title: (unknown) user is always logged in my centos linux machine
body: <p>I was going through logged in user in to my system using who command what i found is very surprising a user named unknown is logged in</p>
  
  <p>Result of command who : </p>
  
  <pre><code> myuser    pts/1        Aug  6 20:27 (localhost)
   (unknown) :0          Aug  5 16:25 (:0) 
   myuser    pts/0        Aug  6 00:48 (localhost.localdomain)
  </code></pre>
  
  <p>But when i tried running w it results different:</p>
  
  <pre><code>20:46:53 up 1 day, 23:11,  3 users,  load average: 1.00, 1.01, 1.05
  USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU WHAT
  myuser    pts/1    localhost        20:27    5.00s  0.20s  0.03s w
  myuser    pts/0    localhost.locald 00:48   19:57m  0.08s  1.71s python2 -m guake.main
  </code></pre>
  
  <p>I am neither able to find any user on my machine named unknown. On trying sudo su unknown/"(unknown)"</p>
  
  <p>I tried running last it shows unknown user still logged in</p>
  
  <pre><code>myuser    pts/1        localhost        Thu Aug  6 20:27   still logged in
  myuser    pts/2        :pts/1:S.0       Thu Aug  6 20:15 - 20:16  (00:00)
  myuser    pts/1        localhost        Thu Aug  6 20:03 - 20:18  (00:15)
  myuser    pts/2        :pts/1:S.0       Thu Aug  6 19:49 - 19:49  (00:00)
  myuser    pts/1        localhost        Thu Aug  6 19:47 - 19:49  (00:02)
  myuser    pts/1        localhost        Thu Aug  6 19:37 - 19:46  (00:09)
  myuser    pts/1        localhost        Thu Aug  6 19:33 - 19:37  (00:03)
  myuser    pts/1        :9               Thu Aug  6 19:32 - 19:33  (00:00)
  myuser    pts/1        localhost        Thu Aug  6 19:26 - 19:32  (00:05)
  myuser    pts/2        :pts/1:S.0       Thu Aug  6 19:22 - 19:22  (00:00)
  myuser    pts/1        localhost        Thu Aug  6 19:22 - 19:22  (00:00)
  myuser    pts/2        :pts/1:S.0       Thu Aug  6 19:15 - 19:16  (00:00)
  myuser    pts/1        localhost        Thu Aug  6 19:15 - 19:16  (00:00)
  myuser    pts/2        :pts/1:S.0       Thu Aug  6 19:13 - 19:13  (00:00)
  myuser    pts/1        localhost        Thu Aug  6 19:13 - 19:13  (00:00)
  myuser    pts/2        :pts/1:S.0       Thu Aug  6 19:12 - 19:13  (00:00)
  myuser    pts/2        :pts/1:S.0       Thu Aug  6 19:11 - 19:11  (00:00)
  myuser    pts/2        :pts/1:S.0       Thu Aug  6 19:10 - 19:10  (00:00)
  myuser    pts/1        localhost        Thu Aug  6 18:37 - 19:13  (00:35)
  myuser    pts/1        localhost        Thu Aug  6 18:17 - 18:21  (00:03)
  myuser    pts/1        localhost        Thu Aug  6 18:09 - 18:13  (00:03)
  myuser    pts/0        localhost.locald Thu Aug  6 00:48   still logged in
  myuser    pts/0        localhost.locald Thu Aug  6 00:34 - 00:48  (00:14)
  myuser    pts/1        :9               Wed Aug  5 23:01 - 23:01  (00:00)
  myuser    pts/0        localhost.locald Wed Aug  5 22:00 - 00:34  (02:34)
  myuser    pts/0        localhost        Wed Aug  5 21:06 - 21:06  (00:00)
  myuser    pts/0        localhost        Wed Aug  5 20:57 - 20:59  (00:01)
  myuser    pts/0        localhost        Wed Aug  5 20:56 - 20:56  (00:00)
  myuser    pts/0        localhost        Wed Aug  5 20:56 - 20:56  (00:00)
  myuser    pts/0        :9               Wed Aug  5 20:55 - 20:56  (00:00)
  myuser    pts/4        localhost        Wed Aug  5 20:14 - 20:55  (00:40)
  myuser    pts/4        localhost        Wed Aug  5 20:11 - 20:12  (00:00)
  myuser    pts/5        localhost        Wed Aug  5 19:52 - 19:56  (00:04)
  myuser    pts/4        localhost        Wed Aug  5 19:29 - 19:31  (00:02)
  myuser    pts/2        localhost        Wed Aug  5 18:42 - 19:32  (00:49)
  myuser    pts/2        localhost        Wed Aug  5 18:42 - 18:42  (00:00)
  myuser    pts/3        :9               Wed Aug  5 18:38 - 18:42  (00:04)
  myuser    pts/3        localhost        Wed Aug  5 16:28 - 16:28  (00:00)
  myuser    pts/2        :9               Wed Aug  5 16:26 - 16:28  (00:02)
  (unknown :0           :0               Wed Aug  5 16:25   still logged in
  </code></pre>
  
  <p>Any idea how ?</p>