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Changing hostname

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Normally we will set the hostname of a system during the installation process. But if we need to change it after that we are in uncharted territory. For example Red hat by default uses as hostname fully qualified DNS name which for many people including me does not sound as a great idea. In this case you need to find a way to change it to a short name.  The problem here is that this name is present in multiple files and generally is Unix/Linux flavour dependent.

While command hostname can change the current hostname, this change is temporary. You can't use the command hostname  new_name for permanent changes as hostname command changes only relevant memory structure which would be wiped out after reboot.  Also remains unchanged the file /etc/hosts/ that usually contains the association of primary network interface of the box with this name. 

Note:

Instead of command hostname  new_name you can use command   sysctl kernel.hostname=new_name or direct write to /proc pseudo filesystem. for example: 

echo splab02 > /proc/sys/kernel/hostname

You can also print the value /proc/sys/kernel/hostname or use command sysctl kernel.hostname to verify the change.

GNU version of hostname has --file option that provides the opportunity to read the name from the file which is useful in SLES as permanent hostname in SLES is stored in /etc/HOSTNAME.  For example:

hostname --file /etc/HOSTNAME

should permanently set the hostname of the system to name you already put in /etc/HOSTNAME. Again this will work only in SLES. Here is a relevant quote from the man page about --file option:

Set Name

When called with one argument or with the --file option, the commands set the host name, the NIS/YP domain name or the node name.

Note, that only the super-user can change the names.

It is not possible to set the FQDN or the DNS domain name with the dnsdomainname command (see THE FQDN below).

The host name is usually set once at system startup in /etc/rc.d/rc.inet1 or /etc/init.d/boot (normally by reading the contents of a file which contains the host name, e.g. /etc/hostname).

If you issue the command

hostname newname
it is equivalent to writing the specified name into  /proc/sys/kernel/hostname so it is important to understand that this is temporary "in-memory-only" change. This change should be active right away and will remain after the system will be rebooted. If after the execution of the command your shell prompt reflects the old host name you probably need either to re-source .profile or (or .bash_profile)  or to exit the current shell in order to see the change in your shell prompt.
If after the execution of the command your shell prompt reflects the old hostname you probably need either to re-source .profile (or .bash_profile) or to exit the current shell in order to see the change in your shell prompt.

To make the change persistent you still need manually edit two files:

To check the change you can use either command

hostname

or

hostname -s
Again it is important to understand that the command hostname does not change niether /etc/hosts  nor /etc/sysconfig/network in RHEL (/etc/HOSTNAME in SLES) and that should be done manually.

Manual modification of /etc/sysconfig/network

This is the place where hostname in stored in RHEL and its derivatives. As such this is a distribution dependent place and other Linux distributions has thier own way of storing this information. So this is Red Hat and its derivatives (CentOS, Oracle Unbreakable Linux)  centric discussion.  

For those distributions you can modify the file /etc/sysconfig/network to read the hostname at system boot. This files is sourced by the init script /etc/rc.d/rc.sysinit.

For example in the following /etc/sysconfig/network you need to enter the appropriate name using the HOSTNAME variable.

NETWORKING=yes
HOSTNAME="myhost"
GATEWAY="192.168.0.1"
GATEWAYDEV="eth0"
FORWARD_IPV4="yes"

In this example, the new hostname would be myhost

To verify that the value of HOSTNAME parameter was changed correctly use:

cat  /etc/sysconfig/network

Please note that this does not change the current hostname as this is "in-memory" information. It will change hostname only on reboot or anytime /etc/rc.d/rc.sysinit startup script will be re-executed (for example in case of runlevel change). Sometimes the latter can be useful


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[Jan 09, 2012] Change Hostname in SUSE

12-Jan-2010

ckozler

How do you change the hostname in SLES11? I have normally used the /etc/hostname file and rebooted the server in other distros.

I only notice the way to change it is in yast2 -> network devices -> network settings -> Hostnames

I am looking for where it is stored because I want to write a script to update it (apart of a server deployment process).

Thank you for your time

I hate bumping but I'd really like to know since I can not find anything on google or anywhere else about this.

syampillai

Put it in /etc/hostname as well as in /etc/hosts


ckozler

Put it in /etc/hostname as well as in /etc/hosts
I have done that and tried restarting but my hostname does not change unless I change it in yast.

I tried putting it in /etc/hostname and /etc/hosts and then rebooting. Executed "hostname" and it still reported the old one.

Changing it via Yast allowed me to update it right away without having to even reboot, just logout and log back in.

hcvv

I normaly advice people to use YaST because there are a few places where it should be done and YaST knows them where I always forget one or more.

I rely on YaST now and do not know any more all the places where to go.

Does anybody know if YaST keeps a lof of what it does realy?


Henk van Velden

malcolmlewis

mmarif4u;2103002 Wrote:
> Maybe you could try SLES forum, as you can get better response from
> the tech and support team there.
>
> 'SUSE Linux Enterprise Server (SLES) - NOVELL FORUMS'
> (http://tinyurl.com/69jvat)

Tried it. They never seem to respond over there
Hi
Which SLE forum did you post in and when?

The three files to change are /etc/HOSTNAME (note case) and /etc/hosts
against the 127.0.0.2 address and also postfix/main.cf Its also the
fully qualified name (FQDN).

--
Cheers Malcolm

[Apr 05, 2011] How to change the hostname of a Linux system MDLog-sysadmin

Permanent hostname change on RedHat based systems

RedHat based system use the file /etc/sysconfig/network to read the saved hostname at system boot. This is set using the init script /etc/rc.d/rc.sysinit

/etc/sysconfig/network
NETWORKING=yes
HOSTNAME="plain.domainname.com"
GATEWAY="192.168.0.1"
GATEWAYDEV="eth0"
FORWARD_IPV4="yes"

So in order to preserve your change on system reboot edit this file and enter the appropriate name using the HOSTNAME variable.

Use sysctl to change the hostname

Why would someone need a different method of doing the same thing as above? No idea, but here is anyway: use sysctl to change the variable kernel.hostname:
Use:

sysctl kernel.hostname

to read the current hostname, and

sysctl kernel.hostname=NEW_HOSTNAME

to change it.

Linux setting hostname and domain name of my server

Local hostname and domain name of your server defined in text configuration located in /etc directory.

If you are using Red Hat or Fedora Linux
Use redhat-config-network GUI tool. Type following command and click on DNS tab > Setup hostname and domain name:
# redhat-config-network
On other hand you can edit a text file. Find out and set up the value for HOSTNAME in the file /etc/sysconfig/network:
# vi /etc/sysconfig/network
Setup/replace HOSTNAME
HOSTNAME=web.nixcraft.com
Where, web is hostname and nixcraft.com is your DNS domain name

networking - Configuring the hostname on Red Hat Enterprise Linux - Server Fault

The box in your example will have hydrogen.lan as its hostname, not hydrogen.

The only way I know of to have hostname return the short hostname and to have hostname -f return the FQDN, is to use both the mentioned options.

So add HOSTNAME=mybox to /etc/sysconfig/network and add

10.10.10.10 mybox.example.com mybox

to /etc/hosts. I like having hostname and hostname -f return different things. By default, Anaconda sets it up like you have it set up now.

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