[DOCUMENTATION] Setting the number of cores for rebuild using nh

[dwilliam62]

In the installation instructions regarding limiting cores you have :

For some computers, the default rebuild command might get stuck due to CPU cores running out of RAM. To fix that modify the install script line: sudo nixos-rebuild switch --flake .#${HOST} to sudo nixos-rebuild switch --cores <less than your max number of cores> --flake .#${HOST}

However you are now calling nh to do the rebuild. I didn't see online where I can set nh to limit cores. I changed that line to the nixos-rebuild as shown on the page, and I am trying the build now. As it did fail using nh. It's a VM on a proxmox server it has 2x processors and a total of 24 cores. but only 8GB of RAM.

If you know of a way to limit nh please add that to the instructions or maybe leave a commented version of the old command in the file if not.

Thanks and regards,

[Frost-Phoenix]

Hi, your right I completely forgot about that.
I think I fount how to do it: nix-shell -p nh --run "nh os switch -H ${HOST} . -- --cores <nb_cores>" with <nb_cores> the number of cores you want to use and ${HOST} beeing vm in your case, it should give the same result as the old one.
Let me know if this works for you, if not then I will simply put back the old command in a comment as you suggested.

[dwilliam62]

OK I will try that. I did end up using the old command and it worked well and I dbl'd the ram to 16GB as well. Thanks! I did look on nh page.

[dwilliam62]

Hi, your right I completely forgot about that. I think I fount how to do it: nix-shell -p nh --run "nh os switch -H ${HOST} . -- --cores <nb_cores>" with <nb_cores> the number of cores you want to use and ${HOST} beeing vm in your case, it should give the same result as the old one. Let me know if this works for you, if not then I will simply put back the old command in a comment as you suggested.

this does work, however, you seem to have to cut the number in 1/2. I have a 16 core VM. If I set it to 8 it still spawned builds on all 16 cores I had to drop it to 4. Thanks !