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       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


       The  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_UTMP in <paths.h>

              user accounting log file, configured through _PATH_WTMP in <paths.h>


       For an explanation of the terms used in this section, see attributes(7).

       │InterfaceAttributeValue                │
       │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(3) and logout(3) 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)


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