setfsgid(2)

1SETFSGID(2)                Linux Programmer's Manual               SETFSGID(2)
2
3
4

NAME

6       setfsgid - set group identity used for file system checks
7

SYNOPSIS

9       #include <unistd.h> /* glibc uses <sys/fsuid.h> */
10
11       int setfsgid(uid_t fsgid);
12

DESCRIPTION

14       The system call setfsgid() sets the group ID that the Linux kernel uses
15       to check for all accesses to the file system. Normally,  the  value  of
16       fsgid  will  shadow the value of the effective group ID. In fact, when‐
17       ever the effective group ID is changed, fsgid will also be  changed  to
18       the new value of the effective group ID.
19
20       Explicit  calls  to  setfsuid() and setfsgid() are usually only used by
21       programs such as the Linux NFS server that need to change what user and
22       group  ID is used for file access without a corresponding change in the
23       real and effective user and group IDs.  A change in the normal user IDs
24       for a program such as the NFS server is a security hole that can expose
25       it to unwanted signals. (But see below.)
26
27       setfsgid() will only succeed if the caller is the superuser or if fsgid
28       matches  either the real group ID, effective group ID, saved set-group-
29       ID, or the current value of fsgid.
30

RETURN VALUE

32       On success, the previous value of fsgid is  returned.   On  error,  the
33       current value of fsgid is returned.
34

CONFORMING TO

36       setfsgid()  is  Linux  specific  and  should  not  be  used in programs
37       intended to be portable.  It is present since Linux 1.1.44 and in  libc
38       since libc 4.7.6.
39

BUGS

41       No  error  messages of any kind are returned to the caller. At the very
42       least, EPERM should be returned when the call fails (because the caller
43       lacks the CAP_SETGID capability).
44

NOTES

46       When  glibc  determines  that  the argument is not a valid group ID, it
47       will return -1 and set errno to EINVAL without  attempting  the  system
48       call.
49
50       Note  that at the time this system call was introduced, a process could
51       send a signal to a process with the same effective user ID.  Today sig‐
52       nal permission handling is slightly different.
53