Linux Lab: System Information Commands

Learn the essential commands for inspecting system resources, processes, memory, disk usage, and network configuration.

Lab Objectives

View system hostname, kernel version, and OS information.
Monitor running processes with top and ps.
Check memory, disk, and CPU usage.
View network configuration and active connections.
Identify logged-in users and system uptime.

Prerequisites

A Linux system with terminal access (Kali, Ubuntu, or any distribution).
No special permissions required for most commands; some require sudo.

Part 1: System Identity

Step 1: Display the hostname:

hostname

Shows the name of your machine on the network.

Step 2: Show kernel and OS information:

uname -a

Displays kernel name, version, architecture, and build date.

Step 3: Show the Linux distribution:

cat /etc/os-release

Shows the distribution name, version, and ID.

Step 4: Check system uptime:

uptime

Shows how long the system has been running, number of users, and load averages.

Part 2: CPU and Memory

Step 1: View CPU information:

lscpu

Shows CPU architecture, cores, threads, clock speed, and cache sizes.

Step 2: Check memory usage:

free -h

-h shows human-readable sizes (MB/GB). Look at total, used, free, and available.

Step 3: Detailed memory info from /proc:

cat /proc/meminfo | head -10

The /proc filesystem provides raw kernel data. This shows the first 10 lines of memory details.

Step 4: View CPU details from /proc:

cat /proc/cpuinfo | head -20

Shows processor model, speed, and features for each CPU core.

Part 3: Disk Usage

Step 1: Check filesystem disk space:

df -h

Shows mounted filesystems with total size, used space, available space, and mount point.

Step 2: Check disk usage of a specific directory:

du -sh ~

-s gives a summary total. -h makes it human-readable.

Step 3: List block devices:

lsblk

Shows all block devices (disks, partitions) and their sizes and mount points.

Part 4: Process Monitoring

Step 1: View running processes interactively with top:

top

Shows a live, updating view of processes sorted by CPU usage. Press q to quit. Press M to sort by memory instead.

Step 2: Use htop for a more user-friendly view (if installed):

htop

htop adds colour, mouse support, and easier navigation. Press F10 or q to quit. Install with sudo apt install htop if not available.

Step 3: List all running processes:

ps aux

a = all users, u = user-oriented format, x = include processes without a terminal.

Step 4: Find a specific process:

ps aux | grep bash

Filters the process list for lines containing "bash".

Step 5: Show process tree:

pstree

Displays processes in a tree hierarchy showing parent-child relationships.

Part 5: Network Information

Step 1: View network interfaces and IP addresses:

ip addr show

Shows all network interfaces with their IP addresses, MAC addresses, and status.

Step 2: View the routing table:

ip route show

Shows how traffic is routed. The default via line shows your gateway.

Step 3: Check DNS configuration:

cat /etc/resolv.conf

Shows the DNS servers your system uses for name resolution.

Step 4: View active network connections:

ss -tuln

-t TCP, -u UDP, -l listening, -n numeric (no DNS resolution).

Step 5: View all active connections with process info:

sudo ss -tulnp

-p shows the process using each port. Requires sudo to see all processes.

Part 6: User Information

Step 1: See who is logged in:

who

Shows currently logged-in users, their terminal, and login time.

Step 2: Show your own user and group info:

id

Displays your user ID (uid), group ID (gid), and all groups you belong to.

Step 3: Show recent login history:

last -10

Shows the last 10 login sessions with user, terminal, IP, and duration.

Deliverables

Screenshot of uname -a and cat /etc/os-release.
Screenshot of free -h showing memory usage.
Screenshot of df -h showing disk usage.
Screenshot of top showing running processes.
Screenshot of ip addr show and ss -tuln.
Screenshot of who and id.

Commands Reference

hostname — System name
uname -a — Kernel info
uptime — System uptime
lscpu — CPU details
free -h — Memory usage
df -h — Disk space
du -sh — Directory size
lsblk — Block devices
top / htop — Live processes
ps aux — Process list
pstree — Process tree
ip addr — Network interfaces
ip route — Routing table
ss -tuln — Open ports
who — Logged-in users
id — User/group info
last — Login history

/proc Filesystem

/proc/cpuinfo — CPU details
/proc/meminfo — Memory details
/proc/version — Kernel version
/proc/uptime — Uptime in seconds
/proc/loadavg — Load averages

/proc is a virtual filesystem — these are not real files on disk but live kernel data.