criu man page
criu — checkpoint/restore in userspace
criu command [option ...]
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.
Most of the true / false long options (the ones without arguments) can be prefixed with --no- to negate the option (example: --display-stats and --no-display-stats).
Common options are applicable to any command.
- -v[v...], --verbosity
Increase verbosity up from the default level. Multiple v can be used, each increasing verbosity by one level. Using long option without argument increases verbosity by one level.
- -vnum, --verbosity=num
Set verbosity level to num. The higher the level, the more output is produced.
The following levels are available:
- -v0 no output;
- -v1 only errors;
- -v2 above plus warnings (this is the default level);
- -v3 above plus information messages and timestamps;
- -v4 above plus 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.
Write separate logging files per each pid.
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:
run prior to beginning a dump
run upon dump completion
run prior to beginning a restore
run when all processes and resources are restored but tasks are stopped waiting for final kick to run. Must not fail.
run upon restore completion
run to lock network in a target network namespace
run to unlock network in a target network namespace
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.
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.
Turn on memory changes tracker in the kernel. If the option is not passed the memory tracker get turned on implicitly.
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.
Use cgroup freezer to collect processes.
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.
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.
Checkpoint established TCP connections.
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.
Restore connected TCP sockets in closed state.
Use any path to a device file if the original one is inaccessible.
Send pages to a page server (see the page-server command).
Force resolving names for inotify and fsnotify watches.
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.
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.
Perform the dump procedure without writing memory pages into the image files and prepare to service page requests over the network. When dump runs in this mode it presumes that lazy-pages daemon will connect to it and fetch memory pages to lazily inject them into the restored process address space. This option is intended for post-copy (lazy) migration and should be used in conjunction with restore with appropriate options.
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:
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:
Do not restore cgroup properties but require cgroup to pre-exist at the moment of restore procedure.
Restore cgroup properties and require cgroup to pre-exist.
Restore cgroup properties if only cgroup has been created by criu, otherwise do not restore properties. This is the default if mode is unspecified.
Always restore all cgroups and their properties.
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.
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.
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):
Require all capabilities. This is default mode if --cpu-cap is passed without arguments. Most safe mode.
Require the CPU to have all capabilities in image to match runtime CPU.
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.
Require CPU compatibility on instructions level.
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.
Silently skip restoring sysctls that are not available. This allows to restore on an older kernel, or a kernel configured without some options.
Restore the processes without filling out the entire memory contents. When this option is used, restore sets up the infrastructure required to fill memory pages either on demand when the process accesses them or in the background without stopping the restored process. This option requires running lazy-pages daemon.
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.
Absolutely required. These are features like support for /proc/PID/map_files, NETLINK_SOCK_DIAG socket monitoring, /proc/sys/kernel/ns_last_pid etc.
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.
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:
Check kernel support for Category 2 features.
Check kernel support for Category 3 features.
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.
Launches criu in page server mode.
Runs page server as a daemon (background process).
Write \\0 to the FD and close it once page-server is ready to handle requests. The status-fd allows to not daemonize a process and get its exit code at the end. It isn’t supposed to use --daemon and --status-fd together.
- --address address
Page server IP address.
- --port number
Page server port number.
Serve local memory dump to a remote lazy-pages daemon. In this mode the page-server reads local memory dump and allows the remote lazy-pages deamon to request memory pages in random order.
Launches criu in lazy-pages daemon mode.
The lazy-pages daemon is responsible for managing user-level demand paging for the restored processes. It gets information required to fill the process memory pages from the restore and from the checkpont directory. When a restored process access certain memory page for the first time, the lazy-pages daemon injects its contents into the process address space. The memory pages that are not yet requested by the restored processes are injected in the background.
Executes a system call inside a destination task's context. This functionality is deprecated; please use Compel instead.
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.
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.
Fetches current CPU features and write them into an image file.
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.
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
The CRIU team.
Copyright (C) 2011-2016, Parallels Holdings, Inc.