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
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 new value of effective group ID. An explicit call to setfsgid is usually only used by programs such as the Linux NFS server that need to change what group ID is used for file access without a corresponding change in the real and effective group IDs. A change in the normal group IDs for a program such as the NFS server is a security hole that can expose it to unwanted signals from other group IDs. 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.

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

NOTE
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.

SEE ALSO
setfsuid(2)