V4/man/man2/setuid.2

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.th SETUID II 8/5/73
.sh NAME
setuid \*- set process user ID
.sh SYNOPSIS
(setuid = 23.)
.br
(user ID in r0)
.ft B
.br
sys setuid
.s3
setuid(uid)
.ft R
.sh DESCRIPTION
The user ID of the current process is set to
the argument.
Both the effective and the real user ID are set.
This call is only permitted to the super-user
or if the argument is the real user ID.
.sh "SEE ALSO"
getuid(II)
.sh DIAGNOSTICS
Error bit
(c-bit) is set as indicated;
from C, a \*-1 value is returned.