TL;DR Recover individual cluster configuration without need for a bogus node. Both from previous backup or a corrupt database. The source does not need to originate from the same cluster.
ORIGINAL POST Extract Cluster configuration - /etc/pve
There are cases when you make changes in your configurations, only to want to partially revert it back.
TIP
There is a separate post on full backup and recovery of pmxcfs, i.e. the configuration state residing in /etc/pve.
Alternatively, you get hold of stale (from non-quorate node) or partially corrupt config.db and want to take out only some of the previous files. without making it your current node’s cluster filesystem.
Less often, you might want to edit the contents of the database-backed filesystem without side effects to the node or cluster, e.g. in order to implant it into a separate/cloned/new cluster.
WARNING If you do not understand the summary above, do NOT proceed.
This is actually possible, however since the pmxcfs ^ relies on hardcoded locations for its backend database file as well as mountpoint, you would need to use chroot.
mkdir -p ~/jail-pmxcfs/{dev,usr,bin,sbin,lib,lib64,etc,var/lib/pve-cluster,var/run}
for i in /dev /usr /bin /sbin /lib /lib64 /etc; do mount --bind -o ro $i /root/jail-pmxcfs$i; done
This will create alternative root structure for your own instance of pmxcfs, the only thing left is to implant the database of interest, in this example from existing one:
sqlite3 /var/lib/pve-cluster/config.db .dump > ~/config.dump.sql sqlite3 ~/jail-pmxcfs/var/lib/pve-cluster/config.db < ~/config.dump.sql
Now launch your own pmxcfs instance in local mode (-l) in the chroot environment:
chroot ~/jail-pmxcfs/ pmxcfs -l
You can double check your instance runs using the database file that was just provided:
lsof ~/jail-pmxcfs/var/lib/pve-cluster/config.db
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME pmxcfs 1225 root 4u REG 252,1 77824 61 /root/jail-pmxcfs/var/lib/pve-cluster/config.db
In fact, if you have the regular pve-cluster service running, you will be able to see there’s two instances running, each over its own database, the new one in local mode (-l):
ps -C pmxcfs -f
UID PID PPID C STIME TTY TIME CMD root 656 1 0 10:34 ? 00:00:02 /usr/bin/pmxcfs root 1225 1 0 10:37 ? 00:00:00 pmxcfs -l
Now you can copy out your files or perform changes in ~/jail-pmxcfs/etc/pve without affecting your regular operation.
You can also make an SQL dump ^ of ~/jail-pmxcfs/var/lib/pve-cluster/config.db - your now modified database.
Once you are finished, you will want to get rid of the extra instance (based on the PID of the local (-l) instance obtained above):
kill $PID
And destroy the temporary chroot structure:
umount ~/jail-pmxcfs/etc/pve ~/jail-pmxcfs/* && rm -rf ~/jail-pmxcfs/