getlogin, cuserid - get user name
char * getlogin ( void );
char * cuserid ( char *string );
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 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 environ
ment variable LOGNAME to find out who the user is. This
is more flexible precisely because the user can set LOG
ENOMEM Insufficient memory to allocate passwd structure.
/etc/passwd password database file
/var/run/utmp (traditionally /etc/utmp;
some libc versions used /var/adm/utmp)
POSIX.1. System V has a cuserid function which uses the
POSIX, but removed from the 1990 version.
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
Nobody knows precisely what cuserid() does - avoid it in
portable programs - avoid it altogether - use getp
wuid(geteuid()) instead, if that is what you meant. DO
NOT USE cuserid().