GETLOGIN(3)						     Linux Programmer's Manual						       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.)

       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
       /var/run/utmp  (traditionally /etc/utmp;
		      some libc versions used /var/adm/utmp)

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.  Avoid getlogin() for security-related purposes.

       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)

Linux 1.2.13							    1995-09-03							       GETLOGIN(3)