Hostname

Main part from: http://www.cpqlinux.com/hostname.html
Checking your Linux host name First, see if your host name is set correclty using the following commands:

uname -n
hostname -a
hostname -s
hostname -d
hostname -f
hostname

If the above commands return correctly with no errors then all may be well; however, you may want to read on to verify that all settings are correct.
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Configuring /etc/hosts If your IP address is assigned to you by a DHCP server, then /etc/hosts is configured as follows:

127.0.0.1	mybox.mydomain.com	localhost.localdomain localhost mybox

If you have a static IP address, then /etc/hosts is configured as follows:

127.0.0.1	localhost.localdomain localhost
192.168.0.10	mybox.mydomain.com	mybox
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Setting the Host Name using "hostname" After updating the /etc/hosts file correctly, the "hostname" command should be run as follows to set your hostname:
hostname mybox.mydomain.com
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Checking /etc/HOSTNAME (if present) You may or may not have the file /etc/HOSTNAME:

mybox.mydomain.com
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Checking /proc/sys/kernel/hostname This is checked with the following command: cat /proc/sys/kernel/hostname If you need to set this file, you can either reboot or set it now with the following command:
echo mybox.mydomain.com > /proc/sys/kernel/hostname
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It is not reliable to use X tool for my experience.What is relationship in these files? I will discover in the future.