Processes, Packages and the Network

Processes

Every running program is a process with a numeric ID (PID). Inspect and control them:

ps aux              # list all processes
top                 # live view of CPU/memory (q to quit)
htop                # nicer interactive version (if installed)
kill 1234           # ask process 1234 to stop
kill -9 1234        # force-kill (last resort)

Background jobs and services

./server &           # run in the background
jobs                 # list background jobs
nohup ./server &     # keep running after you log out

Long-running programs are usually managed as systemd services rather than by hand:

sudo systemctl status nginx     # is it running?
sudo systemctl restart nginx    # restart it
sudo systemctl enable nginx     # start on boot
journalctl -u nginx -f          # follow its logs

Installing software

A package manager installs software and its dependencies. On Debian/Ubuntu it is apt; on Red Hat/Fedora, dnf:

sudo apt update              # refresh the package list
sudo apt install nginx       # install a package
sudo apt remove nginx        # remove it
sudo apt upgrade             # update everything

Networking basics

ping google.com             # test connectivity
curl https://example.com    # fetch a URL
curl -I https://example.com # headers only
ss -lntp                    # list listening ports and their processes
ssh user@host               # log into a remote machine

Key points

• Processes have PIDs; inspect with ps/top, stop with kill.
• Manage long-running programs with systemctl and read logs via journalctl.
• Install software with the package manager (apt or dnf).
• ping, curl, ss and ssh cover everyday network tasks.