Linux manual pages Section 3  

Name

login, logout — write utmp and wtmp entries

Synopsis

#include <utmp.h>
void login( const struct utmp *ut);
 
int logout( const char *ut_line);
 
[Note] Note

Link with −lutil.

DESCRIPTION

The utmp file records who is currently using the system. The wtmp file records all logins and logouts. See utmp(5).

The function login() takes the supplied struct utmp, ut, and writes it to both the utmp and the wtmp file.

The function logout() clears the entry in the utmp file again.

GNU details

More precisely, login() takes the argument ut struct, fills the field ut−>ut_type (if there is such a field) with the value USER_PROCESS, and fills the field ut−>ut_pid (if there is such a field) with the process ID of the calling process. Then it tries to fill the field ut−>ut_line. It takes the first of stdin, stdout, stderr that is a terminal, and stores the corresponding pathname minus a possible leading /dev/ into this field, and then writes the struct to the utmp file. On the other hand, if no terminal name was found, this field is filled with "???" and the struct is not written to the utmp file. After this, the struct is written to the wtmp file.

The logout() function searches the utmp file for an entry matching the ut_line argument. If a record is found, it is updated by zeroing out the ut_name and ut_host fields, updating the ut_tv timestamp field and setting ut_type (if there is such a field) to DEAD_PROCESS.

RETURN VALUE

The logout() function returns 1 if the entry was successfully written to the database, or 0 if an error occurred.

FILES

/var/run/utmp

user accounting database, configured through _PATH_UTMP in <paths.h>

/var/log/wtmp

user accounting log file, configured through _PATH_WTMP in <paths.h>

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value

login(),

logout()

 Thread safety

MT-Unsafe race:utent

sig:ALRM timer

In the above table, utent in race:utent signifies that if any of the functions setutent(3), getutent(3), or endutent(3) are used in parallel in different threads of a program, then data races could occur. login(3) and logout(3) calls those functions, so we use race:utent to remind users.

CONFORMING TO

Not in POSIX.1. Present on the BSDs.

NOTES

Note that the member ut_user of struct utmp is called ut_name in BSD. Therefore, ut_name is defined as an alias for ut_user in <utmp.h>

SEE ALSO

getutent(3), utmp(5)

COLOPHON

This page is part of release 4.07 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man−pages/.


  Derived from text written by Martin Schulze (or taken from glibc.info)
and text written by Paul Thompson - both copyright 2002.

%%%LICENSE_START(GPLv2+_DOC_FULL)
This is free documentation; you can redistribute it and/or
modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2 of
the License, or (at your option) any later version.

The GNU General Public License's references to "object code"
and "executables" are to be interpreted as the output of any
document formatting or typesetting system, including
intermediate and printed output.

This manual is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public
License along with this manual; if not, see
<http://www.gnu.org/licenses/>.
%%%LICENSE_END