refuses to start if this option was given. The ls command silently ignores this flag. " ################# section "Logging" ################# option "loglevel" l #~~~~~~~~~~~~~~~~~~ "Set loglevel (0-6)" int typestr="level" default="3" optional details=" Lower values mean more verbose logging. " option "logfile" - #~~~~~~~~~~~~~~~~~ "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. " ################## 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 "create" C #~~~~~~~~~~~~~~~~~~~~~ "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. " groupoption "prune" P #~~~~~~~~~~~~~~~~~~~~ "Remove redundant and outdated snapshots" group="command" details=" 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 #~~~~~~~~~~~~~~~~~ "Print a list of all snapshots" group="command" details=" The list will contain all snapshots no matter of their state, i. e. incomplete snapshots and snapshots being deleted will also be listed. " groupoption "run" R #~~~~~~~~~~~~~~~~~~ "Start creating and pruning snapshots" group="command" details=" This is the main mode of operation. Snapshots will be created 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. " ############################### section "Rsync-related options" ############################### option "remote-host" H #~~~~~~~~~~~~~~~~~~~~~ "Remote host" string typestr="hostname" default="localhost" optional details=" If this option is given and its value differs from the local host, then rsync uses ssh. Make sure there is no password needed for the ssh connection. To achieve that, use public key authentication for ssh and, if needed, set the remote user name by using the --remote-user option. " option "remote-user" U #~~~~~~~~~~~~~~~~~~~~~ "Remote user name (default: current user)" string typestr="username" optional details=" Set this if the user running dss is different from the user at the remote host when using ssh. " option "source-dir" - #~~~~~~~~~~~~~~~~~~~~ "The data directory" string typestr="dirname" required details=" The directory on the remote host from which snapshots are taken. Of course, the user specified as --remote-user must have read access to this directory. " option "dest-dir" - #~~~~~~~~~~~~~~~~~~ "Snapshot dir" string typestr="dirname" required details=" The destination directory on the local host where snapshots will be written. This must be writable by the user who runs 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" string typestr="option" optional multiple details=" 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 " ################### section "Intervals" ################### option "unit-interval" u #~~~~~~~~~~~~~~~~~~~~~~~ "The duration of a unit interval" int typestr="days" 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^(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 #~~~~~~~~~~~~~~~~~~~~~~~ "The number of unit intervals" int typestr="num" default="5" optional ############### section "Hooks" ############### option "pre-create-hook" r #~~~~~~~~~~~~~~~~~~~~~~~~~~ "Executed before snapshot creation" string typestr="command" default = "true" optional details=" Execute this command before trying to create a new snapshot. 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 = "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 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 "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. " ############################### section "Disk space monitoring" ############################### option "min-free-mb" m #~~~~~~~~~~~~~~~~~~~~~ "Minimal amount of free disk space" int typestr="megabytes" default="100" optional details=" 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 #~~~~~~~~~~~~~~~~~~~~~~~~~~ "Minimal percent of free disk space" int typestr="percent" default="2" optional details=" 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=" 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 number of free inodes becomes low. Use this flag if the file system containing the destination directory is used for snapshots only. "