получить / установить список дополнительных идентификаторов групп (get/set list of supplementary group IDs)
Имя (Name)
getgroups, setgroups - get/set list of supplementary group IDs
Синопсис (Synopsis)
#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():
Since glibc 2.19:
_DEFAULT_SOURCE
Glibc 2.19 and earlier:
_BSD_SOURCE
Описание (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 are required (see the
description of the EPERM error, below). The size argument
specifies the number of supplementary group IDs in the buffer
pointed to by list. A process can drop all of its supplementary
groups with the call:
setgroups(0, NULL);
Возвращаемое значение (Return value)
On success, getgroups() returns the number of supplementary group
IDs. On error, -1 is returned, and errno is set to indicate the
error.
On success, setgroups() returns 0. On error, -1 is returned, and
errno is set to indicate the error.
Ошибки (Error)
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 (the caller
does not have the CAP_SETGID capability in the user
namespace in which it resides).
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).
Стандарты (Conforming to)
getgroups(): SVr4, 4.3BSD, POSIX.1-2001, POSIX.1-2008.
setgroups(): SVr4, 4.3BSD. Since setgroups() requires privilege,
it is not covered by POSIX.1.
Примечание (Note)
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.
C library/kernel differences
At the kernel level, user IDs and group IDs are a per-thread
attribute. However, POSIX requires that all threads in a process
share the same credentials. The NPTL threading implementation
handles the POSIX requirements by providing wrapper functions for
the various system calls that change process UIDs and GIDs.
These wrapper functions (including the one for setgroups())
employ a signal-based technique to ensure that when one thread
changes credentials, all of the other threads in the process also
change their credentials. For details, see nptl(7).
Смотри также (See also)
getgid(2), setgid(2), getgrouplist(3), group_member(3),
initgroups(3), capabilities(7), credentials(7)
