Linux super-duper admin tools: screen


Updated: March 1, 2010


This article includes a Flash movie!

Time to learn about yet another cool little admin application that will change the way you think and work. We had strace, a mighty, versatile debugging tool that helped us diagnose and categorize system programs quickly and effectively and point us in the right direction in our investigation of problems. We had OProfile, a powerful profiling utility that can be used to time the system and application performance and identify chokepoints and bottlenecks in program executions. Time to step back and appraise screen.

Teaser

screen

screen is a full-screen window manager that multiplexes a physical terminal between several processes, typically interactive shells. Each virtual terminal provides the functions of the legendary DEC VT100 terminal.

Additionally, the utility has insert/delete line, support for multiple character sets, a scrollback history buffer for each virtual terminal, and a copy-and-paste mechanism that allows moving text regions between windows.

When screen is called, it creates a single window with a shell in it and then gets out of your way so that you can use the program as you normally would. Then, at any time, you can create new full-screen windows with other programs in them, including more shells, kill existing windows, view a list of windows, turn output logging on and off, copy & paste text between windows, view the scrollback history, switch between windows in whatever manner you wish, etc.

All windows run their programs completely independent of each other. Programs continue to run when their window is currently invisible and even when the whole screen session is detached from the user's terminal. When a program terminates, screen kills the window that contained it. If this window was in the foreground, the display switches to the previous window; if none are left, screen exits.

In a nutshell, if Ctrl + F buttons allow you to switch between up to seven virtual consoles, horizontally, screen lets you create an infinite vertical stack of consoles in each one of these.

Home users running full GUI desktops and playing with tabbed terminal utilities would be hard-tempted to find merit in screen, but when you're running in runlevel 3 and the monitor space is limited, screen is a blessing.

Screen in action

Let's begin with a few screenshots. To start screen, just type screen in any one console windows, be it gnome-terminal, xterm, Konsole, or any other.

Launch

This will display an introduction messages. Press Enter to exit.

Started

You're inside a new virtual console. Why not fire another?

First

And here's the second:

Second

Using the right keyboard shortcuts, we can switch between them, back and forth. Use Ctrl + a then 0 to go to the zeroth (first) screen, Ctrl + a then 1 to go to the second one, and so forth.

First toggled

Now, demonstrating screen with still images is difficult, so here's a Flash movie! Created using Wink, which served us well so many times, including the tutorial itself, as well as the Windows PowerShell article, and a few others.

So here we go:

Lovely, right! Damn right!

Help window

Don't hesitate to call for help. Ctrl + a, then ? will pop the help screen.

Help

Of course, you can also read the man page for more details. There's a plenty you can do with screen, attach/detach/reattach sessions, specify the history scrollback buffer, turn login mode on and off, suppress error messages, and more. screen is a powerful marvel and you should start using it.

Conclusion

Yet another powerful tool mastered. Our list grows bigger, and so does our knowledge. screen may seem trivial to you, but what if you need to debug problems across multiple session and you can't afford to have tons of Konsole or xterm windows strewn about the desktop like mad. Then, there's the issue of practical visibility. Never take your eyes off the screen and yet enjoy full multi-view console.

I hope you liked this little surprise. Now, off to new wonders. Stay tuned for many more articles of great admin tools, aptly called super-duper, by me. Be excellent to each other and party on.

Cheers.

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