setfsgid - set group identity used for file system checks
#include <unistd.h> /* glibc uses <sys/fsuid.h> */
int setfsgid(uid_t fsgid);
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
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-groupID,
or the current value of fsgid.
On success, the previous value of fsgid is returned. On error, the
current value of fsgid is returned.
setfsgid is Linux specific and should not be used in programs intended
to be portable.
No error messages of any kind are returned to the caller. At the very
least, EPERM should be returned when the call fails.
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.
Linux 1.3.15 1995-08-06 SETFSGID(2)
[ Back ]