NAME¶
setfsgid - set group identity used for file system checks
SYNOPSIS¶
#include <unistd.h> /* glibc uses <sys/fsuid.h> */
int setfsgid(uid_t fsgid);
DESCRIPTION¶
The system call
setfsgid() sets the group ID that the Linux kernel uses
to check for all accesses to the file system. Normally, the value of
fsgid will shadow the value of the effective group ID. In fact,
whenever the effective group ID is changed,
fsgid will also be changed
to the new value of the effective group ID.
Explicit calls to
setfsuid(2) and
setfsgid() are usually only used
by programs such as the Linux NFS server that need to change what user and
group ID is used for file access without a corresponding change in the real
and effective user and group IDs. A change in the normal user IDs for a
program such as the NFS server is a security hole that can expose it to
unwanted signals. (But see below.)
setfsgid() will only succeed if the caller is the superuser or if
fsgid matches either the real group ID, effective group ID, saved
set-group-ID, or the current value of
fsgid.
RETURN VALUE¶
On success, the previous value of
fsgid is returned. On error, the
current value of
fsgid is returned.
VERSIONS¶
This system call is present in Linux since version 1.2.
setfsgid() is Linux-specific and should not be used in programs intended
to be portable.
NOTES¶
When glibc determines that the argument is not a valid group ID, it will return
-1 and set
errno to
EINVAL without attempting the system call.
Note that at the time this system call was introduced, a process could send a
signal to a process with the same effective user ID. Today signal permission
handling is slightly different.
The original Linux
setfsgid() system call supported only 16-bit group
IDs. Subsequently, Linux 2.4 added
setfsgid32() supporting 32-bit IDs.
The glibc
setfsgid() wrapper function transparently deals with the
variation across kernel versions.
BUGS¶
No error messages of any kind are returned to the caller. At the very least,
EPERM should be returned when the call fails (because the caller lacks
the
CAP_SETGID capability).
SEE ALSO¶
kill(2),
setfsuid(2),
capabilities(7),
credentials(7)
COLOPHON¶
This page is part of release 3.44 of the Linux
man-pages project. A
description of the project, and information about reporting bugs, can be found
at
http://www.kernel.org/doc/man-pages/.