title: How to change MTU setting permanently
body: <p>I need to permanently change <code>MTU</code> to <code>1500</code>. By permanently I mean if I reboot the system or will do <code>service network restart</code> it will alway be <code>1500</code>.</p>
  
  <p>I followed this article <a href="http://www.cyberciti.biz/faq/centos-rhel-redhat-fedora-debian-linux-mtu-size/" rel="noreferrer">http://www.cyberciti.biz/faq/centos-rhel-redhat-fedora-debian-linux-mtu-size/</a></p>
  
  <p>But unfortunately it doens't work for me.</p>
  
  <p>Here is what I did:</p>
  
  <p>check current <code>MTU</code> :</p>
  
  <pre><code>eth0: &lt;BROADCAST,MULTICAST,UP,LOWER_UP&gt; mtu 9001 qdisc pfifo_fast state UP qlen 1000 
  </code></pre>
  
  <p>Added <code>MTU="1500"</code> to <code>/etc/sysconfig/network-scripts/ifcfg-eth0</code>:</p>
  
  <pre><code>[root@ip-xx-xx-xxx~]# cat /etc/sysconfig/network-scripts/ifcfg-eth0
  DEVICE=eth0
  BOOTPROTO=dhcp
  ONBOOT=yes
  TYPE=Ethernet
  USERCTL=yes
  PEERDNS=yes
  IPV6INIT=no
  PERSISTENT_DHCLIENT=yes
  IPV6_MTU="1500"
  MTU="1500"
  </code></pre>
  
  <p>Then check <code>MTU</code> again, ( no luck ):</p>
  
  <pre><code>root@ip-xx-xx-xxx ~]# service network restart 
  Shutting down interface eth0:                              [  OK  ]
  Shutting down loopback interface:                          [  OK  ]
  Bringing up loopback interface:                            [  OK  ]
  Bringing up interface eth0:  
  Determining IP information for eth0... done.
                                                             [  OK  ]
  [root@ip-xx-xx-xxx ~]# ip addr show eth0 
  2: eth0: &lt;BROADCAST,MULTICAST,UP,LOWER_UP&gt; mtu 9001 qdisc pfifo_fast state UP qlen 1000
  </code></pre>
  
  <p><code>/sbin/ifconfig</code> changed <code>MTU</code> but only temporally </p>
  
  <pre><code>[root@ip-xx-xx-xxx ~]# /sbin/ifconfig eth0 mtu 1500 up
  [root@ip-xx-xx-xxx ~]# ip addr show eth0 
  2: eth0: &lt;BROADCAST,MULTICAST,UP,LOWER_UP&gt; mtu 1500 qdisc pfifo_fast state UP qlen 1000
  </code></pre>
  
  <p>If i restart <code>network</code> it is 9001 again:</p>
  
  <pre><code>[root@ip-xx-xx-xxx ~]# service network restart 
  Shutting down interface eth0:                              [  OK  ]
  Shutting down loopback interface:                          [  OK  ]
  Bringing up loopback interface:                            [  OK  ]
  Bringing up interface eth0:  
  Determining IP information for eth0... done.
                                                             [  OK  ]
  [root@ip-10-0-1-135 ~]# ip addr show eth0 
  2: eth0: &lt;BROADCAST,MULTICAST,UP,LOWER_UP&gt; mtu 9001 qdisc pfifo_fast state UP qlen 1000
  </code></pre>