💬 Linux/Unix: Messaging Commands – write, wall, mail Explained with Output & Examples

🧲 Introduction – Why Learn Messaging Commands in Linux?

In multi-user Linux/Unix environments, messaging between logged-in users or sending system-wide announcements is crucial—especially on servers and remote systems. Tools like write, wall, and mail allow communication right from the terminal without requiring external apps.

🎯 In this guide, you’ll learn:

• How to send private messages to another terminal user with write
• How to broadcast messages to all users with wall
• How to send and read system email with mail
• Real examples and expected outputs

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📨 1. write – Send a Message to Another Logged-In User

✅ What is write?

The write command sends a direct message to another logged-in user’s terminal session.

🛠️ Syntax:

write [username] [tty]

🔹 How to Use:

1. Find active users and terminals: who 📤 Output: alice pts/0 2025-06-15 09:12 bob pts/1 2025-06-15 09:14
2. Write a message: write bob pts/1 Then type your message. To finish, press Ctrl+D.

📤 Receiver (bob) sees:

Message from alice@hostname on pts/0 at 09:20 ...
Hey Bob! Please check your email. Thanks.

🧠 If you skip tty, it goes to the user’s first active session.

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📢 2. wall – Broadcast Message to All Logged-In Users

✅ What is wall?

wall (write all) broadcasts a system-wide message to all logged-in terminals.

🛠️ Syntax:

wall [file]

Or enter interactive mode:

wall
[Type message here, end with Ctrl+D]

🧪 Example:

wall <<EOF
⚠️ System maintenance at 11:00 PM.
Please save your work.
EOF

📤 Output on all terminals:

Broadcast message from root@server (pts/0) at 21:45 ...
⚠️ System maintenance at 11:00 PM.
Please save your work.

🧠 Requires write permissions enabled on terminals (mesg y).

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📬 3. mail – Send & Read System Email

✅ What is mail?

mail sends and reads messages via the local mail system—often used for automated alerts or system notifications.

🛠️ Syntax:

mail [user]

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🧪 Example 1: Send a message to a user

echo "Backup completed successfully." | mail -s "Backup Report" bob

🧪 Example 2: Check your inbox

mail

📤 Output:

Heirloom Mail version 12.5.  Type ? for help.
"/var/mail/alice": 1 message 1 new
>N  1 bob      Mon Jun 15 10:05  16/512  "Backup Report"

📬 Inside mail:

• 1 – View message
• d – Delete message
• q – Quit mail client

📦 To install:

sudo apt install mailutils  # Debian/Ubuntu
sudo yum install mailx      # RHEL/CentOS

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🧠 Messaging Tools Comparison

Tool	Purpose	Targets	Interactive	Common Usage
write	Send message to one user	Specific TTY	✅	User-to-user chat
wall	Broadcast to all users	All TTYs	✅	Maintenance alerts, announcements
mail	Send/read system email	User’s inbox	❌ (shell)	System logs, job alerts, cron output

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📌 Summary – Recap & Next Steps

Messaging commands help Linux users and admins communicate instantly, alert others, and manage system notifications—especially in remote or multi-user server environments.

🔍 Key Takeaways:

• Use write to chat with individual users in real time.
• Use wall to send announcements to all active users.
• Use mail to send/read system messages, especially in automation.

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❓ FAQs

❓ How do I prevent messages from appearing in my terminal?
✅ Run:

mesg n

❓ How do I allow messages again?
✅ Use:

mesg y

❓ Where are mail messages stored?
✅ Usually in /var/mail/<username> or /var/spool/mail/<username>.

❓ Can mail send emails to external addresses?
✅ Yes, but you must configure Sendmail or Postfix.

❓ What’s the difference between wall and write?
✅ write is one-on-one, wall sends to all logged-in users.

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