Some of the commonly encountered technical errors on TSD.

**1. Host key verification failed **
 
When ssh-ing to submit or appnode, users may get this error if they login to TSD after sometime not using it. In this case, use the following command, and connect to the node again.


  
  rm ~/.ssh/known_hosts

** 2. Permission denied error while accessing cluster ** 

The TSD cluster follows kerberos authentication (https://www.uio.no/english/services/it/research/sensitive-data/help/hpc/data.html. Login to the submit and appn automatically creates a kerberos ticket which renews itself for 7 days. After the ticket expires, you would get permission denied message while trying to access the cluster folder. Please log out and log in again to generate a new ticket and don't use 'kinit' command manually as it will expire in 10 hours and will not renew automatically. Having ssh keys in ~/.ssh folder (which is strictly not recommended) can also hinder creating a new ticket, so delete the ssh keys, for ex: rm ~/.ssh/id_rsa*  command will remove the default ssh keys. Simple log out and log in again should fix the issue otherwise.

