V4/usr/man/man2/setgid.2

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.th SETGID II 8/5/73
.sh NAME
setgid \*- set process group ID
.sh SYNOPSIS
(setgid = 46.; not in assembler)
.br
(group ID in r0)
.ft B
.br
sys setgid
.s3
setgid(gid)
.ft R
.sh DESCRIPTION
The group ID of the current process is set to
the argument.
Both the effective and the real group ID are set.
This call is only permitted to the super-user
or if the argument is the real group ID.
.sh "SEE ALSO"
getgid(II)
.sh DIAGNOSTICS
Error bit
(c-bit) is set as indicated;
from C, a \*-1 value is returned.