Lxc exec results in "Error: Failed to retrieve PID of executing child process"

[tomp (Thomas Parrott)]

If you’re running the snap package it could well be related to one of these:

LXD snap transitioning to core20 and losing i386 support

There have been a few issues caused by the switch to core20 which I thought would be worth documenting in case any body is affected: Core20 prevented LXD’s ability to detect and use the xtables firewall driver LXD supports two firewall drivers; xtables (iptables, ip6tables, ebtables and arptables), and nftables. LXD will detect the presence of the firewall commands available, as well as the rule sets already in use, and will pick what it thinks is the most appropriate firewall driver to use. …

LXD stopped generating firewall rules after switch to core20

This is a workaround in meantime Lxd bridge doesn't work with IPv4 and UFW with nftables - #17 by tomp