Index · Directives systemd 229

Name

nss-myhostname, libnss_myhostname.so.2 — Provide hostname resolution for the locally configured system hostname.

Synopsis

libnss_myhostname.so.2

Description

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 hostname "localhost" (as well as any hostname ending in ".localhost", ".localdomain" or equal to "localdomain") is 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.

Example

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.

See Also

systemd(1), nss-resolve(8), nss-mymachines(8), nsswitch.conf(5), getent(1)