Linux Hostname

External

• Understanding host names https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Networking_Guide/ch-Configure_Host_Names.html#sec_Understanding_Host_Names
• http://man7.org/linux/man-pages/man1/hostname.1.html

Internal

• Linux Network Concepts

Overview

There are three different hostnames:

• The high-level "pretty" hostname which might include special characters.
• The static hostname which is used to initialize the kernel hostname at boot. The static hostname is stored in /etc/hostname, see hostname(5) for more information.
• The transient hostname is a dynamic hostname maintained by the kernel; the initial value is the static host name value. The transient hostname may be changed by DHCP or mDNS at runtime, but might revert back to the static hostname if network connectivity is lost and is only temporarily written to the kernel hostname.

The static and transient hostnames are limited to the usually accepted characters of Internet domain names.

The pretty hostname, chassis type, and icon name are stored in /etc/machine-info.

If the host name must be changed, to permanently set name, use hostnamectl.

The host name can be read with hostname. If hostname is used to change the host name, the name set is such a way is ephemeral - will disappear at reboot.

There's also a daemon that reacts to network events and sets the hostname: systemd-hostnamed.

Host Name and the Domain Name

When a machine is initially configured, the installation program usually suggest a fully qualified host name that usually has a host name component and a domain name component.

Finish this.

Getting the Hostname

Display the hostname:

hostname

Display the fully qualified domain name (the long host name):

hostname -f

Display the DNS domain:

hostname -d

/etc/hostname

The /etc/hostname file configures the name of the local system that is set during boot using the sethostname(2) system call. It should contain a single newline-terminated hostname string. Depending on the operating system, other configuration files might be checked for configuration of the hostname as well, however only as fallback.

You may use hostnamectl to change the value of this file from the command line. Also see systemd-hostnamed /etc/hostname.

/proc/sys/kernel/hostname

cat /proc/sys/kernel/hostname

cloud-init and hostname

could-init may interfere with setting hostname at boot. For more details see cloud-init - Setting hostname.

Changing the Host Name

Changing the Host Name with hostnamectl