openssh-server 升级后，无法从known_hosts文件中删除旧密钥，因为ssh-keygen出现以下情况：
$ ssh-keygen -R oldserver
/home/grin/.ssh/known_hosts:1: invalid line
/home/grin/.ssh/known_hosts:12: invalid line
/home/grin/.ssh/known_hosts:123: invalid line
Not replacing existing known_hosts file because of errors
我是否必须逐一删除这些行？