When logging into any Computer Science Department machine, you are authenticated (i.e. verified) as a user in this department's Active Directory domain, DEPT.CS.PITT.EDU. The authentication process associates a Kerberos 5 token and an AFS token with your login process. The tokens you receive at each login are good for a period of 25 hours. If you are logged in for more than this time, your tokens automatically expire and you will not be able to access files in your home directories that are not publicly readable/writeable. To get new tokens,
issue the command "kinit", which will prompt you for your password
and reauthenticate you to the Active Directory Kerberos 5 domain. Next, issue the command "aklog" to obtain a new AFS token based on your Kerberos 5 token.
If your Kerberos 5 token has not yet expired and its maximum renewal period has not expired, you may type "krenew;aklog" to renew that token and reissue your AFS token.