NAME
getlogin(), getlogin_r() — get name of user logged in on this terminal
SYNOPSIS
#include <unistd.h>
char *getlogin(void);
int getlogin_r(char *buf, size_t buflen);
DESCRIPTION
The
getlogin()
function retrieves the name of the user currently logged in on
a terminal associated with the calling process, as found in
user-accounting database maintained by
utmpd(1M).
At least one of the standard input,
standard output, or standard error
must be a terminal.
For the first of these found that is a terminal,
a user must have logged in on that terminal,
and that terminal must be the controlling terminal of
the session leader process of the calling process's
session.
The
getlogin()
function can be used in conjunction with
getpwnam()
to locate the correct password file entry when the same user
ID is shared by several login names.
The recommended procedure to obtain the user name
associated with the real user
ID of the calling process is to call
getlogin(),
and if that fails, to call
getpwuid(getuid()).
To get the user name associated with the effective user ID, call
getpwuid(geteuid()).
getlogin_r()
performs the same operations as
getlogin(),
but returns the login name in the buffer to which
buf
points, whose size in bytes should be passed in
buflen.
buf
should have space for the name and the terminating null character.
The maximum size of the login name can be obtained using the
sysconf()
API with
_SC_LOGIN_NAME_MAX
as the argument.
APPLICATION USAGE
The return value from
getlogin()
points to static data whose content is overwritten by each call.
RETURN VALUE
Upon successfully finding and validating the login name of the user
logged in on the terminal,
getlogin()
returns a pointer to the name.
Otherwise, it returns a null
pointer, and sets
errno
to indicate the error.
Upon successfully finding, validating, and copying to the buffer the login
name of the user
logged in on the terminal,
getlogin_r()
returns 0 upon success and returns an error number upon failure.
ERRORS
getlogin()
and
getlogin_r()
fail if any of the following is true:
- [EACCES]
Access permission to get the status of the
terminal device file, was denied.
- [EMFILE]
Too many file descriptors are in use by this process.
- [ENFILE]
Too many file descriptors are in use on the system.
- [ENOENT]
The terminal device file cannot be found.
- [ENOTTY]
None of the standard input, standard output,
or standard error is a terminal,
or for the first of these that is a terminal, no current login is
registered on that terminal, or the session leader process of the
calling process has no controlling terminal.
- [EPERM]
One of the standard input, standard output,
or standard error is a terminal,
and a current login was found on that terminal,
but that terminal is not the
same as the controlling terminal of the session of the calling process.
- [ESRCH]
The session leader process of the calling process is no longer running.
The error condition associated with [EPERM]
prevents processes that have access to some other user's terminal
from believing that they are related to that other user's login session.
getlogin_r()
also fails if the following is true:
- [ERANGE]
The length of the name to be returned,
including the terminating null byte,
exceeds
buflen.
WARNINGS
Users of
getlogin_r()
should note
getlogin_r()
now conforms with the POSIX.1c Threads
standard. The old prototype of
getlogin_r()
is supported for compatibility with existing DCE applications only.
STANDARDS CONFORMANCE
getlogin(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1
getlogin_r(): POSIX.1c
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