[ale] Adding entry to utmp

[Joe Steele]

1)  When you use pututent() with type USER_PROCESS, it will first 
search through utmp for an existing entry that matches entry.ut_id, 
if entry.ut_id is not an empty string.  If entry.ut_id is empty, then 
a match will be attempted with entry.ut_line.  If no match is found,
a new entry is added.

I can't tell from your code whether entry is declared static or auto, 
which affects whether it's initialized to zero or not.  If entry is 
uninitialized, then entry.ut_id may be a non-empty string at runtime.  
And by chance, it may be the same non-empty string every time it is 
run.  If so, then the second time it is run will it will match the 
ut_id of the entry that was made the first time it was run, thus 
overwriting it.

2) As for the removal of the entry on logout -- this is handled by 
telnetd (along with an entry in wtmp).

--Joe

-----Original Message-----
From:	Chris Fowler [SMTP:cfowler at outpostsentinel.com]
Sent:	Wednesday, December 12, 2001 4:26 PM
To:	ale at ale.org
Subject:	[ale] Adding entry to utmp

I'm creating my own replacement for login.c and I'm am assuming that it is login's responsibility to add entries to /var/run/utmp.  Basically the standard netkit-telnet 
daemon calls my login program via exec().  My login program continues the process of loging in a user.  Below it my utmp code.

        
       struct utmp entry;
        /* Time to write to UTMP */
        entry.ut_type = USER_PROCESS;
        entry.ut_pid = getpid();
        strcpy(entry.ut_line, ttyname(0) + strlen("/dev/"));
        time(&entry.ut_time);
        strcpy(entry.ut_user, user->username);
        memset(entry.ut_host, 0 , UT_HOSTSIZE);
        entry.ut_addr = 0;

        setutent();
        pututline(&entry);
        endutent();

       /* Do some stuff */
       exec("/bin/sh", "/bin/sh", environ);


Output of who  It will be cleaned up.
Users:
user       port              login         idle   host
root       /dev/ports/kvm      Dec 12 13:24  00:04  local
root       ttyp0             Dec 12 13:30         local

Now if I go to another machine and telnet in again I get the following who output
Users:
user       port              login         idle   host
root       /dev/ports/kvm      Dec 12 13:24  00:04  local
root       ttyp1             Dec 12 13:30         local

It appears to have overwritten my last entry and now I have an invisible user.    What did I do wrong?

I also notice that if I exit from the shell on ttyp1 then the entry is removed.  My login does exec()  so it is not removing the
entry.  Who is? Or is a value changed that my Who skips over?

Thanks,
Chris Fowler


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