Index: sys/boot/forth/loader.conf.5
===================================================================
--- sys/boot/forth/loader.conf.5
+++ sys/boot/forth/loader.conf.5
@@ -112,6 +112,30 @@
 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
+The value of this tunable is automatically set by
+.Xr loader 8
+after reading and parsing
+.Pa /etc/fstab .
+This parameter can be set when the calculated value is known to be incorrect
+and it would take precedence over what has been read.
+.Pp
+The parameter can also be used when
+.Pa /etc/fstab
+is inaccessible at the time
+.Xr loader 8
+runs, like during diskless booting from NFS.
+.Pp
+It is also possible to override that value from the
+.Xr loader 8
+CLI, which could be helpful for system recovery if the
+.Pa /etc/fstab
+is damaged, lost or read from wrong partition.
 .It Ar password
 Protect boot menu with a password without interrupting
 .Ic autoboot