4.3Notifying Users

Stopping a system without warning can cost users their in-progress work. Notifying users may look mundane, but it is a basic practice that underpins operational trust—the file or command you use depends on when, where, and to whom the message is shown.

4.3.1Static messages before and after login

• /etc/issue is shown before the local console login prompt. /etc/issue.net is shown before a network login such as telnet (many SSH implementations do not use it by default).
• /etc/motd (message of the day) is displayed after a successful login—used for scheduled maintenance notices or policy announcements.

4.3.2Immediate notification and shutdown

• wall broadcasts a message immediately to every currently logged-in user's terminal (e.g., wall "Rebooting in 10 minutes").
• shutdown schedules a stop or reboot at a given time and automatically broadcasts a warning message to users before executing (e.g., shutdown -r +10 "Rebooting for maintenance").
• systemctl performs service-level stop/restart operations (e.g., systemctl restart); operational practice is to announce with wall or similar before acting.