Message of the Day (motd) support

[pbalduino]

Summary

Implement a message of the day (motd) utility that displays a randomly selected message from /etc/motd when users log in or start a shell session.

Description

Add motd (message of the day) functionality to display welcome messages, system information, or tips when users log in. The utility should randomly select one message from /etc/motd and display it, with support for users to suppress display via ~/.hushlogin.

Inspiration

Idea borrowed from OpenBSD's motd system, which provides a clean way to communicate system information and welcome users.

Proposed Behavior

Display Trigger

• Display motd when shell starts (integration with #314 .moshrc)
• Display motd when user logs in (future login mechanism)
• Can be invoked manually via /bin/motd command

Message Selection

• Read messages from /etc/motd file
• Messages separated by delimiter (e.g., --- or blank line)
• Randomly select one message to display
• Simple sequential display if randomization not desired

Suppression Mechanism

• Check for ~/.hushlogin file in user's home directory
• If .hushlogin exists, skip motd display
• Allows users to opt out of motd without system changes

Example /etc/motd Format

Option 1: Simple (single message)

Welcome to meniOS!

System uptime: 3 days, 4 hours
Kernel version: 0.2.0

Option 2: Multiple messages (delimited)

Welcome to meniOS - A modern OS from scratch!
---
"Programs must be written for people to read, and only incidentally for machines to execute." - Abelson & Sussman
---
Tip: Use Ctrl+R for reverse command search in the shell!
---
Fun fact: meniOS can run Doom (1993)!
---
Remember: All bugs are shallow with enough eyeballs.

Implementation Details

Phase 1: Basic motd Command

• Create /bin/motd utility
• Read /etc/motd file
• Display content to stdout
• Simple, no randomization yet

Phase 2: Message Selection

• Parse multi-message format (delimiter-separated)
• Implement random selection using rand() (#241 ✅)
• Seed random generator with time (time() #240 ✅)

Phase 3: .hushlogin Support

• Check for ~/.hushlogin before display
• Requires home directory path resolution
• Silent skip if hushlogin exists

Phase 4: Shell Integration

• Integrate with .moshrc (#314) for automatic display
• Add motd call to default shell initialization
• Respect .hushlogin in automatic context

File Locations

System Message File

• /etc/motd - System-wide message of the day
• Root-owned, world-readable
• Created/maintained by administrator

User Suppression File

• ~/.hushlogin - User-specific suppression flag
• Empty file (existence check only)
• Created by user to disable motd

Example Usage

Display motd

$ motd
Welcome to meniOS!

System uptime: 3 days, 4 hours
Kernel version: 0.2.0

Suppress motd

$ touch ~/.hushlogin
$ # motd will no longer display automatically

Re-enable motd

$ rm ~/.hushlogin
$ # motd will display on next login/shell

Implementation Considerations

File Format

• Simple plain text for MVP
• Delimiter-based multi-message support
• No special formatting required initially
• Future: support for ANSI colors, system variable expansion

Randomization

• Use existing rand()/srand() from libc (#241 ✅)
• Seed with time() for variety (#240 ✅)
• Fallback to sequential/first message if random fails

Error Handling

• Missing /etc/motd: silent skip (not an error)
• Missing ~/.hushlogin: display motd (default behavior)
• Read errors: log warning but don't block login
• Malformed file: display what's parseable, ignore errors

Performance

• Keep it fast - login shouldn't hang on motd
• Limit message file size (e.g., 64 KiB max)
• Avoid complex parsing or processing

Benefits

• User Welcome: Friendly greeting for new users
• System Information: Communicate uptime, version, news
• Tips & Education: Share shell tips, keyboard shortcuts
• Personality: Give meniOS character and charm
• Community: Share quotes, facts, fun messages
• Announcements: Notify users of maintenance, changes

Use Cases

Development/Testing

Welcome to meniOS Development Build!

Last build: 2025-10-19
Kernel features: buddy allocator, FAT32 writes, Doom support!

Happy hacking!

Production

meniOS v1.0 - Stable Release

Uptime: 42 days
Users online: 3
Disk usage: 45%

For support, see /usr/share/doc/README

Fun/Educational

"Talk is cheap. Show me the code." - Linus Torvalds

Did you know? meniOS implements a buddy allocator for efficient memory management!

Tip of the day: Use 'ps' to see running processes.

Dependencies

• #193 (libc) ✅ - For file I/O, string operations
• #240 (time()) ✅ - For random seed
• #241 (rand()) ✅ - For message selection
• #313 (filesystem organization) - For /etc directory structure
• #314 (shell startup scripts) - For automatic motd integration
• Ideally: home directory support for ~/.hushlogin

Testing

1. Create /etc/motd with single message, verify display
2. Create /etc/motd with multiple messages (delimiter-separated), verify random selection
3. Create ~/.hushlogin, verify motd suppression
4. Test with missing /etc/motd, verify silent skip
5. Test with malformed /etc/motd, verify graceful handling
6. Integrate with .moshrc, verify automatic display

Future Enhancements (Out of Scope)

• Variable expansion (e.g., $USER, $HOSTNAME, $UPTIME)
• ANSI color support for formatted messages
• Multiple motd files (e.g., /etc/motd.d/*.motd)
• Dynamic content generation (fortune-style)
• Per-user custom motd overrides
• Network-fetched motd (fetch from URL)
• motd rotation schedule (daily/weekly/random)

Priority

Low - Nice-to-have feature, enhances user experience but not critical

Related Issues

• #313 (Filesystem organization) - Establishes /etc directory
• #314 (Shell startup scripts) - Provides automatic execution mechanism

Inspiration Examples

OpenBSD motd

• Simple, clean, informative
• Suppressible via .hushlogin
• Administrator-controlled content

Linux motd

• Often combined with dynamic scripts (/etc/update-motd.d/)
• Can show system stats, package updates, etc.

FreeBSD motd

• Traditional static message file
• Often used for maintenance announcements