[cobalt-users] How To: Automatically restart login services

["Joe Seitzer" <joe@xxxxxxxxxxx>]

I have seen many posts about users who "are not able to telnet or SSH"
into there cobalt's for many reasons.  I was reading an article in Sys
Admin Magazine (www.sysadminmag.com (If you don't read it I would
recommend it, very straight to the point with real world solutions)) by
Hiu F. Ho (plug) that talked about automatically restarting login
services on a remote host.  Below is a synopsis that does work on a RAQ3
and should work on all other cobalt boxes, actually it should work on
any Linux and *nix platform.  The standard disclaimer applies, Use at
your own risk.  I will say that I am using this on my Cobalt, a bunch of
Solaris and some Red Hat 7.0 servers.  

Step 1 - Find out the process name of you login daemon 

$ ps ax 
494 ?   s       0:02 /usr/sbin/shhd 
679 ?   s       0:05 /usr/local/psionic/portsentry/portsentry -atcp 
681 ?   s       0:00 /usr/local/psionic/portsentry/portsentry -audp 

This will list the processes that are currently running on your box.
Look for the name that you are currently looking to automatically start.
i.e. SSH or Telnet (please install SSH if you are still using Telnet).
Write down the process name it will have to be entered into the perl
script later. Also If you don't have the portsentry process running I
would recommend installing it.

Step 2 - Specify the path to the login daemon 

$ which sshd 
/usr/sbin/sshd 

This list the path to the Daemon that you are looking to restart
automatically. White the output down this will also have to be entered
into the perl script.

Step 3 - Copy the perl script to your box. 

#!/usr/bin/perl -w 
#  This script was written by Hiu F. Ho and posted 
#  to Cobalt users by Joe Seitzer (joe@xxxxxxxxxxxxxx) 

# The first line looks for your process 
# name, output from step 1 
# You may need to customize. 

$ps_entry = "/usr/sbin/sshd"; 

# The next line sets the path to the 
# process you want to restart, 
# output from step 2. 
# May need to customize 

$sshd_path = "/usr/sbin/sshd";             
  
# There is nothing else that you need to edit. 
# The next 8 lines will determine if the 
# process you specified is running 
@processes = `ps ax`; 
$n = @processes; 
$is_running = 0; 
for ($i=0; $i<$n; $i++) { 
  if ($processes[$i] =~ /$ps_entry/) { 
    $is_running = 1; 
  } 
} 

# If the process you specified is not running 
# the next 3 lines will start it 
if (not $is_running) { 
   `$sshd_path &`; 
} 



Step 4 - chmod and chown so that it can only be read, written and run by
root. 

$chmod 700 chk-sshd.pl 
$chown root chk-sshd.pl 

Step 5 - Add a new cron job for root or append to one that already
exists. Below is the line you want in the cron tab.  I have it set to
check the sshd every 5 min, you can change this.

0.5.10.15.20.25.30.35.40.45.50.55 * * * * /path to script/chk-sshd.pl 

after you have added the above line re-run crontab to check for errors. 

$ crontab -u root mycrontab 

You are done.  You should now have an almost fool proof login service.  

You can test this by killing the login service and logging back in 5 min
latter. 

$ killall -9 sshd 

After 5 min you should be able to log back into you box.  Remember this
is only good if your Login Daemon stops or is killed.  This will not
help if you lose conductivity, hardware failure, software crash or have
any other problems with your server. 

Enjoy:-) 

Joe Seitzer 
www.pkicentral.net