setfsgid - set group identity used for file system checks
#include /* glibc uses
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 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.
On success, the previous value of fsgid is returned.
On error, the current value of fsgid is
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
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.