CentOS で ssh に突然パスワードが求められるようになった。。

事象

ある日気がついたら、vagrant up で起動中に

    default: Warning: Authentication failure. Retrying...
    default: Warning: Authentication failure. Retrying...
    default: Warning: Authentication failure. Retrying...
    default: Warning: Authentication failure. Retrying...
Timed out while waiting for the machine to boot. This means that
Vagrant was unable to communicate with the guest machine within
the configured ("config.vm.boot_timeout" value) time period.

If you look above, you should be able to see the error(s) that
Vagrant had when attempting to connect to the machine. These errors
are usually good hints as to what may be wrong.

If you're using a custom box, make sure that networking is properly
working and you're able to connect to the machine. It is a common
problem that networking isn't setup properly in these boxes.
Verify that authentication configurations are also setup properly,
as well.

If the box appears to be booting properly, you may want to increase
the timeout ("config.vm.boot_timeout") value.

となって起動に失敗する
とはいえ、vagrant sshでpasswordがもとめられ、passwordを入力したらログインはできる。

$  vagrant ssh
vagrant@127.0.0.1's password:
Last login: Sun Dec  8 21:25:06 2019 from 10.0.2.2

でも、ローカルのディレクトリはマウントされていないんです。。

環境

windows10 + vagrant + CentOS

解決方法

環境構築したてだと、.sshの権限周りとか、
windows updateに伴う、vagrant ssh-configから確認できるホスト側の秘密鍵の権限とか
あるみたいですが、

今回の場合、ちょっとした必要があって、 /home/vagrant のpermissionを777にしたのが原因でした。

chmod 700 /home/vagrant
で無事解決