criu/Documentation/criu.txt

CRIU(8)
=======
include::footer.txt[]

NAME
----
criu - checkpoint/restore in userspace


SYNOPSIS
--------
*criu* 'command' ['option' ...]


DESCRIPTION
-----------
*criu* is a tool for checkpointing and restoring running applications.
It does this by saving their state as a collection of files (see the *dump*
command) and creating equivalent processes from those files (see the *restore*
command). The restore operation can be performed at a later time,
on a different system, or both.


OPTIONS
-------

Common options
~~~~~~~~~~~~~~
Common options are applicable to any 'command'.

*-v*['num'|*v*...]::
    Set logging level to 'num'. The higher the level, the more output
    is produced. Either numeric values or multiple *v* can be used.
    +
The following levels are available:
    * *-v1*, *-v*
        only messages and errors;
    * *-v2*, *-vv*
        also warnings (default level);
    * *-v3*, *-vvv*
        also information messages and timestamps;
    * *-v4*, *-vvvv*
        lots of debug.

*--pidfile* 'file'::
    Write root task, service or page-server pid into a 'file'.

*-o*, *--log-file* 'file'::
    Write logging messages to 'file'.

*--log-pid*::
    Write separate logging files per each pid.

*--display-stats*::
    During dump as well as during restore *criu* collects information
    like the time required to dump or restore the process or the
    number of pages dumped or restored. This information is always
    written to the files 'stats-dump' and 'stats-restore' and can
    be easily displayed using *crit*. The option *--display-stats*
    additionally prints out this information on the console at the end
    of a dump or a restore.

*-D*, *--images-dir* 'path'::
    Use 'path' as a base directory where to look for sets of image files.

*--prev-images-dir* 'path'::
    Use 'path' as a parent directory where to look for sets of image files.
    This option makes sense in case of incremental dumps.

*-W*, *--work-dir* 'dir'::
    Use directory 'dir' for putting logs, pidfiles and statistics. If not
    specified, 'path' from *-D* option is taken.

*--close* 'fd'::
    Close file descriptor 'fd' before performing any actions.

*-L*, *--libdir* 'path'::
    Path to plugins directory.

*--action-script* 'script'::
    Add an external action script to be executed at certain stages.
    The environment variable *CRTOOLS_SCRIPT_ACTION* is available
    to the script to find out which action is being executed, and
    its value can be one of the following:
        *pre-dump*:::
            run prior to beginning a *dump*

        *post-dump*:::
            run upon *dump* completion

        *pre-restore*:::
            run prior to beginning a *restore*

        *post-restore*:::
            run upon *restore* completion

        *network-lock*:::
            run to lock network in a target network namespace

        *network-unlock*:::
            run to unlock network in a target network namespace

        *setup-namespaces*:::
            run once root task just been created
            with required namespaces. Note it is an early stage
            of restore, when nothing is restored yet except for namespaces
            themselves

*-V*, *--version*::
    Print program version and exit.

*-h*, *--help*::
    Print some help and exit.

*pre-dump*
~~~~~~~~~~
Performs the pre-dump procedure, during which *criu* creates a snapshot of
memory changes since the previous *pre-dump*. Note that during this
*criu* also creates the fsnotify cache which speeds up the *restore*
procedure. *pre-dump* requires at least *-t* option (see *dump* below).
In addition, *page-server* options may be specified.

*--track-mem*::
    Turn on memory changes tracker in the kernel. If the option is
    not passed the memory tracker get turned on implicitly.

*dump*
~~~~~~
Performs a checkpoint procedure.

*-t*, *--tree* 'pid'::
    Checkpoint the whole process tree starting from 'pid'.

*-R*, *--leave-running*::
    Leave tasks in running state after checkpoint, instead of killing. This
    option is pretty dangerous and should be used only if you understand
    what you are doing.
+
Note if task is about to run after been checkpointed, it can modify
TCP connections, delete files and do other dangerous actions. Therefore,
*criu* can not guarantee that the next *restore* action will succeed.
Most likely if this option is used, at least the file system snapshot
must be made with the help of *post-dump* action script.
+
In other words, do not use it unless really needed.

*-s*, *--leave-stopped*::
    Leave tasks in stopped state after checkpoint, instead of killing.

*--external* 'type'*[*'id'*]:*'value'::
    Dump an instance of an external resource. The generic syntax is
    'type' of resource, followed by resource 'id' (enclosed in literal
    square brackets), and optional 'value' (prepended by a literal semicolon).
    The following resource types are currently supported: *mnt*, *dev*,
    *file*, *tty*, *unix*. Syntax depends on type.
    Note to restore external resources, either *--external* or *--inherit-fd*
    is used, depending on resource type.

*--external mnt[*'mountpoint'*]:*'name'::
    Dump an external bind mount referenced by 'mountpoint', saving it
    to image under the identifier 'name'.

*--external mnt[]:*'flags'::
    Dump all external bind mounts, autodetecting those. Optional 'flags'
    can contain *m* to also dump external master mounts, *s* to also
    dump external shared mounts (default behavior is to abort dumping
    if such mounts are found). If 'flags' are not provided, semicolon
    is optional.

*--external dev[*'major'*/*'minor'*]:*'name'::
    Allow to dump a mount namespace having a real block device mounted.
    A block device is identified by its 'major' and 'minor' numbers,
    and *criu* saves its information to image under the identifier 'name'.

*--external file[*'mnt_id'*:*'inode'*]*::
    Dump an external file, i.e. an opened file that is can not be resolved
    from the current mount namespace, which can not be dumped without using
    this option. The file is identified by 'mnt_id' (a field obtained from
    */proc/*'pid'*/fdinfo/*'N') and 'inode' (as returned by *stat*(2)).

*--external tty[*'rdev'*:*'dev'*]*::
    Dump an external TTY, identified by *st_rdev* and *st_dev* fields
    returned by *stat*(2).

*--external unix[*'id'*]*::
    Tell *criu* that one end of a pair of UNIX sockets (created by
    *socketpair*(2)) with 'id' is OK to be disconnected.

*--freeze-cgroup*::
   Use cgroup freezer to collect processes.

*--manage-cgroups*::
    Collect cgroups into the image thus they gonna be restored then.
    Without this option, *criu* will not save cgroups configuration
    associated with a task.

*--cgroup-props* 'spec'::
    Specify controllers and their properties to be saved into the
    image file. *criu* predefines specifications for common controllers,
    but since the kernel can add new controllers and modify their
    properties, there should be a way to specify ones matched the kernel.
+
'spec' argument describes the controller and properties specification in
a simplified YAML form:
+
----------
"c1":
 - "strategy": "merge"
 - "properties": ["a", "b"]
"c2":
 - "strategy": "replace"
 - "properties": ["c", "d"]
----------
+
where 'c1' and 'c2' are controllers names, and 'a', 'b', 'c', 'd' are
their properties.
+
Note the format: double quotes, spaces and new lines are required.
The 'strategy' specifies what to do if a controller specified already
exists as a built-in one: *criu* can either *merge* or *replace* such.
+
For example, the command line for the above example should look like this:
+
----------
--cgroup-props "\"c1\":\n - \"strategy\": \"merge\"\n - \"properties\": [\"a\", \"b\"]\n \"c2\":\n - \"strategy\": \"replace\"\n - \"properties\": [\"c\", \"d\"]"
----------

*--cgroup-props-file* 'file'::
    Same as *--cgroup-props*, except the specification is read from
    the 'file'.

*--cgroup-dump-controller* 'name'::
    Dump a controller with 'name' only, skipping anything else that was
    discovered automatically (usually via */proc*). This option is
    useful when one needs *criu* to skip some controllers.

*--cgroup-props-ignore-default*::
    When combined with *--cgroup-props*, makes *criu* substitute
    a predefined controller property with the new one shipped. If the option
    is not used, the predefined properties are merged with the provided ones.

*--tcp-established*::
    Checkpoint established TCP connections.

*--skip-in-flight*::
    This option skips in-flight TCP connections. If any TCP connections
    that are not yet completely established are found, *criu* ignores
    these connections, rather than errors out.
    The TCP stack on the client side is expected to handle the
    re-connect gracefully.

*--evasive-devices*::
    Use any path to a device file if the original one is inaccessible.

*--page-server*::
    Send pages to a page server (see the *page-server* command).

*--force-irmap*::
    Force resolving names for inotify and fsnotify watches.

*--auto-dedup*::
    Deduplicate "old" data in pages images of previous *dump*. This option
    implies incremental *dump* mode (see the *pre-dump* command).

*-l*, *--file-locks*::
    Dump file locks. It is necessary to make sure that all file lock users
    are taken into dump, so it is only safe to use this for enclosed containers
    where locks are not held by any processes outside of dumped process tree.

*--link-remap*::
    Allows to link unlinked files back, if possible (modifies filesystem
    during *restore*).

*--ghost-limit* 'size'::
    Set the maximum size of deleted file to be carried inside image.
    By default, up to 1M file is allowed. Using this
    option allows to not put big deleted files inside images. Argument
    'size' may be postfixed with a *K*, *M* or *G*, which stands for kilo-,
    mega, and gigabytes, accordingly.

*-j*, *--shell-job*::
    Allow one to dump shell jobs. This implies the restored task will
    inherit session and process group ID from the *criu* itself.
    This option also allows to migrate a single external tty connection,
    to migrate applications like *top*. If used with *dump* command,
    it must be specified with *restore* as well.

*--cpu-cap* ['cap'[,'cap'...]]::
    Specify CPU capabilities to write to an image file. The argument is a
    comma-separated list of *none*, *fpu*, *cpu*, *ins*, *all*. If the
    argument is omitted or set to *none*, capabilities will not be written,
    which is the default behavior.

*--cgroup-root* ['controller':]/'newroot'::
    Change the root for the controller that will be dumped. By default, *criu*
    simply dumps everything below where any of the tasks live. However, if a
    container moves all of its tasks into a cgroup directory below the container
    engine's default directory for tasks, permissions will not be preserved on
    the upper directories with no tasks in them, which may cause problems.

*restore*
~~~~~~~~~
Restores previously checkpointed processes.

*--inherit-fd* *fd[*'N'*]:*'resource'::
    Inherit a file descriptor. This option lets *criu* use an already opened
    file descriptor 'N' for restoring a file identified by 'resource'.
    This option can be used to restore an external resource dumped
    with the help of *--external* *file*, *tty*, and *unix* options.
+
The 'resource' argument can be one of the following:
+
    - *tty[*'rdev'*:*'dev'*]*
    - *pipe[*'inode'*]*
    - *socket[*'inode'*]*
    - *file[*'mnt_id'*:*'inode'*]*
    - 'path/to/file'

+
Note that square brackets used in this option arguments are literals and
usually need to be escaped from shell.

*-d*, *--restore-detached*::
    Detach *criu* itself once restore is complete.

*-s*, *--leave-stopped*::
    Leave tasks in stopped state after restore (rather than resuming
    their execution).

*-S*, *--restore-sibling*::
    Restore root task as a sibling (makes sense only with
    *--restore-detached*).

*-r*, *--root* 'path'::
    Change the root filesystem to 'path' (when run in a mount namespace).

*--external* 'type'*[*'id'*]:*'value'::
    Restore an instance of an external resource. The generic syntax is
    'type' of resource, followed by resource 'id' (enclosed in literal
    square brackets), and optional 'value' (prepended by a literal semicolon).
    The following resource types are currently supported: *mnt*, *dev*,
    *veth*, *macvlan*. Syntax depends on type. Note to restore external
    resources dealing with opened file descriptors (such as dumped with
    the help of *--external* *file*, *tty*, and *unix* options), option
    *--inherit-fd* should be used.

*--external mnt[*'name'*]:*'mountpoint'::
    Restore an external bind mount referenced in the image by 'name',
    bind-mounting it from the host 'mountpoint' to a proper mount point.

*--external mnt[]*::
    Restore all external bind mounts (dumped with the help of
    *--external mnt[]* auto-detection).

*--external dev[*'name'*]:*'/dev/path'::
    Restore an external mount device, identified in the image by 'name',
    using the existing block device '/dev/path'.

*--external veth[*'inner_dev'*]:*'outer_dev'*@*'bridge'::
    Set the outer VETH device name (corresponding to 'inner_dev' being
    restored) to 'outer_dev'. If optional *@*'bridge' is specified,
    'outer_dev' is added to that bridge. If the option is not used,
    'outer_dev' will be autogenerated by the kernel.

*--external macvlan[*'inner_dev'*]:*'outer_dev'::
    When restoring an image that have a MacVLAN device in it, this option
    must be used to specify to which 'outer_dev' (an existing network device
    in CRIU namespace) the restored 'inner_dev' should be bound to.

*--manage-cgroups* ['mode']::
    Restore cgroups configuration associated with a task from the image.
    Controllers are always restored in an optimistic way -- if already present
    in system, *criu* reuses it, otherwise it will be created.

The 'mode' may be one of the following:

    *none*:::   Do not restore cgroup properties but require cgroup to
                pre-exist at the moment of *restore* procedure.

    *props*:::  Restore cgroup properties and require cgroup to pre-exist.

    *soft*:::   Restore cgroup properties if only cgroup has been created
                by *criu*, otherwise do not restore properties. This is the
		default if mode is unspecified.

    *full*:::   Always restore all cgroups and their properties.

    *strict*::: Restore all cgroups and their properties from the scratch,
                requiring them to not present in the system.

*--cgroup-root* ['controller'*:*]/'newroot'::
    Change the root cgroup the controller will be installed into. No controller
    means that root is the default for all controllers not specified.

*--tcp-established*::
    Restore previously dumped established TCP connections. This implies that
    the network has been locked between *dump* and *restore* phases so other
    side of a connection simply notice a kind of lag.

*--veth-pair* 'IN'*=*'OUT'::
    Correspondence between outside and inside names of veth devices.

*-l*, *--file-locks*::
    Restore file locks from the image.

*--auto-dedup*::
    As soon as a page is restored it get punched out from image.

*-j*, *--shell-job*::
    Restore shell jobs, in other words inherit session and process group
    ID from the criu itself.

*--cpu-cap* ['cap'[,'cap'...]]::
    Specify CPU capabilities to be present on the CPU the process is
    restoring. To inverse a capability, prefix it with *^*. This option implies
    that *--cpu-cap* has been passed on *dump* as well, except *fpu* option
    case. The 'cap' argument can be the following (or a set of comma-separated
    values):

    *all*:::    Require all capabilities. This is *default* mode if *--cpu-cap*
                is passed without arguments. Most safe mode.

    *cpu*:::    Require the CPU to have all capabilities in image to match
                runtime CPU.

    *fpu*:::    Require the CPU to have compatible FPU. For example the process
                might be dumped with xsave capability but attempted to restore
                without it present on target CPU. In such case we refuse to
                proceed. This is *default* mode if *--cpu-cap* is not present
                in command line. Note this argument might be passed even if
                on the *dump* no *--cpu-cap* have been specified because FPU
                frames are always encoded into images.

    *ins*:::    Require CPU compatibility on instructions level.

    *none*:::   Ignore capabilities. Most dangerous mode. The behaviour is
                implementation dependent. Try to not use it until really
                required.
+
For example, this option can be used in case *--cpu-cap=cpu* was used
during *dump*, and images are migrated to a less capable CPU and are
to be restored. By default, *criu* shows an error that CPU capabilities
are not adequate, but this can be suppressed by using *--cpu-cap=none*.

*--weak-sysctls*::
   Silently skip restoring sysctls that are not available. This allows
   to restore on an older kernel, or a kernel configured without some
   options.

*check*
~~~~~~~
Checks whether the kernel supports the features needed by *criu* to
dump and restore a process tree.

There are three categories of kernel support, as described below. *criu
check* always checks Category 1 features unless *--feature* is specified
which only checks a specified feature.

*Category 1*::: Absolutely required. These are features like support for
		*/proc/PID/map_files*, *NETLINK_SOCK_DIAG* socket
		monitoring, */proc/sys/kernel/ns_last_pid* etc.

*Category 2*::: Required only for specific cases. These are features
		like AIO remap, */dev/net/tun* and others that are only
		required if a process being dumped or restored
		is using those.

*Category 3*::: Experimental. These are features like *task-diag* that
		are used for experimental purposes (mostly
		during development).

If there are no errors or warnings, *criu* prints "Looks good." and its
exit code is 0.

A missing Category 1 feature causes *criu* to print "Does not look good."
and its exit code is non-zero.

Missing Category 2 and 3 features cause *criu* to print "Looks good but
..." and its exit code is be non-zero.

Without any options, *criu check* checks Category 1 features. This
behavior can be changed by using the following options:

*--extra*::
    Check kernel support for Category 2 features.

*--experimental*::
    Check kernel support for Category 3 features.

*--all*::
    Check kernel support for Category 1, 2, and 3 features.

*--feature* 'name'::
    Check a specific feature.  If 'name' is *list*, a list of valid
    kernel feature names that can be checked will be printed.

*page-server*
~~~~~~~~~~~~~
Launches *criu* in page server mode.

*--daemon*::
    Runs page server as a daemon (background process).

*--address* 'address'::
    Page server IP address.

*--port* 'number'::
    Page server port number.

*exec*
~~~~~~
Executes a system call inside a destination task\'s context. This functionality
is deprecated; please use *Compel* instead.

*service*
~~~~~~~~~
Launches *criu* in RPC daemon mode, where *criu* is listening for
RPC commands over socket to perform. This is convenient for a
case where daemon itself is running in a privileged (superuser) mode
but clients are not.

dedup
~~~~~
Starts pagemap data deduplication procedure, where *criu* scans over all
pagemap files and tries to minimize the number of pagemap entries by
obtaining the references from a parent pagemap image.

cpuinfo dump
~~~~~~~~~~~~
Fetches current CPU features and write them into an image file.

cpuinfo check
~~~~~~~~~~~~~
Fetches current CPU features (i.e. CPU the *criu* is running on) and test if
they are compatible with the ones present in an image file.


EXAMPLES
--------
To checkpoint a program with pid of *1234* and write all image files into
directory *checkpoint*:

----------
    criu dump -D checkpoint -t 1234
----------

To restore this program detaching criu itself:

----------
    criu restore -d -D checkpoint
----------


AUTHOR
------
The CRIU team.


COPYRIGHT
---------
Copyright \(C) 2011-2016, Parallels Holdings, Inc.