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UNSHARE

Section: User Commands (1)
Updated: July 2014
Index Return to Main Contents
 

NAME

unshare - run program with some namespaces unshared from parent  

SYNOPSIS

unshare [options] program [arguments]  

DESCRIPTION

Unshares the indicated namespaces from the parent process and then executes the specified program. The namespaces to be unshared are indicated via options. Unshareable namespaces are:
mount namespace
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 for the shared flags).

It's recommended to use mount --make-rprivate or mount --make-rslave after unshare --mount to make sure that mountpoints in the new namespace are really unshared from the parental namespace.

UTS namespace
Setting hostname or domainname will not affect the rest of the system. (CLONE_NEWUTS flag)
IPC namespace
The process will have an independent namespace for System V message queues, semaphore sets and shared memory segments. (CLONE_NEWIPC flag)
network namespace
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)
pid namespace
Children will have a distinct set of PID to process mappings from their parent. (CLONE_NEWPID flag)
user namespace
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.  

OPTIONS

-i, --ipc
Unshare the IPC namespace.
-m, --mount
Unshare the mount namespace.
-n, --net
Unshare the network namespace.
-p, --pid
Unshare the pid namespace. See also the --fork and --mount-proc options.
-u, --uts
Unshare the UTS namespace.
-U, --user
Unshare the user namespace.
-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.
-s, --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.
 

EXAMPLES

# unshare --fork --pid --mount-proc readlink /proc/self
1
Establish a PID namespace, ensure we're PID 1 in it against newly mounted procfs instance.
$ unshare --map-root-user --user sh -c whoami
root
Establish a user namespace as an unprivileged user with a root user within it.
 

SEE ALSO

unshare(2), clone(2), mount(8)  

BUGS

None known so far.  

AUTHOR

Mikhail Gusarov <dottedmag@dottedmag.net>  

AVAILABILITY

The unshare command is part of the util-linux package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.


 

Index

NAME
SYNOPSIS
DESCRIPTION
OPTIONS
EXAMPLES
SEE ALSO
BUGS
AUTHOR
AVAILABILITY


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