Help! lost /etc/passwd
Is there any other way to get it back? or recover to at least can let root login?
If you don't have backups you can boot up in rescue mode and copy a stock install version of the file to the server that will at least get root back. (note /etc/passwd doesn't actually contain the password)
The Rescue tab in the Linode manager will set up a dynamic Finnix boot, or you can define an explicit configuration using the Finnix initrd and kernel. I find the latter makes it easier to maintain my desired disk image mapping for the recovery boot, but if you don't have one already, using the Rescue tab is definitely quicker/easier.
Now what to do??