login(3) — Linux manual pages

Linux manual pages	Section 3

Name

Synopsis

#include <utmp.h>

void login( const struct utmp *ut);

int logout( const char *ut_line);

	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 tty, 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 tty 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>

CONFORMING TO

Not in POSIX.1-2001. 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>

COLOPHON

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