GETLOGIN
NAME
getlogin, getlogin_r, cuserid - get user name
SYNOPSIS
#include <unistd.h>
char *getlogin(void);
I int getlogin_r(char * buf , size_t bufsize );
#include <stdio.h>
I char *cuserid(char * string );
DESCRIPTION
R 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
R cuserid ().
R getlogin_r ()
returns this same user name in the array
buf
of size
R bufsize .
R 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
R 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 set-user-ID 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.
RETURN VALUE
R getlogin ()
returns a pointer to the user name when successful,
and NULL on failure.
R getlogin_r ()
returns 0 when successful, and non-zero on failure.
ERRORS
POSIX specifies
EMFILE
The calling process already has the maximum allowed number of open files.
ENFILE
The system already has the maximum allowed number of open files.
ENXIO
The calling process has no controlling tty.
ERANGE
(getlogin_r)
The length of the user name, including the terminating null byte,
is larger than
R bufsize .
Linux/glibc also has
ENOENT
There was no corresponding entry in the utmp-file.
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
R getlogin ()
and
R getlogin_r ()
specified in POSIX.1-2001.
System V has a
R cuserid ()
function which uses the real
user ID rather than the effective user ID.
The
R cuserid ()
function
was included in the 1988 version of POSIX,
but removed from the 1990 version.
It was present in SUSv2, but removed in POSIX.1-2001.
OpenBSD has
R getlogin ()
and
R setlogin (),
and a username
associated with a session, even if it has no controlling tty.
BUGS
Unfortunately, it is often rather easy to fool
R 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
R getlogin ()
for security-related purposes.
Note that glibc does not follow the POSIX spec and uses
stdin
instead of
R /dev/tty .
A bug.
(Other recent systems, like SunOS 5.8 and HP-UX 11.11 and FreeBSD 4.8
all return the login name also when
stdin
is redirected.)
Nobody knows precisely what
R cuserid ()
does; avoid it in portable programs.
Or avoid it altogether: use
getpwuid(geteuid())
instead, if that is
what you meant.
DO NOT USE
R cuserid ().
SEE ALSO
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