updated nix.md

Author: djsnipa1

nix.md

@@ -1,5 +1,61 @@
 # Nix
 
+## Garbage Collecting Error - Disk Full
+
+If you try to 
+
+# cd /nix/var/nix/db
+# nix-shell -p sqlite
+
+[nix-shell:/nix/var/nix/db]# sqlite3 db.sqlite ".backup 'db.bak.sqlite' "
+
+[nix-shell:/nix/var/nix/db]# sqlite3 db.sqlite 
+SQLite version 3.24.0 2018-06-04 19:24:41
+Enter ".help" for usage hints.
+sqlite> .output db.sql
+sqlite> .dump
+sqlite> 
+
+[nix-shell:/nix/var/nix/db]# sqlite3 db.new.sqlite < db.sql
+
+[nix-shell:/nix/var/nix/db]# mv db.new.sqlite db.sqlite
+```
+
+---
+nix-env --delete-generations old
+nix-collect-garbage
+sudo nix-collect-garbage
+We're down to 19.1 GiB
+Let's do a full rebuild and make sure we're as compact as possible. Note that this removes old generations, make sure your system is stable first.
+nix-channel --update
+sudo nix-channel --update
+sudo rm /nix/var/nix/gcroots/auto/*
+nix-collect-garbage -d
+sudo nix-collect-garbage -d
+Down to 9.4 GiB
+By hardlinking identical files we can save some additional space:
+sudo nix-store --optimize
+Now we're down to a nice trim 9.0 GiB - a savings of 15.1 GiB at the cost of losing some history.
+Note that any shells you have will have to be rebuilt or refetched.
+Pruning docker
+I use docker for application development, this was done before but can save considerable space:
+docker system prune
+Note that this will delete a whole bunch of stuff, if you have any data not stored in volumes it will be lost.
+Clearing your .cache folder
+My .cache folder stands at 9.9 GiB
+The highest amount is currently spotify. By editing ~/.config/spotify/prefs and adding:
+storage.size=2048
+then restarting spotify it will trim down its storage.
+Next up is yarn.
+yarn cache clean
+saves me another 2.1 GiB
+~/.local/share/Trash has considerable data in it, which after quick verification doesn't have anything I care about.
+rm -rf ~/.local/share/Trash/files/*
+rm -rf ~/.local/share/Trash/files/.*
+After this I spent a bit poking around in ncdu and deleting old projects and forks that were not longer used.
+
+---
+
 ## Get sha256 of URL or URL tarball
 
 ```bash