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Linux 2.6 - man page for setns (linux section 2)

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 calling thread with that

       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  con-
       straints imposed by the nstype argument.

       The  nstype argument specifies which type of namespace the calling thread may be reassoci-
       ated 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 names-
       pace  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  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

       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 created 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 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 names-
       pace,  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 3.55 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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