GETLOGIN(3)

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 arbitrarily.

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)