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From: Maxim Sobolev <sobomax@FreeBSD.org>
Date: Fri, 8 Apr 2016 00:24:21 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r297690 - head/sys/boot/forth
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Author: sobomax
Date: Fri Apr  8 00:24:21 2016
New Revision: 297690
URL: https://svnweb.freebsd.org/changeset/base/297690

Log:
  Document vfs.root.mountfrom.
  
  Reviewed by:	imp, wblock
  Differential Revision:	https://reviews.freebsd.org/D5332

Modified:
  head/sys/boot/forth/loader.conf.5

Modified: head/sys/boot/forth/loader.conf.5
==============================================================================
--- head/sys/boot/forth/loader.conf.5	Fri Apr  8 00:01:19 2016	(r297689)
+++ head/sys/boot/forth/loader.conf.5	Fri Apr  8 00:24:21 2016	(r297690)
@@ -112,6 +112,31 @@ The name must be a subdirectory of
 that contains a kernel.
 .It Ar kernel_options
 Flags to be passed to the kernel.
+.It Ar vfs.root.mountfrom
+Specify the root partition to mount.
+For example:
+.Pp
+.Dl vfs.root.mountfrom="ufs:/dev/da0s1a"
+.Pp
+.Xr loader 8
+automatically calculates the value of this tunable from
+.Pa /etc/fstab
+from the partition the kernel was loaded from.
+The calculated value might be calculated incorrectly when
+.Pa /etc/fstab
+is not available during
+.Xr loader 8
+startup (as during diskless booting from NFS), or if a different
+device is desired by the user.
+The preferred value can be set in
+.Pa /loader.conf .
+.Pp
+The value can also be overridden from the
+.Xr loader 8
+command line.
+This is useful for system recovery when
+.Pa /etc/fstab
+is damaged, lost, or read from the wrong partition.
 .It Ar password
 Protect boot menu with a password without interrupting
 .Ic autoboot