hostname: Usage, Options & Common CI Errors

hostname prints (or sets) the machine name and can show its IP addresses.

hostname seems trivial until a container's own name does not resolve. The FQDN flag (-f) needs a working resolver, and -I vs -i behave very differently - a frequent source of confusing CI failures.

What it does

hostname prints or sets the system's network name. With flags it also reports the FQDN (-f) or the host's IP addresses (-I, -i). In containers the hostname is usually the container ID, which may not be resolvable.

Common usage

Terminal

hostname                       # the short hostname
hostname -f                    # fully qualified domain name
hostname -I                    # all IP addresses (space separated)
hostname -i                    # IP from name resolution (can fail)
hostname new-name              # set the hostname (needs privilege)

Options

Flag	What it does
(none)	Print the short hostname
-f / --fqdn	Print the fully qualified domain name
-I / --all-ip-addresses	All addresses, no name resolution
-i / --ip-address	Resolve the hostname to an IP (uses DNS)
-s / --short	Short name (up to the first dot)

Common errors in CI

hostname -f / hostname -i fail with "hostname: Name or service not known" when the container's own name is not in /etc/hosts and DNS cannot resolve it - common with random container IDs. Prefer hostname -I, which reads addresses from the interfaces and does NOT need resolution. -I returns a space-separated list (possibly several IPs) - do not assume a single value. Setting the hostname needs privilege ("hostname: you must be root to change the host name").