NAME
getlogin, cuserid - get user name
SYNOPSIS
#include <unistd.h>
char * getlogin ( void );
#include <stdio.h>
char * cuserid ( char *string );
DESCRIPTION
getlogin returns a pointer to a string containing the name
of the user logged in on the controlling terminal of the
process, or a null pointer if this information cannot be
determined. The string is statically allocated and might be
overwritten on subsequent calls to this function or to
cuserid.
cuserid returns a pointer to a string containing a user name
associated with the effective user ID of the process. If
string is not a null pointer, it should be an array that can
hold at least L_cuserid characters; the string is returned
in this array. Otherwise, a pointer to a string in a static
area is returned. This string is statically allocated and
might be overwritten on subsequent calls to this function or
to getlogin.
The macro L_cuserid is an integer constant that indicates
how long an array you might need to store a user name.
L_cuserid is declared in stdio.h.
These functions let your program identify positively the
user who is running (cuserid) or the user who logged in this
session (getlogin). (These can differ when setuid programs
are involved.) The user cannot do anything to fool these
functions.
For most purposes, it is more useful to use the environment
variable LOGNAME to find out who the user is. This is more
flexible precisely because the user can set LOGNAME arbi-
trarily.
ERRORS
ENOMEM
Insufficient memory to allocate passwd structure.
FILES
/etc/passwd password database file
/etc/utmp (or /var/adm/utmp, or wherever your utmp file
lives these days - the proper location depends on your libc
version)
CONFORMING TO
POSIX.1. System V has a cuserid function which uses the
real user ID rather than the effective user ID. The cuserid
function was included in the 1988 version of POSIX, but
removed from the 1990 version.
BUGS
Unfortunately, it is often rather easy to fool getlogin().
Sometimes it does not work at all, because some program
messed up the utmp file. Often, it gives only the first 8
characters of the login name. The user currently logged in
on the controlling tty of our program need not be the user
who started it.
Nobody knows precisely what cuserid() does - avoid it in
portable programs - avoid it altogether - use
getpwuid(geteuid()) instead, if that is what you meant. DO
NOT USE cuserid().
SEE ALSO
geteuid(2), getuid(2)