Nix daemon fails to start on macOS 10.15 Catalina

[callahad]

Describe the bug
The Nix daemon does not start after boot for multi-user installations on macOS 10.15 (Catalina).

To Reproduce

1. Prepare macOS 10.15 (Catalina) for Nix:

   1. echo 'nix' | sudo tee -a /etc/synthetic.conf

   2. Reboot

   3. Create the Nix volume:

      sudo diskutil apfs addVolume disk1 APFSX Nix -mountpoint /nix
      sudo diskutil enableOwnership /nix
      sudo chflags hidden /nix
      echo "LABEL=Nix /nix apfs rw" | sudo tee -a /etc/fstab
      

2. Install Nix with sh <(curl https://nixos.org/nix/install) --daemon

3. Reboot

Observed behavior

Nix stops working after reboot; commands fail with:

error: cannot connect to daemon at `/nix/var/nix/daemon-socket/socket': Connection refused

Similarly, the Nix daemon is not seen by launchd: launchctl list | grep nix finds nothing.

Root Cause

Nix installs /Library/LaunchDaemons/org.nixos.nix-daemon.plist as a symlink into the Nix store.

At boot, launchd sees this as a dangling symlink as the Nix volume is not mounted early enough. Thus, it is unable to load the plist, and the nix daemon does not start.

Workaround

You can manually start the daemon after each boot with launchctl load /Library/LaunchDaemons/org.nixos.nix-daemon.plist && launchctl start org.nixos.nix-daemon.

Alternatively, manually copy the plist into /Library/LaunchDaemons, replacing the symlink with an actual copy of the file.

If you do the latter, you may want to adjust the paths inside the plist to point to /nix/var/nix/profiles/default/bin/nix-daemon rather than a specific derivation inside the Nix store.

Metadata

• system: "x86_64-darwin"
• host os: Darwin 19.0.0, macOS 10.15
• multi-user?: yes
• sandbox: no
• version: nix-env (Nix) 2.3
• channels(root): "nixpkgs-20.03pre194957.bef773ed53f"
• nixpkgs: /nix/var/nix/profiles/per-user/root/channels/nixpkgs

[mroi]

Isn’t this issue supposed to be fixed by 800fba1?

[callahad]

That commit is a necessary but incomplete fix.

It only ensures that org.nixos.nix-daemon.plist waits until /nix is mounted before it tries to run nix-daemon.

But if launchd can't read org.nixos.nix-daemon.plist, then it fails immediately and nothing we put inside that file matters.

This fails because the multi-user installer symlinks the plist, and that symlink is broken if /nix isn't mounted. Apparently /nix is not yet mounted when launchd attempts to read that file at boot.

[mroi]

Damn. Thanks for clearing this up.

[ElvishJerricco]

How reasonable would it be to just copy the plist instead of symlinking it?

[matthewbauer]

Yeah missed this one. Copying the file would be necessary unfortunately. The reason we do the symlink is to get updates automatically for Nix. Migration step would be:

sudo cp -f `readlink /Library/LaunchDaemons/org.nixos.nix-daemon.plist` /Library/LaunchDaemons/org.nixos.nix-daemon.plist

[matthewbauer]

Opened #3128

[arnalyse]

Although this issue is closed, I wanted to mention that the installation fails with the copy command, in case the target file exists. I got the following error:

---- sudo execution ------------------------------------------------------------
I am executing:

    $ sudo cp -f /nix/var/nix/profiles/default/Library/LaunchDaemons/org.nixos.nix-daemon.plist /Library/LaunchDaemons/org.nixos.nix-daemon.plist

to set up the nix-daemon as a LaunchDaemon

cp: /Library/LaunchDaemons/org.nixos.nix-daemon.plist and /nix/var/nix/profiles/default/Library/LaunchDaemons/org.nixos.nix-daemon.plist are identical (not copied).

Maybe it would be safer to remove the file and then do the copy.

[matthewbauer]

Although this issue is closed, I wanted to mention that the installation fails with the copy command, in case the target file exists. I got the following error:

---- sudo execution ------------------------------------------------------------
I am executing:

    $ sudo cp -f /nix/var/nix/profiles/default/Library/LaunchDaemons/org.nixos.nix-daemon.plist /Library/LaunchDaemons/org.nixos.nix-daemon.plist

to set up the nix-daemon as a LaunchDaemon

cp: /Library/LaunchDaemons/org.nixos.nix-daemon.plist and /nix/var/nix/profiles/default/Library/LaunchDaemons/org.nixos.nix-daemon.plist are identical (not copied).

Maybe it would be safer to remove the file and then do the copy.

Is that a fatal error? If so, that sounds like the sane thing to do.

[domenkozar]

i also hit this, but I don't think it should be fatal. It's a leftover from previous installation and can be just copied over.

[domenkozar]

It would be better to use install ...

[domenkozar]

#3532