Linux stuff

Links to useful Linux things

- Common Commands - https://matomo.mintarc.com/mediawiki/index.php?title=SSH_Stuff

systemd

https://matomo.mintarc.com/mediawiki/index.php?title=SystemD_Stuff

Create, monitor and terminate process

& - Run a command in the background

The & symbol is used to run a command or script in the background, allowing you to continue using the terminal.

Examples:

• long_running_script.sh &: Run the script in the background
• sleep 60 &: Run the sleep command for 60 seconds in the background
• nohup command &: Run a command in the background, immune to hangups

bg - Resume suspended jobs in the background

bg resumes execution of a suspended job in the background.

Examples:

• bg %1: Resume the first suspended job in the background
• bg %vim: Resume the suspended vim job in the background
• bg: Resume the most recently suspended job in the background

fg - Bring background jobs to the foreground

fg brings a background job into the foreground, allowing direct interaction.

Examples:

• fg %2: Bring the second background job to the foreground
• fg %emacs: Bring the background emacs job to the foreground
• fg: Bring the most recent background job to the foreground

jobs - Display status of jobs in the current session

jobs lists the active jobs in the current shell session.

Examples:

• jobs: List all jobs
• jobs -l: List jobs with process IDs
• jobs -p: List only process IDs of the active jobs

nohup - Run a command immune to hangups

nohup allows a command to continue running after the user logs out.

Examples:

• nohup long_running_script.sh &: Run a script that continues after logout
• nohup command > output.log 2>&1 &: Run a command, redirecting output and errors
• nohup python script.py &: Run a Python script that persists after terminal closure

screen - Terminal multiplexer

screen creates a virtual terminal that can be detached and reattached, allowing sessions to persist.

Examples:

• screen: Start a new screen session
• screen -S session_name: Start a named screen session
• screen -r: Reattach to a detached screen session
• screen -list: List available screen sessions

tmux - Terminal multiplexer

tmux, like screen, allows for persistent terminal sessions and window management.

Examples:

• tmux: Start a new tmux session
• tmux new -s session_name: Create a named tmux session
• tmux attach -t session_name: Attach to an existing session
• tmux ls: List active tmux sessions

top - Display and update sorted information about processes

top provides a dynamic real-time view of running system processes.

Examples:

• top: Display system processes, updating every 3 seconds
• top -u username: Show processes for a specific user
• top -p 1234,5678: Monitor specific processes by PID

ps - Report a snapshot of current processes

ps displays information about a selection of the active processes.

Examples:

• ps aux: Display detailed information about all processes
• ps -ef: Show all processes in full format
• ps --sort=-%cpu: List processes sorted by CPU usage (descending)

pstree - Display a tree of processes

pstree shows the running processes as a tree, which is helpful for understanding process relationships.

Examples:

• pstree: Display process tree
• pstree -p: Show process IDs along with the tree
• pstree -u: Show user names for each process

uptime - Show how long the system has been running

uptime displays the current time, system uptime, number of users, and load average.

Examples:

• uptime: Display system uptime and load
• uptime -p: Show uptime in a pretty format
• uptime -s: Display the system up since time

pgrep - Look up or signal processes based on name and other attributes

pgrep looks through the currently running processes and lists the process IDs which match the selection criteria.

Examples:

• pgrep firefox: List PIDs of firefox processes
• pgrep -u root: List PIDs of processes owned by root
• pgrep -l sshd: List PIDs and names of sshd processes

kill - Send a signal to a process

kill sends a signal to a process, by default the TERM signal to request termination.

Examples:

• kill 1234: Send SIGTERM to process with PID 1234
• kill -9 5678: Send SIGKILL to forcefully terminate process 5678
• kill -l: List available signals

pkill - Signal processes based on name and other attributes

pkill looks up processes based on name and other attributes and sends them a signal.

Examples:

• pkill firefox: Send SIGTERM to all firefox processes
• pkill -9 httpd: Send SIGKILL to all httpd processes
• pkill -u username: Terminate all processes owned by username

killall - Kill processes by name

killall sends a signal to all processes running any of the specified commands.

Examples:

• killall nginx: Terminate all processes named nginx
• killall -9 apache2: Forcefully kill all apache2 processes
• killall -u username bash: Kill all bash processes for a specific user

Desktop environment

startx - Start the X Window System

startx is a script that initializes the X Window System session. It sets up the environment and launches the X server along with initial clients.

Examples:

• startx: Start the X session with default settings
• startx -- :1: Start X on display :1
• startx ~/.xinitrc: Use a custom initialization script

X server - Core component of the X Window System

The X server manages the display, keyboard, and mouse, handling rendering and input for client applications.

Examples:

• Xorg: The most common X server implementation
• Xvfb: X virtual framebuffer, a display server without a physical display
• Xnest: Nested X server, allowing an X session within another X session

X client - Application that uses the X protocol

X clients are programs that use the X protocol to display their graphical user interface.

Examples:

• xterm: Terminal emulator for X
• xclock: Simple clock application
• xeyes: Demo program showing eyes that follow the mouse cursor

Display Manager - Graphical login manager

A display manager provides a graphical login interface and starts the X session after user authentication.

Examples:

• gdm: GNOME Display Manager
• lightdm: Lightweight Display Manager
• sddm: Simple Desktop Display Manager

Window Manager - Controls window placement and appearance

The window manager handles the positioning, resizing, and decorations of windows within the X environment.

Examples:

• i3: Tiling window manager
• openbox: Lightweight stacking window manager
• awesome: Highly configurable window manager

X Window System - Network-transparent windowing system

The X Window System is a complete architecture for creating graphical user interfaces on Unix-like operating systems.

Examples:

• X11: The current version of the X Window System protocol
• Xlib: C library for X Window System client-side programming
• XCB: C library for X protocol connections

Integrated Desktop Environment - Complete graphical user interface

An integrated desktop environment provides a consistent user interface, including window management, file management, and system settings.

Examples:

• GNOME: Popular desktop environment with a focus on simplicity
• KDE Plasma: Feature-rich desktop environment
• Xfce: Lightweight desktop environment for Unix-like operating systems

xauth - X authority file utility

xauth is used to edit and display the authorization information used in connecting to the X server.

Examples:

• xauth list: Display the list of authority entries
• xauth add :0 . $(mcookie): Add a new authority entry for display :0
• xauth extract - $DISPLAY | ssh remote_host xauth merge -: Transfer X authority to a remote host

DISPLAY - Environment variable for X display

The DISPLAY environment variable tells X clients which display and screen to use.

Examples:

• export DISPLAY=:0: Set the display to the first local X server
• echo $DISPLAY: Print the current DISPLAY value
• DISPLAY=:1 xterm: Run xterm on display :1

Terminal program - Text-based interface for interacting with the system

Terminal programs provide a command-line interface within the X environment.

Examples:

• xterm: Standard terminal emulator for X
• gnome-terminal: GNOME's terminal emulator
• konsole: KDE's terminal emulator