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.Dd $Mdocdate: July 11 2014 $
.Dt ISSETUGID 2
.Os
.Sh NAME
.Nm issetugid
.Nd is current executable running setuid or setgid
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft int
.Fn issetugid void
.Sh DESCRIPTION
The
.Fn issetugid
function returns 1 if the process was made setuid or setgid as
the result of the last or other previous
.Fn execve
system calls.
Otherwise it returns 0.
.Pp
This system call exists so that library routines (inside libtermlib, libc,
or other libraries) can guarantee safe behavior when used inside
setuid or setgid programs.
Some library routines may be passed insufficient information and hence
not know whether the current program was started setuid or setgid
because higher level calling code may have made changes to the uid, euid,
gid, or egid.
Hence these low-level library routines are unable to determine if they
are being run with elevated or normal privileges.
.Pp
In particular, it is wise to use this call to determine if a
pathname returned from a
.Fn getenv
call may safely be used to
.Fn open
the specified file.
Quite often this is not wise because the status of the effective uid
is not known.
.Pp
The
.Fn issetugid
system call's result is unaffected by calls to
.Fn setuid ,
.Fn setgid ,
or other such calls.
In case of a
.Fn fork ,
the child process inherits the same status.
.Pp
The status of
.Fn issetugid
is only affected by
.Fn execve .
If a child process executes a new executable file, a new issetugid
status will be determined.
This status is based on the existing process's uid, euid, gid,
and egid permissions and on the modes of the executable file.
If the new executable file modes are setuid or setgid, or if
the existing process is executing the new image with
uid != euid or gid != egid, the new process will be considered
issetugid.
.Sh ERRORS
The
.Fn issetugid
function is always successful, and no return value is reserved to
indicate an error.
.Sh SEE ALSO
.Xr execve 2 ,
.Xr setegid 2 ,
.Xr seteuid 2 ,
.Xr setgid 2 ,
.Xr setuid 2 ,
.Xr getenv 3
.Sh HISTORY
The
.Fn issetugid
function call first appeared in
.Ox 2.0 .