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NSS-MYMACHINES(8) nss-mymachines NSS-MYMACHINES(8)

NAME

nss-mymachines, libnss_mymachines.so.2 - Provide 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.
The module also provides name resolution for user and group identifiers mapped to containers. All names from the range allocated to a given container container are exposed on the host as "vu- container-uid" and "vg- container-gid" (see example below). This functionality only applies to containers using user namespacing (see the description of --private-users in systemd-nspawn(1)).
To activate the NSS module, add "mymachines" to the lines starting with "hosts:", "passwd:" and "group:" in /etc/nsswitch.conf.
It is recommended to place "mymachines" after the "files" or "compat" entry of the /etc/nsswitch.conf lines to make sure that its mappings are preferred over other resolvers such as DNS, but so that /etc/hosts, /etc/passwd and /etc/group based mappings take precedence.

CONFIGURATION IN /ETC/NSSWITCH.CONF

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

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
$ getent passwd vu-rawhide-0 vu-rawhide-81 vu-rawhide-0:*:20119552:65534:vu-rawhide-0:/:/sbin/nologin vu-rawhide-81:*:20119633:65534:vu-rawhide-81:/:/sbin/nologin
$ getent group vg-rawhide-0 vg-rawhide-81 vg-rawhide-0:*:20119552: vg-rawhide-81:*:20119633:
$ ps -o user:15,pid,tty,command -e|grep '^vu-rawhide' vu-rawhide-0 692 ? /lib/systemd/systemd vu-rawhide-0 731 ? /lib/systemd/systemd-journald vu-rawhide-192 734 ? /lib/systemd/systemd-networkd vu-rawhide-193 738 ? /lib/systemd/systemd-resolved vu-rawhide-0 742 ? /lib/systemd/systemd-logind vu-rawhide-81 744 ? /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only vu-rawhide-0 746 ? /usr/sbin/sshd -D ... vu-rawhide-0 752 ? /lib/systemd/systemd --user vu-rawhide-0 753 ? (sd-pam) vu-rawhide-0 1628 ? login -- zbyszek vu-rawhide-1000 1630 ? /lib/systemd/systemd --user vu-rawhide-1000 1631 ? (sd-pam) vu-rawhide-1000 1637 pts/8 -zsh
$ 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)
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