Index: head/sys/boot/forth/loader.conf.5
===================================================================
--- head/sys/boot/forth/loader.conf.5
+++ head/sys/boot/forth/loader.conf.5
@@ -112,6 +112,31 @@
 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