No space left on device 의 원인과 해결을 찾아보려고 합니다

취미삼아 웹서버로 운용하는 우분투가 하나 있습니다.
여느날과 같이 업데이트를 하는데 용량이 가득 찼다며 업데이트를 할 수 없었습니다.

$ sudo apt-get update

Ign:1 http://us.archive.ubuntu.com/ubuntu focal InRelease                                                 
Get:2 https://artifacts.elastic.co/packages/7.x/apt stable InRelease [13.7 kB]                            
Ign:3 http://ppa.launchpad.net/ondrej/php/ubuntu focal InRelease                 
Err:2 https://artifacts.elastic.co/packages/7.x/apt stable InRelease
  Couldn't create temporary file /tmp/apt.conf.NcZqRk for passing config to apt-key
Ign:4 http://security.ubuntu.com/ubuntu focal-security InRelease         
Get:5 http://us.archive.ubuntu.com/ubuntu focal-updates InRelease [114 kB]
Err:6 http://ppa.launchpad.net/ondrej/php/ubuntu focal Release                                            
  Could not open file /var/lib/apt/lists/partial/ppa.launchpad.net_ondrej_php_ubuntu_dists_focal_Release - open (28: No space left on device) [IP: 91.189.95.85 80]
Err:7 http://security.ubuntu.com/ubuntu focal-security Release                                            
  Could not open file /var/lib/apt/lists/partial/security.ubuntu.com_ubuntu_dists_focal-security_Release - open (28: No space left on device) [IP: 91.189.91.38 80]
Err:5 http://us.archive.ubuntu.com/ubuntu focal-updates InRelease                     
  Couldn't create temporary file /tmp/apt.conf.F39QHn for passing config to apt-key
Err:8 http://us.archive.ubuntu.com/ubuntu focal Release
  Could not open file /var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_focal_Release - open (28: No space left on device) [IP: 91.189.91.38 80]
                        
** (appstreamcli:892436): CRITICAL **: 14:03:58.756: Unable to open temporary cache: Unable to open temporary cache file: No space left on device
Traceback (most recent call last):
  File "/usr/lib/cnf-update-db", line 26, in <module>
    col.create(db)
  File "/usr/lib/python3/dist-packages/CommandNotFound/db/creator.py", line 108, in create
    os.rename(tmpdb, dbname)
OSError: [Errno 28] No space left on device: '/var/lib/command-not-found/commands.db.tmp' -> '/var/lib/command-not-found/commands.db'
Error in sys.excepthook:
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/apport_python_hook.py", line 153, in apport_excepthook
    with os.fdopen(os.open(pr_filename,
OSError: [Errno 28] No space left on device: '/var/crash/_usr_lib_cnf-update-db.0.crash'

Original exception was:
Traceback (most recent call last):
  File "/usr/lib/cnf-update-db", line 26, in <module>
    col.create(db)
  File "/usr/lib/python3/dist-packages/CommandNotFound/db/creator.py", line 108, in create
    os.rename(tmpdb, dbname)
OSError: [Errno 28] No space left on device: '/var/lib/command-not-found/commands.db.tmp' -> '/var/lib/command-not-found/commands.db'
Reading package lists... Error!
W: GPG error: https://artifacts.elastic.co/packages/7.x/apt stable InRelease: Couldn't create temporary file /tmp/apt.conf.NcZqRk for passing config to apt-key
E: The repository 'https://artifacts.elastic.co/packages/7.x/apt stable InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://ppa.launchpad.net/ondrej/php/ubuntu focal Release' no longer has a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://security.ubuntu.com/ubuntu focal-security Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: GPG error: http://us.archive.ubuntu.com/ubuntu focal-updates InRelease: Couldn't create temporary file /tmp/apt.conf.F39QHn for passing config to apt-key
E: The repository 'http://us.archive.ubuntu.com/ubuntu focal-updates InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://us.archive.ubuntu.com/ubuntu focal Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: Problem executing scripts APT::Update::Post-Invoke-Success 'if /usr/bin/test -w /var/lib/command-not-found/ -a -e /usr/lib/cnf-update-db; then /usr/lib/cnf-update-db > /dev/null; fi'
E: Sub-process returned an error code
E: Unable to mkstemp /tmp/clearsigned.message.1SYkdy - GetTempFile (2: No such file or directory)
E: The package lists or status file could not be parsed or opened.

로그가 가득 쌓여서 그런가 싶어 로그를 지웠는데 그래도 용량이 모자르다고 합니다.
저장공간은 충분한거 같습니다.

$ df -h
Filesystem      Size  Used Avail Use% Mounted on
udev            1.9G     0  1.9G   0% /dev
tmpfs           381M   40M  342M  11% /run
/dev/sda2        41G   15G   26G  37% /
tmpfs           1.9G     0  1.9G   0% /dev/shm
tmpfs           5.0M  4.0K  5.0M   1% /run/lock
tmpfs           1.9G     0  1.9G   0% /sys/fs/cgroup
/dev/loop7       56M   56M     0 100% /snap/core18/2066
/dev/loop5      219M  219M     0 100% /snap/gnome-3-34-1804/66
/dev/loop2      100M  100M     0 100% /snap/core/10908
/dev/loop1      162M  162M     0 100% /snap/gnome-3-28-1804/128
/dev/loop9      2.3M  2.3M     0 100% /snap/gnome-system-monitor/148
/dev/loop10     218M  218M     0 100% /snap/gnome-3-34-1804/60
/dev/loop4      100M  100M     0 100% /snap/core/10958
/dev/loop14      66M   66M     0 100% /snap/gtk-common-themes/1515
/dev/loop11      52M   52M     0 100% /snap/snap-store/498
/dev/loop12     2.3M  2.3M     0 100% /snap/gnome-system-monitor/157
/dev/loop3      141M  141M     0 100% /snap/gnome-3-26-1604/102
/dev/loop15      52M   52M     0 100% /snap/snap-store/518
/dev/loop13     163M  163M     0 100% /snap/gnome-3-28-1804/145
/dev/loop6       56M   56M     0 100% /snap/core18/1997
/dev/loop8       65M   65M     0 100% /snap/gtk-common-themes/1514
/dev/loop0      141M  141M     0 100% /snap/gnome-3-26-1604/100
/dev/sda3       424G   43G  382G  10% /home

파일시스템을 btrsf를 사용해서 그런걸까 싶어.
이곳저곳의 백업 지우는 방법을 찾아 용량을 확보했는데도 용량이 모자르다고 합니다.
이 다음 무엇을 해보는것이 좋을까요?