SETFSGID - phpMan

SETFSGID(2) Linux Programmer’s Manual SETFSGID(2)

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 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.

CONFORMING TO
setfsgid is Linux specific and should not be used in programs intended to be
portable. It is present since Linux 1.1.44 and in libc since libc 4.7.6.

BUGS
No error messages of any kind are returned to the caller. At the very least, EPERM
should be returned when the call fails.

NOTES
When glibc determines that the argument is not a valid gid, 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 sig-
nal to a process with the same effective user ID. Today signal permission handling
is slightly different.