German license plate - 40 years of Unix

I found a license plate generator online and as you probably guessed, this was the result:

This is actually a valid German license plate (Unna county in Northrhine-Westfalia, just around the corner from here) and it is very likely already taken (two-digit numbers are rare, except for motorcycle plates; this is a full-size car plate however).

I occasionally spot geek license plates; here in Bochum, several BO-FH's are on the road, and some guy from Münster who regularly parks two streets away has a MS-FT plate.

dvtm - a console based tiled window manager

In my last post, I outlined how to do some form of rudimentary multitasking in Bash, but I was still not satisfied. Further research showed that there would be no way around a terminal multiplexer, however screen sucks for me due to its steep and unintuitive learning curve. On K.Mandla's great blog I found the solution: dvtm, a very lightweight tiled window manager for the console. Its beauty lies in that it occupies just around 100k of disk space, does not hog the memory and does not try to accomplish more than it is supposed to.

Becoming familiar with dvtm is a matter of minutes. Install the package from your distribution repositories, go to a console or open an xterm, then input dvtm. You will see Bash within a blue frame. The blue frame indicates that this is the active window. Now press CTRL-G C (press CTRL-G, release the keys, then type a C). A new Bash window pops open next to the existing one and becomes the active window. You can close that window by either logging out of that instance (input exit or press CTRL-D), or by pressing CTRL-G X.

With multiple windows open, you can input CTRL-G <number> to activate window <number> (as designated by its "title bar" text), or CTRL-G J / CTRL-G K to activate the next/previous window. CTRL-G . minimizes or unminimizes the active window. CTRL-G M maximizes the active window. Use CTRL-G SPACE to toggle between grid layouts; this is also the only way to unmaximize a window. CTRL-G ENTER moves the active window in and out of the "master area", which is usually the tile of the biggest size. Finally, dvtm can be left by means of CTRL-G Q, or logging off all hosted shells.

If you need a lightweight multi-window shell environment, dvtm should be surely worth checking out.

How to work with multiple jobs in Bash

An important feature often overlooked by novice console users is job control. It allows some amount of multitasking on a shell by delegating processes to the background and resuming them at a later point. That way, you don't have to launch a second shell or use additional utilities like screen to manage multiple tasks.

Job control is easy. Let's say you have Midnight Commander running. Hit CTRL+Z and you end up back at the shell prompt. You will notice a line above the prompt stating that mc is suspended. The beginning of the line shows mc's job number in square brackets (1 in this case). Ok, let's use that job number to resurrect mc. Input %1 and voíla, mc is back! Similarly, you can use %1 & to unsuspend mc and continue running it as a background job. Note that background jobs are detached from the terminal and will be suspended as soon as they try to read from or write to it.

When working with multiple jobs, you will find the jobs command very useful, which lists the running jobs with their numbers and status.

A more intuitive way to unsuspend a job is to give part of its command line. %mc will unsuspend Midnight Commander, however if you have multiple instances running it will result in an error. Finally, just inputting % will unsuspend the most recently suspended job.

As you can certainly see, this feature is a real time-saver by allowing you to get running applications out of the way and resume them later.

Store volatile data in RAM using tmpfs

There are several reasons why you might want to hold certain data in non-permanent memory. Applications that create a lot of temporary data, causing system slowdown and strain on the storage medium, are an example, or you want the data to be gone after every power cycle because it is of no use anymore at that point, or the data would simply eat up too much storage over time.

Unix-like platforms support a file system named tmpfs, which is a RAM filesystem growing and shrinking dynamically with its contents. Setup is straightforward. To mount /tmp as tmpfs, you add the following line to /etc/fstab, after the physical partition mounts:

none /tmp tmpfs defaults 0 0

Be sure to clear out the contents of the old /tmp directory before remounting, because the mount will "overlay" what was previously there and the data will not be accessible but still occupy space.

Other locations that are good candidates for a tmpfs: /var/tmp, /home/username/tmp, /var/cache/apt/archives, web browser and other caches in your home directory. Don't be tempted to put /var/log on a tmpfs because the logs are important information sources for troubleshooting and forensics. Use logrotate instead for limiting the amount of log storage.

When you are done setting up the temporary file systems, issue a mount -a to remount everything from fstab.