NAME
nss-myhostname, libnss_myhostname.so.2 - Hostname resolution for the locally configured system hostnameSYNOPSIS
libnss_myhostname.so.2DESCRIPTION
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.
•The hostname "_outbound" is
resolved to the local IPv4 and IPv6 addresses that are most likely used for
communication with other hosts. This is determined by requesting a routing
decision to the configured default gateways from the kernel and then using the
local IP addresses selected by this decision. This hostname is only available
if there is at least one local default gateway configured. This assigns a
stable hostname to the local outbound IP addresses, useful for referencing
them 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" after "file" and
before "dns". This resolves well-known hostnames like
"localhost" and the machine hostnames locally. It is consistent with
the behaviour of nss-resolve, and still allows overriding via
/etc/hosts.
Please keep in mind that nss-myhostname (and nss-resolve) also
resolve in the other direction — from locally attached IP addresses to
hostnames. If you rely on that lookup being provided by DNS, you might want to
order things differently.
EXAMPLE
Here is an example /etc/nsswitch.conf file that enables nss-myhostname correctly:passwd: compat systemd group: compat [SUCCESS=merge] systemd shadow: compat systemd gshadow: files systemd hosts: mymachines resolve [!UNAVAIL=return] files myhostname dns networks: files protocols: db files services: db files ethers: db files rpc: db files netgroup: nis
$ 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
SEE ALSO
systemd(1), nss-systemd(8), nss-resolve(8), nss-mymachines(8), nsswitch.conf(5), getent(1)systemd 252 |