SSH

ssh-copy-id -p $PORT user@hostname

# Beginning with Redhat Enterprise Linux and CentOS 7, the default settings for sshd do not create a DSA host key. This can result in the following error: sshd[pid]: fatal: no hostkey alg [preauth]. This can cause session setup failures for older ssh clients. To allow those connections, perform the below steps. Bear in mind that this change was made to improve security, and this workaround allows weaker encryptions on the affected connections.
 
cd /etc/ssh
ssh-keygen -t dsa -f /etc/ssh/ssh_host_dsa_key
sudo vi /etc/ssh/sshd_config
# Add this line:
# HostKey /etc/ssh/ssh_host_dsa_key
sudo chgrp ssh_keys ssh_host_dsa_key
# test the ssh configuration
sudo sshd -t
# restart sshd
service sshd restart
# Then retry the connection with the older client.