DevOps Lesson 2: Linux Basics

90% of servers run Linux. These commands are used every day by every DevOps engineer. Learn them well.

Essential Commands

# Navigation
pwd                    # current directory
ls -la                 # list all files (including hidden)
cd /etc/nginx          # change directory
cd ..                  # go up one level

# File operations
cp file.txt backup.txt  # copy
mv file.txt /tmp/       # move or rename
rm file.txt             # delete
mkdir -p app/src/utils  # create nested dirs
cat file.txt            # view file
less file.txt           # paginated view
tail -f /var/log/app.log # watch log in real time

# Permissions
chmod 755 script.sh     # rwxr-xr-x
chown user:group file   # change owner

# Process management
ps aux                  # all running processes
kill 1234               # kill process by PID
top / htop              # interactive process viewer
nohup ./app &           # run in background

SSH & File Transfer

# Connect to remote server
ssh user@192.168.1.100
ssh -i ~/.ssh/mykey.pem ubuntu@54.123.45.67  # with key

# Copy files to/from server
scp file.txt user@server:/home/user/
scp user@server:/var/log/app.log ./  # download

# Sync directories
rsync -avz ./app/ user@server:/var/www/app/

Essential Tools

grep "ERROR" /var/log/app.log       # search in files
grep -r "TODO" ./src/               # recursive search
awk '{print $2}' file.txt           # print column 2
sed 's/old/new/g' file.txt         # find and replace
curl https://api.example.com/users  # HTTP request
wget https://example.com/file.zip   # download file
cron / crontab -e                   # scheduled tasks