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]](../stylesheet/note.png) |
Note |
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Link with |
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_UTMPin<paths.h> /var/log/wtmp-
user accounting log file, configured through
_PATH_WTMPin<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.
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>