SNAPPER(8)

NAME
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 and ext4 (discontinued) as well as snapshots of LVM logical volumes with thin-provisioning. Some filesystems might not be supported depending on your installation.

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.

Do not use non-ASCII characters for the snapshot description, userdata or any other strings, unless you always use the UTF-8 character encoding.

  Automatic Snapshot Creation

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

    • A cronjob or systemd timer creates hourly snapshots, if TIMELINE_CREATE is enabled for a config.

    • 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 an hourly cronjob or systemd timer. 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, quarterly and yearly snapshots.

empty-pre-post
    Deletes pre/post snapshot pairs with empty diffs.

The number and timeline cleanup algorithms can also try to keep the space used by snapshots below a limit and the free space of the filesystem above a limit. For the first condition quota must be setup, see command setup-quota. Additional the NUMBER_LIMIT and TIMELINE_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 snapshot and filesystem space.

    2. Delete snapshots above the min-value until the limits for the snapshot and filesystem are 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 space used by snapshots.

The limit for the free space can be configured via the FREE_LIMIT variable.

Note: Since the cleanup is performed asynchronous from creating snapshots the observed snapshots can differ from the expected snapshots according to the limits. Also btrfs stale qgroups can exist temporarily.

  Filters

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

Filters are read from the files /etc/snapper/filters/*.txt and /usr/share/snapper/filters/*.txt, where for files with the same name the former location has precedence. Each line in those files 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.

--logger-type type
    Set the logger type. Possible values are none, stdout, logfile and syslog.

--debug
    Turn on debugging.

--utc
    Display dates and times in UTC. By default, local time is used.

--iso
    Display dates and times in ISO format. ISO format is always used for machine-readable outputs.

-t, --table-style style
    Specifies table style. Table style is identified by an integer number.

--abbreviate
    Try to abbreviate texts in some columns so that tables fit the width of the screen.

--machine-readable format
    Specifies a machine-readable output format. Possible options are csv and json.

--csvout
    Sets CSV output format. See RFC 4180[1] for the details, except lines end with a LF, not CR+LF.

--jsonout
    Sets JSON output format.

--separator character
    Specifies the character separator for CSV output format.

--no-headers
    Suppress headers for CSV output format.

-c, --config name
    Use specified configuration instead of the default configuration. The default configuration is named "root".

--no-dbus
    Operate without a DBus connection.

    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.

-a, --ambit ambit
    Operate in the specified ambit. Can be used to override the ambit detection. Allowed ambits are auto, classic and transactional.

--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 [options]
    List available configurations.

    --columns columns
        Select columns to show separated by comma.

        Possible columns are: config, subvolume.

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, ext4 (discontinued) 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 including all snapshots. For this command you will likely need to global option --config, see GLOBAL OPTIONS and CONCEPTS.

get-config [options]
    Displays the settings of the configuration.

    --columns columns
        Select columns to show separated by comma.

        Possible columns are: key, value.

        Columns are not selected when JSON format is used.

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.

    --disable-used-space
        Disable display of used space.

        Calculating the used space needs some time. Thus this option can speedup the listing.

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

    --columns columns
        Select columns to show separated by comma.

        Possible columns are: config, subvolume, number, default, active, date, user, used-space, cleanup, description, userdata, pre-number, post-number, post-date, read-only.

    For each snapshot the output consists of several columns. Some need explanation:

    #, Pre # and Post #
        The number of the snapshot.

        For btrfs the number can be followed by a sign. A "-" indicates that the snapshot is the currently mounted snapshot and a "+" indicates that the snapshot will be mounted next time (It is the btrfs default subvolume). If both conditions apply a "*" is displayed.

    Used Space
        For btrfs the exclusive space of the btrfs quota group corresponding to the snapshot.

        Display of used space is automatically disabled if not available, e.g. quota not enabled on btrfs.

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. If snapper is unable to execute the command at all, it does not take the post snapshot. If the command exits with a non-zero exit code, snapper takes the post snapshot and exits with that same exit code.

    --read-only
        Create a read-only snapshot. This is the default.

    --read-write
        Create a read-write snapshot.

    --from number
        Create a snapshot from the snapshot with the provided number instead of snapshot 0.

    --empty
        Create an empty snapshot. Only supported on btrfs and with --no-dbus.

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.

    --read-only
        Set the snapshot read-only.

    --read-write
        Set the snapshot read-write.

    --default
        Set the snapshot as default snapshot. Only for btrfs.

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.

    Snapshot 0 cannot be deleted. For btrfs the currently mounted snapshot and the snapshot that will be mounted next time (the btrfs default subvolume) can also not be deleted.

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 is 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.

    The rollback command also sets the description, the cleanup algorithm and some userdata unless the values are specified on the command line. This will automate cleanup of snapshots created by rollbacks.

    In other ambits than classic the rollback command does what is required to do a rollback. Anyway it is recommended to use specific programs in that case.

setup-quota
    Sets up quota. Currently only supported with btrfs.

cleanup [options] cleanup-algorithm
    Run the cleanup algorithm cleanup-algorithm. Currently implemented cleanup algorithms are number, timeline and empty-pre-post. To run all cleanup algorithms, all can be provided as cleanup-algorithm.

    --path path
        Cleanup all configs affecting path. Only useful for btrfs.

    --free-space free-space
        Try to make free-space available. Only useful for btrfs.

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).

PLUGINS

snapper can execute external scripts after certain actions. Scripts have to be placed in /usr/lib/snapper/plugins. The name has to start with a digit, execution order is alphabetical.

The first argument of a script is the action snapper executed. The following actions are defined:

create-config-pre subvolume fstype
    Executed before a new config is created

create-config-post subvolume fstype
    Executed after a new config was created

delete-config-pre subvolume fstype
    Executed before a config is deleted

delete-config-post subvolume fstype
    Executed after a config was deleted

create-snapshot-pre subvolume fstype snapshot-number
    Executed before a new snapshot is created

create-snapshot-post subvolume fstype snapshot-number
    Executed after a new snapshot was created

modify-snapshot-pre subvolume fstype snapshot-number
    Executed before a snapshot is modified

modify-snapshot-post subvolume fstype snapshot-number
    Executed after a snapshot was modified

delete-snapshot-pre subvolume fstype snapshot-number
    Executed before a snapshot is removed

delete-snapshot-post subvolume fstype snapshot-number
    Executed after a snapshot was removed

set-read-only-pre subvolume fstype snapshot-number
    Executed before a snapshot is set read-only or read-write

set-read-only-post subvolume fstype snapshot-number
    Executed after a snapshot is set read-only or read-write

set-default-snapshot-pre subvolume fstype snapshot-number
    Executed before the default snapshot is changed

set-default-snapshot-post subvolume fstype snapshot-number
    Executed after the default snapshot was changed

rollback-post subvolume fstype old-snapshot-number new-snapshot-number
    Executed after a rollback was done

More actions and arguments can be added any time. Using snapper in the plugins is not allowed.

It is undefined whether the plugins are called from the client (snapper) or server (snapperd).

FILES

/etc/conf.d/snapper
    Global configuration file.

/etc/snapper/configs
    Directory containing configuration files.

/etc/snapper/config-templates
    Directory containing configuration templates.

/usr/share/snapper/config-templates
    Fallback directory containing configuration templates.

/etc/snapper/filters/*.txt
    Filter files.

/usr/share/snapper/filters/*.txt
    Fallback filter files.

/var/log/snapper.log
    Logfile. Please include this file in bug reports.

EXIT STATUS

Normally the exit status is 0. If an error occurred the exit status is 1. It is also an error if the exit status of a plugin is not 0.

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), snbk(8), pam_snapper(8), btrfs(8), lvm(8), attr(5), acl(5)

NOTES

1.  RFC 4180
    https://tools.ietf.org/html/rfc4180