I got this error when trying to run a few commads with sudo right after I set password expiration on my RHEL7 box. Immediately after, I couldn’t use sudo for any commands… This how I got to resolve it.
sudo: pam_open_session: System error
sudo: policy plugin failed session initialization

I realised the issue comes from password expiration. The moment I set my expiration period as 20 days, it seems to have immediately expired my password – perhaps because its been over 90 days since I installed my OS and I have never changed the password.
To resolve this, I simply changed the password usng passwd command
[wm@serv0-wal Downloads]$ passwd Changing password for user wm. Changing password for wm. (current) UNIX password: New password: Retype new password: passwd: all authentication tokens updated successfully.
After that, I could now run my commands in sudo normally.
