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NAME

       setns - reassociate thread with a namespace

SYNOPSIS

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

       int setns(int fd, int nstype);

DESCRIPTION

       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

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

ERRORS

       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

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

CONFORMING TO

       The setns() system call is Linux-specific.

NOTES

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

EXAMPLE

       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...
", 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

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

COLOPHON

       This page is part of release 3.65 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/.



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