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Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
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NAME
login, logout - write utmp and wtmp entries
SYNOPSIS
#include <utmp.h>
void login(const struct utmp *ut);
int logout(const char *ut_line);
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()
and
logout()
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 4.13 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- GNU details
-
- RETURN VALUE
-
- FILES
-
- ATTRIBUTES
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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- Running on 
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