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Linux in a Nutshell

This directory of Linux commands is from Linux in a Nutshell, 5th Edition.

Click on any of the 687 commands below to get a description and list of available options. All links in the command summaries point to the online version of the book on Safari Bookshelf.

Buy it now, or read it online on Safari Bookshelf.


poweroff [options]

System administration command. Close out filesystems, shut down the system, and power off. Because this command immediately stops all processes, it should be run only in single-user mode. If the system is not in runlevel 0 or 6, poweroff calls shutdown -h, then performs a poweroff.



Suppress writing to /var/log/wtmp.


Call reboot or halt and not shutdown, even when shutdown would normally be called. This option is used to force a hard halt or reboot.


Place hard drives in standby mode before halt or poweroff.


Shut down network interfaces before reboot.


Suppress normal call to sync.


Suppress normal execution; simply write to /var/log/wtmp.

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