Advanced Shell Simulation

A lightweight C-based shell simulation for OS coursework demos. The program includes:

• Login/authentication with SHA-256 password verification and default users.
• Role/permission flow (admin and standard) with su/sudo behavior.
• Command passthrough to host shell (supports pipelines like ls | grep txt).
• Scheduling demo outputs for Round-Robin and Priority modes.
• Paging demo outputs for FIFO and LRU replacement.
• Synchronization demo using producer/consumer with pthread mutex + condition variables.

Repository layout

• shell_sim.c — simulator implementation.
• Makefile — build targets (make, make clean).
• sample_logfile.log — data for grep/sort pipeline demo.
• notes.txt — sample .txt entry for pipe demo.
• admin_secret.txt — admin-only target file in permission demo.
• scripts/run_demo.sh — non-interactive end-to-end demonstration script.
• docs/DELIVERABLE4_REPORT_APA.md — APA-style report template.

Build

make clean && make

Run interactively

./shell

Default users (created in users.db on first run):

• Admin: admin / admin123
• Standard: user / user123

Demonstration commands

After login:

# piping
ls | grep txt
cat sample_logfile.log | grep error | sort

# scheduling
scheduler rr
scheduler priority

# paging
paging fifo
paging lru

# synchronization
sync_demo

# permissions
su user user123
cat admin_secret.txt
sudo admin123
cat admin_secret.txt

Automated validation

Run the scripted demonstration and capture output:

bash scripts/run_demo.sh

This writes demo_output.txt with a complete transcript you can cite in a paper appendix.

Screenshot checklist for Deliverable 4

Save terminal screenshots with these names:

• login.png
• piping.png
• scheduling_rr.png
• scheduling_priority.png
• paging_fifo.png
• paging_lru.png
• sync.png
• permission_denial.png
• permission_success.png

You can place them in docs/screenshots/ for submission packaging.