SETREUID(2) BSD Programmer's Manual SETREUID(2)
setreuid - set real and effective user ID's
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 effec-
tive user ID and vice-versa; only the super-user may make other changes.
The setreuid() function 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()
function (see setuid(2)).
When setting the real and effective user IDs to the same value, the stan-
dard setuid() function is preferred.
Upon successful completion, a value of 0 is returned. Otherwise, a value
of -1 is returned and errno is set to indicate 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
getuid(2), seteuid(2), setuid(2)
The setreuid function call appeared in 4.2BSD and was dropped in 4.4BSD.
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