OpenSSH to deprecate SHA-1 logins due to security risk

To check whether a server is using the weak ssh-rsa public key algorithm, for host authentication, try to connect to it after removing the ssh-rsa algorithm from ssh(1)'s allowed list:

ssh -oHostKeyAlgorithms=-ssh-rsa user@host

If the host key verification fails and no other supported host key types are available, the server software on that host should be upgraded.