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NSS−MYHOSTNAME

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 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.

EXAMPLE

Here is an example /etc/nsswitch.conf file that enables nss−myhostname correctly:

passwd: compat mymachines systemd
group: compat mymachines systemd
shadow: compat

hosts: files mymachines resolve [!UNAVAIL=return] dns 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-systemd(8), nss-resolve(8), nss-mymachines(8), nsswitch.conf(5), getent(1)

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