Linux System Information and Documentation: Complete Beginner's Guide to uname, man, and Help Systems

Every Linux user needs to know two fundamental skills: finding out about their system and knowing where to get help. In this comprehensive guide, you'll learn how to discover your system's information and master Linux's built-in documentation system.

💡

🎯 What You'll Learn: In this hands-on tutorial, you'll discover:

Checking Linux kernel and system information with uname
Viewing OS release details
Checking SELinux status and service information
Viewing network configuration with ip a
Customizing your bash prompt (PS1)
Mastering the man command for manual pages
Using info for detailed documentation
Getting quick help with --help
Finding commands with whatis and apropos
Exploring /usr/share/doc for package documentation

🖥️ Part 1: System Information Commands

Understanding your Linux system starts with knowing what you're running. Let's explore the essential commands for gathering system information.

Prerequisites

Before we dive in, you should have:

Access to a Linux terminal
Basic command line familiarity
User account (root not required for most commands)

🐧 The uname Command: Discovering Your System

The uname command displays system information about your Linux installation.

Basic uname Usage

uname

What this command does:

uname - Print system information
Without options, it prints the kernel name

Output:

Linux

Understanding the output:

Simply shows "Linux" - confirms you're running a Linux-based operating system
This is the kernel name (the core of the operating system)

Checking Kernel Version

uname -r

What this command does:

uname - System information command
-r - Print the kernel release version

Output:

5.14.0-620.el9.x86_64

Breaking down the output:

Part	Value	Meaning
Major version	5.14.0	Kernel version 5, minor version 14, patch 0
Build number	620	Distribution-specific build number
Distribution	el9	"Enterprise Linux 9" (RHEL/CentOS 9)
Architecture	x86_64	64-bit Intel/AMD processor

Complete System Information

uname -a

What this command does:

uname - System information command
-a - Print ALL system information

Output:

Linux vbox 5.14.0-620.el9.x86_64 #1 SMP PREEMPT_DYNAMIC Fri Sep 26 01:13:23 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux

Breaking down the complete output:

Linux - Kernel name
vbox - Hostname (network name of this computer)
5.14.0-620.el9.x86_64 - Kernel release (version)
#1 SMP PREEMPT_DYNAMIC - Kernel build info
- #1 = First build
- SMP = Symmetric Multi-Processing (multi-core support)
- PREEMPT_DYNAMIC = Preemptive kernel (better responsiveness)
Fri Sep 26 01:13:23 UTC 2025 - When the kernel was compiled
x86_64 x86_64 x86_64 - Machine architecture (processor type)
GNU/Linux - Operating system name

💡

💡 When to Use uname: Use uname -r to check kernel compatibility for software installation. Use uname -a when reporting system information for troubleshooting.

📋 Operating System Release Information

The /etc/os-release file contains detailed information about your Linux distribution.

Viewing OS Release Details

cat /etc/os-release

What this command does:

Reads and displays the contents of /etc/os-release
This file contains distribution-specific information
Standardized across most modern Linux distributions

Output:

NAME="CentOS Stream"
VERSION="9"
ID="centos"
ID_LIKE="rhel fedora"
VERSION_ID="9"
PLATFORM_ID="platform:el9"
PRETTY_NAME="CentOS Stream 9"
ANSI_COLOR="0;31"
LOGO="fedora-logo-icon"
CPE_NAME="cpe:/o:centos:centos:9"
HOME_URL="https://centos.org/"
BUG_REPORT_URL="https://issues.redhat.com/"
REDHAT_SUPPORT_PRODUCT="Red Hat Enterprise Linux 9"
REDHAT_SUPPORT_PRODUCT_VERSION="CentOS Stream"

Understanding each field:

Field	Value	Purpose
`NAME`	CentOS Stream	Human-readable OS name
`VERSION`	9	Version number
`ID`	centos	Short identifier for scripts
`ID_LIKE`	rhel fedora	Compatible with RHEL and Fedora
`PRETTY_NAME`	CentOS Stream 9	Full display name
`HOME_URL`	https://centos.org/	Project homepage
`BUG_REPORT_URL`	https://issues.redhat.com/	Where to report bugs

✅

✅ Use Case: Scripts often parse /etc/os-release to detect which distribution they're running on and adjust behavior accordingly.

🔐 SELinux Status

SELinux (Security-Enhanced Linux) is a security framework that provides access control security policies.

Checking SELinux Status

sestatus

What this command does:

sestatus - Display SELinux status
Shows whether SELinux is enabled and its current mode
Provides configuration details

Output:

SELinux status:                 enabled
SELinuxfs mount:                /sys/fs/selinux
SELinux root directory:         /etc/selinux
Loaded policy name:             targeted
Current mode:                   enforcing
Mode from config file:          enforcing
Policy MLS status:              enabled
Policy deny_unknown status:     allowed
Memory protection checking:     actual (secure)
Max kernel policy version:      33

Understanding SELinux output:

Field	Value	Meaning
SELinux status	enabled	SELinux is active on this system
Current mode	enforcing	SELinux actively blocks unauthorized access
Loaded policy	targeted	Protects specific system services
MLS status	enabled	Multi-Level Security support is active

SELinux Modes Explained:

Enforcing: SELinux policy is enforced. Denies access and logs actions.
Permissive: SELinux logs policy violations but doesn't enforce them (testing mode).
Disabled: SELinux is completely turned off.

🔧 Checking Service Status with systemctl

Systemd is the system and service manager for modern Linux distributions.

Viewing SSH Service Status

sudo systemctl status sshd

What this command does:

sudo - Run command with superuser privileges
systemctl - Control systemd system and service manager
status - Show runtime status of a service
sshd - The OpenSSH server daemon

Output:

● sshd.service - OpenSSH server daemon
     Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled; preset: enabled)
     Active: active (running) since Mon 2025-10-06 15:43:12 PKT; 39min ago
       Docs: man:sshd(8)
             man:sshd_config(5)
   Main PID: 1861 (sshd)
      Tasks: 1 (limit: 48732)
     Memory: 2.0M (peak: 2.3M)
        CPU: 31ms
     CGroup: /system.slice/sshd.service
             └─1861 "sshd: /usr/sbin/sshd -D [listener] 0 of 10-100 startups"

Oct 06 15:43:12 localhost.localdomain systemd[1]: Starting OpenSSH server daemon...
Oct 06 15:43:12 localhost.localdomain sshd[1861]: Server listening on 0.0.0.0 port 22.
Oct 06 15:43:12 localhost.localdomain sshd[1861]: Server listening on :: port 22.
Oct 06 15:43:12 localhost.localdomain systemd[1]: Started OpenSSH server daemon.

Understanding systemctl status output:

Header section:

● sshd.service - Service name (● indicates status: green = running, red = failed)
Loaded: Service definition file location and startup configuration
- enabled = starts automatically at boot
- disabled = doesn't start at boot
Active: Current running state
- active (running) = service is running
- inactive (dead) = service is stopped
- failed = service crashed

Resource usage:

Main PID: Process ID of the main service process (1861)
Tasks: Number of threads/tasks (1)
Memory: Current and peak memory usage
CPU: Cumulative CPU time used

Logs section: Shows recent log entries for this service:

Started the SSH server
Listening on 0.0.0.0 (all IPv4 addresses) port 22
Listening on :: (all IPv6 addresses) port 22

🌐 Network Configuration with ip Command

The ip command displays and configures network interfaces.

Viewing Network Addresses

ip a

What this command does:

ip - Show/manipulate routing, network devices, interfaces
a - Short for address - show protocol addresses

Output (Partial):

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: enp0s3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 08:00:27:3c:80:d2 brd ff:ff:ff:ff:ff:ff
    inet 192.168.100.154/24 brd 192.168.100.255 scope global dynamic noprefixroute enp0s3
       valid_lft 83999sec preferred_lft 83999sec
    inet6 fe80::9b6f:96bb:eae6:4030/64 scope link noprefixroute
       valid_lft forever preferred_lft forever

Understanding network interface output:

Interface 1: lo (Loopback)

lo: Loopback interface (internal network for the computer to talk to itself)
LOOPBACK,UP,LOWER_UP: Flags indicating the interface type and status
mtu 65536: Maximum Transmission Unit (largest packet size)
inet 127.0.0.1/8: IPv4 loopback address (localhost)
inet6 ::1/128: IPv6 loopback address

Interface 2: enp0s3 (Network Card)

enp0s3: Physical network interface name
- en = ethernet
- p0s3 = PCI bus location
link/ether 08:00:27:3c:80:d2: MAC address (hardware address)
inet 192.168.100.154/24: IPv4 address assigned to this interface
- /24 = subnet mask (255.255.255.0)
brd 192.168.100.255: Broadcast address for this network
state UP: Interface is active and connected

💡

💡 Common Use Cases: Use ip a to find your IP address, check network connectivity, or troubleshoot network issues. The output shows all network interfaces and their addresses.

🎨 Customizing Your Bash Prompt (PS1)

The PS1 variable controls how your bash prompt looks.

Viewing Current Prompt

echo $PS1

What this command does:

echo - Display text
$PS1 - Environment variable containing the prompt format

Output:

[\u@\h \W \t]$

Understanding PS1 escape sequences:

Sequence	Meaning	Example Output
`\u`	Username	centos9
`\h`	Hostname	vbox
`\W`	Current directory (basename)	random
`\w`	Full working directory path	~/Documents/project
`\t`	Current time (24-hour HH:MM:SS)	16:23:28
`\d`	Date (Weekday Month Date)	Mon Oct 06
`$`	# for root, $ for regular user	$ or #

Modifying PS1

You can customize your prompt by editing the PS1 variable. After changing the prompt order:

# Change time to appear first
export PS1="[\t \u@\h \W]$ "

New prompt:

[16:25:03 centos9@vbox random]$

Making changes permanent: Edit ~/.bashrc file and add your PS1 customization, then reload:

source ~/.bashrc

📚 Part 2: Linux Documentation and Help Systems

Linux has excellent built-in documentation. Let's explore how to access and use it effectively.

📖 The man Command: Manual Pages

The man command displays the manual (documentation) for commands.

Reading a Manual Page

man ls | head

What this command does:

man - Display manual pages
ls - The command we want documentation for
| head - Show only first 10 lines (for demonstration)

Output:

LS(1)                                User Commands                                LS(1)

NAME
       ls - list directory contents

SYNOPSIS
       ls [OPTION]... [FILE]...

DESCRIPTION
       List information about the FILEs (the current directory by default).
       Sort entries alphabetically if none of -cftuvSUX nor --sort is specified.

Understanding man page structure:

Header: LS(1)
- LS = command name
- (1) = manual section number (1 = user commands)
NAME: Brief description of the command
SYNOPSIS: How to use the command (syntax)
DESCRIPTION: Detailed explanation

Viewing More Content

man ls | head -n15

What -n15 does:

Shows first 15 lines instead of 10
Useful to see more of the description

Additional output:

       Mandatory arguments to long options are mandatory for short options too.

       -a, --all
              do not ignore entries starting with .

Navigating Manual Pages

When you run man ls (without piping to head), you enter an interactive viewer:

Navigation keys:

Space - Scroll down one page
b - Scroll up one page (back)
/ - Search (e.g., type /color then Enter to find "color")
n - Next search result
q - Quit the manual page

Manual Sections

Man pages are organized into sections:

Section	Contents	Example
1	User commands	man 1 ls
2	System calls	man 2 open
3	Library functions	man 3 printf
4	Special files	man 4 null
5	File formats and conventions	man 5 passwd
6	Games	man 6 fortune
7	Miscellaneous	man 7 signal
8	System administration	man 8 systemctl

Example - File Format Documentation:

man 5 passwd

This shows documentation for the /etc/passwd file format (section 5), not the passwd command.

⚠️

⚠️ Troubleshooting: If man isn't installed, run sudo dnf install man-db on RHEL/CentOS systems or sudo apt install man-db on Debian/Ubuntu.

ℹ️ The info Command

The info command provides more detailed documentation than man pages, with hyperlinked sections.

Using info

The rough file mentions:

info coreutils

What this does:

Displays info pages for GNU core utilities
Provides comprehensive, hyperlinked documentation
More detailed than man pages

Navigation in info:

Enter - Follow links
n - Next page
p - Previous page
u - Up one level in hierarchy
q - Quit

💡

💡 Info vs Man: Use man for quick reference. Use info for comprehensive tutorials and detailed explanations.

❓ Quick Help with --help

Most commands support the --help option for quick reference.

Using --help

ls --help

Sample output (first few lines):

Usage: ls [OPTION]... [FILE]...
List information about the FILEs (the current directory by default).
Sort entries alphabetically if none of -cftuvSUX nor --sort is specified.

Mandatory arguments to long options are mandatory for short options too.
  -a, --all                  do not ignore entries starting with .
  -A, --almost-all           do not list implied . and ..
      --author               with -l, print the author of each file
  -b, --escape               print C-style escapes for nongraphic characters
  -h, --human-readable       with -l and -s, print sizes like 1K 234M 2G etc.

Why use --help:

Quick reference - No need to open full man page
Prints to terminal - Can pipe to grep to search options
Always available - Doesn't require man pages to be installed

Another example:

pwd --help

Output:

pwd: pwd [-LP]
    Print the name of the current working directory.

    Options:
      -L	print the value of $PWD if it names the current working
    		directory
      -P	print the physical directory, without any symbolic links

    By default, `pwd' behaves as if `-L' were specified.

📁 Package Documentation Directory

Installed packages often include additional documentation in /usr/share/doc.

Exploring Documentation

ls /usr/share/doc

This shows all installed packages that have documentation. Example entry from output:

bash  podman  git  docker-ce-cli  ...

Reading Package Documentation

cat /usr/share/doc/bash/README | head

Output:

This directory contains the bash documentation.

FAQ		- a set of frequently-asked questions about Bash with answers
INTRO		- a short introduction to bash
article.ms	- an article I wrote about bash for The Linux Journal
bash.1		- the bash man page
builtins.1	- a man page that documents the builtins, extracted from bash.1
bashref.texi	- the `bash reference manual'
bashref.info	- the `bash reference manual' processed by `makeinfo'
readline.3	- the readline man page

What's in /usr/share/doc:

README files
Example configuration files
Changelog information
License files
Additional tutorials

🔍 Finding Commands: whatis and apropos

whatis: Quick Command Description

The whatis command provides one-line descriptions of commands.

whatis ls

Output:

ls (1)               - list directory contents

What the output means:

ls - Command name
(1) - Manual section 1 (user commands)
Description - Brief explanation

More examples:

whatis podman

Output:

podman (1)           - Simple management tool for pods, containers and images

whatis pwd

Output:

pwd (1)              - print name of current/working directory

apropos: Search for Commands

The apropos command searches manual page descriptions.

apropos "list directory"

Output:

dir (1)              - list directory contents
ls (1)               - list directory contents
vdir (1)             - list directory contents

What this does:

Searches ALL manual page descriptions
Finds commands related to "list directory"
Returns all matches with their descriptions

More powerful example:

apropos container

Output (first few lines):

containerignore (5)  - files to ignore buildah or podman build context directory
buildah (1)          - A command line tool that facilitates building OCI container images.
buildah-add (1)      - Add the contents of a file, URL, or a directory to a container.
buildah-bud (1)      - Build an image using instructions from Containerfiles
docker (1)           - Docker image and container command line interface
podman (1)           - Simple management tool for pods, containers and images
podman-build (1)     - Build a container image using a Containerfile

Use cases for apropos:

Don't know the command name - Search by functionality
Discovering related commands - Find alternatives
Learning the system - Explore available tools

✅

✅ Pro Tip: Use apropos when you know what you want to do but don't know which command to use. For example, apropos "create user" finds user management commands.

🎯 Best Practices

✅ System Information

Check kernel version before installing software
- Use uname -r to verify compatibility
- Some software requires specific kernel versions
Document your system details
- Save /etc/os-release info for troubleshooting
- Note your kernel version when reporting bugs
Monitor service status regularly
- Use systemctl status service_name to check critical services
- Look for "failed" status indicators
Understand your network configuration
- Use ip a to verify connectivity
- Note your IP addresses for remote access

✅ Using Documentation

Start with --help for quick reference
- Faster than man pages for simple questions
- Good for checking available options
Use man pages for detailed information
- Read DESCRIPTION section to understand purpose
- Check EXAMPLES section for usage patterns
- Note the SEE ALSO section for related commands
Search efficiently
- Use apropos when you don't know the command name
- Use whatis for quick confirmation of command purpose
- Use / to search within man pages
Keep documentation handy
- Explore /usr/share/doc for package-specific guides
- Look for README files and examples
- Check for configuration file templates
Master navigation
- Learn man page navigation keys (Space, b, /, q)
- Practice info command navigation
- Use less for comfortable reading

📝 Command Cheat Sheet

System Information Commands

# Kernel and OS information
uname                    # Show kernel name
uname -r                 # Show kernel version
uname -a                 # Show all system information
cat /etc/os-release      # Show distribution information

# Security and services
sestatus                 # Check SELinux status
sudo systemctl status service_name    # Check service status
sudo systemctl start service_name     # Start a service
sudo systemctl stop service_name      # Stop a service
sudo systemctl enable service_name    # Enable at boot
sudo systemctl disable service_name   # Disable at boot

# Network information
ip a                     # Show all network interfaces and addresses
ip addr show eth0        # Show specific interface
ip link                  # Show link layer information
ip route                 # Show routing table

Prompt Customization

# View current prompt
echo $PS1

# Set prompt temporarily (current session only)
export PS1="[\u@\h \W]$ "

# Common PS1 escape sequences
\u    # Username
\h    # Hostname
\H    # Full hostname
\w    # Full working directory
\W    # Current directory name only
\t    # Time HH:MM:SS
\d    # Date
\$    # # for root, $ for regular users
\n    # Newline

# Make permanent - add to ~/.bashrc
echo 'export PS1="[\t \u@\h \W]$ "' >> ~/.bashrc
source ~/.bashrc

Documentation Commands

# Manual pages
man command_name         # Open manual page
man 5 passwd             # Open section 5 (file formats)
man -k keyword           # Search manual pages (same as apropos)

# Quick help
command --help           # Quick option reference
command -h               # Short version (some commands)

# Info pages
info command_name        # Open info documentation
info coreutils           # GNU core utilities info

# Command search and description
whatis command_name      # One-line description
apropos keyword          # Search command descriptions
apropos "search phrase"  # Search with multiple words

# Package documentation
ls /usr/share/doc        # List all package docs
ls /usr/share/doc/bash   # View specific package docs
cat /usr/share/doc/package/README    # Read README file

# Man page navigation
Space         # Next page
b             # Previous page
/pattern      # Search forward
?pattern      # Search backward
n             # Next search result
N             # Previous search result
q             # Quit

# Info navigation
Enter         # Follow link
n             # Next node
p             # Previous node
u             # Up to parent node
l             # Last visited node
d             # Return to top
q             # Quit

# Less navigation (for --help output)
command --help | less
# Then use Space, b, /, q like man pages

Useful Combinations

# Find all commands related to networking
apropos network

# Get one-line description of multiple commands
whatis ls pwd cd mkdir

# Search for specific option in man page
man ls | grep -A 5 "human-readable"

# View help and save to file for reference
ls --help > ls_help.txt

# Search package documentation
ls /usr/share/doc | grep -i docker

# Check if a command has a man page
man -w command_name    # Shows path to man page

🚀 What's Next?

📚 Continue Learning

Package Management with DNF - Learn to install, update, and manage software packages
systemd Service Management - Master service control and system initialization
Network Configuration - Deep dive into Linux networking
SELinux Administration - Comprehensive security policy management

🛠️ Practice Projects

Create a system information script using uname, hostname, and ip commands
Customize your PS1 prompt with colors and Git branch information
Build a service monitoring script with systemctl
Create a command reference sheet for your most-used commands

✅

🎉 Congratulations! You now know how to discover system information and navigate Linux's comprehensive documentation system. These skills are foundational for every Linux user and administrator!

💬 Discussion

I'd love to hear about your experience:

What system information commands do you use most frequently?
Have you customized your bash prompt? Share your PS1 configuration!
Which documentation method do you prefer: man, info, or --help?
What other system administration topics would you like to learn about?

Connect with me:

🐙 GitHub - More Linux tutorials and scripts
📧 Contact - Questions about Linux administration

🖥️ Part 1: System Information Commands

Prerequisites

🐧 The uname Command: Discovering Your System

Basic uname Usage

Checking Kernel Version

Complete System Information

📋 Operating System Release Information

Viewing OS Release Details

🔐 SELinux Status

Checking SELinux Status

🔧 Checking Service Status with systemctl

Viewing SSH Service Status

🌐 Network Configuration with ip Command

Viewing Network Addresses

🎨 Customizing Your Bash Prompt (PS1)

Viewing Current Prompt

Modifying PS1

📚 Part 2: Linux Documentation and Help Systems

📖 The man Command: Manual Pages

Reading a Manual Page

Viewing More Content

Navigating Manual Pages

Manual Sections

ℹ️ The info Command

Using info

❓ Quick Help with --help

Using --help

📁 Package Documentation Directory

Exploring Documentation

Reading Package Documentation

🔍 Finding Commands: whatis and apropos

whatis: Quick Command Description

apropos: Search for Commands

🎯 Best Practices

✅ System Information

✅ Using Documentation

📝 Command Cheat Sheet

System Information Commands

Prompt Customization

Documentation Commands

Navigation in Documentation

Useful Combinations

🚀 What's Next?

📚 Continue Learning

🛠️ Practice Projects

💬 Discussion

Written by Owais

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