Copied from my post on the Nix forums:
I had a home server that I built some applications on about a year ago. The design was NixOS as the host, which ran a Go executable natively. In a container (I think I called it dabba, but so much has happened between setting it up and now that I can’t really remember) was the mysql database.
I noticed one day that the Go program was throwing errors, so I checked my logs and noticed that the database wasn’t being connected to. I wasn’t too surprised, as we’ve had random power outages in my area as long as I can remember. I’d recently restarted my home server after one and assumed that I’d forgotten to restart my mariadb lxd container. I issued the command (I think it was sudo lxc exec dabba -- /bin/bash) to enter into and restart the db container and got an error telling me that
Unsupported command 'exec'
Known commands:
attach autostart cgroup checkpoint config console copy create destroy device execute freeze info ls monitor snapshot start stop top unfreeze unshare wait
I’m pretty sure this is the command that I’ve used for eternity, so it doesn’t make sense to me that it would now be telling me that the command doesn’t exist. I will say that I had recently done an upgrade with sudo nixos-rebuild switch but I’m pretty sure I’d started it since that upgrade.
From what I’ve found online, that’s the output of an older version of lxc, but I just did an upgrade so I don’t know why one particular executable is now older. Doing sudo lxc ls shows two containers, neither of which is my db container. They look like containers that I would have created while originally learning lxc/lxd.