setreuid(2) System Calls Manual setreuid(2)Name
setreuid - set real and effective user ID's
The real and effective user ID's of the current process are set according to the arguments. If ruid or euid is -1, the current uid is
filled in by the system.
Upon successful completion, a value of zero (0) is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error.
If the process is superuser, or and matches with the real user ID, the effective user ID, or the saved set-user-id (as described in ), then
the real, effective, and the saved set-user-id are set to and respectively.
When your program is compiled in the POSIX or SYSTEM-FIVE mode, if both arguments to are -1, the system call returns a value of -1 and
errno is set to [EINVAL].
The following semantics apply when using the function:
If the process is the superuser, the real, effective, and saved set-user-id (as described in ) are set to and respectively.
If the process is not the superuser, but the and matches with the real user ID, the effective user ID (only in the SYSTEM-FIVE and BSD
environments), or the saved set-user-id, then the effective ID is set to The real user ID and the saved set-user-id are left unchanged.
[EPERM] The current process is not the superuser and the and specified does not match with the real user ID, the effective user ID
(only in SYSTEM-FIVE and BSD environment), or the saved set-user-id.
See Alsogetuid(2), setregid(2), setuid(3)setreuid(2)
Check Out this Related Man Page
SETREUID(2) BSD System Calls Manual SETREUID(2)NAME
setreuid -- set real and effective user ID's
Standard C Library (libc, -lc)
setreuid(uid_t ruid, uid_t euid);
The real and effective user IDs of the current process are set according to the arguments. If ruid or euid is -1, the current uid is filled
in by the system. Unprivileged users may change the real user ID to the effective user ID and vice-versa; only the super-user may make other
If the real user ID is changed (i.e. ruid is not -1) or the effective user ID is changed to something other than the real user ID, then the
saved user ID will be set to the effective user ID.
The setreuid() system call has been used to swap the real and effective user IDs in set-user-ID programs to temporarily relinquish the set-
user-ID value. This purpose is now better served by the use of the seteuid(2) system call.
When setting the real and effective user IDs to the same value, the standard setuid() system call is preferred.
The setreuid() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indi-
cate the error.
[EPERM] The current process is not the super-user and a change other than changing the effective user-id to the real user-id was
SEE ALSO getuid(2), issetugid(2), seteuid(2), setuid(2)HISTORY
The setreuid() system call appeared in 4.2BSD.
BSD February 8, 2001 BSD
I know that in order to get a real user name I should use the following command: cut -d: -f5 /etc/passwd. But how can I get the real user name for those users who are currently logged in to the system??? :confused: Can somebody help me??? (3 Replies)
I would like to know the difference between the real user-id and the
effective user-id. If user-A runs a program owned by user-B then
which is the real user-id and which is the effective user-id ? (1 Reply)
Ok, bear with me on this one, I am a bit new to Unix and it might take me a little bit of time to articulate my question.
I know that every process has a user id and an effective user id. This seems to include the shell itself, because when I type 'ps', I see 'bash' listed as a... (2 Replies)
Despite the exec man page, the exec system call seems to turn my effective-user-id into my real-user-id.
I coded and compiled 2 very simple c programs as user 1 (uid=501)
The first one (A) prints real and effective user IDs and then execs the second one (B), which in turn prints... (7 Replies)