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@(#)reboot.8 8.1 (Berkeley) 6/9/93
.Dd February 16, 2011 .Dt REBOOT 8 .Os .Sh NAME .Nm reboot , .Nm poweroff , .Nm halt .Nd restarting, powering down and stopping the system .Sh SYNOPSIS .Nm halt .Op Fl dlnpqvxz .Nm poweroff .Op Fl dlnqvxz .Nm .Op Fl dlnqvxz .Op Ar arg ... .Sh DESCRIPTION The .Nm poweroff , .Nm halt and .Nm utilities flush the file system cache to disk, send all running processes a .Dv SIGTERM , wait for up to 30 seconds for them to die, send a .Dv SIGKILL to the survivors and, respectively, power down, halt or restart the system. The action is logged, including entering a shutdown record into the login accounting file and sending a message via .Xr syslog 3 .
p The options are as follows: l -tag -width Ds t Fl d Create a dump before halting or restarting. This option is useful for debugging system dump procedures or capturing the state of a corrupted or misbehaving system. t Fl l Suppress sending a message via .Xr syslog 3 before halting or restarting. t Fl n Do not flush the file system cache. This option should be used with extreme caution. It can be used if a disk or a processor is on fire. t Fl p Attempt to powerdown the system. If the powerdown fails, or the system does not support software powerdown, the system will halt. This option is only valid for .Nm halt . t Fl v To enable verbose messages on the console, pass the .Xr boothowto 9 flag .Dv AB_VERBOSE to .Xr reboot 2 . t Fl x To enable debugging messages on the console, pass the .Xr boothowto 9 flag .Dv AB_DEBUG to .Xr reboot 2 . t Fl z To silence some shutdown messages on the console, pass the .Xr boothowto 9 flag .Dv AB_SILENT to .Xr reboot 2 . t Fl q Do not give processes a chance to shut down before halting or restarting. This option should not normally be used. .El
p If there are any arguments passed to .Nm reboot they are concatenated with spaces and passed as .Fa bootstr to the .Xr reboot 2 system call. The string is passed to the firmware on platforms that support it.
p Normally, the .Xr shutdown 8 utility is used when the system needs to be halted or restarted, giving users advance warning of their impending doom. .Sh SEE ALSO .Xr reboot 2 , .Xr syslog 3 , .Xr utmp 5 , .Xr boot 8 , .Xr init 8 , .Xr rescue 8 , .Xr shutdown 8 , .Xr sync 8 .Sh HISTORY A .Nm command appeared in .At v6 .
p The .Nm poweroff command first appeared in .Nx 1.5 . .Sh CAVEATS Once the command has begun its work, stopping it before it completes will probably result in a system so crippled it must be physically reset. To prevent premature termination, the command blocks many signals early in its execution. However, nothing can defend against deliberate attempts to evade this.
p This command will stop the system without running any .Xr shutdown 8 scripts. Amongst other things, this means that swapping will not be disabled so that .Xr raid 4 can shutdown cleanly. You should normally use .Xr shutdown 8 unless you are running in single user mode. .Sh BUGS The single user shell will ignore the .Dv SIGTERM signal. To avoid waiting for the timeout when rebooting or halting from the single user shell, you have to c exec reboot or c exec halt .