1NSS-MYHOSTNAME(8) nss-myhostname NSS-MYHOSTNAME(8)
2
6 nss-myhostname, libnss_myhostname.so.2 - Hostname resolution for the
7 locally configured system hostname
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10 libnss_myhostname.so.2
11
13 nss-myhostname is a plug-in module for the GNU Name Service Switch
14 (NSS) functionality of the GNU C Library (glibc), primarily providing
15 hostname resolution for the locally configured system hostname as
16 returned by gethostname(2). The precise hostnames resolved by this
17 module are:
18 • The local, configured hostname is resolved to all locally
20 configured IP addresses ordered by their scope, or — if none are
21 configured — the IPv4 address 127.0.0.2 (which is on the local
22 loopback) and the IPv6 address ::1 (which is the local host).
23 • The hostnames "localhost" and "localhost.localdomain" (as well as
25 any hostname ending in ".localhost" or ".localhost.localdomain")
26 are resolved to the IP addresses 127.0.0.1 and ::1.
27 • The hostname "_gateway" is resolved to all current default routing
29 gateway addresses, ordered by their metric. This assigns a stable
30 hostname to the current gateway, useful for referencing it
31 independently of the current network configuration state.
32 • The hostname "_outbound" is resolved to the local IPv4 and IPv6
34 addresses that are most likely used for communication with other
35 hosts. This is determined by requesting a routing decision to the
36 configured default gateways from the kernel and then using the
37 local IP addresses selected by this decision. This hostname is only
38 available if there is at least one local default gateway
39 configured. This assigns a stable hostname to the local outbound IP
40 addresses, useful for referencing them independently of the current
41 network configuration state.
42 Various software relies on an always-resolvable local hostname. When
44 using dynamic hostnames, this is traditionally achieved by patching
45 /etc/hosts at the same time as changing the hostname. This is
46 problematic since it requires a writable /etc/ file system and is
47 fragile because the file might be edited by the administrator at the
48 same time. With nss-myhostname enabled, changing /etc/hosts is
49 unnecessary, and on many systems, the file becomes entirely optional.
50 To activate the NSS modules, add "myhostname" to the line starting with
52 "hosts:" in /etc/nsswitch.conf.
53 It is recommended to place "myhostname" after "file" and before "dns".
55 This resolves well-known hostnames like "localhost" and the machine
56 hostnames locally. It is consistent with the behaviour of nss-resolve,
57 and still allows overriding via /etc/hosts.
58 Please keep in mind that nss-myhostname (and nss-resolve) also resolve
60 in the other direction — from locally attached IP addresses to
61 hostnames. If you rely on that lookup being provided by DNS, you might
62 want to order things differently.
63
65 Here is an example /etc/nsswitch.conf file that enables nss-myhostname
66 correctly:
67 passwd: compat systemd
69 group: compat [SUCCESS=merge] systemd
70 shadow: compat systemd
71 gshadow: files systemd
72 hosts: mymachines resolve [!UNAVAIL=return] files myhostname dns
75 networks: files
76 protocols: db files
78 services: db files
79 ethers: db files
80 rpc: db files
81 netgroup: nis
83 To test, use glibc's getent tool:
85 $ getent ahosts `hostname`
87 ::1 STREAM omega
88 ::1 DGRAM
89 ::1 RAW
90 127.0.0.2 STREAM
91 127.0.0.2 DGRAM
92 127.0.0.2 RAW
93 In this case, the local hostname is omega.
95
97 systemd(1), nss-systemd(8), nss-resolve(8), nss-mymachines(8),
98 nsswitch.conf(5), getent(1)
99systemd 250 NSS-MYHOSTNAME(8)