Linux hostname command

Updated: 06/16/2017 by Computer Hope

About hostname

The hostname command shows or sets the system hostname.

Description

hostname is used to display the system's DNS name, and to display or set its hostname or NIS (Network Information Services) domain name.

When called without any arguments, hostname will display the name of the system as returned by the gethostname function.

When called with one argument or with the --file option, hostname will set the system's host name using the sethostname function. Only the superuser can set the host name.

The host name is usually set once at system startup in the script /etc/init.d/hostname.sh normally by reading the contents of a file which contains the host name, e.g. /etc/hostname.

hostname syntax

hostname [-v] [-a|--alias] [-d|--domain] [-f|--fqdn|--long] [-A|--all-fqdns] 
         [-i|--ip-address] [-I|--all-ip-addresses] [-s|--short] [-y|--yp|--nis]
hostname [-v] [-b|--boot] [-F|--file filename] [hostname]
hostname [-v] [-h|--help] [-V|--version]

Options

-a, --alias Display the alias name of the host (if used). This option is deprecated and should not be used anymore.
-A, --all-fqdns Displays every FQDN of the machine. This option enumerates all configured network addresses on all configured network interfaces, and translates them to DNS domain names. Addresses that cannot be translated (i.e. because they do not have an appropriate reverse DNS entry) are skipped. Note that different addresses may resolve to the same name, therefore the output may contain duplicate entries. Do not make any assumptions about the order of the output.
-b, --boot Always set a hostname; this allows the file specified by -F to be non-existant or empty, in which case the default hostname localhost will be used if none is yet set.
-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. See the warnings in section The FQDN, and avoid using this option if at all possible.
-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 (Berkeley Internet Domain Name) 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. See the warnings in section The FQDN, and avoid using this option if at all possible; use hostname --all-fqdns instead.
-F, --file filename Read the host name from the specified file. Comments (lines starting with a `#') are ignored.
-i, --ip-address Display the network address(es) of the host name. Note that this works only if the host name can be resolved. Avoid using this option if at all possible; use hostname --all-ip-addresses instead.
-I, --all-ip-addresses Display all network addresses of the host. This option enumerates all configured addresses on all network interfaces. The loopback interface and IPv6 link-local addresses are omitted. Contrary to option -i, this option does not depend on name resolution. Do not make any assumptions about the order of the output.
-s, --short Display the short host name. This is the host name cut at the first dot.
-v, --verbose Be verbose with all output.
-V, --version Print version information on standard output and exit successfully.
-y, --yp, --nis Display the NIS domain name. If a parameter is given (or --file name ) then root (the superuser) can also set a new NIS domain.
-h, --help Print a help message and exit.

The FQDN

The FQDN (Fully Qualified Domain Name) of the system is the name that the resolver returns for the host name, such as mysubdomain.example.com. It is usually the hostname followed by the DNS domain name (the part after the first dot). You can check the FQDN using hostname --fqdn or the domain name using dnsdomainname.

You cannot change the FQDN with hostname or dnsdomainname.

The recommended method of setting the FQDN is to make the hostname be an alias for the fully qualified name using /etc/hosts, DNS, or NIS. For example, if the hostname was "mysubdomain", one might have a line in /etc/hosts which reads

127.0.1.1 ursula.example.com ursula

Technically: The FQDN is the name getaddrinfo returns for the host name returned by gethostname. The DNS domain name is the part after the first dot.

Therefore it depends on the configuration of the resolver (usually in /etc/host.conf) how you can change it. Usually the hosts file is parsed before DNS or NIS, so it is most common to change the FQDN in /etc/hosts.

If a machine has multiple network interfaces/addresses or is used in a mobile environment, then it may either have multiple FQDNs/domain names or none at all. Therefore avoid using hostname --fqdn, hostname --domain and dnsdomainname.

hostname --ip-address is subject to the same limitations so it should be avoided as well.

Files

/etc/hostname Historically this file was supposed to only contain the hostname and not the full canonical FQDN. Nowadays most software is able to cope with a full FQDN here. This file is read at boot time by the system initialization scripts to set the hostname.
/etc/hosts Usually, this is where one sets the domain name by aliasing the host name to the FQDN.

hostname examples

hostname

Displays the system host name.

hostid — Print the numeric identifier for the current host.
uname — Print information about the current system.