Users removed by system update

[mahesh]

Hello friends , I am new to Ubuntu , I have installed a very clean system with very little packages .
Now I am facing a serious problem for the server system.

I installed the system 2022-05-21 with a default user myname which could login SSH and SUDO ,
after 5 days , I found I could not login the system via SSH , so I connected the console and recover the system by removing ROOT password .
After I logged to the system with recovered ROOT , I found the users are deleted when system apt update ran.

The log of the apt as follow:

     Code:

Code Select Expand

Start-Date: 2022-05-26  09:11:41
Commandline: apt-get -qq install python -y
[COLOR=#000000][FONT=Menlo]Install: libpython2-stdlib:amd64 (2.7.17-2ubuntu4, automatic), python2.7-minimal:amd64 (2.7.18-1~20.04.1, automatic), python2.7:amd64 (2.7.18-1~20.04.1, automatic), python2:amd64 (2.7.17-2ubuntu4, automatic), python2-minimal:amd64 (2.7.17-2ubuntu4, automatic), python-is-python2:amd64 (2.7.17-4), libpython2.7-minimal:amd64 (2.7.18-1~20.04.1, automatic), libpython2.7-stdlib:amd64 (2.7.18-1~20.04.1, automatic)
End-Date: 2022-05-26  09:11:46
and the auth.log as follow:

    Code:

Code Select Expand

/var/log/auth.log.1:May 26 09:12:23 webserver userdel[2579]: delete user 'myuser'
/var/log/auth.log.1:May 26 09:12:23 webserver userdel[2579]: delete 'myuser' from group 'adm'
/var/log/auth.log.1:May 26 09:12:23 webserver userdel[2579]: delete 'myuser' from group 'cdrom'
/var/log/auth.log.1:May 26 09:12:23 webserver userdel[2579]: delete 'myuser' from group 'sudo'
/var/log/auth.log.1:May 26 09:12:23 webserver userdel[2579]: delete 'myuser' from group 'dip'
/var/log/auth.log.1:May 26 09:12:23 webserver userdel[2579]: delete 'myuser' from group 'plugdev'
/var/log/auth.log.1:May 26 09:12:23 webserver userdel[2579]: delete 'myuser' from group 'lxd'
/var/log/auth.log.1:May 26 09:12:23 webserver userdel[2579]: removed group 'myuser' owned by 'myuser'
/var/log/auth.log.1:May 26 09:12:23 webserver userdel[2579]: removed shadow group 'myuser' owned by 'myuser'
/var/log/auth.log.1:May 26 09:12:23 webserver userdel[2579]: delete 'myuser' from shadow group 'adm'
/var/log/auth.log.1:May 26 09:12:23 webserver userdel[2579]: delete 'myuser' from shadow group 'cdrom'
/var/log/auth.log.1:May 26 09:12:23 webserver userdel[2579]: delete 'myuser' from shadow group 'sudo'
/var/log/auth.log.1:May 26 09:12:23 webserver userdel[2579]: delete 'myuser' from shadow group 'dip'
/var/log/auth.log.1:May 26 09:12:23 webserver userdel[2579]: delete 'myuser' from shadow group 'plugdev'
/var/log/auth.log.1:May 26 09:12:23 webserver userdel[2579]: delete 'myuser' from shadow group 'lxd'
I have lost system control serval times for Ubuntu with username rather than ROOT ,
am I have any mis-understanding of Ubuntu systems ?
Was it cause by my mistakes ? Thanks for any advise.