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
--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 compatible
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
query-ext-files
called after the process tree is stopped and network is
locked. This hook is used only in the RPC mode. The notification reply
contains file ids to be added to external file list (may be empty).
--unprivileged
This option tells criu to accept the limitations
when running as non-root. Running as non-root requires criu at least to
have CAP_SYS_ADMIN or CAP_CHECKPOINT_RESTORE. For details about
running criu as non-root please consult the NON-ROOT
section.
-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 net[inode]:name
Mark a network namespace as external and do not include
it in the checkpoint. The label name can be used with
--inherit-fd during restore to specify a file descriptor to a
preconfigured network namespace.
--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 (including the connection is once established but now closed).
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).
--timeout number
Set a time limit in seconds for collecting tasks during
the dump operation. The timeout is 10 seconds by default.
--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.
--ghost-fiemap
Enable an optimization based on fiemap ioctl that can
reduce the number of system calls used when checkpointing highly sparse ghost
files. This option is enabled by default, and it can be disabled with
--no-ghost-fiemap. An automatic fallback to SEEK_HOLE/SEEK_DATA is used
when fiemap is not supported.
-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.
skip
Don’t lock the network. If --tcp-close is
not used, the network must be locked externally to allow CRIU to dump TCP
connections.
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.
--skip-file-rwx-check
Skip checking file permissions (r/w/x for u/g/o) on
restore.
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.