First modify the permissions of the PEM file:

sudo chmod 600 key.pem

The command for Mac OS to connect to a server using a PEM file is as follows:

ssh -i key.pem root@IP

You can also use ssh-add to add the key file:

ssh-add -k key.pem  

Then just log in normally:

ssh root@IP

In addition, we often experience disconnection issues during use, which can be solved by modifying the following configuration.

Log in to the server:

vim /etc/ssh/sshd_config

Find the following two lines:

ClientAliveInterval 0
ClientAliveCountMax 3

Uncomment and change them to:

ClientAliveInterval 30 
ClientAliveCountMax 86400

The meanings of these two lines are:

  • 1. The client sends a heartbeat packet to the server every certain number of seconds.
  • 2. If the client does not respond within a certain number of seconds, the server automatically disconnects.

Restart the sshd service:

service sshd restart