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home | helpx minix x x minixx SETNS(2) Linux Programmer's Manual SETNS(2) 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 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 namespaces(7) for further information on /proc/[pid]/ns/. The calling thread will be reassoci- ated with the corresponding namespace, subject to any constraints im- posed 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_NEWCGROUP (since Linux 4.6) fd must refer to a cgroup namespace. CLONE_NEWIPC (since Linux 3.0) fd must refer to an IPC namespace. CLONE_NEWNET (since Linux 3.0) fd must refer to a network namespace. CLONE_NEWNS (since Linux 3.8) fd must refer to a mount namespace. CLONE_NEWPID (since Linux 3.8) fd must refer to a descendant PID namespace. CLONE_NEWUSER (since Linux 3.8) fd must refer to a user namespace. CLONE_NEWUTS (since Linux 3.0) 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 an- other process and, for example, passed to the caller via a UNIX domain socket.) Details for specific namespace types Note the following details and restrictions when reassociating with specific namespace types: User namespaces A process reassociating itself with a user namespace must have the CAP_SYS_ADMIN capability in the target user namespace. (This necessarily implies that it is only possible to join a de- scendant user namespace.) Upon successfully joining a user namespace, a process is granted all capabilities in that name- space, regardless of its user and group IDs. A multithreaded process may not change user namespace with setns(). It is not permitted to use setns() to reenter the caller's cur- rent user namespace. This prevents a caller that has dropped capabilities from regaining those capabilities via a call to setns(). For security reasons, a process can't join a new user namespace if it is sharing filesystem-related attributes (the attributes whose sharing is controlled by the clone(2) CLONE_FS flag) with another process. For further details on user namespaces, see user_namespaces(7). Mount namespaces Changing the mount namespace requires that the caller possess both CAP_SYS_CHROOT and CAP_SYS_ADMIN capabilities in its own user namespace and CAP_SYS_ADMIN in the user namespace that owns the target mount namespace. A process can't join a new mount namespace if it is sharing filesystem-related attributes (the attributes whose sharing is controlled by the clone(2) CLONE_FS flag) with another process. See user_namespaces(7) for details on the interaction of user namespaces and mount namespaces. PID namespaces In order to reassociate itself with a new PID namespace, the caller must have the CAP_SYS_ADMIN capability both in its own user namespace and in the user namespace that owns the target PID namespace. If fd refers to a PID namespace, the semantics are somewhat dif- ferent from other namespace types: reassociating the calling thread with a PID namespace changes only the PID namespace that subsequently created child processes of the caller will be placed in; it does not change the PID namespace of the caller itself. Reassociating with a PID namespace is allowed only if the PID namespace specified by fd is a descendant (child, grandchild, etc.) of the PID namespace of the caller. For further details on PID namespaces, see pid_namespaces(7). Cgroup namespaces In order to reassociate itself with a new cgroup namespace, the caller must have the CAP_SYS_ADMIN capability both in its own user namespace and in the user namespace that owns the target cgroup namespace. Using setns() to change the caller's cgroup namespace does not change the caller's cgroup memberships. Network, IPC, and UTS namespaces In order to reassociate itself with a new network, IPC, or UTS namespace, the caller must have the CAP_SYS_ADMIN capability both in its own user namespace and in the user namespace that owns the target namespace. 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 speci- fied in nstype. EINVAL There is problem with reassociating the thread with the speci- fied namespace. EINVAL The caller tried to join an ancestor (parent, grandparent, and so on) PID namespace. EINVAL The caller attempted to join the user namespace in which it is already a member. EINVAL The caller shares filesystem (CLONE_FS) state (in particular, the root directory) with other processes and tried to join a new user namespace. EINVAL The caller is multithreaded and tried to join a new user name- space. ENOMEM Cannot allocate sufficient memory to change the specified name- space. EPERM The calling thread did not have the required capability 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 cre- ated 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 (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 newuts). 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 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. In- side 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...\n", argv[0]); exit(EXIT_FAILURE); } fd = open(argv[1], O_RDONLY); /* Get file 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 nsenter(1), clone(2), fork(2), unshare(2), vfork(2), namespaces(7), unix(7) COLOPHON This page is part of release 5.05 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. Linux 2019-10-10 SETNS(2)
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON