NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON

SETNS(2)                  Linux Programmer's Manual                 SETNS(2)

NAME         top

       setns - reassociate thread with a namespace

SYNOPSIS         top

       #define _GNU_SOURCE             /* See feature_test_macros(7) */
       #include <sched.h>

       int setns(int fd, int nstype);

DESCRIPTION         top

       Given a file descriptor referring to a namespace, reassociate the
       calling thread with that namespace.

       The fd argument is a file descriptor referring to one of the
       namespace entries in a /proc/[pid]/ns/ directory; see proc(5) for
       further information on /proc/[pid]/ns/.  The calling thread will be
       reassociated with the corresponding namespace, subject to any
       constraints imposed by the nstype argument.

       The nstype argument specifies which type of namespace the calling
       thread may be reassociated with.  This argument can have one of the
       following values:

       0      Allow any type of namespace to be joined.

       CLONE_NEWIPC
              fd must refer to an IPC namespace.

       CLONE_NEWNET
              fd must refer to a network namespace.

       CLONE_NEWUTS
              fd must refer to a UTS namespace.

       Specifying nstype as 0 suffices if the caller knows (or does not
       care) what type of namespace is referred to by fd.  Specifying a
       nonzero value for nstype is useful if the caller does not know what
       type of namespace is referred to by fd and wants to ensure that the
       namespace is of a particular type.  (The caller might not know the
       type of the namespace referred to by fd if the file descriptor was
       opened by another process and, for example, passed to the caller via
       a UNIX domain socket.)

RETURN VALUE         top

       On success, setns() returns 0.  On failure, -1 is returned and errno
       is set to indicate the error.

ERRORS         top

       EBADF  fd is not a valid file descriptor.

       EINVAL fd refers to a namespace whose type does not match that
              specified in nstype, or there is problem with reassociating
              the the thread with the specified namespace.

       ENOMEM Cannot allocate sufficient memory to change the specified
              namespace.

       EPERM  The calling thread did not have the required privilege
              (CAP_SYS_ADMIN) for this operation.

VERSIONS         top

       The setns() system call first appeared in Linux in kernel 3.0;
       library support was added to glibc in version 2.14.

CONFORMING TO         top

       The setns() system call is Linux-specific.

NOTES         top

       Not all of the attributes that can be shared when a new thread is
       created using clone(2) can be changed using setns().

EXAMPLE         top

       The program below takes two or more arguments.  The first argument
       specifies the pathname of a namespace file in an existing
       /proc/[pid]/ns/ directory.  The remaining arguments specify a command
       and its arguments.  The program opens the namespace file, joins that
       namespace using setns(), and executes the specified command inside
       that namespace.

       The following shell session demonstrates the use of this program
       (compiled as a binary named ns_exec) in conjunction with the
       CLONE_NEWUTS example program in the clone(2) man page (complied as a
       binary named newuts).

       We begin by executing the example program in clone(2) in the
       background.  That program creates a child in a separate UTS
       namespace.  The child changes the hostname in its namespace, and then
       both processes display the hostnames in their UTS namespaces, so that
       we can see that they are different.

           $ su                   # Need privilege for namespace operations
           Password:
           # ./newuts bizarro &
           [1] 3549
           clone() returned 3550
           uts.nodename in child:  bizarro
           uts.nodename in parent: antero
           # uname -n             # Verify hostname in the shell
           antero

       We then run the program shown below, using it to execute a shell.
       Inside that shell, we verify that the hostname is the one set by the
       child created by the first program:

           # ./ns_exec /proc/3550/ns/uts /bin/bash
           # uname -n             # Executed in shell started by ns_exec
           bizarro

   Program source
       #define _GNU_SOURCE
       #include <fcntl.h>
       #include <sched.h>
       #include <unistd.h>
       #include <stdlib.h>
       #include <stdio.h>

       #define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \
                               } while (0)

       int
       main(int argc, char *argv[])
       {
           int fd;

           if (argc < 3) {
               fprintf(stderr, "%s /proc/PID/ns/FILE cmd args...\n", argv[0]);
               exit(EXIT_FAILURE);
           }

           fd = open(argv[1], O_RDONLY);   /* Get descriptor for namespace */
           if (fd == -1)
               errExit("open");

           if (setns(fd, 0) == -1)         /* Join that namespace */
               errExit("setns");

           execvp(argv[2], &argv[2]);      /* Execute a command in namespace */
           errExit("execvp");
       }

SEE ALSO         top

       clone(2), fork(2), vfork(2), proc(5), unix(7)

COLOPHON         top

       This page is part of release 3.64 of the Linux man-pages project.  A
       description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux                            2013-01-01                         SETNS(2)