Manpage of LOGIN

LOGIN

Section: Linux Programmer's Manual (3)
Updated: 2015-04-19
Index
 

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 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 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).
InterfaceAttributeValue
login(),
logout()
Thread safetyMT-Unsafe race:utent
sig:ALRM timer

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(3) and logout(3) 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_userof struct utmpis called ut_namein BSD. Therefore, ut_nameis defined as an alias for ut_userin <utmp.h>.  

SEE ALSO

getutent(3), utmp(5)


 

Index

NAME
SYNOPSIS
DESCRIPTION
GNU details
RETURN VALUE
FILES
ATTRIBUTES
CONFORMING TO
NOTES
SEE ALSO

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Time: 22:27:45 GMT, June 20, 2016