Provided by: criu_3.16.1-2_amd64 
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
Most of the long flags can be prefixed with no- to negate the option (example: --display-stats and
--no-display-stats).
Common options
Common options are applicable to any command.
-v[v...], --verbosity
Increase verbosity up from the default level. In case of short option, multiple v can be used, each
increasing verbosity by one.
-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.
--config file
Pass a specific configuration file to criu.
--no-default-config
Disable parsing of default configuration files.
--pidfile file
Write root task, service or page-server pid into a file.
-o, --log-file file
Write logging messages to a file.
--display-stats
During dump, as well as during restore, criu collects some statistics, like the time required to dump
or restore the process, or the number of pages dumped or restored. This information is always saved
to the stats-dump and stats-restore files, and can be shown using crit(1). The option --display-stats
prints out this information on the console at the end of a dump or restore operation.
-D, --images-dir path
Use path as a base directory where to look for sets of image files.
--stream
dump/restore images using criu-image-streamer. See
https://github.com/checkpoint-restore/criu-image-streamer for detailed usage.
--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.
--enable-fs [fs[,fs...]]
Specify a comma-separated list of filesystem names that should be auto-detected. The value all
enables auto-detection for all filesystems.
Note: This option is not safe, use at your own risk. Auto-detecting a filesystem mount assumes that
the mountpoint can be restored with mount(src, mountpoint, flags, options). When used, dump is
expected to always succeed if a mountpoint is to be auto-detected, however restore may fail (or do
something wrong) if the assumption for restore logic is incorrect. This option is not compatable with
--external dev.
--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
pre-resume
run when all processes and resources are restored but tasks are stopped waiting for final kick to
run. Must not fail.
post-resume
called at the very end, when everything is restored and processes were resumed
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 has just been created with required namespaces. Note it is an early stage of
restore, when nothing is restored yet, except for namespaces themselves
post-setup-namespaces
called after the namespaces are configured
orphan-pts-master
called after master pty is opened and unlocked. This hook can be used only in the RPC mode, and
the notification message contains a file descriptor for the master pty
-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.
--pre-dump-mode=mode
There are two mode to operate pre-dump algorithm. The splice mode is parasite based, whereas read
mode is based on process_vm_readv syscall. The read mode incurs reduced frozen time and reduced
memory pressure as compared to splice mode. Default is splice mode.
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 colon).
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, colon 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 the given id is OK
to be disconnected.
--external pid[inode]:name
Mark a PID namespace as external. This can be later used to restore a process into an existing PID
namespace. The label name can be used to assign another PID namespace during restore with the help of
--inherit-fd.
--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-yard path
Instead of trying to mount cgroups in CRIU, provide a path to a directory with already created cgroup
yard. Useful if you don’t want to grant CAP_SYS_ADMIN to CRIU. For every cgroup mount there should be
exactly one directory. If there is only one controller in this mount, the dir’s name should be just
the name of the controller. If there are multiple controllers comounted, the directory name should
have them be separated by a comma.
For example, if /proc/cgroups looks like this:
#subsys_name hierarchy num_cgroups enabled
cpu 1 1 1
devices 2 2 1
freezer 2 2 1
then you can create the cgroup yard by the following commands:
mkdir private_yard
cd private_yard
mkdir cpu
mount -t cgroup -o cpu none cpu
mkdir devices,freezer
mount -t cgroup -o devices,freezer none devices,freezer
--tcp-established
Checkpoint established TCP connections.
--tcp-close
Don’t dump the state of, or block, established tcp connections. This is useful when tcp connections
are not going to be restored.
--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 to ignore capabilities at all; the image will not be produced on dump, neither any check
performed on restore;
• fpu to check if FPU module is compatible;
• ins to check if CPU supports all instructions required;
• cpu to check if CPU capabilities are exactly matching;
• all for all above set.
By default the option is set to fpu and ins.
--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.
--lazy-pages
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.
--file-validation [mode]
Set the method to be used to validate open files. Validation is done to ensure that the version of
the file being restored is the same version when it was dumped.
The mode may be one of the following:
filesize
To explicitly use only the file size check all the time. This is the fastest and least intensive
check.
buildid
To validate ELF files with their build-ID. If the build-ID cannot be obtained, chksm-first method
will be used. This is the default if mode is unspecified.
--network-lock [mode]
Set the method to be used for network locking/unlocking. Locking is done to ensure that tcp
packets are dropped between dump and restore. This is done to avoid the kernel sending RST when a
packet arrives destined for the dumped process.
The mode may be one of the following:
iptables
Use iptables rules to drop the packets. This is the default if mode is not specified.
nftables
Use nftables rules to drop the packets.
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, pid 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).
--log-pid
Write separate logging files per each pid.
-r, --root path
Change the root filesystem to path (when run in a mount namespace). This option is required to
restore a mount namespace. The directory path must be a mount point and its parent must not be
overmounted.
--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 colon).
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.
-J, --join-ns NS:{PID|NS_FILE}[,EXTRA_OPTS]
Restore process tree inside an existing namespace. The namespace can be specified in PID or NS_FILE
path format (example: --join-ns net:12345 or --join-ns net:/foo/bar). Currently supported values for
NS are: ipc, net, time, user, and uts. This option doesn’t support joining a PID namespace, however,
this is possible using --external and --inheritfd. EXTRA_OPTS is optional and can be used to specify
UID and GID for user namespace (e.g., --join-ns user:PID,UID,GID).
--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.
ignore
Don’t deal with cgroups and pretend that they don’t exist.
--cgroup-yard path
Instead of trying to mount cgroups in CRIU, provide a path to a directory with already created
cgroup yard. For more information look in the dump section.
--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.
--tcp-close
Restore connected TCP sockets in closed state.
--veth-pair IN=OUT
Correspondence between outside and inside names of veth devices.
-l, --file-locks
Restore file locks from the image.
--lsm-profile type:name
Specify an LSM profile to be used during restore. The type can be either apparmor or selinux.
--lsm-mount-context context
Specify a new mount context to be used during restore.
This option will only replace existing mount context information with the one specified with this
option. Mounts without the context= option will not be changed.
If a mountpoint has been checkpointed with an option like
context="system_u:object_r:container_file_t:s0:c82,c137"
it is possible to change this option using
--lsm-mount-context "system_u:object_r:container_file_t:s0:c204,c495"
which will result that the mountpoint will be restored with the new context=.
This option is useful if using selinux and if the selinux labels need to be changed on restore
like if a container is restored into an existing Pod.
--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.
--lazy-pages
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.
--file-validation [mode]
Set the method to be used to validate open files. Validation is done to ensure that the version
of the file being restored is the same version when it was dumped.
The mode may be one of the following:
filesize
To explicitly use only the file size check all the time. This is the fastest and least intensive
check.
buildid
To validate ELF files with their build-ID. If the build-ID cannot be obtained, chksm-first method
will be used. This is the default if mode is unspecified.
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).
--status-fd
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 or hostname.
--port number
Page server port number.
--ps-socket fd
Use provided file descriptor as socket for incoming connection. In this case --address and --port are
ignored. Useful for intercepting page-server traffic e.g. to add encryption or authentication.
--lazy-pages
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 daemon to request memory pages in random order.
--tls-cacert file
Specifies the path to a trusted Certificate Authority (CA) certificate file to be used for
verification of a client or server certificate. The file must be in PEM format. When this option is
used only the specified CA is used for verification. Otherwise, the system’s trusted CAs and, if
present, /etc/pki/CA/cacert.pem will be used.
--tls-cacrl file
Specifies a path to a Certificate Revocation List (CRL) file which contains a list of revoked
certificates that should no longer be trusted. The file must be in PEM format. When this option is
not specified, the file, if present, /etc/pki/CA/cacrl.pem will be used.
--tls-cert file
Specifies a path to a file that contains a X.509 certificate to present to the remote entity. The
file must be in PEM format. When this option is not specified, the default location
(/etc/pki/criu/cert.pem) will be used.
--tls-key file
Specifies a path to a file that contains TLS private key. The file must be in PEM format. When this
option is not the default location (/etc/pki/criu/private/key.pem) will be used.
--tls
Use TLS to secure remote connections.
lazy-pages
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 checkpoint
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.
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.
CONFIGURATION FILES
Criu supports usage of configuration files to avoid the need of writing every option on command line,
which is useful especially with repeated usage of same options. A specific configuration file can be
passed with the "--config file" option. If no file is passed, the default configuration files
/etc/criu/default.conf and $HOME/.criu/default.conf are parsed (if present on the system). If the
environment variable CRIU_CONFIG_FILE is set, it will also be parsed.
The options passed to CRIU via CLI, RPC or configuration file are evaluated in the following order:
• apply_config(/etc/criu/default.conf)
• apply_config($HOME/.criu/default.conf)
• apply_config(CRIU_CONFIG_FILE)
• apply_config(--config file)
• apply_config(CLI) or apply_config(RPC)
• apply_config(RPC configuration file) (only for RPC mode)
Default configuration file parsing can be deactivated with "--no-default-config" if needed. Parsed
configuration files are merged with command line options, which allows overriding boolean options.
Configuration file syntax
Comments are supported using '#' sign. The rest of the line is ignored. Options are the same as command
line options without the '--' prefix, use one option per line (with corresponding argument if applicable,
divided by whitespaces). If needed, the argument can be provided in double quotes (this should be needed
only if the argument contains whitespaces). In case this type of argument contains a literal double quote
as well, it can be escaped using the '\' sign. Usage of commands is disallowed and all other escape
sequences are interpreted literally.
Example of configuration file to illustrate syntax:
$ cat ~/.criu/default.conf
tcp-established
work-dir "/home/USERNAME/criu/my \"work\" directory"
#this is a comment
no-restore-sibling # this is another comment
Configuration files in RPC mode
Not only does criu evaluate configuration files in CLI mode, it also evaluates configuration files in RPC
mode. Just as in CLI mode the configuration file values are evaluated first. This means that any option
set via RPC will overwrite the configuration file setting. The user can thus change criu's default
behavior but it is not possible to change settings which are explicitly set by the RPC client.
The RPC client can, however, specify an additional configuration file which will be evaluated after the
RPC options (see above for option evaluation order). The RPC client can specify this additional
configuration file via "req.opts.config_file = /path/to/file". The values from this configuration file
will overwrite all other configuration file settings or RPC options. This can lead to undesired behavior
of criu and should only be used carefully.
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.
criu 3.16.1 12/04/2021 CRIU(8)