Linux
Specifically using Ubuntu.
SSH
Type exit
to exit out of a SSH session.
# SSH into a server with Raspberry Pi's default user.
ssh pi@<ip_address>
# SSH into a server as a particular user.
ssh <user_name>@<ip_address>
# Output current user's name.
whoami
# View last hour of SSH logs.
sudo journalctl -u ssh --since "1 hour ago"
# Determine shell being used.
ps -p "$$"
# Find process having a process id (PID).
ps -p <pid>
System information
# View OS information.
cat /etc/os-release
# View system information on Ubuntu, which is displayed on SSH login:
landscape-sysinfo
# System monitoring.
top
# Prettier version of top.
htop
# Memory usage.
free
# Human readable.
free -h
# Show in MBs.
free -m
# IP address
ip a
hostname -I
# Server uptime.
uptime
# View path variable.
echo $PATH
# Find path of binary.
which cd
Package management
# Show manually installed packages.
apt-mark showmanual
apt list --manual-installed
# List installed packages.
apt list --installed
dpkg --list
sudo dpkg --audit
sudo dpkg --get-selections
Service logs
# View logs for a particular service.
sudo journalctl -fu mycustom.service
sudo journalctl -fu mycustom.service --since "1 hour ago"
Copy files
# Copy a file to a directory.
scp file-name.ext <user>@<server>:~/path/to/directory/
# Copy the contents of a folder to a remote folder.
scp -r .\path\to\directory\* <user>@<server>:/path/to/remove/directory
Sudo
# Start a root shell. `exit` when done.
sudo -s
Firewall (ufw)
# Show status of firewall. If active, also lists rules.
sudo ufw status
# Show rules even when ufw is inactive.
sudo ufw show added
# Allow by service.
sudo ufw allow ssh
# Allows 80 and 443.
sudo ufw allow 'Nginx Full'
# Allow port-number.
sudo ufw allow <port-number>
sudo ufw allow 8080
# Remove allowed port-number.
sudo ufw delete allow <port-number>
sudo ufw delete allow 9041