Index: head/sbin/reboot/reboot.8
===================================================================
--- head/sbin/reboot/reboot.8	(revision 327024)
+++ head/sbin/reboot/reboot.8	(revision 327025)
@@ -1,190 +1,193 @@
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 .\"	@(#)reboot.8	8.1 (Berkeley) 6/9/93
 .\" $FreeBSD$
 .\"
-.Dd October 23, 2017
+.Dd December 20, 2017
 .Dt REBOOT 8
 .Os
 .Sh NAME
 .Nm reboot ,
 .Nm halt ,
 .Nm fastboot ,
 .Nm fasthalt
 .Nd stopping and restarting the system
 .Sh SYNOPSIS
 .Nm halt
 .Op Fl lNnpq
 .Op Fl k Ar kernel
 .Nm
 .Op Fl cdlNnpqr
 .Op Fl k Ar kernel
 .Nm fasthalt
 .Op Fl lNnpq
 .Op Fl k Ar kernel
 .Nm fastboot
 .Op Fl dlNnpq
 .Op Fl k Ar kernel
 .Sh DESCRIPTION
 The
 .Nm halt
 and
 .Nm
 utilities flush the file system cache to disk, send all running processes
 a
 .Dv SIGTERM
 (and subsequently a
 .Dv SIGKILL )
 and, respectively, halt or restart the system.
 The action is logged, including entering a shutdown record into the user
 accounting database.
 .Pp
 The options are as follows:
 .Bl -tag -width indent
 .It Fl c
 The system will turn off the power and then turn it back on if it can.
 If the power down action fails, the system
 will halt or reboot normally, depending on whether
 .Nm halt
 or
 .Nm
 was called.
 At the present time, only the
 .Xr ipmi 4
 driver implements the power cycle functionality and only on hardware
 with a BMC that supports power cycling.
 Unlike power off, the amount of hardware that supports power cycling
 is small.
 .It Fl d
 The system is requested to create a crash dump.
 This option is
 supported only when rebooting, and it has no effect unless a dump
 device has previously been specified with
 .Xr dumpon 8 .
 .It Fl k Ar kernel
 Boot the specified
 .Ar kernel
 on the next system boot.
 If the kernel boots successfully, the
 .Em default
 kernel will be booted on successive boots, this is a one-shot option.
 If the boot fails, the system will continue attempting to boot
 .Ar kernel
 until the boot process is interrupted and a valid kernel booted.
 This may change in the future.
 .It Fl l
 The halt or reboot is
 .Em not
 logged to the system log.
 This option is intended for applications such as
 .Xr shutdown 8 ,
 that call
 .Nm
 or
 .Nm halt
 and log this themselves.
 .It Fl N
 The file system cache is not flushed during the initial process clean-up,
 however the kernel level
 .Xr reboot 2
 is still processed with a sync.
 This option can be useful for performing a
 .Dq best-effort
 reboot when devices might be unavailable.
 This can happen when devices have been disconnected, such as with
 .Xr iscsi 4 .
 .It Fl n
 The file system cache is not flushed.
 This option should probably not be used.
 .It Fl p
 The system will turn off the power if it can.
 If the power down action fails, the system
 will halt or reboot normally, depending on whether
 .Nm halt
 or
 .Nm
 was called.
 .It Fl q
 The system is halted or restarted quickly and ungracefully, and only
 the flushing of the file system cache is performed (if the
 .Fl n
 option is not specified).
 This option should probably not be used.
 .It Fl r
 The system kills all processes, unmounts all filesystems, mounts the new
 root filesystem, and begins the usual startup sequence.
 After changing vfs.root.mountfrom with
 .Xr kenv 1 ,
 .Nm Fl r
 can be used to change the root filesystem while preserving kernel state.
+This requires the
+.Xr tmpfs 5
+kernel module to be loaded.
 .El
 .Pp
 The
 .Nm fasthalt
 and
 .Nm fastboot
 utilities are nothing more than aliases for the
 .Nm halt
 and
 .Nm
 utilities.
 .Pp
 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 and cleanly terminating
 specific programs.
 .Sh EXAMPLES
 Replace current root filesystem with UFS mounted from
 .Pa /dev/ada0s1a :
 .Bd -literal -offset indent
 kenv vfs.root.mountfrom=ufs:/dev/ada0s1a
 reboot -r
 .Ed
 .Pp
 This mechanism can also be used with NFS, with a caveat that
 it only works with NFSv4, and requires a numeric IPv4 address:
 .Bd -literal -offset indent
 kenv vfs.root.mountfrom=nfs:192.168.1.1:/share/name
 reboot -r
 .Ed
 .Sh SEE ALSO
 .Xr kenv 1 ,
 .Xr getutxent 3 ,
 .Xr ipmi 4 ,
 .Xr boot 8 ,
 .Xr dumpon 8 ,
 .Xr nextboot 8 ,
 .Xr savecore 8 ,
 .Xr shutdown 8 ,
 .Xr sync 8
 .Sh HISTORY
 A
 .Nm
 utility appeared in
 .Bx 4.0 .