hostname command in Red Hat Linux

Utility hostname displays the current host, domain or node name of the system. As such it is close to DNS commands such as nslookup, but historically the concept of hostname preceded the DNS and the name of the system  used in DNS does not necessary corresponds to the hostname.  Often hostname is "unqualified" name, although in RHEL default is fully qualified name.  It has several options. Among the most useful:

-i, --ip-address

Display the IP address(es) of the host.

-s, --short

Display the short host name. This is the host name cut at the first dot.

In all Linuxes hostname command is just one of a half dozen command that return various part of information about current hostname and current DNS name 

In linux hostname is a memory field stored in /proc filesystem. That means that you can emulate the actions of the hostname command by accessing this memory structure directly via /proc filesystem.  You can read and write (as root) to it

cat /proc/sys/kernel/hostname

splab01

to write new hostname (will not survive reboot):

echo splab02 > /proc/sys/kernel/hostname

As hostname command changes only memory structure it is not suitable to making permanent changes. This is  distribution dependent part. We will discuss Red Hat only.

For permanent change of the hostname in Red Hat (but not SLES) you should modify the file /etc/sysconfig/network  (in SLES the file /etc/HOSTNAME) as well as file /etc/hosts.

Here is how file /etc/sysconfig/network looks on a typical Red Hat 5.6 box:

cat /etc/sysconfig/network
NETWORKING=yes
NETWORKING_IPV6=no
HOSTNAME=splab14
GATEWAY=10.10.1.1

This file is sourced by /etc/init.d/network script on reboot. You can make change permanent without reboot by restarting /etc/init.d/network script:

/etc/init.d/network restart
Shutting down interface eth0:                              [  OK  ]
Shutting down interface eth1:                              [  OK  ]
Shutting down loopback interface:                          [  OK  ]
Bringing up loopback interface:                            [  OK  ]
Bringing up interface eth0:
Determining IP information for eth0... failed; no link present.  Check cable?
                                                           [FAILED]
Bringing up interface eth1:                                [  OK  ]

If the system does not have HOSTNAME entry in /etc/sysconfig/network the first matching entry in /etc/hosts will be used.

Syntax:

• hostname [-v] [-a] [--alias] [-d] [--domain] [-f] [--fqdn] [-i] [--ip-address] [--long] [-s] [--short] [-y] [--yp] [--nis] [-n] [--node]
• hostname [-v] [-F filename] [--file filename] [hostname]
• hostname [-v] [-h] [--help] [-V] [--version]

• domainname [-v] [-F filename] [--file filename] [name]
• nodename [-v] [-F filename] [--file filename] [name]

There are also additional utilities that allow getting DNS and NIS/YP information:

• dnsdomainname [-v]
• nisdomainname [-v]
• ypdomainname [-v]

These names are used by many of the networking programs to identify the machine. The domain name is also used by .

hostname can perform two basic operations

1. Get name: if called without any arguments, the program displays the current system name as returned by the gethostname(2) function.

   dnsdomainname will print the domain part of the FQDN (Fully Qualified Domain Name). The complete FQDN of the system is returned with hostname --fqdn.

   If  hostname -s is called  gethostbyname(3) call will be used. The difference in gethostname(2) and gethostbyname(3) is that gethostbyname(3) is network aware, so it consults /etc/nsswitch.conf and /etc/host.conf to decide whether to read information in /etc/sysconfig/network or /etc/hosts the hostname is also set when the network interface is brought up.

2. 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.

Notes:  

1. Sometimes during the installation the anaconda sets the value HOSTNAME in /etc/sysconfig/network to localhost.localdomain.   That leads to difficult to troubleshoot errors, for example in Sun Grid Engine. Always verify if HOSTNAME field in /etc/sysconfig/network is set correctly
2. Note that hostname doesn't change anything permanently. After reboot original names from /etc/sysconfig/network or if HOSTNAME is not defined in this file, /etc/hosts is used.
3. You can't change the FQDN (as returned by hostname --fqdn) or the DNS domain name (as returned by dnsdomainname) with this command. The FQDN of the system is the name that the resolver(3) returns for the host name. Technically: The FQDN is the name gethostbyname(2) returns for the host name returned by gethostname(2). The DNS domain name is the part after the first dot. 

Options

-a, --alias

Display the alias name of the host (if used).

-d, --domain

Display the name of the DNS domain. Don't use the command domainname to get the DNS domain name because it will show the NIS domain name and not the DNS domain name. Use dnsdomainname instead.

-F, --file filename

Read the host name from the specified file. Comments (lines starting with a '#') are ignored.

-f, --fqdn, --long

Display the FQDN (Fully Qualified Domain Name). A FQDN consists of a short host name and the DNS domain name. Unless you are using bind or NIS for host lookups you can change the FQDN and the DNS domain name (which is part of the FQDN) in the /etc/hosts file.

-h, --help

Print a usage message and exit.

-i, --ip-address

Display the IP address(es) of the host.

-s, --short

Display the short host name. This is the host name cut at the first dot.

-V, --version

Print version information on standard output and exit successfully.

-v, --verbose

Be verbose and tell what's going on.

-y, --yp, --nis

Display the NIS domain name. If a parameter is given (or --file name ) then root can also set a new NIS domain.

NEWS CONTENTS

• 20120109 : Change Hostname in SUSE ( Change Hostname in SUSE, Jan 09, 2012 )
• 20120109 : How to change the hostname of a Linux system MDLog-sysadmin ( How to change the hostname of a Linux system MDLog-sysadmin, )
• 20120109 : Linux setting hostname and domain name of my server ( Linux setting hostname and domain name of my server, )
• 20120109 : networking - Configuring the hostname on Red Hat Enterprise Linux - Server Fault ( networking - Configuring the hostname on Red Hat Enterprise Linux - Server Fault, )

Old News ;-)

[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

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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