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

       setns - reassociate thread with a namespace

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

       int setns(int fd, int nstype);

       Given a file descriptor referring to a namespace, reassociate the call‐
       ing 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 infor‐
       mation 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.

	      fd must refer to an IPC namespace.

	      fd must refer to a network namespace.

	      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.)

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

       EBADF  fd is not a valid file descriptor.

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

       ENOMEM Cannot allocate sufficient memory to change the specified names‐

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

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

       The setns() system call is Linux-specific.

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

       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

       The  following shell session demonstrates the use of this program (com‐
       piled 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

       We begin by executing the example program  in  clone(2)	in  the	 back‐
       ground.	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
	   # ./newuts bizarro &
	   [1] 3549
	   clone() returned 3550
	   uts.nodename in child:  bizarro
	   uts.nodename in parent: antero
	   # uname -n		  # Verify hostname in the shell

       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

   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)

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

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

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

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

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

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

       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

Linux				  2013-01-01			      SETNS(2)

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