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Linux 2.6 - man page for setfsgid32 (linux section 2)

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 with-
       out 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.ker-
       nel.org/doc/man-pages/.

Linux					    2008-12-05				      SETFSGID(2)


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