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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | FILES | ATTRIBUTES | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
LOGIN(3) Linux Programmer's Manual LOGIN(3)
login, logout - write utmp and wtmp entries
#include <utmp.h>
void login(const struct utmp *ut);
int logout(const char *ut_line);
Link with -lutil.
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.
The logout() function returns 1 if the entry was successfully written
to the database, or 0 if an error occurred.
/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>
For an explanation of the terms used in this section, see
attributes(7).
┌──────────┬───────────────┬──────────────────────┐
│Interface │ Attribute │ Value │
├──────────┼───────────────┼──────────────────────┤
│login(), │ Thread safety │ MT-Unsafe race:utent │
│logout() │ │ 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.
Not in POSIX.1. Present on the BSDs.
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>.
getutent(3), utmp(5)
This page is part of release 4.12 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/.
GNU 2016-10-08 LOGIN(3)
Pages that refer to this page: utmp(5)