halt - macOS

Overview

The halt command in macOS is used to stop all CPU functions in a safe manner, essentially bringing the system to a halt. It is primarily utilized by system administrators and those with suitable privileges to safely shutdown or reboot the system directly from the command line. This tool is particularly useful in remote administration scenarios, automated scripts or during system maintenance.

Syntax

The basic syntax for the halt command is as follows:

halt [options]

The command can be run without options, but options can modify the behavior of the command.

Options/Flags

  • -q, --quiet: Reduces the output of the command. This is beneficial in scripts or when output needs to be minimized.
  • -l, --halt: Halts the machine without actually powering it down. This is useful for systems that need to remain in a minimal power state.
  • -p, --poweroff: Powers down the system after halting. This is the typical end goal when halting a system as part of maintenance.
  • -f, --force: Forces the halt or power off, bypassing the init system. This can be necessary if the system is unresponsive but should be used with caution as it may lead to data loss.
  • -w, --write: Only writes the wtmp (who) shutdown entry, without actually halting the system.

Examples

1. Basic halt command:

sudo halt

This command halts the system in the usual manner, going through the normal shutdown sequence.

2. Force halt the system:

sudo halt -f

Forces the system to halt even if the standard shutdown processes fail.

3. Power off the system post halt:

sudo halt -p

This command will safely halt the system and then power it off.

Common Issues

  • Permission Denied: Users might encounter this error if they try to execute halt without sufficient privileges. Ensure you are using sudo or logged in as a root user.
  • System Does Not Halt: Sometimes, the system services may prevent the system from halting. Using the -f flag can overcome such issues, though it should be used as a last resort.

Integration

halt can be scheduled in crontabs or combined with scripts to automate system maintenance:

Automate system shutdown at a specific time every day:

# Run crontab with the -e flag to edit the cron table:
crontab -e

# Add this line to schedule a shutdown at 11 PM daily:
0 23 * * * /sbin/halt
  • shutdown – Allows more detailed control over stopping the system.
  • reboot – Used specifically to restart the system safely.
  • poweroff – Similar to halt -p, it stops all processes and then powers down the computer.

For more detailed information visit Apple’s official documentation on system commands or consult the man pages (man halt).