System Admin: Roles, Tasks & OS Fundamentals

What is System Administration?

System administration (sysadmin) is the management and maintenance of computer systems and networks to ensure smooth operation, security, and efficiency. Sysadmins perform tasks such as:

• Installing, configuring, and troubleshooting hardware/software.
• Managing user accounts and permissions.
• Monitoring system performance and security.
• Automating repetitive tasks (e.g., backups, updates).
• Ensuring data integrity and disaster recovery.

The Three Pillars of System Administration

Every sysadmin role revolves around three core areas:

Types of Operating Systems (OS)

Operating systems act as intermediaries between hardware and software. The three main types are:

1. Batch Operating System

• Definition: Executes jobs in non-interactive batches (predefined sequences).
• How it works:
  • Jobs are grouped into batches and submitted to the OS.
  • The OS processes them sequentially without user intervention.
  • Output is generated after all jobs complete.
• Example Workflow:

  User → Job Submission → OS Scheduler → CPU Execution → Output Generation
  

• Advantages:
  • Efficient for large-scale, repetitive tasks (e.g., payroll processing).
  • Minimal user interaction required.
• Disadvantages:
  • No real-time processing (slow for interactive tasks).
  • No error handling during execution (jobs fail silently).
• Real-World Use:
  • Old mainframe systems (e.g., legacy banking transaction processing).
  • Automated backup scripts running overnight.

2. Time-Sharing (Multitasking) Operating System

• Definition: Allows multiple users to share a single system simultaneously by dividing CPU time.
• How it works:
  • The OS uses a scheduler to allocate CPU time slices (e.g., 100ms per user).
  • Users interact via terminals or remote sessions.
  • Round-robin scheduling ensures fairness.
• Example Workflow:

  User 1 → Requests Task → OS Scheduler → CPU (Time Slot 1) → User 2 → CPU (Time Slot 2) → ...
  

• Advantages:
  • Interactive and responsive (ideal for desktops, servers).
  • Resource sharing (multiple users on one machine).
• Disadvantages:
  • Slower for CPU-intensive tasks (time slicing adds overhead).
  • Requires memory management to avoid conflicts.
• Real-World Use:
  • Linux servers (hosting websites like Daraz or NTC’s internal systems).
  • Cloud computing (AWS, Google Cloud share resources across users).
  • University lab computers (multiple students accessing the same machine).

sequenceDiagram
    participant User1 as User 1
    participant OS as Time-Sharing OS
    participant CPU
    participant User2 as User 2

    User1->>OS: Requests task (e.g., eSewa payment)
    OS->>CPU: Allocates 100ms time slice
    CPU-->>User1: Processes request
    User2->>OS: Requests task (e.g., Khalti transfer)
    OS->>CPU: Allocates next 100ms slice
    CPU-->>User2: Processes request
    Note right of CPU: Round-robin scheduling ensures fairness

3. Distributed Operating System

• Definition: Manages multiple interconnected computers as a single system.
• How it works:
  • No central OS: Each node has its own OS but communicates via network protocols.
  • Transparent resource sharing: Users access files, printers, or CPUs across the network as if local.
  • Example: Google’s Borg system (used for YouTube and Gmail).
• Advantages:
  • Scalability (add more nodes for power).
  • Fault tolerance (if one node fails, others take over).
  • Load balancing (distributes tasks dynamically).
• Disadvantages:
  • Complex to implement (requires high-speed networking).
  • Security challenges (data spread across multiple machines).
• Real-World Use:
  • Google’s distributed systems (handles billions of queries/day).
  • Blockchain networks (e.g., Bitcoin’s peer-to-peer transactions).
  • Nepal’s NEPSE trading system (distributed servers for real-time stock data).

In the Real World

1. eSewa & Khalti: Time-Sharing OS for Payment Processing

• How it uses OS concepts:
  • Thousands of users access eSewa/Khalti simultaneously.
  • The time-sharing OS (Linux-based servers) allocates CPU time to each transaction.
  • Database management (MySQL/PostgreSQL) ensures transactions are processed in order without conflicts.
• Example:
  • When you pay a bill via eSewa, your request is queued, processed in a time slice, and confirmed—all within milliseconds.

2. Daraz’s Order Fulfillment: Batch Processing

• How it uses OS concepts:
  • During off-peak hours (night), Daraz processes batch orders (e.g., 10,000 pending orders at once).
  • The OS schedules these jobs in background batches to avoid slowing down the live website.
• Example:
  • If you order a product at 3 PM, it may be processed in a batch job at 2 AM when server load is low.

3. Ncell’s Network: Distributed OS for Call Routing

• How it uses OS concepts:
  • Ncell’s telecom switches use a distributed OS to route calls across multiple towers.
  • If one tower fails, the system reroutes calls to another tower without dropping calls.
• Example:
  • When you call a friend, your request is handled by a load balancer that picks the nearest available tower.

Key Components of an Operating System

Every OS has four essential functions (visualized below):

classDiagram
    class OS {
        +Process Management
        +Memory Management
        +File System Management
        +Device Management
    }
    class Process {
        +CPU Scheduling
        +Inter-Process Communication
    }
    class Memory {
        +Allocation (RAM/Disk)
        +Swapping (Virtual Memory)
    }
    class FileSystem {
        +Directory Structure
        +File Permissions
        +Backup & Recovery
    }
    class Device {
        +Driver Management
        +I/O Operations
    }
    OS --> Process : Manages
    OS --> Memory : Allocates
    OS --> FileSystem : Organizes
    OS --> Device : Controls

1. Process Management

• Definition: The OS controls how programs (processes) run on the CPU.
• Key Mechanisms:
  • Process Scheduling: Decides which process gets CPU time (e.g., Round Robin, Priority Scheduling).
  • Inter-Process Communication (IPC): Processes share data (e.g., pipes, sockets, shared memory).
• Example:
  • When you open WhatsApp and YouTube simultaneously, the OS switches between them using time-sharing.

2. Memory Management

• Definition: The OS manages RAM and virtual memory to run multiple programs.
• Key Mechanisms:
  • Pagination: Splits memory into fixed-size blocks (pages).
  • Swapping: Moves inactive pages to disk (slow but saves RAM).
  • Memory Protection: Prevents one process from accessing another’s memory.
• Example:
  • If your laptop runs out of RAM, the OS swaps less-used apps to the hard drive (slowing them down temporarily).

3. File System Management

• Definition: Organizes files and directories on storage devices.
• Key Concepts:
  • File Allocation Table (FAT): Tracks file locations (used in older systems).
  • Journaling: Recovers files after crashes (used in Linux’s ext4, Windows’ NTFS).
  • Permissions: Controls who can read/write/execute files (e.g., chmod in Linux).
• Example:
  • When you save a file in Google Drive, the OS stores it in a distributed file system (spread across multiple servers).

4. Device Management

• Definition: Controls hardware devices (keyboard, printer, network card).
• Key Mechanisms:
  • Device Drivers: Software that lets the OS communicate with hardware.
  • I/O Scheduling: Manages input/output operations (e.g., Elevator Algorithm for disk access).
• Example:
  • When you print a document, the OS uses a printer driver to send data to the printer.

System Administrator Roles in Different Environments

Sysadmins work in three main environments, each with unique challenges:

Worked Example: Linux Server Configuration for a Web Host

Scenario: You are a sysadmin for a small hosting company in Nepal. A client wants to host a website with:

• Apache web server (serves HTML pages).
• MySQL database (stores user data).
• SSH access (for remote management).

Step-by-Step Setup

1. Install the OS (Ubuntu Server):

   • Download Ubuntu Server ISO from ubuntu.com.
   • Install via text mode (no GUI needed for servers).
   • Configure static IP (e.g., 192.168.1.100) for reliability.

2. Update the System:

   sudo apt update && sudo apt upgrade -y
   

3. Install Apache (Web Server):

   sudo apt install apache2 -y
   

   • Verify it’s running:

     sudo systemctl status apache2
     

   • IMAGE: "Ubuntu server terminal apache2 install" | Installing Apache on Ubuntu Server

4. Install MySQL (Database):

   sudo apt install mysql-server -y
   sudo mysql_secure_installation  # Set root password
   

5. Configure SSH (Remote Access):

   • Edit SSH config:

     sudo nano /etc/ssh/sshd_config
     

   • Change PermitRootLogin to no (security best practice).
   • Restart SSH:

     sudo systemctl restart sshd
     

6. Automate Backups (Cron Job):

   • Schedule daily backups at 2 AM:

     crontab -e
     

     Add:

     0 2 * * * tar -czf /backups/website_$(date +\%Y-\%m-\%d).tar.gz /var/www/html
     

Exam Tip

What to Expect in TU/PU Exams

1. Definitions & Comparisons:

   • Expect short-answer questions comparing batch vs. time-sharing vs. distributed OS.
   • Example: "Why is a distributed OS better than a time-sharing OS for Google’s search engine?" Answer: Distributed OS handles millions of queries simultaneously across servers, while time-sharing would bottleneck on a single machine.

2. Scenario-Based Questions:

   • You’ll be given a real-world scenario (e.g., "A bank’s ATM system fails. How would a distributed OS help?").
   • Key points to mention:
     • Fault tolerance (if one ATM server crashes, others take over).
     • Load balancing (distributes transactions evenly).
     • Real-time processing (no delays in batch mode).

3. Command-Line Practicality:

   • Linux commands (e.g., ps, top, df, cron) may appear in practical exams.
   • Example: "How would you check running processes in Linux?" Answer: ps aux or top.

4. Diagrams & Flowcharts:

   • Draw process scheduling diagrams (e.g., Round Robin).
   • Example:

     Process A → CPU (Time Slot 1) → Process B → CPU (Time Slot 2) → ...
     

5. Security & Best Practices:

   • Questions on permissions (chmod), firewalls (iptables), and backups are common.
   • Example: "Why should you never use chmod 777 on a web directory?" Answer: It gives read/write/execute to everyone, including hackers.

Final Checklist for Full Marks

While not in Unit 1, this sets up Unit 5 (Network Configuration) by showing how OS interacts with networking (Image: Ardika6879, CC BY-SA 4.0, via Wikimedia Commons)

In the real world

• eSewa/Khalti: Uses time-sharing OS (Linux) to handle 10,000+ simultaneous transactions via CPU time-slicing, ensuring no user waits longer than 2 seconds for payment confirmation.
• Daraz: Employs batch processing to handle 50,000+ nightly orders during off-peak hours, reducing daytime server load by 40%.
• Ncell: Deploys distributed OS across 50+ telecom towers to reroute calls instantly if a tower fails, maintaining 99.9% uptime.