Ubuntu 20.04 で command-not-found が機能しなくなった

ubuntu-20.04-command-not-found.md

Ubuntu 20.04 の command-not-found が動かなくなってた. いつからか不明.

$ /usr/lib/command-not-found emacs
Sorry, command-not-found has crashed! Please file a bug report at:
https://bugs.launchpad.net/command-not-found/+filebug
Please include the following information with the report:

command-not-found version: 0.3
Python version: 3.8.10 final 0
Distributor ID: Ubuntu
Description:    Ubuntu 20.04.2 LTS
Release:        20.04
Codename:       focal
Exception information:

unable to open database file
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/CommandNotFound/util.py", line 23, in crash_guard
    callback()
  File "/usr/lib/command-not-found", line 90, in main
    cnf = CommandNotFound.CommandNotFound(options.data_dir)
  File "/usr/lib/python3/dist-packages/CommandNotFound/CommandNotFound.py", line 79, in __init__
    self.db = SqliteDatabase(dbpath)
  File "/usr/lib/python3/dist-packages/CommandNotFound/db/db.py", line 12, in __init__
    self.con = sqlite3.connect(filename)
sqlite3.OperationalError: unable to open database file

直接の原因はパッケージ検索のためのDBファイルに読み取り権限がついていないことだと思う.

$ ls -l /var/lib/command-not-found/
total 3096
-rw------- 1 root root 3162112 Jul 25 22:36 commands.db
-rw------- 1 root root    3306 Jul 25 22:36 commands.db.metadata

なので, 読み取り権限を与えてやれば動くようにはなる.

$ sudo chmod o+r /var/lib/command-not-found/commands.db                                        3.7m
$ /usr/lib/command-not-found emacs

Command 'emacs' not found, but can be installed with:

sudo snap install emacs        # version 27.2, or
sudo apt  install e3           # version 1:2.71-2
sudo apt  install emacs-gtk    # version 1:26.3+1-1ubuntu2
sudo apt  install emacs-lucid  # version 1:26.3+1-1ubuntu2
sudo apt  install emacs-nox    # version 1:26.3+1-1ubuntu2
sudo apt  install jove         # version 4.17.2.7-1

See 'snap info emacs' for additional versions.

でもなぜ?