The famous sudo warning message that appears on first use is controlled by the sudoers configuration system. The specific file containing this message varies by Linux distribution:

# For most Linux distributions:
/etc/sudoers
or
/etc/sudoers.d/README

# On Debian/Ubuntu systems:
/usr/share/doc/sudo/examples/sudoers

To customize the warning, you'll need to edit the sudoers file with visudo for safety:

sudo visudo

Look for the section containing the "lecture" message. Here's the standard template:

Defaults    lecture = always
Defaults    lecture_file = "/path/to/your/custom_message.txt"

You can create your own message file (requires root privileges):

sudo nano /etc/sudo.custom.msg

Example content for a custom message (keep it professional but fun):

========================================================================
SECURITY NOTICE: Unauthorized access to this system is prohibited.
All sudo commands are logged and monitored. 

Before proceeding, please ensure you:
1. Understand the command's impact
2. Have proper authorization
3. Know how to undo changes if needed

Contact sysadmin@yourdomain.com with questions.
========================================================================

For different user groups, you can set custom messages:

# For admin group
Defaults:%admin lecture_file = "/etc/sudo.admin.msg"

# For developers group  
Defaults:%dev lecture_file = "/etc/sudo.dev.msg"

After saving changes, test with:

sudo -k  # Clear cached credentials
sudo -v  # Trigger new authentication

Remember that syntax errors in sudoers can lock you out of sudo access, so always verify with visudo -c before saving.

The default sudo warning message is stored in the /etc/sudoers file or a dedicated message file depending on your Linux distribution. The most common locations are:

# Default location on most systems
/etc/sudoers

# Alternative location on some distros
/etc/sudoers.d/README

To modify the message, always use visudo for safety as it performs syntax checking:

sudo visudo /etc/sudoers

Look for the following line (usually around line 60-80):

Defaults    lecture="always"

Below this, you can find or add the message template:

Defaults    lecture_file = "/etc/sudoers.d/sudo-motd"

Create a new file for your custom message:

sudo nano /etc/sudoers.d/sudo-motd

Add your custom warning (supports multi-line messages):

WARNING: Unauthorized access to this system is forbidden!
This system is monitored and all activities are logged.
By proceeding, you acknowledge that your actions may be audited.

Here are some practical examples:

# Simple security warning
echo "SECURITY NOTICE: All sudo actions are logged and monitored" | sudo tee /etc/sudoers.d/sudo-warning

# Multi-line legal notice
cat <
To verify your new message appears:
sudo -k  # Clear cached credentials
sudo ls  # Should show new message

When customizing the sudo message:

Keep the file permissions strict (440 or 640)
Include legal/security disclaimers where required
Consider adding compliance references (PCI DSS, HIPAA, etc.)
Update messages when policies change