Blocky on NixOS cannot write logs to certain directory

[underdog54]

Hello I am trying to use Blocky with NixOS, and I specified a path on where the logs get written, but I keep getting an error saying fileQueryLogWriter: can't create/open fileopen /logs/2024-11-06_ALL.log: read-only file system. I am quite new to NixOS so I think this is expected anyway, but I am not fully sure.

This is the part of my config I have that tells where to write the logs:

queryLog = { type = "csv"; target = "/logs"; logRetentionDays = 1; };
Thanks in advance!

[ThinkChaos]

Hey, yes the root filesystem is read-only so you can't just create a directory there.

Putting stuff at the root is anyways not a good practice, the filesytem layout actually follows something called the Filesystem Hierarchy Standard (FHS). It's common to put things at the root for containers, but that's generally an ugly hack if you ask me.

In the NixOS community you might see people mention the FHS because NixOS doesn't strictly follow it since it puts most things in the Nix store and then symlinks only some of them at the more standard path. This breaks a lot of programs, for instance running all prebuilt dynamically linked binaries since those binaries hardcode a path to the dynamic linker like /lib/ld-linux.so.6 which doesn't exist on NixOS. You can still wrap such programs so they're run in a fake FHS and work; steam-run for instance does that.

Anyways here, you should point blocky to something in a directory it has write access to. Systemd can create a directory for you, see LogsDirectory (untested):

# This modifies the blocky systemd unit (it will be merged with what's defined in the NixOS module)
# It needs to go at the root of the config, basically at the same level as where you wrote services.blocky
systemd.services.blocky.serviceConfig.LogsDirectory = "blocky";

# Configure the query log to be under the LogsDirectory
# I wrote the full path to the config value but this would work just as well copied into your snippet
services.blocky.config.queryLog.target = "/var/log/blocky/queries";

It's possible to avoid needing to knowing the log dir value in advance, doing something like this (untested). In this case it's not too useful, but shows off BindPaths which is good to know about:

# Think of `BindPaths` like a container volume mount, the bound path is only visible to the unit
# The idea here is we use %L which Systemd expands to the `LogsDirectory`, and make it accessible at a known path
# See man systemd.unit for %L and others
systemd.services.blocky.serviceConfig.BindPaths = [ "%L/blocky/queries:/run/blocky-query-logs" ];

# Then we can hard code that known path in the blocky config
services.blocky.config.queryLog.target = "/run/blocky-query-logs";

P.S. I happen to use NixOS so can reply, but this kind of question would better be posted on the NixOS community forum.

[underdog54]

Hi, thank you so much! I didn't know that you can specify the Logs Directory of a Systemd unit in NixOS ( lol still have a lot more to learn). I am currently in the process of moving my home server and laptop to NixOS entirely. This really helps. Thanks again!