snapper man page

snapper — Command-line program for filesystem snapshot management

Synopsis

snapper [--global-opts] command [--command-opts] [command-arguments]

snapper {--help}

Description

Snapper is a command-line program for filesystem snapshot management. It can create, delete and compare snapshots and undo changes done between snapshots.

Snapper never modifies the content of snapshots. Thus snapper creates read-only snapshots if supported by the kernel. Supported filesystems are btrfs as well as snapshots of LVM logical volumes with thin-provisioning.

Concepts

Configurations

For each filesystem or subvolume that should be snapshotted by snapper, a configuration file is required, see snapper-configs(5). The setup can be done with the create-config command.

Snapshots

Snapper distinguishes three types of snapshots.

pre

Pre snapshots should always have a corresponding post snapshot. The intention of pre/post snapshot pairs is to snapshot the filesystem before and after a modification.

post

See pre type.

single

These snapshots have no special relationship to other snapshots.

Note that filesystem-wise all three types are the same.

Snapshot Description and Userdata

With each snapshot a description and some userdata can be associated. The description is a string. The userdata is a list of key-value pairs where the keys and values are strings.

Automatic Snapshot Creation

Next to manual snapshot creation, snapshots are also created automatically.

· A cron-job creates hourly snapshots.

· Certain programs like YaST and zypper create pre/post snapshot pairs when modifying the system.

Cleanup Algorithms

Snapper provides several algorithms to clean up old snapshots. The algorithms are executed in a daily cron-job. This can be configured in the corresponding configurations files along with parameters for every algorithm.

number

Deletes old snapshots when a certain number of snapshots is reached.

timeline

Deletes old snapshots but keeps a number of hourly, daily, weekly, monthly and yearly snapshots.

empty-pre-post

Deletes pre/post snapshot pairs with empty diffs.

The number and timeline cleanup algorithm can also try to keep the space used by snapshots below a limit. For that quota must be setup, see command setup-quota, and the LIMIT variables in the config file must have ranges (min- and max-value). The algorithms will then make two passes:

1. Delete snapshots above the max-value independent of the used space.

2. Delete snapshots above the min-value until the limit for the used space is reached.

The limit for the used space can be configured via the SPACE_LIMIT variable. Note: Only snapshots that have a cleanup algorithm set are taken into account when calculating the used space.

Filters

Some files keep state information of the system, e.g. /etc/mtab. Such files should never be reverted. To help users, snapper allows to ignore these files.

Each line in all files /etc/snapper/filters/*.txt specifies a pattern. When snapper computes the difference between two snapshots it ignores all files and directories matching any of those patterns by using fnmatch(3) with the flag FNM_LEADING_DIR.

Note that filters do not exclude files or directories from being snapshotted. For that, use subvolumes or mount points.

Global Options

-q, --quiet

Suppress normal output. Error messages will still be printed, though.

-v, --verbose

Increase verbosity.

--utc

Display dates and times in UTC.

--iso

Display dates and times in ISO format.

-t, --table-style

Specifies table style. Table style is identified by an integer number.

-c, --config name

Use specified configuration instead of the default configuration. The default configuration is named "root".

--no-dbus

Operate without a DBus connection. Only works for some commands.

Use with caution since a running snapperd will not know about modifications made to the system.

-r, --root path

Operate on target root. Only works together with no-dbus and only for some commands.

--version

Print version and exit.

Commands

Snapper provides a number of commands. Each command accepts the options listed in the Global Options section. These options must be specified before the command name. In addition, many commands have specific options, which are listed in this section. These command-specific options must be specified after the name of the command and before any of the command arguments.

help

Show short help text.

list-configs

List available configurations.

create-config [options] subvolume

Create a new configuration for a filesystem or subvolume. For this command you will likely need the global option --config, see Global Options and Concepts.

-f, --fstype fstype
Manually set filesystem type. Supported values are btrfs and lvm. For lvm, snapper uses LVM thin-provisioned snapshots. The filesystem type on top of LVM must be provided in parentheses, e.g. lvm(xfs).

Without this option snapper tries to detect the filesystem.

-t, --template name
Name of template for the new configuration file.

delete-config

Delete a configuration for a filesystem or subvolume. For this command you will likely need to global option --config, see Global Options and Concepts.

get-config

Displays the settings of the configuration.

set-config configdata

Changes the settings of the configuration. The settings configdata are a list of key-value-pairs separated by spaces and the key and value must be separated by an equal sign, e.g. "NUMBER_CLEANUP=yes NUMBER_LIMIT=10". The value of SUBVOLUME and FSTYPE cannot be changed.

list (ls) [options]

List snapshots.

-t, --type type
Selects type of snapshots to list. Possible values are all, single and pre-post.

-a, --all-configs
List snapshots from all configs accessible by the user.

create [options]

Create a new snapshot.

-t, --type type
Specifies the type of the new snapshot. Possible values are single, pre and post.

--pre-number number
For post snapshots the number of the pre snapshot must be provided.

-p, --print-number
Print number of the created snapshot.

-d, --description description
Description for the snapshot.

-c, --cleanup-algorithm cleanup-algorithm
Set the cleanup algorithm for the snapshot.

-u, --userdata userdata
Set userdata for the snapshot. The key-value pairs must be separated by comma and the key and value must be separated by an equal sign, e.g. requestid=42,user=arthur.

--command command
Create a pre and post snapshot and run command in between.

modify [options] number

Modify a snapshot.

-d, --description description
New description for snapshot.

-c, --cleanup-algorithm cleanup-algorithm
Set the cleanup algorithm for the snapshot.

-u, --userdata userdata
Set userdata for the snapshot. The key-value pairs must be separated by comma and the key and value must be separated by an equal sign, e.g. requestid=42,user=arthur.

delete (remove|rm) number | number1-number2

Delete a snapshot or a range of snapshots.

-s, --sync
Sync the filesystem after deleting the snapshots. The details depend on the filesystem type.

Btrfs normally asynchronously frees space after deleting snapshots. With this option snapper will wait until the space once used by the deleted snapshots is actually available again.

mount number

Mount a snapshot. Not required for all filesystem types.

umount number

Unmount a snapshot. Not required for all filesystem types.

status [options] number1..number2

Compare the snapshots number1 and number2. This will show a list of files and directories that have been created, modified or deleted in the time between the two snapshots have been made.

-o, --output file
Write output to file file.

The output consists of a string encoding the status followed by the filename. The characters of the status string are:

1. A "+" means the file was created, a "-" means the file was deleted. A "c" means the content of the file has changed and a "t" means the type of the file has changed (e.g. from regular file to directory).

2. A "p" means the permissions are have changed.

3. An "u" means the user ownership has changed.

4. A "g" means the group ownership has changed.

5. A "x" means the extended attribute information has changed.

6. An "a" means the ACL information has changed.

If there is no change a "." is outputted.

diff [options] number1..number2 [files]

Compare the snapshots number1 and number2. This will show a diff of the content of files and directories that have been created, modified or deleted in the time between the two snapshots have been made.

-i, --input file
Read files to diff from file file.

--diff-cmd command
Command used for comparing files. The default is /usr/bin/diff --new-file --unified. The two files to compare are passed as parameters to the command.

-x, --extensions options
Extra options passed to the diff command.

undochange [options] number1..number2 [files]

Undo changes done between snapshot number1 and number2.

-i, --input file
Read files for which to undo changes from file file.

rollback [options] [number]

Creates two new snapshots and sets the default subvolume. Per default the system boots from the default subvolume of the root filesystem. The exact actions depend on whether a number is provided or not:

· Without a number, a first read-only snapshot of the default subvolume is created. A second read-write snapshot of the current system is created. The system is set to boot from the second snapshot.

· With a number, a first read-only snapshot of the current system in created. A second read-write snapshot is created of number. The system is set to boot from the second snapshot.

Rollback is only supported with btrfs and requires a properly configured system.

-p, --print-number
Print number of the second created snapshot.

-d, --description description
Description for the snapshot.

-c, --cleanup-algorithm cleanup-algorithm
Set the cleanup algorithm for the snapshot.

-u, --userdata userdata
Set userdata for the snapshot. The key-value pairs must be separated by comma and the key and value must be separated by an equal sign, e.g. requestid=42,user=arthur.

setup-quota

Sets up quota. Currently only supported with btrfs.

cleanup cleanup-algorithm

Run the cleanup algorithm cleanup-algorithm. Currently implemented cleanup algorithms are number, timeline and empty-pre-post.

xadiff number1..number2 [files]

Compare the extended attributes between snapshot number1 and number2. See examples below:

· +:user.foo for created attributes

· -:user.bar for removed attributes

· -+:security.selinux for modified attributes

Permissions

Non-root users can be allowed to use a configuration by setting ALLOW_USERS or ALLOW_GROUPS in the config file. For all operations to work, the user must also be able to read and access the .snapshots directory inside the subvolume. The .snapshots directory must be owned by root and must not be writable by anybody else.

Here are some methods how to achieve that:

· Make the directory accessible for everyone:

chmod a+rx .snapshots

· Make the directory accessible for a group the user belongs to, e.g.:

chown :users .snapshots

· Make the directory accessible for the user using ACLs, e.g.:

setfacl -m u:tux:rx .snapshots

The last method can be performed by snapper, see the SYNC_ACL setting in snapper-configs(5).

Files

/etc/sysconfig/snapper

Global configuration file.

/etc/snapper/configs

Directory containing configuration files.

/etc/snapper/config-templates

Directory containing configuration templates.

/etc/snapper/filters/*.txt

Filter files.

/var/log/snapper.log

Logfile. Please include this file in bug reports.

Notes

There is no mechanism to ensure consistency of the files while a snapshot it made. E.g. the files of a database can be inconsistent while the database is running.

Consistency after undochange is not guaranteed. E.g. when the creation of a user is undone, there might still exist files from that user.

Support for individual filesystems, rollback and extended attributes are compile-time options and may not be available.

Homepage

http://snapper.io/

Authors

Arvin Schnell <aschnell@suse.com>

See Also

snapper-configs(5), snapper-zypp-plugin(8), pam_snapper(8), btrfs(8), lvm(8), attr(5), acl(5)

Referenced By

pam_snapper(8), snapper-configs(5), snapperd(8).

2014-04-07 0.3.3 Filesystem Snapshot Management