unshare — run program with some namespaces unshared from parent
unshare
[options] program
[arguments]
Unshares the indicated namespaces from the parent process
and then executes the specified program
.
The namespaces can optionally be persisted by bind
mounting /proc/[pid]/ns/[type] files to a filesystem path and
entered with nsenter(1) even after
program
terminates.
Once a persistent namespace is no longer needed it can be
unpersisted with umount(8). See EXAMPLES
section for more details.
The namespaces to be unshared are indicated via options. Unshareable namespaces are:
Mounting and unmounting filesystems will not affect
the rest of the system (CLONE_NEWNS
flag), except for
filesystems which are explicitly marked as shared (with
mount
--make-shared; see /proc/self/mountinfo
or findmnt -o+PROPAGATION for
the shared flags).
unshare since
util-linux version 2.27 automatically sets propagation
to private in the new
mount namespace to make sure that the new namespace is
really unshared. This feature is possible to disable by
option −−propagation
unchanged
. Note that private is the kernel
default.
Setting hostname or domainname will not affect the
rest of the system. (CLONE_NEWUTS
flag)
The process will have an independent namespace for
System V message queues, semaphore sets and shared
memory segments. (CLONE_NEWIPC
flag)
The process will have independent IPv4 and IPv6
stacks, IP routing tables, firewall rules, the
/proc/net
and
/sys/class/net
directory
trees, sockets, etc. (CLONE_NEWNET
flag)
Children will have a distinct set of PID to process
mappings from their parent. (CLONE_NEWPID
flag)
The process will have a distinct set of UIDs, GIDs
and capabilities. (CLONE_NEWUSER
flag)
See clone(2) for the exact semantics of the flags.
−i,
−−ipc[=file
]
Unshare the IPC namespace. If file is specified then persistent namespace is created by bind mount.
−m,
−−mount[=file
]
Unshare the mount namespace. If file is specified then persistent namespace is created by bind mount.
−n,
−−net[=file
]
Unshare the network namespace. If file is specified then persistent namespace is created by bind mount.
−p,
−−pid[=file
]
Unshare the pid namespace. If file is specified
then persistent namespace is created by bind mount. See
also the −−fork
and −−mount−proc
options.
−u,
−−uts[=file
]
Unshare the UTS namespace. If file is specified then persistent namespace is created by bind mount.
−U,
−−user[=file
]
Unshare the user namespace. If file is specified then persistent namespace is created by bind mount.
−f,
−−fork
Fork the specified program
as a child
process of unshare rather than
running it directly. This is useful when creating a new
pid namespace.
−−mount−proc[=mountpoint
]
Just before running the program, mount the proc filesystem at mountpoint (default is /proc). This is useful when creating a new pid namespace. It also implies creating a new mount namespace since the /proc mount would otherwise mess up existing programs on the system. The new proc filesystem is explicitly mounted as private (by MS_PRIVATE|MS_REC).
−r,
−−map−root−user
Run the program only after the current effective user and group IDs have been mapped to the superuser UID and GID in the newly created user namespace. This makes it possible to conveniently gain capabilities needed to manage various aspects of the newly created namespaces (such as configuring interfaces in the network namespace or mounting filesystems in the mount namespace) even when run unprivileged. As a mere convenience feature, it does not support more sophisticated use cases, such as mapping multiple ranges of UIDs and GIDs. This option implies --setgroups=deny.
−−propagation private|shared|slave|unchanged
Recursively sets mount propagation flag in the new
mount namespace. The default is to set the propagation
to private, this feature
is possible to disable by unchanged argument.
The options is silently ignored when mount namespace
(−−mount
) is
not requested.
−−setgroups allow|deny
Allow or deny setgroups(2) syscall in user namespaces.
setgroups(2) is only callable with CAP_SETGID and CAP_SETGID in a user namespace (since Linux 3.19) does not give you permission to call setgroups(2) until after GID map has been set. The GID map is writable by root when setgroups(2) is enabled and GID map becomes writable by unprivileged processes when setgroups(2) is permanently disabled.
−V,
−−version
Display version information and exit.
−h,
−−help
Display help text and exit.
1
Establish a PID namespace, ensure we're PID 1 in it against newly mounted procfs instance.
root
Establish a user namespace as an unprivileged user with a root user within it.
# touch /root/uts-ns # unshare --uts=/root/uts-ns hostanme FOO # nsenter --uts=/root/uts-ns hostname FOO # umount /root/uts-ns
Establish a persistent UTS namespace, modify hostname. The namespace maybe later entered by nsenter. The namespace is destroyed by umount the bind reference.