4.2BSD/usr/man/man2/setregid.2

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.TH SETREGID 2 "12 February 1983"
.UC 4
.SH NAME
setregid \- set real and effective group ID
.SH SYNOPSIS
.ft B
setregid(rgid, egid)
.br
int rgid, egid;
.ft R
.SH DESCRIPTION
The real and effective group ID's of the current process
are set to the arguments.
Only the super-user may change the real group ID
of a process.  Unpriviledged users may change the
effective group ID to the real group ID, but to
no other.
.PP
Supplying a value of \-1 for either the real or effective
group ID forces the system to substitute the current
ID in place of the \-1 parameter.
.SH "RETURN VALUE
Upon successful completion, a value of 0 is returned.  Otherwise,
a value of \-1 is returned and \fIerrno\fP is set to indicate the error.
.SH "ERRORS
.TP 15
[EPERM]
The current process is not the super-user and a change
other than changing the effective group-id to the real group-id
was specified.
.SH "SEE ALSO"
getgid(2), setreuid(2), setgid(3)