Linux

Users

Create new user

useradd \
    --gid 0 \
    --groups sudo,docker,users \
    --create-home \
    --shell /bin/bash \
    user

Create new user

useradd -g 0 -G sudo,docker,users -m -s /bin/bash user

List all groups

cat /etc/groups

List ports with TCP listeners

sudo ss -tulpn

Flags explained

Flag	Description
-t	Show TCP sockets
-u	Show UDP sockets
-l	Show only listening sockets
-p	Show the process using each socket
-n	Show numeric addresses (no DNS)
-w	Show raw socket information (opt.)

Search installed packages

dpkg -l | grep <package-name>

List installed files

dpkg -L <package-name>