05.12.2024 02:05, Vincent Lefevre wrote:
OK, but I'm still a bit uncomfortable with the fact that the implementation of cp is not specified (at least some missing guarantee that several cp's of the same file to the same target is OK). In the past, I had bad surprised with concurrent writes, but this could have been more complex cases (in my archives I can only find an issue with the zsh history, but truncate operations were also involved).
it's definitely a more complex case. There's no way you can get different result by running multiple `cp a b` in parallel, - they will be writing the same data to the same places, with the end result being the same.
BTW, I'm wondering whether when a second interface is brought up, /etc/resolv.conf could be modified, which would also be a problem.
That could happen to, in some theory. It's now a question how resolv.conf itself is updated - here, it is much more important to guard against multiple updates from DIFFERENT destinations. So if things are running in parallel there, there's a much more serious bug somewhere. Anyway. Today, with big shift from /etc/network/interfaces towards systemd-networkd or network-manager, so parallel execution of things managed by if-up.d/ et al becomes significantly less probable, I'm not going to spend more time on this. Also, a good advise here is to not run postfix chrooted to begin with, as upstream pleaded for decades. So I don't really see a point anymore. Thanks, /mjt
