As a consultant who works with remote clients and, before that, a telecommuting systems engineer for companies who used linux I have often encountered the problem of collaborating inside of a remote client that does not have X and who’s only access is ssh. Servers with GUI interfaces like Windows or Mac OS X have a long history of tools to share the desktop with multiple users, oddly enough both are called Remote Desktop. Servers that only have a command line interface, like most linux servers, do not have such an obvious tool for sharing the terminal with another user. While bash and ssh can be manipulated to accomplish this, screen fills this roll nicely.

Screen allows you to create virtual terminals that you can detach from and attach to at will. Detaching from a screen will leave it running in the background. Attaching to it again allows you to keep executing commands where you were or see the current state of a process you left running. If you are the user who started the screen you can attach to a screen that is already attached to, this is is how the shared screen is accomplished.

To set it up, one user logs in to the server and, using su or sudo su, changes to either the second users account or an account that all parties can access. Next, start screen with the -S option and give it a meaningful name.

me@jjtest:~# sudo su – theOtherGuy
theOtherGuy@jjtest:~# screen -S blogTest

If screen is not installed, it is available as a package on most popular linux distributions. You are now in a screen session as theOtherGuy. Now just tell theOtherGuy to log in and that your screen is called blogTest and he will simply need to run screen with the -x option and give the screen name.

theOtherGuy@jjtest:~# screen -x blogTest

At this point you are both in the same screen session and can both interact with it. This is great for showing another user what kind of problems you may be having or how to do a certain process. It can also be used to accomplish remote pair programing on the remote system. And this doesn’t have to be limited to just two users, as long as someone can get to that system as that user they can join the screen as well.

Typing exit at this point will kill the screen and kick both of you out. If one user wants to leave but not kick the other person off the user just presses Ctrl+a and then d, this will detach you from the screen. Ctrl+a is the default hot key for activating screen commands. You can read more about the variety of command available on screen at this site or read abut it fully on the man page.

Screen can be used to do so much more than I’ve talked about here but it’s ability to facilitate the sharing of a terminal between users can be a life saver when you need it. It is not normally installed by default to may linux systems so you may have to install it or ask that it be installed.

This post originally written for my personal blog on June 14th 2009.

As a systems administrator in many mixed Windows and linux environments I have seen and made many of my own attempts at integrating the linux servers into the Windows Active Directory structure with mixed results. Linux registration and authentication inside of a Windows domain is akin to the bigfoot: some have claimed to see one, many have worked long hours to find them, no one can produce consistent results. Until now.

At the suggestion by a coworker I decided to give Likewise a try on my most recent attempt at bringing our linux servers into the windows domain. Skeptically I built a new CentOS 5.3 server and proceeded to follow the instructions for installing Likewise. The seemed too simple and with each step I waited for the fatal issue that would bring the test to it’s demise. Software installed, no issues. As I reviewed the instructions for adding the system to the domain and found that it only required one command and no further configuration of files I thought, “This is so going to fall on it’s face.” Command executed and I’m waiting, then it comes up on the screen: Success. Success? Really? I don’t believe it, I log onto the domain controller and there it is, right where new computers are supposed to go in the domain. I quickly flip over to the manual and look up how to authenticate for ssh, simple DOMAIN\\username@host, and give it the final test. Success. In the span of 15 minutes I was able to install the app, add my computer to the domain and authenticate against the domain. 15 more minutes and I was able to limit who could log in and give them sudo access. This is a huge win for any admin who deals with linux servers in a domain.

I’m still testing the limits of Likewise and I will say that it hasn’t been without it’s speed bumps but I plan on paying for a little support and getting the answers I need. Like may open source products, Likewise is making it’s money on support and by selling upgraded functionality. I applaud this model, allowing the flexibility of open source while still finding a way to pay for all that hard work. I will be continuing to test the limits of Likewise but as of now I am thoroughly impressed and will continue to use it.