Essential Linux Commands Every Engineer Should Master

Linux offers a vast array of commands that can overwhelm beginners; this concise guide highlights the essential commands you need to master for everyday work and internal training.

Directory Operations

Commonly used commands for handling directories and files:

mkdir – create directories

cp – copy files

mv – move or rename files

rm – remove files

# Create directory and parent directories a/b/c/d
mkdir -p a/b/c/d

# Copy folder a to /tmp
cp -rvf a/ /tmp/

# Move file a to /tmp and rename to b
mv -vf a /tmp/b

# Delete everything (dangerous!)
rm -rvf /

Navigation

Use these commands to know where you are and where you want to go: ls – list current directory contents ls -l – detailed listing (helps identify the user) pwd – print working directory cd – change directory find – locate files by criteria

Text Processing

Advanced text manipulation skills are valuable; refer to the linked series for the most common vim, sed, and awk techniques.

Viewing Files

To display file contents:

cat – quick view (use Ctrl+C to stop large output)

less – paginated view with search ( / then n / N)

tail – view the last lines; tail -f follows a growing file (e.g., logs)

# Show file size
du -h file

# Show file content
cat file

Statistics

Combine sort and uniq to aggregate data; the example extracts the top 10 IPs by page views from an Nginx log:

# Extract IP column and count occurrences
awk -F"|" '{print $3}' access.log | sort | uniq -c | sort -nk1 -r | head -n10

Other Useful Commands

grep – filter content; --color for highlighted matches, -n to show line numbers

diff – compare two files (also used for patching source code)

# Find POST requests in Nginx logs
grep -rn --color POST access.log

Compression

Common archive formats and their commands:

.tar – tar.bz2 – bzip2.gz – gzip.zip – unzip.rar – unrar The most frequently used format is .tar.gz (tar archive compressed with gzip).

# Create a tar.gz archive
tar cvfz archive.tar.gz dir/

# Extract a tar.gz archive
tar xvfz archive.tar.gz

Daily Operations

mount – mount external devices (USB, ISO, SSD)

chown – change file owner/group

chmod – modify file permissions (e.g., chmod 000 -R / is destructive)

yum – package manager for CentOS (e.g., yum install wget -y)

service / systemctl – manage services (e.g., restart MySQL)

kill – send signals to processes ( -9, -15, -3)

su – switch user (use - for a clean environment)

System Overview

uname -a – kernel and system information

ps -ef | grep java – list processes

top -H -p pid – interactive view of threads

free – memory usage

df -h – disk usage

ifconfig / ip addr – network interfaces

ping – test connectivity

netstat -ant – show active TCP connections

Work‑Common Commands

export – set environment variables (e.g., export PATH=$PATH:/home/xjj/jdk/bin)

whereis – locate binaries

crontab – schedule recurring jobs (e.g., every 10 minutes)

date – display or set system time ( hwclock for hardware clock)

xargs – build and execute command lines from input (e.g., delete all .class files)

# Delete all .class files
find . | grep .class$ | xargs rm -rvf

# Copy all .rmvb files to a directory
ls *.rmvb | xargs -n1 -i cp {} /mount/xiaodianying

Networking

ssh – remote login (use -v for verbose output, configure tunnels as needed)

scp – copy files or directories over SSH

wget -c – download files with resume support

# Copy a file via scp
scp a.txt 192.168.0.12:/tmp/a.txt

# Recursively copy a directory
scp -r a_dir 192.168.0.12:/tmp/

Database Access

Connect to MySQL from the command line: mysql -u root -p -h 192.168.1.2 These commands form a practical toolbox for Linux users, enabling efficient file handling, system monitoring, automation, and troubleshooting.