login, logout - write utmp and wtmp entries
System utilities library (
libutil,
-lutil)
#include <utmp.h>
void login(const struct utmp *ut);
int logout(const char *ut_line);
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.
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 (), 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.
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)