Index · Directives systemd 246

Name

nss-mymachines, libnss_mymachines.so.2 — Hostname resolution for local container instances

Synopsis

libnss_mymachines.so.2

Description

nss-mymachines is a plug-in module for the GNU Name Service Switch (NSS) functionality of the GNU C Library (glibc), providing hostname resolution for the names of containers running locally that are registered with systemd-machined.service(8). The container names are resolved to the IP addresses of the specific container, ordered by their scope. This functionality only applies to containers using network namespacing (see the description of --private-network in systemd-nspawn(1)). Note that the name that is resolved is the one registered with systemd-machined, which may be different than the hostname configured inside of the container.

To activate the NSS module, add "mymachines" to the line starting with "hosts:" in /etc/nsswitch.conf.

It is recommended to place "mymachines" after the "files" or "compat" entry of the /etc/nsswitch.conf line to make sure that its mappings are preferred over other resolvers such as DNS, but so that /etc/hosts based mappings take precedence.

Configuration in /etc/nsswitch.conf

Here is an example /etc/nsswitch.conf file that enables nss-mymachines correctly:

passwd:         compat systemd
group:          compat systemd
shadow:         compat

hosts:          mymachines resolve [!UNAVAIL=return] myhostname files dns
networks:       files

protocols:      db files
services:       db files
ethers:         db files
rpc:            db files

netgroup:       nis

Example: Mappings provided by nss-mymachines

The container "rawhide" is spawned using systemd-nspawn(1):

# systemd-nspawn -M rawhide --boot --network-veth --private-users=pick
Spawning container rawhide on /var/lib/machines/rawhide.
Selected user namespace base 20119552 and range 65536.
...

$ machinectl --max-addresses=3
MACHINE CLASS     SERVICE        OS     VERSION ADDRESSES
rawhide container systemd-nspawn fedora 30      169.254.40.164 fe80::94aa:3aff:fe7b:d4b9

$ ping -c1 rawhide
PING rawhide(fe80::94aa:3aff:fe7b:d4b9%ve-rawhide (fe80::94aa:3aff:fe7b:d4b9%ve-rawhide)) 56 data bytes
64 bytes from fe80::94aa:3aff:fe7b:d4b9%ve-rawhide (fe80::94aa:3aff:fe7b:d4b9%ve-rawhide): icmp_seq=1 ttl=64 time=0.045 ms
...
$ ping -c1 -4 rawhide
PING rawhide (169.254.40.164) 56(84) bytes of data.
64 bytes from 169.254.40.164 (169.254.40.164): icmp_seq=1 ttl=64 time=0.064 ms
...

# machinectl shell rawhide /sbin/ip a
Connected to machine rawhide. Press ^] three times within 1s to exit session.
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    ...
2: host0@if21: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether 96:aa:3a:7b:d4:b9 brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet 169.254.40.164/16 brd 169.254.255.255 scope link host0
       valid_lft forever preferred_lft forever
    inet6 fe80::94aa:3aff:fe7b:d4b9/64 scope link
       valid_lft forever preferred_lft forever
Connection to machine rawhide terminated.

See Also

systemd(1), systemd-machined.service(8), machinectl(1), nss-systemd(8), nss-resolve(8), nss-myhostname(8), nsswitch.conf(5), getent(1)