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?
### crypt
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.
### kill
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
```
### shred
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
▒oΛ▒▒9▒lm▒▒▒▒▒o▒1־▒▒f▒f▒▒▒i▒▒h^}&▒▒▒{▒▒
```
### Zombies
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
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'
at> <EOT>
job 3 at Thu Oct 31 00:00:00 2017
```
### daemons
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.
