Manpage of LOGIN
LOGINSection: Linux Programmer's Manual (3)
NAMElogin, logout - write utmp and wtmp entries
void login(const struct utmp *ut);
int logout(const char *ut_line);
DESCRIPTIONThe 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.
GNU detailsMore precisely, login() takes the argument utstruct, 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, stderrthat 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_lineargument. If a record is found, it is updated by zeroing out the ut_nameand ut_hostfields, updating the ut_tvtimestamp field and setting ut_type(if there is such a field) to DEAD_PROCESS.
RETURN VALUEThe logout() function returns 1 if the entry was successfully written to the database, or 0 if an error occurred.
- user accounting database, configured through _PATH_UTMPin <paths.h>
- user accounting log file, configured through _PATH_WTMPin <paths.h>
ATTRIBUTESFor an explanation of the terms used in this section, see attributes(7).
|Thread safety||MT-Unsafe race:utent
In the above table, utentin race:utentsignifies 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 TONot in POSIX.1. Present on the BSDs.
NOTESNote that the member ut_userof struct utmpis called ut_namein BSD. Therefore, ut_nameis defined as an alias for ut_userin <utmp.h>.
SEE ALSOgetutent(3), utmp(5)
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