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GETLOGIN(3) Linux Programmer's Manual GETLOGIN(3)
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
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-
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 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 char-
acters of the login name. The user currently logged in on the controlling tty of our pro-
gram 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
Linux 1.2.13 1995-09-03 GETLOGIN(3)
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