How to login to a Linux server with a second ssh key

ssh-key-login.sh

# generate your new ssh key (e.g. id_rsa_second)
ssh-keygen

# add the public key to server manually (from your host panel) or by:
ssh-copy-id -i ~/.ssh/id_rsa_second.pub root@server_ip_address_here

vim ~/.ssh/config
# enter this code:
Host server_ip_address_here
  AddKeysToAgent yes
  UseKeychain yes
  IdentityFile ~/.ssh/id_rsa_second
  
# now login to server
ssh root@server_ip_address_here
# no password is required