1SETNS(2) Linux Programmer's Manual SETNS(2)
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6 setns - reassociate thread with a namespace
7
9 #define _GNU_SOURCE /* See feature_test_macros(7) */
10 #include <sched.h>
11 int setns(int fd, int nstype);
13
15 Given a file descriptor referring to a namespace, reassociate the call‐
16 ing thread with that namespace.
17 The fd argument is a file descriptor referring to one of the namespace
19 entries in a /proc/[pid]/ns/ directory; see proc(5) for further infor‐
20 mation on /proc/[pid]/ns/. The calling thread will be reassociated
21 with the corresponding namespace, subject to any constraints imposed by
22 the nstype argument.
23 The nstype argument specifies which type of namespace the calling
25 thread may be reassociated with. This argument can have one of the
26 following values:
27 0 Allow any type of namespace to be joined.
29 CLONE_NEWIPC
31 fd must refer to an IPC namespace.
32 CLONE_NEWNET
34 fd must refer to a network namespace.
35 CLONE_NEWUTS
37 fd must refer to a UTS namespace.
38 Specifying nstype as 0 suffices if the caller knows (or does not care)
40 what type of namespace is referred to by fd. Specifying a nonzero
41 value for nstype is useful if the caller does not know what type of
42 namespace is referred to by fd and wants to ensure that the namespace
43 is of a particular type. (The caller might not know the type of the
44 namespace referred to by fd if the file descriptor was opened by
45 another process and, for example, passed to the caller via a UNIX
46 domain socket.)
47
49 On success, setns() returns 0. On failure, -1 is returned and errno is
50 set to indicate the error.
51
53 EBADF fd is not a valid file descriptor.
54 EINVAL fd refers to a namespace whose type does not match that speci‐
56 fied in nstype, or there is problem with reassociating the the
57 thread with the specified namespace.
58 ENOMEM Cannot allocate sufficient memory to change the specified names‐
60 pace.
61 EPERM The calling thread did not have the required privilege
63 (CAP_SYS_ADMIN) for this operation.
64
66 The setns() system call first appeared in Linux in kernel 3.0; library
67 support was added to glibc in version 2.14.
68
70 The setns() system call is Linux-specific.
71
73 Not all of the attributes that can be shared when a new thread is cre‐
74 ated using clone(2) can be changed using setns().
75
77 The program below takes two or more arguments. The first argument
78 specifies the pathname of a namespace file in an existing
79 /proc/[pid]/ns/ directory. The remaining arguments specify a command
80 and its arguments. The program opens the namespace file, joins that
81 namespace using setns(), and executes the specified command inside that
82 namespace.
83 The following shell session demonstrates the use of this program (com‐
85 piled as a binary named ns_exec) in conjunction with the CLONE_NEWUTS
86 example program in the clone(2) man page (complied as a binary named
87 newuts).
88 We begin by executing the example program in clone(2) in the back‐
90 ground. That program creates a child in a separate UTS namespace. The
91 child changes the hostname in its namespace, and then both processes
92 display the hostnames in their UTS namespaces, so that we can see that
93 they are different.
94 $ su # Need privilege for namespace operations
96 Password:
97 # ./newuts bizarro &
98 [1] 3549
99 clone() returned 3550
100 uts.nodename in child: bizarro
101 uts.nodename in parent: antero
102 # uname -n # Verify hostname in the shell
103 antero
104 We then run the program shown below, using it to execute a shell.
106 Inside that shell, we verify that the hostname is the one set by the
107 child created by the first program:
108 # ./ns_exec /proc/3550/ns/uts /bin/bash
110 # uname -n # Executed in shell started by ns_exec
111 bizarro
112 Program source
114 #define _GNU_SOURCE
115 #include <fcntl.h>
116 #include <sched.h>
117 #include <unistd.h>
118 #include <stdlib.h>
119 #include <stdio.h>
120 #define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \
122 } while (0)
123 int
125 main(int argc, char *argv[])
126 {
127 int fd;
128 if (argc < 3) {
130 fprintf(stderr, "%s /proc/PID/ns/FILE cmd args...\n", argv[0]);
131 exit(EXIT_FAILURE);
132 }
133 fd = open(argv[1], O_RDONLY); /* Get descriptor for namespace */
135 if (fd == -1)
136 errExit("open");
137 if (setns(fd, 0) == -1) /* Join that namespace */
139 errExit("setns");
140 execvp(argv[2], &argv[2]); /* Execute a command in namespace */
142 errExit("execvp");
143 }
144
146 clone(2), fork(2), vfork(2), proc(5), unix(7)
147
149 This page is part of release 3.53 of the Linux man-pages project. A
150 description of the project, and information about reporting bugs, can
151 be found at http://www.kernel.org/doc/man-pages/.
152Linux 2013-01-01 SETNS(2)