title: Possible Reasons for Linux SSH hang
body: <p>We have Linux server run java application,this morning the server did not response for the ssh connection.when I ssh -v, it shows " <strong>connection refused by remote host</strong> ".We also have a vnc server run in that Linux and it does not work either.But the ftp server is ok in that server,we can upload file into the server.In the end,we did not found a way to remote connect to the system.</p>
  
  <p>After we reboot the computer on site,the ssh server is working again.But We did not found a clue why ssh is not working? Have someone ever met ssh hang problem like this? Which file should we look into?How to prevent ssh hang? Thanks in advanced.</p>
  
  <p>added:
  I check the log from secure.log.it states many failed attemps like following and i check the ipaddress is not ours:</p>
  
  <pre><code>Feb 23 04:13:30 localhost sshd[1276]: Failed password for invalid user mantis from 112.78.127.235 port 57140 ssh2
  </code></pre>
  
  <p>It seems like the attacker is trying to login into my server all the time until our ssh service is not responding.</p>