• United States
Unix Dweeb

Scary Linux commands for Halloween

Oct 27, 20174 mins

What Linux commands bring up visions of monsters and ghosts? Let’s look and see!

With Halloween so fast approaching, it’s time for a little focus on the spookier side of Linux. What commands might bring up images of ghosts, witches and zombies? Which might encourage the spirit of trick or treat?


Well, we’ve always got crypt. Despite its name, crypt is not an underground vault or a burial pit for trashed files, but a command that encrypts file content. These days “crypt” is generally implemented as a script that emulates the older crypt command by calling a binary called mcrypt to do its work. Using the mycrypt command directly is an even better option.

$ mcrypt x
Enter the passphrase (maximum of 512 characters)
Please use a combination of upper and lower case letters and numbers.
Enter passphrase:
Enter passphrase:

File x was encrypted.

Note that the mcrypt command creates a second file with an added “.nc” extension. It doesn’t overwrite the file you are encrypting.

The mcrypt command has options for key size and encryption algorithm. You can specify the key as an option too, though the mcrypt command discourages this.


There’s also the kill command – not exactly a reference to murder, of course, but the command that we use for terminating processes gently or with considerable force, depending on what is required to properly terminate them. And Linux doesn’t stop there, of course. Instead, it has all sorts of kill commands to bloody up your command line. We’ve got kill, pkill, killall, killpg, rfkill, skill (read es-kill), tgkill, tkill and xkill.

$ killall runme
[1]   Terminated              ./runme
[2]   Terminated              ./runme
[3]-  Terminated              ./runme
[4]+  Terminated              ./runme


Linux systems also support a command called shred. The shred command overwrites files to hide their former content and ensure that they cannot be recovered using hard drive recovery tools. Keep in mind that the rm command basically just removes a file’s reference in the directory file, but does not necessarily scrape the content off the disk or overwrite it. The shred command overwrites the files’ content.

$ shred dupes.txt
$ more dupes.txt


Although not a command, zombies have a strong presence on Linux systems. Zombies are basically the remains of dead processes that haven’t quite been cleaned away. Processes aren’t supposed to work this way – leaving dead processes wandering around instead of simply having them die and go to digital Heaven, so the presence of zombies indicates that the processes that left them behind had some kind of flaws.

One easy way to check if your system has zombie processes stumbling around is to take a look at the header lines of the top command.

$ top
top - 18:50:38 up 6 days,  6:36,  2 users,  load average: 0.00, 0.00, 0.00
Tasks: 171 total,   1 running, 167 sleeping,   0 stopped,   3 zombie	
%Cpu(s):  0.0 us, 0.0 sy, 0.0 ni, 99.9 id, 0.1 wa, 0.0 hi,  0.0 si, 0.0 st
KiB Mem :  2003388 total,   250840 free,   545832 used,  1206716 buff/cache
KiB Swap:  9765884 total,  9765764 free,      120 used.  1156536 avail Mem

Scary! Three zombies in the above display..

at midnight

It is sometimes said that on Halloween, the spirits of the dead wander from sunset until midnight. Linux makes it possible to track their departure with the “at midnight” command. Used to schedule jobs that will be run the next time the specified time arrives, at works like a one-time cron.

$ at midnight
warning: commands will be executed using /bin/sh
at> echo 'the spirits of the dead have left'
job 3 at Thu Oct 31 00:00:00 2017


Linux systems are also highly dependent on daemons – processes that run in the background and provide a lot of the functionality of the system. Many daemon processes have names that end in “d”. That “d” stands for “daemon” and is an indication that the process is one that runs all of the time and supports some important function. Others have the word “daemon” spelled out.

$ ps -ef | grep sshd
root      1142     1  0 Oct19 ?        00:00:00 /usr/sbin/sshd -D
root     25342  1142  0 18:34 ?        00:00:00 sshd: shs [priv]
$ ps -ef | grep daemon | grep -v grep
message+   790     1  0 Oct19 ?        00:00:01 /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation
root       836     1  0 Oct19 ?        00:00:02 /usr/lib/accountsservice/accounts-daemon

Happy Halloween!

Unix Dweeb

Sandra Henry-Stocker has been administering Unix systems for more than 30 years. She describes herself as "USL" (Unix as a second language) but remembers enough English to write books and buy groceries. She lives in the mountains in Virginia where, when not working with or writing about Unix, she's chasing the bears away from her bird feeders.

The opinions expressed in this blog are those of Sandra Henry-Stocker and do not necessarily represent those of IDG Communications, Inc., its parent, subsidiary or affiliated companies.

More from this author