SETFSGID(2)         Linux Programmer's Manual         SETFSGID(2)

       setfsgid - set group identity used for file system checks

       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 effec-
       tive group ID.

       An explicit call to setfsgid is usually only used by  pro-
       grams  such  as  the  Linux NFS server that need to change
       what group ID is used for file  access  without  a  corre-
       sponding  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 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 returned.

       setfsgid  is Linux specific and should not be used in pro-
       grams 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


Linux 1.3.15              6 August 1995                         1