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.\" 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.
.\"
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.\" 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, write to the Free
.\" Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139,
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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.
.\"
.TH LOGIN 3 2004-05-06 "GNU" "Linux Programmer's Manual"
.SH NAME
login, logout \- write utmp and wtmp entries
.SH SYNOPSIS
.B #include <utmp.h>
.sp
.BI "void login(const struct utmp *" ut );
.sp
.BI "int logout(const char *" ut_line );
.sp
Link with \fI\-lutil\fP.
.SH DESCRIPTION
The utmp file records who is currently using the system.
The wtmp file records all logins and logouts.
See
.BR utmp (5).
.LP
The function
.BR login ()
takes the supplied \fIstruct utmp\fP,
.IR ut ,
and writes it to both the utmp and the wtmp file.
.LP
The function
.BR logout ()
clears the entry in the utmp file again.
.SS "GNU Details"
More precisely,
.BR login ()
takes the argument
.I ut
struct, fills the field
.I ut\->ut_type
(if there is such a field) with the value
.BR USER_PROCESS ,
and fills the field
.I ut\->ut_pid
(if there is such a field) with the process ID of the calling process.
Then it tries to fill the field
.IR ut\->ut_line .
It takes the first of \fIstdin\fP, \fIstdout\fP, \fIstderr\fP
that is a tty, and
stores the corresponding pathname minus a possible leading \fI/dev/\fP
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.
.LP
The
.BR logout ()
function searches the utmp file for an entry matching the
.I ut_line
argument.
If a record is found, it is updated by zeroing out the
.I ut_name
and
.I ut_host
fields, updating the
.I ut_tv
timestamp field and setting
.I ut_type
(if there is such a field) to
.BR DEAD_PROCESS .
.SH "RETURN VALUE"
The
.BR logout ()
function returns 1 if the entry was successfully written to the
database, or 0 if an error occurred.
.SH FILES
.TP
.I /var/run/utmp
user accounting database, configured through
.B _PATH_UTMP
in
.I <paths.h>
.TP
.I /var/log/wtmp
user accounting log file, configured through
.B _PATH_WTMP
in
.I <paths.h>
.SH "CONFORMING TO"
Not in POSIX.1-2001.
Present on the BSDs.
.SH NOTES
Note that the
member
.I ut_user
of
.I struct utmp
is called
.I ut_name
in BSD.
Therefore,
.I ut_name
is defined as an alias for
.I ut_user
in
.IR <utmp.h> .
.SH "SEE ALSO"
.BR getutent (3),
.BR utmp (5)
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