I also have this problem for 2 morning. I checked and my rig is down for 4 hour. The first time, I restart the miner and it goes back to being online and working. This morning, the 2nd time, no matter how many time I restart the miner or reboot the system, it wont work. I hooked up the monitor to it and check and its unable to connect to the server. I did a Hello test but it still didn’t work. I ended up doing the firstrun -f and reconfigure the rig. That ended up working again. I dont know why it did that but I hope this help you.
You can change password in standard linux manner.
First at all you can (must) change password for user “user”. It’s main secure rule for HiveOS because this user account almost as root
It can be done by typing in console
passwd user
User account “root” by default can’t connect to rig by SSH, but still can do this from the local console with empty password. So you can change password for root but … IMHO it’s no sense for rig