☩ Walking in Light with Christ – Faith, Computing, Diary

Often when some of my companies, I’m employed with rents dedicated GNU / Linux servers co-located in data centers,
usually the local hostname is configured while the system is being installed, therefore many times when we forget to tell the Dedicated provider what kind of hostname, we’re intending to use they came up with some kind of hostname which is randomly set based on the dedicated provider’s company name or a server ID number. Cosenquently the machine hostname assigned due to company local server numbering policy.

Hence after one logs in to the newly purchased server with over SSH protocol, then we end up with a hostname like for example:

server56663:~#

This hostname naming, often doesn’t make much sense for the services running on the server and doesn’t have nothing to do to the provided internet services by the server, however its really important for me to orientate myself which server I have logged to. Therefore one of the first things I do while configuring a new server is to change the local server assigned hostname .

Besides having the hostname shown by the shell prompt, there is a quick command to print out the Fully Qualified Domain hostname, by issuing:

>server56663:~# hostname --fqdn
server56663.dedicompany.com

The Universal GNU / Linux way which works on almost all Linux distributions to change the configured hostname goes like this:

Edit /etc/hosts . A default /etc/hosts file looks something like:

server56663:~# cat /etc/hosts127.0.0.1 localhost.localdomain localhost
127.0.1.1 server56663.dedicompany.com server56663
# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

On the second line which assigns the hostname for the loopback IP address 127.0.0.1 , you see the identifier for the local hostname:

127.0.1.1 server56663.dedicompany.com server56663

To change that to a custom local hostname of choice, the line should be modified to look like:

127.0.1.1 CustomHostName server56663.dedicompany.com server56663

On some GNU / Linux distributions the line 127.0.1.1 might be completely absent, this is the case with for example CentOS and Fedora and many other distros
On these Gnu / Linux distributions the /etc/hosts might looks like:

# Do not remove the following line, or various programs# that require network functionality will fail.127.0.0.1 localhost.localdomain localhost

Alas on Fedora, CentOS and other distros to set the localhost hostname, one more line should be added to /etc/hosts . The line to add looks like so:

123.123.123.123 CustomHostName

After modification and adding the custom hostname name there the file should look something like:

[root@centos ~]# cat /etc/hosts127.0.0.1 localhost localhost123.123.123.123 CustomHostName

After including correct records in /etc/hosts , next the hostname command is used to change the localhost name configured to show as a machine name on user ssh login:

server56663:~# hostname CustomHostName
server56663:~#

Further to check that the new hostname is set for all ssh sessions incoming to the ssh server from now on the hostname command is used without arguments:

server56663:~# hostname
CustomHostName

Even though now the hostname is changed to CustomHostName still, the hostname for the current opened ssh session is keeping the old hostname:

server56663:~# hostname
server56663

To see the hostname change in your shell prompt you will have to logout and login again to the system.

Here its good to mention the Linux kernel has a variable kernel.hostname, which can be used to set the local machine hostname. Actually the hostname command automatically set the kernel.hostname kernel variable.
If of course one want to change the kernel var directly without using the hostname command, this can be achieved with sysctl, e.g.:

server56663:~# sysctl kernel.hostname=CustomHostName

On Debian GNU / Linux the way to change the hostname there is a “debian way” approach:

Debian has a file /etc/hostname , which is there just for the sake of configuring the system hostname. During system boot process Debian reads /etc/hostname file and sets the machine hostname to the word inside. The /etc/hostname file is being red and configured by Debian’s /etc/init.d/hostname.sh shell script.

Therefore after changing the hostname in Debian by editting /etc/honstmame , the /etc/init.d/hostname.sh needs to be invoked for the new hostname to be set system wide, like so;

server56663:~# /etc/init.d/hostname.sh

Just like with other GNU / Linux distributions for the new hostname to be active on the current shell a logout and login via ssh is necessery again.

With Fedora, CentOS and other Redhat based distributions the “proper” way to change the hostname is:
a. change the /etc/hosts way described above in the aticle.

b. Edit /etc/sysconfig/network file and write inside the new custom hostname.

[root@centos ~]# grep -i hostname /etc/sysconfig/network
HOSTNAME=localhost.localdomain

After HOSTNAME value is set to the new desired hostname and file is saved, the network script should be invoke with restart argument:

[root@centos ~]# /etc/init.d/network restart One more thing to consider always when changing a hostname is that some of the system services are using the configured local machine hostname, and hence need to be restarted also from a active shell where the new hostname is already set and active.

Since the system hostname is being configured usually, with the rest of server configurations on system boot, after setting the desired hostname it is a good idea to have a system reboot. This will guarantee that all running daemons will read the newly set hostname:
E.g.:

server56663:~# shutdown -r now

On next boot the hostname should be set to whatever you put as a custom hostname.