| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON | The Linux Programming Interface |
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 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.)
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 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
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 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
#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");
}
clone(2), fork(2), vfork(2), proc(5), unix(7)
This page is part of release 3.51 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)
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