As root you can run:

Code:

echo appuser:abc1234 | chpasswd -c

The -c flag will make sure that the password doesn't need to be changed at next logon.

Although if this is shared application account you may wish to consider having users login as themselves and switching to the appuser via sudo - where they enter there own password rather than that of the account. That way it is possible to track which users have been working in the appuser account,