Commonly Used Linux Commands: A Quick Reference Guide

This article compiles the 21 most frequently used Linux commands, often asked in interviews, serving as a quick‑reference manual.

1. File and Directory

cd : change directory (e.g., cd /home, cd .., cd -).

pwd : display current working directory.

ls : list files ( ls -l, ls -a, ls -R, etc.).

2. Viewing File Content

cat : display file, with options like cat -n file.

more , head , tail : paginate or show specific lines (e.g., head -n 2 file, tail -n +1000 file).

Combination example: cat filename | head -n 3000 | tail -n +1000 shows lines 1000‑3000.

3. File Search

find : locate files (e.g., find / -name file1, find /usr/bin -type f -atime +100).

whereis and which : locate binaries or source files.

Delete files larger than 50 M:

find /var/mail/ -size +50M -exec rm {} \;

4. Permissions

chmod : modify mode (e.g., chmod ugo+rwx dir, chmod go-rwx dir).

chown : change owner (e.g., chown user1 file, chown -R user1 dir).

chgrp : change group (e.g., chgrp group1 file).

5. Text Processing

grep : filter lines (e.g., grep Aug /var/log/messages).

sed : stream editor for substitution and deletion.

paste : merge files (e.g., paste file1 file2).

sort and uniq : sort and deduplicate.

comm : compare two sorted files.

6. Archiving and Compression

tar : create, list, extract archives with options -c, -t, -x, -z, -j, -v, -f, -C.

Examples: tar -jcv -f archive.tar.bz2 dir, tar -jxv -f archive.tar.bz2 -C /dest.

Other tools: gzip, bzip2, gunzip, rar, zip, unzip.

7. System Shutdown and Reboot

shutdown -h now

, init 0, telinit 0 – power off. shutdown -r now, reboot – restart. logout – log out. time command – measure execution time.

8. Process Management

jps : list Java processes.

ps : display processes (e.g., ps aux, ps -lA).

kill , killall , pkill : send signals to terminate processes (e.g., kill -9 pid).

top : interactive performance monitor.

Check listening ports: netstat -tunlp | grep PORT.