Originální popis anglicky:
getlogin, getlogin_r, cuserid - get user name
Návod, kniha: Linux Programmer's Manual
#include <unistd.h>
char *getlogin(void);
int getlogin_r(char *buf, size_t bufsize);
#include <stdio.h>
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.
getlogin_r returns this same user name in the array
buf of size
bufsize.
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.
getlogin returns a pointer to the user name when successful, and NULL on
failure.
getlogin_r returns 0 when successful, and nonzero on failure.
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 final
NUL, is larger than bufsize.
Linux/glibc also has
- ENOENT
- There was no corresponding entry in the utmp-file.
- 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.
OpenBSD has
getlogin and
setlogin, and a username associated with
a session, even if it has no controlling tty.
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.
Note that glibc does not follow the POSIX spec and uses stdin instead of
/dev/tty. A bug. (Other recent systems, like SunOS 5.8 and HPUX 11.11
and FreeBSD 4.8 all return the login name also when stdin is redirected.)
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().
geteuid(2),
getuid(2)
