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(2) 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.

VERSIONS

       This system call is present in Linux since version 1.2.

CONFORMING TO

       setfsgid() is Linux-specific and should not be used in programs intended to be portable.

NOTES

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

BUGS

       No error messages of any kind are returned to the caller.  At the very least, EPERM should be returned when the	call  fails  (because  the
       caller lacks the CAP_SETGID capability).

SEE ALSO

       kill(2), setfsuid(2), capabilities(7), credentials(7)

COLOPHON

       This  page is part of release 3.27 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2008-12-05							       SETFSGID(2)