NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | VERSIONS | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON
SETFSGID(2) Linux Programmer's Manual SETFSGID(2)
setfsgid - set group identity used for file system checks
#include <unistd.h> /* glibc uses <sys/fsuid.h> */
int setfsgid(uid_t fsgid);
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.
On success, the previous value of fsgid is returned. On error, the current
value of fsgid is returned.
This system call is present in Linux since version 1.2.
setfsgid() is Linux-specific and should not be used in programs intended to be
portable.
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.
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).
kill(2), setfsuid(2), capabilities(7), credentials(7)
This page is part of release 3.23 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)