While changing FTP user password from the Plesk panel or from the shell the following error is occur.
Unable to update hosting preferences: system user update is failed: Unable to create system user: usermng: PAM password change failed: 20, Authentication token manipulation error
To resolve the above error refer to the following steps from the shell.
Open a file /etc/pam.d/plesk_usermng_encrypted and comment the “password required pam_deny.so” line.
The file should look like
#password required pam_plesk.so try_first_pass
#password required pam_deny.so
password required pam_plesk.so try_first_pass
After making the above changes, if you are still not able to change the FTP account password than login in to the shell and run the command because user information is not available in the /etc/shadow file which need to be re-sync by using the following command.
Now reset the passowrd
Change the password from the Plesk panel.