id_rsa’ are too open.

I get the following error and I can no longer connect to SSH. The problem was solved by restricting the privileges of the private key.

WARNING: UNPROTECTED PRIVATE KEY FILE! @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
Permissions 0777 for '/root/.ssh/id_rsa' are too open.
It is recommended that your private key files are NOT accessible by others.
This private key will be ignored.
bad permissions: ignore key: /root/.ssh/id_rsa

$ chmod 600 /root/.ssh/id_rsa

Reference:　Error permission denied through ssh