setfsgid - set group identity used for file system checks
/* glibc uses <sys/fsuid.h> */
int setfsgid(uid_t fsgid);
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
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)
() 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.)
() will only succeed if the caller is the superuser or if
matches either the real group ID, effective group ID, saved
set-group-ID, or the current value of fsgid
On success, the previous value of fsgid
is returned. On error, the
current value of fsgid
This system call is present in Linux since version 1.2.
() is Linux-specific and should not be used in programs intended
to be portable.
When glibc determines that the argument is not a valid group ID, it will return
-1 and set errno
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.
No error messages of any kind are returned to the caller. At the very least,
should be returned when the call fails (because the caller lacks
This page is part of release 3.44 of the Linux man-pages
description of the project, and information about reporting bugs, can be found