2009-04-09

Linux/BSD: Serial Console vs SSH

We will be setting two different server administration methods against each other. In one corner we have a trusty serial console and in the other corner we have the newer Secure Shell (SSH).
Serial Console
If like many network administrators you have managed devices through a serial port, you may like to know that this can also be done for the command line on *Nix distros. It's set up at the hardware layer in it's most basic form with a null-modem serial cable connected to the serial ports on both computers. Naturally both computers must have a serial port which some newer computers don't as they are being depreciated.
The serial console has the advantage over SSH that it doesn't require the network to be running to work and the serial console adds no network services. A serial console is good for when you need to receive console messages remotely or you want root access restricted to a physical connection.
A Linux configuration example can be found here and the FreeBSD configuration information can be found here.
SSH
Secure Shell is a network service that operates over the network layer (an IPv4 network for example) and give access to a shell account via an encrypted channel. SSH can be used over structured cabling which makes it easy to implement. SSH offers key-based authentication, connection tunneling and secure file transfer which are useful to system administrators.
Configuration to get a working OpenSSH installation isn't typically required but tweeking may be required.
SSH provides Secure File Transfer (sftp) which helps cut down some of the administrative overhead that is part of using a serial connection.
Conclusion
SSH provides access to much more functionality than a serial console and has been around for long enough to be suitability mature. There are times when a serial connection can be useful, for example programmers debugging device drivers. For most people SSH is going to be the better option.

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