sys-utils/unshare.1.adoc

   1 = unshare(1)
   2 :doctype: manpage
   3 :man manual: User commands
   4 :man source: util-linux {release-version}
   5 :page-layout: base
   6 :command: unshare
   7
   8 == NAME
   9
  10 unshare - run program in new namespaces
  11
  12 == SYNOPSIS
  13
  14 *unshare* [options] [_program_ [_arguments_]
  15
  16 == DESCRIPTION
  17
  18 The *unshare* command creates new namespaces (as specified by the command-line options described below) and then executes the specified _program_. If _program_ is not given, then "${SHELL}" is run (default: _/bin/sh_).
  19
  20 By default, a new namespace persists only as long as it has member processes. A new namespace can be made persistent even when it has no member processes by bind mounting /proc/_pid_/ns/_type_ files to a filesystem path. A namespace that has been made persistent in this way can subsequently be entered with *nsenter*(1) even after the _program_ terminates (except PID namespaces where a permanently running init process is required). Once a persistent namespace is no longer needed, it can be unpersisted by using *umount*(8) to remove the bind mount. See the EXAMPLES section for more details.
  21
  22 *unshare* since util-linux version 2.36 uses _/proc/[pid]/ns/pid_for_children_ and _/proc/[pid]/ns/time_for_children_ files for persistent PID and TIME namespaces. This change requires Linux kernel 4.17 or newer.
  23
  24 The following types of namespaces can be created with *unshare*:
  25
  26 *mount namespace*::
  27   Mounting and unmounting filesystems will not affect the rest of the system, 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). For further details, see *mount_namespaces*(7). +
  28   *unshare* since util-linux version 2.27 automatically sets propagation to *private* in a new mount namespace to make sure that the new namespace is really unshared. It's possible to disable this feature with option *--propagation unchanged*. Note that *private* is the kernel default.
  29
  30 *UTS namespace*::
  31   Setting hostname or domainname will not affect the rest of the system. For further details, see *uts_namespaces*(7).
  32
  33 *IPC namespace*::
  34   The process will have an independent namespace for POSIX message queues as well as System V message queues, semaphore sets and shared memory segments. For further details, see *ipc_namespaces*(7).
  35
  36 *network namespace*::
  37   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. For further details, see *network_namespaces*(7).
  38
  39 *PID namespace*::
  40   Children will have a distinct set of PID-to-process mappings from their parent. For further details, see *pid_namespaces*(7).
  41
  42 *cgroup namespace*::
  43   The process will have a virtualized view of _/proc/self/cgroup_, and new cgroup mounts will be rooted at the namespace cgroup root. For further details, see *cgroup_namespaces*(7).
  44
  45 *user namespace*::
  46   The process will have a distinct set of UIDs, GIDs and capabilities. For further details, see *user_namespaces*(7).
  47
  48 *time namespace*::
  49   The process can have a distinct view of *CLOCK_MONOTONIC* and/or *CLOCK_BOOTTIME* which can be changed using _/proc/self/timens_offsets_. For further details, see *time_namespaces*(7).
  50
  51 == OPTIONS
  52
  53 *-i*, *--ipc*[**=**__file__]::
  54   Unshare the IPC namespace. If _file_ is specified, then a persistent namespace is created by a bind mount.
  55
  56 *-m*, *--mount*[**=**__file__]::
  57   Unshare the mount namespace. If _file_ is specified, then a persistent namespace is created by a bind mount. Note that _file_ must be located on a mount whose propagation type is not *shared* (or an error results). Use the command *findmnt -o+PROPAGATION* when not sure about the current setting. See also the examples below.
  58
  59 *-n*, *--net*[**=**__file__]::
  60   Unshare the network namespace. If _file_ is specified, then a persistent namespace is created by a bind mount.
  61
  62 *-p*, *--pid*[**=**__file__]::
  63   Unshare the PID namespace. If _file_ is specified, then a persistent namespace is created by a bind mount. (Creation of a persistent PID namespace will fail if the *--fork* option is not also specified.) +
  64   See also the *--fork* and *--mount-proc* options.
  65
  66 *-u*, *--uts*[**=**__file__]::
  67   Unshare the UTS namespace. If _file_ is specified, then a persistent namespace is created by a bind mount.
  68
  69 *-U*, *--user*[**=**__file__]::
  70   Unshare the user namespace. If _file_ is specified, then a persistent namespace is created by a bind mount.
  71
  72 *-C*, *--cgroup*[**=**__file__]::
  73   Unshare the cgroup namespace. If _file_ is specified, then persistent namespace is created by bind mount.
  74
  75 *-T*, *--time*[**=**__file__]::
  76   Unshare the time namespace. If _file_ is specified, then a persistent namespace is created by a bind mount. The *--monotonic* and *--boottime* options can be used to specify the corresponding offset in the time namespace.
  77
  78 *-f*, *--fork*::
  79   Fork the specified _program_ as a child process of *unshare* rather than running it directly. This is useful when creating a new PID namespace. Note that when *unshare* is waiting for the child process, then it ignores *SIGINT* and *SIGTERM* and does not forward any signals to the child. It is necessary to send signals to the child process.
  80
  81 *--keep-caps*::
  82   When the *--user* option is given, ensure that capabilities granted in the user namespace are preserved in the child process.
  83
  84 *--kill-child*[**=**__signame__]::
  85   When *unshare* terminates, have _signame_ be sent to the forked child process. Combined with *--pid* this allows for an easy and reliable killing of the entire process tree below *unshare*. If not given, _signame_ defaults to *SIGKILL*. This option implies *--fork*.
  86
  87 *--mount-proc*[**=**__mountpoint__]::
  88   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 (with *MS_PRIVATE*|*MS_REC*).
  89
  90 **--map-user=**__uid|name__::
  91   Run the program only after the current effective user ID has been mapped to _uid_. If this option is specified multiple times, the last occurrence takes precedence. This option implies *--user*.
  92
  93 **--map-group=**__gid|name__::
  94   Run the program only after the current effective group ID has been mapped to _gid_. If this option is specified multiple times, the last occurrence takes precedence. This option implies *--setgroups=deny* and *--user*.
  95
  96 *-r*, *--map-root-user*::
  97   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* and *--user*. This option is equivalent to *--map-user=0 --map-group=0*.
  98
  99 *-c*, *--map-current-user*::
 100   Run the program only after the current effective user and group IDs have been mapped to the same UID and GID in the newly created user namespace. This option implies *--setgroups=deny* and *--user*. This option is equivalent to *--map-user=$(id -ru) --map-group=$(id -rg)*.
 101
 102 **--propagation private**|**shared**|**slave**|*unchanged*::
 103   Recursively set the mount propagation flag in the new mount namespace. The default is to set the propagation to _private_. It is possible to disable this feature with the argument *unchanged*. The option is silently ignored when the mount namespace (*--mount*) is not requested.
 104
 105 **--setgroups allow**|*deny*::
 106   Allow or deny the *setgroups*(2) system call in a user namespace. +
 107   To be able to call *setgroups*(2), the calling process must at least have *CAP_SETGID*. But since Linux 3.19 a further restriction applies: the kernel gives permission to call *setgroups*(2) only after the GID map (**/proc/**__pid__*/gid_map*) has been set. The GID map is writable by root when *setgroups*(2) is enabled (i.e., *allow*, the default), and the GID map becomes writable by unprivileged processes when *setgroups*(2) is permanently disabled (with *deny*).
 108
 109 *-R*, **--root=**__dir__::
 110   run the command with root directory set to _dir_.
 111
 112 *-w*, **--wd=**__dir__::
 113   change working directory to _dir_.
 114
 115 *-S*, *--setuid* _uid_::
 116   Set the user ID which will be used in the entered namespace.
 117
 118 *-G*, *--setgid* _gid_::
 119   Set the group ID which will be used in the entered namespace and drop supplementary groups.
 120
 121 *--monotonic* _offset_::
 122   Set the offset of *CLOCK_MONOTONIC* which will be used in the entered time namespace. This option requires unsharing a time namespace with *--time*.
 123
 124 *--boottime* _offset_::
 125   Set the offset of *CLOCK_BOOTTIME* which will be used in the entered time namespace. This option requires unsharing a time namespace with *--time*.
 126
 127 *-V*, *--version*::
 128   Display version information and exit.
 129
 130 *-h*, *--help*::
 131   Display help text and exit.
 132
 133 == NOTES
 134
 135 The proc and sysfs filesystems mounting as root in a user namespace have to be restricted so that a less privileged user can not get more access to sensitive files that a more privileged user made unavailable. In short the rule for proc and sysfs is as close to a bind mount as possible.
 136
 137 == EXAMPLES
 138
 139 The following command creates a PID namespace, using *--fork* to ensure that the executed command is performed in a child process that (being the first process in the namespace) has PID 1. The *--mount-proc* option ensures that a new mount namespace is also simultaneously created and that a new *proc*(5) filesystem is mounted that contains information corresponding to the new PID namespace. When the *readlink* command terminates, the new namespaces are automatically torn down.
 140
 141 ....
 142 # unshare --fork --pid --mount-proc readlink /proc/self
 143 1
 144 ....
 145
 146 As an unprivileged user, create a new user namespace where the user's credentials are mapped to the root IDs inside the namespace:
 147
 148 ....
 149 $ id -u; id -g
 150 1000
 151 1000
 152 $ unshare --user --map-root-user \
 153         sh -c ''whoami; cat /proc/self/uid_map /proc/self/gid_map''
 154 root
 155          0       1000          1
 156          0       1000          1
 157 ....
 158
 159 The first of the following commands creates a new persistent UTS namespace and modifies the hostname as seen in that namespace. The namespace is then entered with *nsenter*(1) in order to display the modified hostname; this step demonstrates that the UTS namespace continues to exist even though the namespace had no member processes after the *unshare* command terminated. The namespace is then destroyed by removing the bind mount.
 160
 161 ....
 162 # touch /root/uts-ns
 163 # unshare --uts=/root/uts-ns hostname FOO
 164 # nsenter --uts=/root/uts-ns hostname
 165 FOO
 166 # umount /root/uts-ns
 167 ....
 168
 169 The following commands establish a persistent mount namespace referenced by the bind mount _/root/namespaces/mnt_. In order to ensure that the creation of that bind mount succeeds, the parent directory (_/root/namespaces_) is made a bind mount whose propagation type is not *shared*.
 170
 171 ....
 172 # mount --bind /root/namespaces /root/namespaces
 173 # mount --make-private /root/namespaces
 174 # touch /root/namespaces/mnt
 175 # unshare --mount=/root/namespaces/mnt
 176 ....
 177
 178 The following commands demonstrate the use of the *--kill-child* option when creating a PID namespace, in order to ensure that when *unshare* is killed, all of the processes within the PID namespace are killed.
 179
 180 ....
 181 # set +m                # Don't print job status messages
 182
 183
 184 # unshare --pid --fork --mount-proc --kill-child -- \
 185
 186
 187        bash --norc -c ''(sleep 555 &) && (ps a &) && sleep 999'' &
 188 [1] 53456
 189 #     PID TTY      STAT   TIME COMMAND
 190       1 pts/3    S+     0:00 sleep 999
 191       3 pts/3    S+     0:00 sleep 555
 192       5 pts/3    R+     0:00 ps a
 193
 194 # ps h -o 'comm' $!     # Show that background job is unshare(1)
 195 unshare
 196 # kill $!               # Kill unshare(1)
 197 # pidof sleep
 198 ....
 199
 200 The *pidof*(1) command prints no output, because the *sleep* processes have been killed. More precisely, when the *sleep* process that has PID 1 in the namespace (i.e., the namespace's init process) was killed, this caused all other processes in the namespace to be killed. By contrast, a similar series of commands where the *--kill-child* option is not used shows that when *unshare* terminates, the processes in the PID namespace are not killed:
 201
 202 ....
 203 # unshare --pid --fork --mount-proc -- \
 204
 205
 206        bash --norc -c ''(sleep 555 &) && (ps a &) && sleep 999'' &
 207 [1] 53479
 208 #     PID TTY      STAT   TIME COMMAND
 209       1 pts/3    S+     0:00 sleep 999
 210       3 pts/3    S+     0:00 sleep 555
 211       5 pts/3    R+     0:00 ps a
 212
 213 # kill $!
 214 # pidof sleep
 215 53482 53480
 216 ....
 217
 218 The following example demonstrates the creation of a time namespace where the boottime clock is set to a point several years in the past:
 219
 220 ....
 221 # uptime -p             # Show uptime in initial time namespace
 222 up 21 hours, 30 minutes
 223 # unshare --time --fork --boottime 300000000 uptime -p
 224 up 9 years, 28 weeks, 1 day, 2 hours, 50 minutes
 225 ....
 226
 227 == AUTHORS
 228
 229 mailto:dottedmag@dottedmag.net[Mikhail Gusarov] +
 230 mailto:kzak@redhat.com[Karel Zak]
 231
 232 == SEE ALSO
 233
 234 *clone*(2),
 235 *unshare*(2),
 236 *namespaces*(7),
 237 *mount*(8)
 238
 239 include::../man-common/bugreports.adoc[]
 240
 241 include::../man-common/footer.adoc[]
 242
 243 ifdef::translation[]
 244 include::../man-common/translation.adoc[]
 245 endif::[]