SSH Key: “Permissions 0644 for 'id_rsa.pub' are too open.” on mac

Question

I generate a ssh key pair on my mac and add the public key to my ubuntu server(in fact, it is a virtual machine on my mac),but when I try to login the ubuntu server,it says:

Answer 1

giving permision 400 makes the key private and not accessible by someone unknown. It makes the key as a protected one.

chmod 400 /Users/tudouya/.ssh/vm/vm_id_rsa.pub