1 About OpenSSH

OpenSSH secures communications between networked systems.

Note:

This document includes content that was tested against Oracle Linux 8 and Oracle Linux 9, but generally applies to most Oracle Linux releases, and might also apply to other distributions.

OpenSSH is suite of network connectivity tools that provides secure communications between systems. The tools include:

• scp - Secure file copying. (Deprecated in Oracle Linux 9)
• sftp - Secure File Transfer Protocol (FTP).
• ssh - Secure shell to log on to or run a command on a remote system.
• sshd - Daemon that supports the OpenSSH services.
• ssh-keygen - Creates RSA authentication keys.

Note:

The Digital Signature Algorithm (DSA) is considered deprecated. As such, authentication mechanisms that depend on DSA keys don't work in the default configuration for Oracle Linux 8 or later. Note also that OpenSSH clients don't accept DSA host keys, even at the LEGACY system-wide cryptographic policy level on Oracle Linux 8 or later.

Unlike utilities such as rcp, ftp, telnet, rsh, and rlogin, OpenSSH tools encrypt all network packets between the client and server, including password authentication.

To use the OpenSSH tools, a user must have an account on both the client and server systems. You don't need to configure these accounts identically on each system. OpenSSH uses the SSH version 2 (SSH2) protocol. You can use any SSH2 client to access an OpenSSH server and equally you can use the OpenSSH client to access any SSH2 server.

OpenSSH also provides a secure way of using graphical applications over a network by using X11 forwarding. You can also use port forwarding as another way to secure otherwise insecure TCP/IP protocols.