我需要永久更改MTU为1500. 永久我的意思是如果我重新启动系统或将这样做service network restart，它将永远是1500。
我关注了这篇文章http://www.cyberciti.biz/faq/centos-rhel-redhat-fedora-debian-linux-mtu-size/
但不幸的是，它对我不起作用。
这是我所做的：
检查电流MTU：
eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9001 qdisc pfifo_fast state UP qlen 1000
添加MTU="1500"到/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"
然后MTU再次检查，（没有运气）：
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/ifconfig改变了MTU，但只是暂时的
[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
如果我重新启动network它又是 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