What is the simplest way to check if one has single or multi-user Nix installed?

toraritte · July 1, 2021, 1:11pm

As far as I can tell, one can just issue

cat /etc/group | grep nixbld

and if there is an output then it is a multi-user install, right?

abathur · July 1, 2021, 4:38pm

Hehe. I’m not sure there’s a good way. I recall seeing this general need come up in Unified profile script that detects single-user vs multi-user · Issue #3630 · NixOS/nix · GitHub

This is a probably a decent signal for some purposes, but it would be wrong if someone had an old multi-user install that hasn’t been completely cleaned.

(aside, you can just grep nixbld /etc/group)

toraritte · July 1, 2021, 4:55pm

Yeah, my solution sounded too simple to be true… Thanks for the issue (at least I know I’m not alone) and also for the CLI-golf; I keep forgetting this form of grep.

(Off-topic, but also thank you for compiling this list of Nix issues!)

lilyball · July 4, 2021, 10:33pm

What I settled on was to test if /nix/store is owned by root with the sticky bit. There’s a long explanatory comment in this code

github.com

lilyball/nix-env.fish/blob/00c6cc762427efe08ac0bd0d1b1d12048d3ca727/conf.d/nix-env.fish

# Setup Nix

# We need to distinguish between single-user and multi-user installs.
# This is difficult because there's no official way to do this.
# We could look for the presence of /nix/var/nix/daemon-socket/socket but this will fail if the
# daemon hasn't started yet. /nix/var/nix/daemon-socket will exist if the daemon has ever run, but
# I don't think there's any protection against accidentally running `nix-daemon` as a user.
# We also can't just look for /nix/var/nix/profiles/default/etc/profile.d/nix-daemon.sh because
# older single-user installs used the default profile instead of a per-user profile.
# We can still check for it first, because all multi-user installs should have it, and so if it's
# not present that's a pretty big indicator that this is a single-user install. If it does exist,
# we still need to verify the install type. To that end we'll look for a root owner and sticky bit
# on /nix/store. Multi-user installs set both, single-user installs don't. It's certainly possible
# someone could do a single-user install as root and then manually set the sticky bit but that
# would be extremely unusual.

set -l nix_profile_path /nix/var/nix/profiles/default/etc/profile.d/nix-daemon.sh
set -l single_user_profile_path ~/.nix-profile/etc/profile.d/nix.sh
if test -e $nix_profile_path
  # The path exists. Double-check that this is a multi-user install.

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Also to note, checking for the nixbld group won’t work if a multi-user install was replaced with a single-user install without fully cleaning it up first. This is true of testing pretty much anything outside of /nix/store.

henry-hz · January 19, 2022, 9:45pm

nix-shell -p nix-info --run "nix-info -m"

teto · September 3, 2022, 10:51am

shouldn’t this simple information be part of nix doctor ? (as well as the rest of nix-info)

Elkellympia · December 3, 2023, 3:49am

what about sudo systemctl status nix-daemon.service, since only multi user setups install the daemon, would not this option also be valid?

abathur · December 3, 2023, 5:25am

The presence of Nix doesn’t imply or require the presence of systemd.