Uncover the Weirdest Linux Commands and Processes You Need to Know

This article explores some of the more unusual or lesser‑known commands and process types in Unix‑like systems, explaining what they do, how they behave, and how to work with them safely.

1. daemon

Daemon (守护进程) is a background process that runs without terminal control, typically started at boot and continues until the system shuts down. Daemons provide services such as httpd, mysqld, syslogd, and their names often end with the letter d.

2. zombie

A zombie process appears after a child process terminates; it remains in the process table until its parent reads its exit status. Zombies cannot be killed directly; you must either have the parent reap it or terminate the parent (often init) so the kernel can clean it up.

3. kill

The kill command sends signals to terminate or control processes. It is commonly used to stop a process that consumes excessive CPU or memory. If a zombie cannot be removed with kill, you need to target its parent process.

4. cat

cat

(short for concatenate) joins files and prints their contents to standard output. It is useful for quickly viewing a file or combining multiple files into one.

5. tail

tail

displays the last N lines of a file, which is handy for checking recent log entries. With the -f option it can follow a file in real time, updating as new lines are appended.

6. which

which

locates the executable file associated with a given command by searching the directories in the user's PATH. For example, which python prints the full path to the Python interpreter.

7. crypt

The crypt command (now often provided by mcrypt) encrypts data, allowing you to protect files from unauthorized reading. It can be used directly or within scripts.

8. shred

shred

overwrites a file repeatedly before deletion, making data recovery extremely difficult. It is preferred over plain rm when secure deletion is required.