Article 4R1W6 Unable to run sudo after upgrading Ubuntu server 14.04 to 16.04

Unable to run sudo after upgrading Ubuntu server 14.04 to 16.04

by
linuxsuser
from LinuxQuestions.org on (#4R1W6)
The Ubuntu server 14.04 was upgraded using "sudo do-release-upgrade' to 16.04. Then I cannot run sudo at all. The weird thing is that I can log in with "sysadmin", but get the error when trying sudo with "sysadmin"

sudo: policy plugin failed session initialization

sysadmin@XXX:~$
login as: sysadmin
sysadmin@XXX's password:
Welcome to Ubuntu 16.04.6 LTS (GNU/Linux 4.4.0-164-generic x86_64)

Documentation: https://help.ubuntu.com
Management: https://landscape.canonical.com
Support: https://ubuntu.com/advantage

System information as of Tue Sep 24 14:42:14 XXX 2019

System load: 0.17 Processes: 121 Usage of /: 14.2% of 35.07GB Users logged in: 0 Memory usage: 10% IP address for eth0: XXX Swap usage: 0%

Graph this data and manage this system at: https://landscape.canonical.com/

Last login: Tue Sep 24 14:31:33 2019 from XXX
sysadmin@XXX:~$ sudo su
[sudo] password for sysadmin:
sudo: policy plugin failed session initialization
sysadmin@XXX:~$latest?d=yIl2AUoC8zA latest?i=Xzk9XXGxy_M:tjYcS2WOFhs:F7zBnMy latest?i=Xzk9XXGxy_M:tjYcS2WOFhs:V_sGLiP latest?d=qj6IDK7rITs latest?i=Xzk9XXGxy_M:tjYcS2WOFhs:gIN9vFwXzk9XXGxy_M
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