How to change MTU settings permanently

Question

I need to change forever MTUon 1500. Constantly, I mean, if I reboot the system or do it service network restart, it will always be 1500.

I followed this article http://www.cyberciti.biz/faq/centos-rhel-redhat-fedora-debian-linux-mtu-size/

But unfortunately this does not work for me.

Here is what I did:

check current MTU:

eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9001 qdisc pfifo_fast state UP qlen 1000 

Posted MTU="1500"in /etc/sysconfig/network-scripts/ifcfg-eth0:

[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"

Then check again MTU(no luck):

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: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9001 qdisc pfifo_fast state UP qlen 1000

/sbin/ifconfigchanged MTUbut only temporarily

[root@ip-xx-xx-xxx ~]# /sbin/ifconfig eth0 mtu 1500 up
[root@ip-xx-xx-xxx ~]# ip addr show eth0 
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000

If I restart network, it will again be 9001:

[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: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9001 qdisc pfifo_fast state UP qlen 1000

Answer 1

MTU DHCP, :

DEVICE=eth0

BOOTPROTO=dhcp

, DHCP MTU. Ubuntu : /etc/dhcp/dhclient.conf

, :

default interface-mtu 1500;

supercede interface-mtu 1500;

, Red Hat, , dhcpd.conf

, !