nss-myhostname is a plug-in module for the GNU Name Service Switch (NSS) functionality of the GNU C Library (glibc), primarily providing hostname resolution for the locally configured system hostname as returned by gethostname(2). The precise hostnames resolved by this module are:
- • The local, configured hostname is resolved to all locally configured IP addresses ordered by their scope, or --- if none are configured --- the IPv4 address 127.0.0.2 (which is on the local loopback) and the IPv6 address ::1 (which is the local host).
- • The hostnames "localhost" and "localhost.localdomain" (as well as any hostname ending in ".localhost" or ".localhost.localdomain") are resolved to the IP addresses 127.0.0.1 and ::1.
- • The hostname "gateway" is resolved to all current default routing gateway addresses, ordered by their metric. This assigns a stable hostname to the current gateway, useful for referencing it independently of the current network configuration state.
Various software relies on an always-resolvable local hostname. When using dynamic hostnames, this is traditionally achieved by patching /etc/hosts at the same time as changing the hostname. This is problematic since it requires a writable /etc file system and is fragile because the file might be edited by the administrator at the same time. With nss-myhostname enabled, changing /etc/hosts is unnecessary, and on many systems, the file becomes entirely optional.
To activate the NSS modules, add "myhostname" to the line starting with "hosts:" in /etc/nsswitch.conf.
It is recommended to place "myhostname" last in the nsswitch.conf' "hosts:" line to make sure that this mapping is only used as fallback, and that any DNS or /etc/hosts based mapping takes precedence.
Here is an example /etc/nsswitch.conf file that enables nss-myhostname correctly:
passwd: compat mymachines group: compat mymachines shadow: compat hosts: files mymachines resolve myhostname networks: files protocols: db files services: db files ethers: db files rpc: db files netgroup: nis
To test, use glibc's getent tool:
$ getent ahosts `hostname` ::1 STREAM omega ::1 DGRAM ::1 RAW 127.0.0.2 STREAM 127.0.0.2 DGRAM 127.0.0.2 RAW
In this case, the local hostname is omega.