Setting correct permissions for the ./ssh folder on Ubuntu
Because I am often setting up servers for testing, and fiddling around with SSH keys, I often get confronted with the error 'Permissions 0664 for '/home/alex/.ssh/id_rsa' are too open'.
This error is, as suggested, caused by permissions being incorrect for the id_rsa private key file used for SSH. Fixing the permissions will cause SSH to then work correctly.
To save me from always struggling to find the permissions, I've decided to just post them here as a reference to myself.