1NSS-MYHOSTNAME(8) nss-myhostname NSS-MYHOSTNAME(8)
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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
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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:
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19 · 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).
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24 · 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.
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28 · 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.
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33 Various software relies on an always-resolvable local hostname. When
34 using dynamic hostnames, this is traditionally achieved by patching
35 /etc/hosts at the same time as changing the hostname. This is
36 problematic since it requires a writable /etc file system and is
37 fragile because the file might be edited by the administrator at the
38 same time. With nss-myhostname enabled, changing /etc/hosts is
39 unnecessary, and on many systems, the file becomes entirely optional.
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41 To activate the NSS modules, add "myhostname" to the line starting with
42 "hosts:" in /etc/nsswitch.conf.
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44 It is recommended to place "myhostname" either between "resolve" and
45 "traditional" modules like "files" and "dns", or after them. In the
46 first version, well-known names like "localhost" and the machine
47 hostname are given higher priority than the external configuration.
48 This is recommended when the external DNS servers and network are not
49 absolutely trusted. In the second version, external configuration is
50 given higher priority and nss-myhostname only provides a fallback
51 mechanism. This might be suitable in closely controlled networks, for
52 example on a company LAN.
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55 Here is an example /etc/nsswitch.conf file that enables nss-myhostname
56 correctly:
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58 passwd: compat systemd
59 group: compat systemd
60 shadow: compat
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62 # Either (untrusted network):
63 hosts: mymachines resolve [!UNAVAIL=return] myhostname files dns
64 # Or (only trusted networks):
65 hosts: mymachines resolve [!UNAVAIL=return] files dns myhostname
66 networks: files
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68 protocols: db files
69 services: db files
70 ethers: db files
71 rpc: db files
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73 netgroup: nis
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75 To test, use glibc's getent tool:
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77 $ getent ahosts `hostname`
78 ::1 STREAM omega
79 ::1 DGRAM
80 ::1 RAW
81 127.0.0.2 STREAM
82 127.0.0.2 DGRAM
83 127.0.0.2 RAW
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85 In this case, the local hostname is omega.
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88 systemd(1), nss-systemd(8), nss-resolve(8), nss-mymachines(8),
89 nsswitch.conf(5), getent(1)
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93systemd 246 NSS-MYHOSTNAME(8)