Ubuntu Manpage: criu - checkpoint/restore in userspace

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 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.

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.

NON-ROOT

       criu can be used as  non-root  with  either  the  CAP_SYS_ADMIN  capability  or  with  the
       CAP_CHECKPOINT_RESTORE  capability  introduces in Linux kernel 5.9. CAP_CHECKPOINT_RESTORE
       is the minimum that is required.

       criu    also    needs    either    CAP_SYS_PTRACE    or    a     value     of     0     in
       /proc/sys/kernel/yama/ptrace_scope (see ptrace(2)) to be able to interrupt the process for
       dumping.

       Running criu as non-root has many limitations and depending on the process  to  checkpoint
       and restore it may not be possible.

       In  addition to CAP_CHECKPOINT_RESTORE it is possible to give criu additional capabilities
       to enable additional features in non-root mode.

       Currently criu can benefit from the following additional capabilities:

       •   CAP_NET_ADMIN

       •   CAP_SYS_CHROOT

       •   CAP_SETUID

       •   CAP_SYS_RESOURCE

       Note that for some operations, having a capability in a  namespace  other  than  the  init
       namespace  (i.e.  the  default/root namespace) is not sufficient. For example, in order to
       read symlinks in proc/[pid]/map_files CRIU requires  CAP_CHECKPOINT_RESTORE  in  the  init
       namespace;  having CAP_CHECKPOINT_RESTORE while running in another user namespace (e.g. in
       a container) does not allow CRIU to read symlinks in /proc/[pid]/map_files.

       Without access to /proc/[pid]/map_files checkpointing/restoring processes that have mapped
       deleted files may not be possible.

       Independent  of  the capabilities it is always necessary to use "--unprivileged" to accept
       criu's limitation in non-root mode.

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.