NS_GET_USERNS(2const) - Linux manual page (original) (raw)
NSGETUSERNS(2const) NSGETUSERNS(2const)
NAME top
NS_GET_USERNS, NS_GET_PARENT - discovering namespace relationshipsSYNOPSIS top
**#include <linux/nsfs.h>** /* Definition of **NS_GET_*** constants */
**#include <sys/ioctl.h>**
**int ioctl(int** _fd_**, unsigned long** _op_**);**DESCRIPTION top
The following [ioctl(2)](../man2/ioctl.2.html) operations are provided to allow discovery
of namespace relationships (see [user_namespaces(7)](../man7/user%5Fnamespaces.7.html) and
[pid_namespaces(7)](../man7/pid%5Fnamespaces.7.html)).
In each case, _fd_ refers to a _/proc/_pid_/ns/*_ file. Both operations
return a new file descriptor on success.
**NS_GET_USERNS**
Returns a file descriptor that refers to the owning user
namespace for the namespace referred to by _fd_.
**NS_GET_PARENT**
Returns a file descriptor that refers to the parent
namespace of the namespace referred to by _fd_. This
operation is valid only for hierarchical namespaces (i.e.,
PID and user namespaces). For user namespaces,
**NS_GET_PARENT** is synonymous with **NS_GET_USERNS**.
The new file descriptor returned by these operations is opened
with the **O_RDONLY** and **O_CLOEXEC** (close-on-exec; see [fcntl(2)](../man2/fcntl.2.html))
flags.
By applying [fstat(2)](../man2/fstat.2.html) to the returned file descriptor, one obtains
a _stat_ structure whose _stdev_ (resident device) and _stino_ (inode
number) fields together identify the owning/parent namespace.
This inode number can be matched with the inode number of another
_/proc/_pid_/ns/_{_pid_,_user_} file to determine whether that is the
owning/parent namespace.RETURN VALUE top
On success, a file descriptor is returned. Or error, -1 is
returned, and _[errno](../man3/errno.3.html)_ is set to indicate the error.ERRORS top
**EPERM** The requested namespace is outside of the caller's
namespace scope. This error can occur if, for example, the
owning user namespace is an ancestor of the caller's
current user namespace. It can also occur on attempts to
obtain the parent of the initial user or PID namespace.
**ENOTTY** The operation is not supported by this kernel version.
Additionally, the **NS_GET_PARENT** operation can fail with the
following error:
**EINVAL** _fd_ refers to a nonhierarchical namespace.STANDARDS top
Linux.HISTORY top
**NS_GET_USERNS**
Linux 4.9.
**NS_GET_PARENT**
Linux 4.9.EXAMPLES top
The example shown below uses the [ioctl(2)](../man2/ioctl.2.html) operations described
above to perform simple discovery of namespace relationships. The
following shell sessions show various examples of the use of this
program.
Trying to get the parent of the initial user namespace fails,
since it has no parent:
$ **./ns_show /proc/self/ns/user p**
The parent namespace is outside your namespace scope
Create a process running [sleep(1)](../man1/sleep.1.html) that resides in new user and UTS
namespaces, and show that the new UTS namespace is associated with
the new user namespace:
$ **unshare -Uu sleep 1000 &**
[1] 23235
$ **./ns_show /proc/23235/ns/uts u**
Device/Inode of owning user namespace is: [0,3] / 4026532448
$ **readlink /proc/23235/ns/user**
user:[4026532448]
Then show that the parent of the new user namespace in the
preceding example is the initial user namespace:
$ **readlink /proc/self/ns/user**
user:[4026531837]
$ **./ns_show /proc/23235/ns/user p**
Device/Inode of parent namespace is: [0,3] / 4026531837
Start a shell in a new user namespace, and show that from within
this shell, the parent user namespace can't be discovered.
Similarly, the UTS namespace (which is associated with the initial
user namespace) can't be discovered.
$ **PS1="sh2$ " unshare -U bash**
sh2$ **./ns_show /proc/self/ns/user p**
The parent namespace is outside your namespace scope
sh2$ **./ns_show /proc/self/ns/uts u**
The owning user namespace is outside your namespace scopeProgram source
/* ns_show.c
Licensed under the GNU General Public License v2 or later.
*/
#include <errno.h>
#include <fcntl.h>
#include <linux/nsfs.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/sysmacros.h>
#include <unistd.h>
int
main(int argc, char *argv[])
{
int fd, userns_fd, parent_fd;
struct stat sb;
if (argc < 2) {
fprintf(stderr, "Usage: %s /proc/[pid]/ns/[file] [p|u]\n",
argv[0]);
fprintf(stderr, "\nDisplay the result of one or both "
"of NS_GET_USERNS (u) or NS_GET_PARENT (p)\n"
"for the specified /proc/[pid]/ns/[file]. If neither "
"'p' nor 'u' is specified,\n"
"NS_GET_USERNS is the default.\n");
exit(EXIT_FAILURE);
}
/* Obtain a file descriptor for the 'ns' file specified
in argv[1]. */
fd = open(argv[1], O_RDONLY);
if (fd == -1) {
perror("open");
exit(EXIT_FAILURE);
}
/* Obtain a file descriptor for the owning user namespace and
then obtain and display the inode number of that namespace. */
if (argc < 3 || strchr(argv[2], 'u')) {
userns_fd = ioctl(fd, NS_GET_USERNS);
if (userns_fd == -1) {
if (errno == EPERM)
printf("The owning user namespace is outside "
"your namespace scope\n");
else
perror("ioctl-NS_GET_USERNS");
exit(EXIT_FAILURE);
}
if (fstat(userns_fd, &sb) == -1) {
perror("fstat-userns");
exit(EXIT_FAILURE);
}
printf("Device/Inode of owning user namespace is: "
"[%x,%x] / %ju\n",
major(sb.st_dev),
minor(sb.st_dev),
(uintmax_t) sb.st_ino);
close(userns_fd);
}
/* Obtain a file descriptor for the parent namespace and
then obtain and display the inode number of that namespace. */
if (argc > 2 && strchr(argv[2], 'p')) {
parent_fd = ioctl(fd, NS_GET_PARENT);
if (parent_fd == -1) {
if (errno == EINVAL)
printf("Can' get parent namespace of a "
"nonhierarchical namespace\n");
else if (errno == EPERM)
printf("The parent namespace is outside "
"your namespace scope\n");
else
perror("ioctl-NS_GET_PARENT");
exit(EXIT_FAILURE);
}
if (fstat(parent_fd, &sb) == -1) {
perror("fstat-parentns");
exit(EXIT_FAILURE);
}
printf("Device/Inode of parent namespace is: [%x,%x] / %ju\n",
major(sb.st_dev),
minor(sb.st_dev),
(uintmax_t) sb.st_ino);
close(parent_fd);
}
exit(EXIT_SUCCESS);
}SEE ALSO top
[ioctl(2)](../man2/ioctl.2.html), [ioctl_nsfs(2)](../man2/ioctl%5Fnsfs.2.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-06-15 NSGETUSERNS(2const)
Pages that refer to this page:ioctl_nsfs(2)