Girgetto / linux-commands

Useful Linux Commands for CKAD Exam

General Navigation and File Operations

ls: List directory contents.

$ ls -l
total 4
drwxr-xr-x 2 user user 4096 Jan  1 12:34 directory
-rw-r--r-- 1 user user    0 Jan  1 12:34 file.txt

cd: Change the current directory.

No output for this command, but it changes the current working directory.

pwd: Print the working directory.

$ pwd
/home/user

mkdir: Create a directory.

No output, but creates a new directory.

rmdir: Remove an empty directory.

No output, but removes an empty directory.

rm: Remove files or directories.

No output, but the specified files/directories are removed.

cp: Copy files or directories.

No output, but the files/directories are copied.

mv: Move or rename files or directories.

No output, but the file/directory is moved or renamed.

touch: Create an empty file or update the file's timestamp.

No output, but the file is created or updated.

cat: Concatenate and display files.

$ cat file.txt
Hello, World!

Text Manipulation

echo: Display a line of text.

$ echo "Hello World"
Hello World

cut: Remove sections from each line of files.

$ echo "name,age" | cut -d',' -f1
name

sort: Sort lines of text files.

$ echo -e "c\nb\na" | sort
a
b
c

uniq: Report or omit repeated lines.

$ echo -e "a\na\nb" | uniq
a
b

awk: Pattern scanning and processing language.

$ echo "field1 field2" | awk '{print $2}'
field2

sed: Stream editor for filtering and transforming text.

$ echo "hello" | sed 's/hello/world/'
world

Process Management

ps: Report a snapshot of the current processes.

Output varies based on running processes.

top: Display Linux processes in real-time.

Interactive output showing process statistics.

kill: Send a signal to a process.

No output, but sends the specified signal to the process.

nohup: Run a command immune to hangups.

$ nohup command &

Output is redirected to nohup.out.

bg: Put jobs in background.

No specific output, but moves the job to the background.

fg: Bring jobs to foreground.

No specific output, but moves the job to the foreground.

Network Operations

curl, wget: Download files from the internet.

Output varies, shows download progress and completion.

ping: Check the network connection to a server.

$ ping example.com
PING example.com (93.184.216.34) 56(84) bytes of data.
64 bytes from 93.184.216.34: icmp_seq=1 ttl=56 time=11.632 ms

netstat: Display network connections, routing tables, etc.

Output varies, shows active connections and listening ports.

nslookup, dig: Query DNS lookup information.

$ nslookup example.com
Server:		192.168.1.1
Address:	192.168.1.1#53

Non-authoritative answer:
Name:	example.com
Address: 93.184.216.34

Permissions and Ownership

chmod: Change file mode bits.

No output, but changes the permissions of the specified file.

chown: Change file owner and group.

No output, but changes the owner and group of the specified file.

This guide provides a quick overview and examples of common Linux commands along with their expected outputs, useful for CKAD exam preparation.