The article provides steps to recover the device when device boots up in Amnesiac mode

1. The device will go down and come-up in Amnesiac state .
2. The device will not accept any local and root credentials do not work.
3. It shows below logs messages in the logon screen i.e "login_getclass: unknown class ;junos-login-defaults;"

FreeBSD/amd64 (Amnesiac) (ttyu0)

login: Username

May 17 01:03:03 last message repeated 5 times

May 17 01:03:37 login: login_getclass: unknown class ;junos-login-defaults;

Password:

May 17 01:03:37 login: login_getclass: unknown class ;junos-login-defaults;

We can try below steps to resolve the issue,

1. Try to power drain the device and check if device boots up in normal mode.
2. Try to login to device with username "root" and press enter without any password , if device is loaded with factory default.
3. The other reason why the switch can be in a bad state is because the switch couldn't apply the configuration as it detected commit errors that need to be fixed manually.This can be easily identified by going into configuration mode and issuing a “show | compare” command from CLI.
4. Issuing a “commit check” from configuration mode will allow to identify any commit errors that can make the configuration incompatible or missing configuration . Correct these errors, commit again and the switch should start to work fine once again.
5. If customer is not able to login into device with any credentials, then we need to do format install using USB.
6. If the above steps does help in resolving  the issue ,please reachout to JTAC