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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.

CONFORMING TO

       setfsgid()  is  Linux-specific  and  should  not  be  used  in programs
       intended to be portable.  It is present since Linux 1.1.44 and in  libc
       since libc 4.7.6.

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 3.01 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/.