setgroups (2)
Leading comments
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NAME
getgroups, setgroups - get/set list of supplementary group IDsSYNOPSIS
#include <sys/types.h>#include <unistd.h>
int getgroups(int size, gid_t list[]);
#include <grp.h>
int setgroups(size_t size, const gid_t *list);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
setgroups(): _BSD_SOURCE
DESCRIPTION
getgroups()
returns the supplementary group IDs of the calling process in
list.
The argument
size
should be set to the maximum number of items that can be stored in the
buffer pointed to by
list.
If the calling process is a member of more than
size
supplementary groups, then an error results.
It is unspecified whether the effective group ID of the calling process
is included in the returned list.
(Thus, an application should also call
getegid(2)
and add or remove the resulting value.)
If
size
is zero,
list
is not modified, but the total number of supplementary group IDs for the
process is returned.
This allows the caller to determine the size of a dynamically allocated
list
to be used in a further call to
getgroups().
setgroups() sets the supplementary group IDs for the calling process. Appropriate privileges (Linux: the CAP_SETGID capability) are required. The size argument specifies the number of supplementary group IDs in the buffer pointed to by list.
RETURN VALUE
On success, getgroups() returns the number of supplementary group IDs. On error, -1 is returned, and errno is set appropriately.On success, setgroups() returns 0. On error, -1 is returned, and errno is set appropriately.
ERRORS
- EFAULT
- list has an invalid address.
getgroups() can additionally fail with the following error:
- EINVAL
- size is less than the number of supplementary group IDs, but is not zero.
setgroups() can additionally fail with the following errors:
- EINVAL
- size is greater than NGROUPS_MAX (32 before Linux 2.6.4; 65536 since Linux 2.6.4).
- ENOMEM
- Out of memory.
- EPERM
- The calling process has insufficient privilege (it does not have the CAP_SETGID capability).
- EPERM (since Linux 3.19)
- The use of setgroups() is denied in this user namespace. See the description of /proc/[pid]/setgroups in user_namespaces(7).
CONFORMING TO
SVr4, 4.3BSD. The getgroups() function is in POSIX.1-2001 and POSIX.1-2008. Since setgroups() requires privilege, it is not covered by POSIX.1.NOTES
A process can have up to NGROUPS_MAX supplementary group IDs in addition to the effective group ID. The constant NGROUPS_MAX is defined in <limits.h>. The set of supplementary group IDs is inherited from the parent process, and preserved across an execve(2).The maximum number of supplementary group IDs can be found at run time using sysconf(3):
long ngroups_max;
ngroups_max = sysconf(_SC_NGROUPS_MAX);
The maximum return value of
getgroups()
cannot be larger than one more than this value.
Since Linux 2.6.4, the maximum number of supplementary group IDs is also
exposed via the Linux-specific read-only file,
/proc/sys/kernel/ngroups_max.
The original Linux getgroups() system call supported only 16-bit group IDs. Subsequently, Linux 2.4 added getgroups32(), supporting 32-bit IDs. The glibc getgroups() wrapper function transparently deals with the variation across kernel versions.