When exactly are "dangling" post-up clauses executed? `post-up|down` clauses in `/etc/network/interfaces` on Debian-based distributions can be either defined right after an interface definition, or "dangling". See a very simple example: auto lo iface lo inet loopback auto eth0 iface eth0 inet static address 10.10.10.10 ... post-up <command1> post-up <command2> It's pretty clear to me that `command1` will be executed once `eth0` is up. However, when is `command2` executed? Is it when _all_ interfaces are up? Or is it when _any_ interface is up?

`command2` is not "dangling", it is a post-up option for eth0, so it will be executed right after `command1`. From man interfaces:

> Options are usually indented for clarity (as in the example above) but are not required to be.

Also, empty lines are ignored in `/etc/network/interfaces` (and in all included files).