Slow rebuild (single threaded)

[taki-sahli]

Hello,
The nixos-rebuild command tooks so much time to build my configuration.
In btop, the command uses only one thread.
Even I add the --max-jobs and --cores flags, but no success.
One built unit takes min 1 minute, so for this task, it needs 3 hours to complete 🤯.

Can you help me fix this issue.
Thank you.

[nzbr]

This is probably not an issue specific to WSL. Was it stuck on the same derivation (builder.pl in the screenshot) the whole time or did every derivation take a long time?

[taki-sahli]

Hello, actualy it was all derivations, the build in the screenshot took 6 hours to finish.
I found the cause the problem, it was the sudo command, when I run sudo nixos-rebuild switch, it was super slow, but when I run nixos-rebuild build, it was super fast, so now I'm using this script to switch:

nixos-rebuild build
sudo ./result/activate
rm ./result

For remote, I use this command:

NIX_SSHOPTS="-i /home/user/.ssh/private.key" \
  nixos-rebuild \
    switch \
    --target-host "user@${hostname}" \
    --use-remote-sudo

Reference: https://discourse.nixos.org/t/can-i-run-nixos-rebuild-switch-flake-rootless/14610/3