2013-01-13 23:45:09 +00:00
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.\" Copyright (c) 2013 by Michael Kerrisk <mtk.manpages@gmail.com>
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2013-01-14 04:33:36 +00:00
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.\" and Copyright (c) 2012 by Eric W. Biederman <ebiederm@xmission.com>
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2013-01-13 23:45:09 +00:00
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.\"
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2014-09-16 07:05:40 +00:00
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.\" %%%LICENSE_START(VERBATIM)
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2013-01-13 23:45:09 +00:00
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" preserved on all copies.
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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2014-09-16 07:05:40 +00:00
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.\" %%%LICENSE_END
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2013-01-13 23:45:09 +00:00
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.\"
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.\"
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clone.2, flock.2, getpid.2, getunwind.2, mount.2, reboot.2, semop.2, seteuid.2, setgid.2, setns.2, setresuid.2, setreuid.2, setuid.2, uname.2, unshare.2, clock.3, drand48.3, proc.5, capabilities.7, credentials.7, mq_overview.7, namespaces.7, pid_namespaces.7, svipc.7, user_namespaces.7: tstamp
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2014-09-21 09:23:07 +00:00
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.TH NAMESPACES 7 2014-09-21 "Linux" "Linux Programmer's Manual"
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2013-01-13 23:45:09 +00:00
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.SH NAME
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namespaces \- overview of Linux namespaces
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.SH DESCRIPTION
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A namespace wraps a global system resource in an abstraction that
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makes it appear to the processes within the namespace that they
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have their own isolated instance of the global resource.
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Changes to the global resource are visible to other processes
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that are members of the namespace, but are invisible to other processes.
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One use of namespaces is to implement containers.
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2014-06-02 13:33:41 +00:00
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Linux provides the following namespaces:
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.TS
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lB lB lB
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l lB l.
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Namespace Constant Isolates
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2014-09-21 20:50:35 +00:00
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IPC CLONE_NEWIPC System V IPC, POSIX message queues
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2014-06-02 13:33:41 +00:00
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Network CLONE_NEWNET Network devices, stacks, ports, etc.
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Mount CLONE_NEWNS Mount points
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PID CLONE_NEWPID Process IDs
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User CLONE_NEWUSER User and group IDs
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UTS CLONE_NEWUTS Hostname and NIS domain name
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.TE
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2013-01-13 23:45:09 +00:00
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This page describes the various namespaces and the associated
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.I /proc
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files, and summarizes the APIs for working with namespaces.
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2013-02-25 13:00:44 +00:00
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.\"
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.\" ==================== The namespaces API ====================
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.\"
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2013-01-13 23:45:09 +00:00
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.SS The namespaces API
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As well as various
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.I /proc
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files described below,
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2013-02-18 15:10:30 +00:00
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the namespaces API includes the following system calls:
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2013-01-13 23:45:09 +00:00
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.TP
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.BR clone (2)
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The
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.BR clone (2)
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system call creates a new process.
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If the
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.I flags
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argument of the call specifies one or more of the
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.B CLONE_NEW*
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flags listed below, then new namespaces are created for each flag,
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and the child process is made a member of those namespaces.
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(This system call also implements a number of features
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unrelated to namespaces.)
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.TP
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.BR setns (2)
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The
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.BR setns (2)
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system call allows the calling process to join an existing namespace.
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The namespace to join is specified via a file descriptor that refers to
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one of the
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.IR /proc/[pid]/ns
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files described below.
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.TP
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.BR unshare (2)
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The
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.BR unshare (2)
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system call moves the calling process to a new namespace.
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If the
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.I flags
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argument of the call specifies one or more of the
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.B CLONE_NEW*
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flags listed below, then new namespaces are created for each flag,
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and the calling process is made a member of those namespaces.
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(This system call also implements a number of features
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unrelated to namespaces.)
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2013-01-16 09:24:52 +00:00
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.PP
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2013-01-14 05:08:22 +00:00
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Creation of new namespaces using
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.BR clone (2)
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and
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.BR unshare (2)
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in most cases requires the
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.BR CAP_SYS_ADMIN
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capability.
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User namespaces are the exception: since Linux 3.8,
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2013-01-14 08:30:04 +00:00
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no privilege is required to create a user namespace.
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2013-02-25 13:00:44 +00:00
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.\"
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.\" ==================== The /proc/[pid]/ns/ directory ====================
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.\"
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2013-01-14 00:22:01 +00:00
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.SS The /proc/[pid]/ns/ directory
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2014-09-21 09:24:24 +00:00
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Each process has a
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2013-01-14 00:22:01 +00:00
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.IR /proc/[pid]/ns/
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.\" See commit 6b4e306aa3dc94a0545eb9279475b1ab6209a31f
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subdirectory containing one entry for each namespace that
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supports being manipulated by
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2013-01-14 00:24:16 +00:00
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.BR setns (2):
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.in +4n
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.nf
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$ \fBls -l /proc/$$/ns\fP
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total 0
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lrwxrwxrwx. 1 mtk mtk 0 Jan 14 01:20 ipc -> ipc:[4026531839]
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lrwxrwxrwx. 1 mtk mtk 0 Jan 14 01:20 mnt -> mnt:[4026531840]
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lrwxrwxrwx. 1 mtk mtk 0 Jan 14 01:20 net -> net:[4026531956]
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lrwxrwxrwx. 1 mtk mtk 0 Jan 14 01:20 pid -> pid:[4026531836]
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lrwxrwxrwx. 1 mtk mtk 0 Jan 14 01:20 user -> user:[4026531837]
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lrwxrwxrwx. 1 mtk mtk 0 Jan 14 01:20 uts -> uts:[4026531838]
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.fi
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.in
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2013-01-14 00:22:01 +00:00
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Bind mounting (see
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.BR mount (2))
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one of the files in this directory
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2014-03-14 18:54:00 +00:00
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to somewhere else in the filesystem keeps
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2013-01-14 00:22:01 +00:00
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the corresponding namespace of the process specified by
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.I pid
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alive even if all processes currently in the namespace terminate.
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Opening one of the files in this directory
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(or a file that is bind mounted to one of these files)
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returns a file handle for
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the corresponding namespace of the process specified by
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.IR pid .
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As long as this file descriptor remains open,
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the namespace will remain alive,
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even if all processes in the namespace terminate.
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The file descriptor can be passed to
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.BR setns (2).
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In Linux 3.7 and earlier, these files were visible as hard links.
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Since Linux 3.8, they appear as symbolic links.
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If two processes are in the same namespace, then the inode numbers of their
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.IR /proc/[pid]/ns/xxx
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symbolic links will be the same; an application can check this using the
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.I stat.st_ino
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field returned by
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.BR stat (2).
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The content of this symbolic link is a string containing
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the namespace type and inode number as in the following example:
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.in +4n
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.nf
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$ \fBreadlink /proc/$$/ns/uts\fP
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uts:[4026531838]
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.fi
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.in
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The files in this subdirectory are as follows:
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.TP
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.IR /proc/[pid]/ns/ipc " (since Linux 3.0)"
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This file is a handle for the IPC namespace of the process.
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.TP
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.IR /proc/[pid]/ns/mnt " (since Linux 3.8)"
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This file is a handle for the mount namespace of the process.
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.TP
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.IR /proc/[pid]/ns/net " (since Linux 3.0)"
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This file is a handle for the network namespace of the process.
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.TP
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.IR /proc/[pid]/ns/pid " (since Linux 3.8)"
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This file is a handle for the PID namespace of the process.
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.TP
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.IR /proc/[pid]/ns/user " (since Linux 3.8)"
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This file is a handle for the user namespace of the process.
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.TP
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.IR /proc/[pid]/ns/uts " (since Linux 3.0)"
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2014-09-01 17:00:32 +00:00
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This file is a handle for the UTS namespace of the process.
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2013-02-25 13:00:44 +00:00
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.\"
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.\" ==================== IPC namespaces ====================
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.\"
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2013-01-13 23:45:09 +00:00
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.SS IPC namespaces (CLONE_NEWIPC)
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IPC namespaces isolate certain IPC resources,
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namely, System V IPC objects (see
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.BR svipc (7))
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2013-01-14 03:21:33 +00:00
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and (since Linux 2.6.30)
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.\" commit 7eafd7c74c3f2e67c27621b987b28397110d643f
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.\" https://lwn.net/Articles/312232/
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POSIX message queues (see
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2014-11-02 19:23:55 +00:00
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.BR mq_overview (7)).
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2013-01-14 03:21:33 +00:00
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The common characteristic of these IPC mechanisms is that IPC
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2014-03-14 18:54:00 +00:00
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objects are identified by mechanisms other than filesystem
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2013-01-14 03:21:33 +00:00
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pathnames.
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2013-01-13 23:45:09 +00:00
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Each IPC namespace has its own set of System V IPC identifiers and
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2014-03-14 18:54:00 +00:00
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its own POSIX message queue filesystem.
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2013-01-14 03:21:33 +00:00
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Objects created in an IPC namespace are visible to all other processes
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that are members of that namespace,
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but are not visible to processes in other IPC namespaces.
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2013-03-18 08:42:04 +00:00
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The following
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.I /proc
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interfaces are distinct in each IPC namespace:
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.IP * 3
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The POSIX message queue interfaces in
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.IR /proc/sys/fs/mqueue .
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.IP *
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2014-06-02 13:22:54 +00:00
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The System V IPC interfaces in
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2013-03-18 08:42:04 +00:00
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.IR /proc/sys/kernel ,
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namely:
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.IR msgmax ,
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.IR msgmnb ,
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.IR msgmni ,
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.IR sem ,
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.IR shmall ,
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.IR shmmax ,
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.IR shmmni ,
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and
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.IR shm_rmid_forced .
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.IP *
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2014-06-02 13:22:54 +00:00
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The System V IPC interfaces in
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2013-03-18 08:42:04 +00:00
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.IR /proc/sysvipc .
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.PP
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2013-01-14 03:21:33 +00:00
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When an IPC namespace is destroyed
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(i.e., when the last process that is a member of the namespace terminates),
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all IPC objects in the namespace are automatically destroyed.
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Use of IPC namespaces requires a kernel that is configured with the
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.B CONFIG_IPC_NS
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option.
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2013-02-25 13:00:44 +00:00
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.\"
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.\" ==================== Network namespaces ====================
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.\"
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2013-01-13 23:45:09 +00:00
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.SS Network namespaces (CLONE_NEWNET)
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Network namespaces provide isolation of the system resources associated
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2013-03-05 11:23:26 +00:00
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with networking: network devices, IPv4 and IPv6 protocol stacks,
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IP routing tables, firewalls, the
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2013-01-13 23:45:09 +00:00
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.I /proc/net
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2014-09-21 09:24:24 +00:00
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directory, the
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.I /sys/class/net
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2014-06-02 13:23:13 +00:00
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directory, port numbers (sockets), and so on.
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2013-01-14 03:24:34 +00:00
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A physical network device can live in exactly one
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network namespace.
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A virtual network device ("veth") pair provides a pipe-like abstraction
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.\" FIXME Add pointer to veth(4) page when it is eventually completed
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that can be used to create tunnels between network namespaces,
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and can be used to create a bridge to a physical network device
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in another namespace.
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When a network namespace is freed
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(i.e., when the last process in the namespace terminates),
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its physical network devices are moved back to the
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initial network namespace (not to the parent of the process).
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Use of network namespaces requires a kernel that is configured with the
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.B CONFIG_NET_NS
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option.
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2013-02-25 13:00:44 +00:00
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.\"
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.\" ==================== Mount namespaces ====================
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.\"
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2013-01-14 00:01:21 +00:00
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.SS Mount namespaces (CLONE_NEWNS)
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2014-03-14 18:54:00 +00:00
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Mount namespaces isolate the set of filesystem mount points,
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2013-01-14 00:01:21 +00:00
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meaning that processes in different mount namespaces can
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2014-03-14 18:54:00 +00:00
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have different views of the filesystem hierarchy.
|
2013-01-14 00:01:21 +00:00
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The set of mounts in a mount namespace is modified using
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.BR mount (2)
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and
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.BR umount (2).
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The
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.IR /proc/[pid]/mounts
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file (present since Linux 2.4.19)
|
2014-03-14 18:54:00 +00:00
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lists all the filesystems currently mounted in the
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2013-01-14 00:01:21 +00:00
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process's mount namespace.
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The format of this file is documented in
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.BR fstab (5).
|
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Since kernel version 2.6.15, this file is pollable:
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after opening the file for reading, a change in this file
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2014-03-14 18:54:00 +00:00
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(i.e., a filesystem mount or unmount) causes
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2013-01-14 00:01:21 +00:00
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.BR select (2)
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|
to mark the file descriptor as readable, and
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.BR poll (2)
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and
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.BR epoll_wait (2)
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|
mark the file as having an error condition.
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|
2013-01-14 00:11:55 +00:00
|
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The
|
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.IR /proc/[pid]/mountstats
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file (present since Linux 2.6.17)
|
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|
exports information (statistics, configuration information)
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|
about the mount points in the process's mount namespace.
|
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|
This file is only readable by the owner of the process.
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|
Lines in this file have the form:
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.RS
|
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|
.in 12
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.nf
|
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device /dev/sda7 mounted on /home with fstype ext3 [statistics]
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|
|
|
( 1 ) ( 2 ) (3 ) (4)
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|
.fi
|
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.in
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|
The fields in each line are:
|
|
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|
.TP 5
|
|
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|
(1)
|
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|
The name of the mounted device
|
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|
(or "nodevice" if there is no corresponding device).
|
|
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|
.TP
|
|
|
|
(2)
|
2014-03-14 18:54:00 +00:00
|
|
|
The mount point within the filesystem tree.
|
2013-01-14 00:11:55 +00:00
|
|
|
.TP
|
|
|
|
(3)
|
2014-03-14 18:54:00 +00:00
|
|
|
The filesystem type.
|
2013-01-14 00:11:55 +00:00
|
|
|
.TP
|
|
|
|
(4)
|
|
|
|
Optional statistics and configuration information.
|
2014-03-14 18:54:00 +00:00
|
|
|
Currently (as at Linux 2.6.26), only NFS filesystems export
|
2013-01-14 00:11:55 +00:00
|
|
|
information via this field.
|
|
|
|
.RE
|
2013-02-25 13:00:44 +00:00
|
|
|
.\"
|
|
|
|
.\" ==================== PID namespaces ====================
|
|
|
|
.\"
|
2013-01-13 23:45:09 +00:00
|
|
|
.SS PID namespaces (CLONE_NEWPID)
|
2013-02-27 06:50:25 +00:00
|
|
|
See
|
|
|
|
.BR pid_namespaces (7).
|
2013-02-25 13:00:44 +00:00
|
|
|
.\"
|
|
|
|
.\" ==================== User namespaces ====================
|
|
|
|
.\"
|
2013-01-13 23:45:09 +00:00
|
|
|
.SS User namespaces (CLONE_NEWUSER)
|
2013-02-27 06:08:06 +00:00
|
|
|
See
|
|
|
|
.BR user_namespaces (7).
|
2013-02-25 13:00:44 +00:00
|
|
|
.\"
|
|
|
|
.\" ==================== UTS namespaces ====================
|
|
|
|
.\"
|
2013-01-13 23:45:09 +00:00
|
|
|
.SS UTS namespaces (CLONE_NEWUTS)
|
|
|
|
UTS namespaces provide isolation of two system identifiers:
|
|
|
|
the hostname and the NIS domain name.
|
|
|
|
These identifiers are set using
|
|
|
|
.BR sethostname (2)
|
|
|
|
and
|
|
|
|
.BR setdomainname (2),
|
|
|
|
and can be retrieved using
|
|
|
|
.BR uname (2),
|
|
|
|
.BR gethostname (2),
|
|
|
|
and
|
|
|
|
.BR getdomainname (2).
|
|
|
|
|
2013-01-14 05:14:16 +00:00
|
|
|
Use of UTS namespaces requires a kernel that is configured with the
|
|
|
|
.B CONFIG_UTS_NS
|
|
|
|
option.
|
2013-01-13 23:45:09 +00:00
|
|
|
.SH CONFORMING TO
|
|
|
|
Namespaces are a Linux-specific feature.
|
2013-03-01 07:53:55 +00:00
|
|
|
.SH EXAMPLE
|
|
|
|
See
|
|
|
|
.BR user_namespaces (7).
|
2013-01-13 23:45:09 +00:00
|
|
|
.SH SEE ALSO
|
2013-01-17 19:02:12 +00:00
|
|
|
.BR nsenter (1),
|
2013-01-13 23:45:09 +00:00
|
|
|
.BR readlink (1),
|
2013-01-17 19:02:12 +00:00
|
|
|
.BR unshare (1),
|
2013-01-13 23:45:09 +00:00
|
|
|
.BR clone (2),
|
|
|
|
.BR setns (2),
|
|
|
|
.BR unshare (2),
|
|
|
|
.BR proc (5),
|
|
|
|
.BR credentials (7),
|
2013-02-11 23:13:01 +00:00
|
|
|
.BR capabilities (7),
|
2013-02-27 06:50:25 +00:00
|
|
|
.BR pid_namespaces (7),
|
2013-02-27 06:08:06 +00:00
|
|
|
.BR user_namespaces (7),
|
2013-02-11 23:13:01 +00:00
|
|
|
.BR switch_root (8)
|