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Ubuntu Cheatsheet - Commonly used commands for Ubuntu (18.04 and 20.04) on DigitalOcean
Raw
ubuntu-do.txt
I use Ubuntu 18.04 and 20.04 Droplets on DigitalOcean often. This is a cheatlist of commands used frequently.
Sign up with https://m.do.co/t/b298d6966c0c (Discount code for newbies, I get referral credits too)
-- System Information --
Check OS version:
cat /etc/os-release
Check kernel version:
cat /proc/version
uname -a
List all users:
grep bash /etc/passwd | cut -d: -f1
Check component versions:
apache2 -v
mysql -V
php -v
-- Initial Server Setup --
Set locales:
sudo dpkg-reconfigure locales
Update system to latest:
sudo apt-get update
sudo apt-get upgrade
Add SSH key to server (assumes SSH key already setup):
ssh-copy-id root@<server_ip>
or
cat ~/.ssh/id_rsa.pub | ssh <user>@<hostname> 'cat >> .ssh/authorized_keys && echo "Key copied"'
Clear known_hosts record before connecting:
nano ~/.ssh/known_hosts
-- DigitalOcean Monitoring Agent --
Remove old do-agent:
sudo apt-get purge do-agent
Install monitoring agent:
curl -sSL https://insights.nyc3.cdn.digitaloceanspaces.com/install.sh | sudo bash
Check installation status:
systemctl status do-agent
-- Service Management --
Apache2 Commands:
systemctl start apache2
systemctl stop apache2
systemctl restart apache2
systemctl status apache2
Nginx Commands:
systemctl start nginx
systemctl stop nginx
systemctl restart nginx
systemctl status nginx
MySQL Commands:
systemctl start mysql
systemctl stop mysql
systemctl restart mysql
systemctl status mysql
PostgreSQL Commands:
systemctl start postgresql
systemctl stop postgresql
systemctl restart postgresql
systemctl status postgresql
-- Let's Encrypt SSL Certificates --
Setup Let's Encrypt with certbot:
cd /usr/local/sbin
sudo wget https://dl.eff.org/certbot-auto
sudo chmod a+x /usr/local/sbin/certbot-auto
Setup for Nginx:
certbot-auto --nginx -d <domainname> -d www.<domainname>
Setup for Apache:
certbot-auto --apache -d <domainname> -d www.<domainname>
Auto-renew certificates (add to crontab):
sudo crontab -e
30 2 * * 1 /usr/local/sbin/certbot-auto renew >> /var/log/le-renew.log
-- Firewall Management --
Important: Don't enable ufw unless certain you won't block SSH access.
Check firewall status:
ufw status verbose
ufw show added
ufw status numbered
Allow HTTP/HTTPS:
sudo ufw allow http
sudo ufw allow 80
sudo ufw allow https
sudo ufw allow 443
Allow port ranges:
sudo ufw allow 6000:6007/tcp
sudo ufw allow 6000:6007/udp
Allow from specific IP:
sudo ufw allow from 203.0.113.4
sudo ufw allow from 203.0.113.4 to any port 22
Deny/reset:
sudo ufw deny http
sudo ufw disable
sudo ufw reset
Enable firewall:
sudo ufw enable
Delete rules by number:
ufw status numbered
ufw delete <NUM>
-- Scheduled Tasks & Startup --
Cron scheduling:
sudo crontab -e
Use @reboot keyword for startup tasks:
@reboot /path/to/script
Alternatively, use rc.local:
sudo nano /etc/rc.local
If rc.local doesn't exist, start with:
#!/bin/bash
Then make executable:
sudo chmod a+x /etc/rc.local
List all cron jobs for all users (run as root):
for user in $(cut -f1 -d: /etc/passwd); do crontab -u $user -l; done
-- Configuration Files --
PHP configuration (7.2 example):
nano /etc/php/7.2/apache2/php.ini
systemctl restart apache2
Nginx configuration:
nano /etc/nginx/nginx.conf
systemctl restart nginx
Apache2 configuration:
nano /etc/apache2/apache2.conf
systemctl restart apache2
-- Database Management --
Backup MySQL to file:
mysqldump -u root -p --all-databases > alldb.sql
gzip -9 alldb.sql
Restore MySQL from backup:
gzip -d alldb.sql.gz
mysql -u root -p < alldb.sql
Backup specific database:
mysqldump -u root -p database_name > database_name.sql
Restore specific database:
mysql -u root -p database_name < database_name.sql
Check MySQL version:
mysql --version
Connect to MySQL:
mysql -u root -p
-- Package Management --
Check package version before install (simulation):
apt-get -s install <package>
or
apt-cache policy <package>
or
aptitude versions <package>
Install package from specific version:
apt-get install <package>=<version>
List installed packages:
apt list --installed
Update single package:
sudo apt-get install --only-upgrade <package>
Remove package:
sudo apt-get remove <package>
Clean package cache:
sudo apt-get clean
sudo apt-get autoclean
-- Compression & Archiving --
Maximum compress folder with tar and gzip:
env GZIP=-9 tar -zcvf archive.tar.gz folder/
Compress with bzip2 (better compression):
tar -cjvf archive.tar.bz2 folder/
Extract tar.gz:
tar -xzvf archive.tar.gz
Extract tar.bz2:
tar -xjvf archive.tar.bz2
List contents without extracting:
tar -tzf archive.tar.gz
Tar/zip each subfolder separately:
find . -maxdepth 1 -type d ! -path . | while read a_dir; do tar -zcvf ${a_dir}.tgz ${a_dir}; done
-- Disk Usage & File Management --
Check folder sizes:
sudo du -shc /var/*
sudo du -sh /home/*
Check disk usage summary:
df -h
Check inode usage:
df -i
Interactive disk usage analysis:
sudo apt-get install ncdu
sudo ncdu /
Move all files from subfolders to current folder:
find . -mindepth 2 -type f -print -exec mv {} . \;
Count files in current folder (no subfolders):
find . -type f | wc -l
Count files recursively:
find . -type f | wc -l
Count subfolders at current level:
ls -lR | grep ^d | wc -l
Find all folders total (including subdirectories):
find . -type d | wc -l
Find folders in root only (no subdirectories):
find . -maxdepth 1 -type d | wc -l
Delete empty folders:
find . -empty -type d -delete
Efficiently delete large folders with many files:
mkdir empty_dir
rsync -a --delete empty_dir/ yourdirectory/
rm -R empty_dir
-- File Operations --
Find files by name:
find . -name "*.log"
Find files by size:
find . -size +100M
find . -size -1M
Find files modified in last day:
find . -mtime -1
Find and delete files:
find . -name "*.tmp" -delete
Find and compress files:
find . -name "*.log" -exec gzip {} \;
Recursive copy preserving structure:
rsync -a --include '*/' --include '*.pdf' --exclude '*' source/ destination/
Search for text in files:
grep -r "search_term" ./
grep -r "search_term" ./ --include="*.php"
Search and replace in files:
sed -i 's/old_text/new_text/g' filename
Replace in all files of a type:
find . -name "*.php" -exec sed -i 's/old/new/g' {} \;
Count lines in file:
wc -l filename
Count total lines in directory:
find . -name "*.php" -exec wc -l {} + | tail -1
-- Monitoring & Logs --
Real-time system monitoring:
top
htop (install if needed: sudo apt-get install htop)
Monitor specific process:
ps aux | grep <process_name>
Monitor disk I/O:
iostat
Memory usage:
free -h
View system logs:
sudo tail -f /var/log/syslog
View Apache error logs:
sudo tail -f /var/log/apache2/error.log
View Nginx error logs:
sudo tail -f /var/log/nginx/error.log
View application logs (example):
sudo tail -f /var/log/application.log
-- Network & SSH --
Check open ports:
sudo netstat -tulpn
ss -tulpn
SSH with specific key:
ssh -i ~/.ssh/custom_key user@hostname
SSH tunnel (local port forwarding):
ssh -NTf -L localhost:3306:remoteserver.com:3306 [email protected]
SSH config file for persistent settings:
nano ~/.ssh/config
Host myserver
HostName api.example.com
User myuser
IdentityFile ~/.ssh/id_rsa_custom
LocalForward 3306 localhost:3306
ServerAliveInterval 60
Connect using config:
ssh myserver
Check SSH key fingerprint:
ssh-keygen -lf ~/.ssh/id_rsa.pub
View SSH connection history:
grep "Accepted publickey" /var/log/auth.log | tail -10
-- Development & Python --
Keep pip updated (fixes many dependency issues):
pip install --upgrade pip
pip3 install --upgrade pip
Install Python package:
pip install package_name
Create virtual environment:
python3 -m venv myenv
source myenv/bin/activate
Deactivate virtual environment:
deactivate
List installed packages:
pip list
pip freeze
Export requirements:
pip freeze > requirements.txt
Install from requirements:
pip install -r requirements.txt
-- Git Operations --
Initialize git repo:
git init
Clone repo:
git clone https://github.com/username/repo.git
Add files:
git add .
git add filename
Commit:
git commit -m "Commit message"
Push to remote:
git push origin main
Pull from remote:
git pull
Check status:
git status
View log:
git log --oneline
Create branch:
git checkout -b new_branch
Switch branch:
git checkout branch_name
Merge branch:
git merge branch_name
-- Performance & Optimization --
Learn about ./configure && make && make install:
https://thoughtbot.com/blog/the-magic-behind-configure-make-make-install
Check file count in large directories:
find /var/www -type f | wc -l
Find largest files:
find / -type f -size +100M | sort -k5 -hr | head -10
Process count by user:
ps -u username | wc -l
Find zombie processes:
ps aux | grep zombie
Kill process by name:
pkill -f process_name
Kill process by PID:
kill -9 <PID>
-- User & Permission Management --
Add new user:
sudo useradd -m -s /bin/bash username
sudo passwd username
Add user to sudo group:
sudo usermod -aG sudo username
Add user to group:
sudo usermod -aG groupname username
List user groups:
groups username
id username
Change file ownership:
sudo chown user:group filename
sudo chown -R user:group directory/
Change file permissions:
chmod 755 filename
chmod -R 755 directory/
Set default permissions for new files:
umask 0022
-- Useful Commands --
System uptime:
uptime
Current date/time:
date
Check hostname:
hostname
Set hostname:
sudo hostnamectl set-hostname newhostname
Measure command execution time:
time command
Redirect output to file:
command > output.txt
Append to file:
command >> output.txt
Redirect errors to file:
command 2> errors.txt
Redirect both output and errors:
command > output.txt 2>&1
Pipe output to another command:
command1 | command2
Execute command in background:
command &
List background jobs:
jobs
Bring job to foreground:
fg %1
Continue stopped job in background:
bg %1
Create symbolic link:
ln -s /path/to/file /path/to/link
Remove symbolic link:
rm /path/to/link
Create file with content:
echo "content" > filename.txt
Append to file:
echo "content" >> filename.txt
View file:
cat filename
less filename (pagination)
more filename (pagination)
Edit file:
nano filename
vi filename
vim filename
Download file:
wget https://example.com/file.zip
curl -O https://example.com/file.zip
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