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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 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-12-05                       SETFSGID(2)