xref: /freebsd/share/man/man9/kern_reboot.9 (revision b7caa912f9df5f76f189be18afc949a775c8e0fe)

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.\" 	Mike Pritchard.  All rights reserved.
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.\" Copyright (c) 1994 Christopher G. Demetriou
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.Dd March 20, 2023
.Dt REBOOT 9
.Os
.Sh NAME
.Nm kern_reboot ,
.Nm shutdown_nice
.Nd reboot, halt, or power off the system
.Sh SYNOPSIS
.In sys/types.h
.In sys/systm.h
.In sys/reboot.h
.Vt extern int rebooting;
.Ft void
.Fn kern_reboot "int howto"
.Ft void
.Fn shutdown_nice "int howto"
.In sys/eventhandler.h
.Fn EVENTHANDLER_REGISTER "shutdown_pre_sync" "shutdown_fn" "private" "priority"
.Fn EVENTHANDLER_REGISTER "shutdown_post_sync" "shutdown_fn" "private" "priority"
.Fn EVENTHANDLER_REGISTER "shutdown_final" "shutdown_fn" "private" "priority"
.Sh DESCRIPTION
The
.Fn kern_reboot
function handles final system shutdown, and either halts, reboots,
or powers down the system.
The exact action to be taken is determined by the flags passed in
.Fa howto .
.Pp
The relevant flags are:
.Bl -tag -compact -offset indent -width "RB_POWERCYCLE"
.It Dv RB_HALT
Halt the system in-place rather than restarting.
.It Dv RB_POWEROFF
Power down the system rather than restarting.
.It Dv RB_POWERCYCLE
Request a power-cycle in addition to restarting.
.It Dv RB_NOSYNC
Do not sync filesystems during shutdown.
.It Dv RB_DUMP
Dump kernel memory during shutdown.
.El
.Pp
The
.Fa howto
field, and its full list of flags are described in additional detail by
.Xr reboot 2 .
.Pp
.Fn kern_reboot
performs the following actions:
.Bl -enum -offset indent
.It
Set the
.Va rebooting
variable to
.Dv 1 ,
indicating that the reboot process has begun and cannot be stopped.
.It
Set the
.Va kdb_active
variable to
.Dv 0 ,
indicating that execution has left the kernel debugger, if it was previously
active.
.It
Unless the
.Dv RB_NOSYNC
flag is set in
.Fa howto ,
sync and unmount the system's disks by calling
.Xr vfs_unmountall 9 .
.It
If rebooting after a panic
.Po
.Dv RB_DUMP
is set in
.Fa howto ,
but
.Dv RB_HALT
is not set
.Pc ,
initiate a system crash dump via
.Fn doadump .
.It
Print a message indicating that the system is about to be halted
or rebooted, and a report of the total system uptime.
.It
Execute all registered shutdown hooks.
.It
As a last resort, if none of the shutdown hooks handled the reboot, call the
machine-dependent
.Fn cpu_reset
function.
In the unlikely case that this is not supported,
.Fn kern_reboot
will loop forever at the end of the function.
This requires a manual reset of the system.
.El
.Pp
.Fn kern_reboot
may be called from a typical kernel execution context, when the system is
running normally.
It may also be called as the final step of a kernel panic, or from the kernel
debugger.
Therefore, the code in this function is subject to restrictions described by
the
.Sx EXECUTION CONTEXT
section of the
.Xr panic 9
man page.
.Pp
The
.Fn shutdown_nice
function is the intended path for performing a clean reboot or shutdown when
the system is operating under normal conditions.
Calling this function will send a signal to the
.Xr init 8
process, instructing it to perform a shutdown.
When
.Xr init 8
has cleanly terminated its children, it will perform the
.Xr reboot 2
system call, which in turn calls
.Fn kern_reboot .
.Pp
If
.Fn shutdown_nice
is called before the
.Xr init 8
process has been spawned, or if the system has panicked or otherwise halted,
.Fn kern_reboot
will be called directly.
.Sh RETURN VALUES
The
.Fn kern_reboot
function does not return.
.Pp
The
.Fn shutdown_nice
function will usually return to its caller, having initiated the asynchronous
system shutdown.
It will not return when called from a panic or debugger context, or during
early boot.
.Sh SEE ALSO
.Xr reboot 2 ,
.Xr init 8 ,
.Xr EVENTHANDLER 9 ,
.Xr panic 9 ,
.Xr vfs_unmountall 9