Linux Commands Cheatsheet for Cloud Engineers

Every cloud platform — AWS, GCP, Azure — runs Linux under the hood. Whether you are SSHing into a VM, debugging a container, or writing a startup script, these are the commands you need.

File and Directory Operations#

File Permissions#

Numeric (octal) notation#

chmod 755 /opt/app/start.sh    # set permissions by octal
chmod +x deploy.sh             # add execute bit (symbolic)
chmod -R 644 /var/www/html     # apply recursively

chown ubuntu:ubuntu /opt/app   # change owner and group
chgrp docker /var/run/docker.sock  # change group only

SSH private keys must be 600. If they are world-readable, SSH will refuse to use them.

Process Management#

systemctl (for services managed by systemd)#

systemctl status nginx          # check if a service is running
systemctl start nginx           # start a service
systemctl stop nginx            # stop a service
systemctl restart nginx         # stop then start
systemctl reload nginx          # reload config without stopping
systemctl enable nginx          # start automatically at boot
systemctl disable nginx         # remove from boot
journalctl -u nginx -f          # stream logs for a service

Text Processing#

# grep — search file contents
grep "ERROR" app.log            # find lines containing ERROR
grep -r "api_key" /etc/         # recursive search across files
grep -i "error" app.log         # case-insensitive
grep -n "timeout" app.log       # show line numbers
grep -v "DEBUG" app.log         # exclude lines matching pattern
grep -E "error|warn" app.log    # extended regex (OR)
grep -c "ERROR" app.log         # count matching lines

# sed — stream editor, mostly used for substitution
sed 's/old/new/' file.txt       # replace first match per line
sed 's/old/new/g' file.txt      # replace all matches
sed -i 's/localhost/db-host/g' config.cfg  # edit file in place

# awk — field-based text processing
awk '{print $1, $4}' access.log       # print columns 1 and 4
awk -F':' '{print $1}' /etc/passwd    # use : as field separator
awk '/ERROR/ {print $0}' app.log      # print lines matching pattern

# Other useful tools
sort app.log | uniq -c | sort -rn    # count unique lines, most frequent first
cut -d',' -f1,3 data.csv             # extract columns 1 and 3 from CSV
tr '[:upper:]' '[:lower:]' < file    # convert to lowercase

Networking Commands#

ping google.com                 # test basic connectivity
curl -I https://example.com     # fetch HTTP headers only
curl -o /tmp/file.zip https://example.com/file.zip  # download a file
wget -q https://example.com/file.zip  # download a file quietly
netstat -tulpn                  # list listening ports and their processes
ss -tulpn                       # same as netstat but faster
ip addr show                    # list network interfaces and IPs
ip route show                   # show routing table
dig example.com                 # DNS lookup (detailed)
nslookup example.com            # DNS lookup (simple)
traceroute example.com          # trace network path to a host
nmap -p 80,443 192.168.1.1      # scan specific ports on a host
iptables -L -n -v               # list firewall rules

SSH#

# Connect to a remote host
ssh ubuntu@192.168.1.10
ssh -i ~/.ssh/my-key.pem ubuntu@ec2-ip.compute.amazonaws.com

# Generate an SSH key pair
ssh-keygen -t ed25519 -C "my-key" -f ~/.ssh/my-key

# Copy your public key to a remote server
ssh-copy-id -i ~/.ssh/my-key.pub ubuntu@192.168.1.10

# Copy files securely
scp -i ~/.ssh/my-key.pem file.txt ubuntu@host:/tmp/
scp -r ./configs ubuntu@host:/opt/app/

# Set correct permissions on key files
chmod 600 ~/.ssh/my-key.pem
chmod 700 ~/.ssh

~/.ssh/config format#

Using a config file avoids typing long ssh commands.

Host myserver
  HostName 203.0.113.10
  User ubuntu
  IdentityFile ~/.ssh/my-key.pem
  Port 22

Then connect with just ssh myserver.

Disk and Storage#

df -h                        # show disk usage for all mounted filesystems
du -sh /var/log              # show total size of a directory
du -sh /var/log/* | sort -h  # sort subdirectories by size
lsblk                        # list block devices (disks and partitions)
mount /dev/sdb1 /mnt/data    # mount a partition
umount /mnt/data             # unmount

Archives#

# tar
tar -czf archive.tar.gz /opt/app    # create compressed archive
tar -xzf archive.tar.gz             # extract compressed archive
tar -tzf archive.tar.gz             # list contents without extracting

# gzip
gzip large-file.log        # compress (replaces original)
gunzip large-file.log.gz   # decompress

# zip
zip -r archive.zip ./folder/
unzip archive.zip -d /opt/dest/

Environment and Shell#

echo $HOME                   # print the value of a variable
export MY_VAR="hello"        # set a variable for child processes
env                          # list all environment variables
printenv PATH                # print one specific variable

# ~/.bashrc runs for interactive non-login shells (new terminal tabs)
# ~/.bash_profile runs for login shells (SSH sessions)
# Put exports in ~/.bashrc for interactive use
source ~/.bashrc             # reload without logging out

Cron#

crontab -e   # edit your crontab
crontab -l   # list your current cron jobs

Cron syntax: minute hour day month weekday command

Package Management#

# Ubuntu / Debian (apt)
sudo apt update && sudo apt upgrade -y
sudo apt install -y nginx curl jq
sudo apt remove nginx

# RHEL / Amazon Linux / CentOS (yum or dnf)
sudo yum update -y
sudo yum install -y nginx
sudo dnf install -y nginx        # dnf is the newer replacement for yum

One-Liners Cloud Engineers Actually Use#

# Find the 10 largest files under /var
find /var -type f -printf '%s %p\n' | sort -rn | head -10

# Grep all .log files recursively for errors from today
grep -r "ERROR" /var/log/ --include="*.log"

# Stream a log file live
tail -f /var/log/nginx/access.log

# Check disk space on all filesystems
df -h | grep -v tmpfs

# Count how many times each status code appears in an access log
awk '{print $9}' /var/log/nginx/access.log | sort | uniq -c | sort -rn

# Test if a port is open on a remote host
nc -zv 203.0.113.10 443

# Find processes using a port
ss -tulpn | grep :8080