getlogin, cuserid - get user name
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.
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
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.
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 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.
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().