Document the init_chroot and init_script variables.

# I didn't check the markup too closely, so doc people, please check

Submitted by: Oliver Fromme

sys/boot/common/loader.8

@@ -423,12 +423,63 @@ userland output (e.g.\& from
 .It Va currdev
 Selects the default device.
 Syntax for devices is odd.
+.It Va init_chroot
+If set to a valid directory in the root file system, it causes
+.Xr init 8
+to perform a
+.Xr chroot 2
+operation on that directory, making it the new root directory.
+That happens before entering single-user mode or multi-user
+mode (but after executing the
+.Va init_script
+if enabled).
 .It Va init_path
 Sets the list of binaries which the kernel will try to run as the initial
 process.
 The first matching binary is used.
 The default list is
 .Dq Li /sbin/init:/sbin/oinit:/sbin/init.bak:\:/rescue/init:/stand/sysinstall .
+.It Va init_script
+If set to a valid file name in the root file system,
+instructs
+.Xr init 8
+to run that script as the very first action,
+before doing anything else.
+Signal handling and exit code interpretation is similar to
+running the
+.Pa /etc/rc
+script.
+In particular, single-user operation is enforced
+if the script terminates with a non-zero exit code,
+or if a SIGTERM is delivered to the
+.Xr init 8
+process (PID 1).
+.It Va init_script
+Defines the shell binary to be used for executing the various shell scripts.
+The default is
+.Dq Li /bin/sh .
+It is used for running the
+.Va init_script
+if set, as well as for the
+.Pa /etc/rc
+and
+.Pa /etc/rc.shutdown
+scripts.
+The value of the corresponding
+.Xr kenv 2
+variable is evaluated every time
+.Xr init 8
+calls a shell script, so it can be changed later on using the
+.Xr kenv 1
+utility.
+In particular, if a non-default shell is used for running an
+.Va init_script ,
+it might be desirable to have that script reset the value of
+.Va init_shell
+back to the default, so that the
+.Pa /etc/rc
+script is executed with the standard shell
+.Pa /bin/sh .
 .It Va interpret
 Has the value
 .Dq Li OK

sys/boot/forth/loader.conf

@@ -77,6 +77,9 @@ module_path="/boot/modules"	# Set the module search path
 #boot_verbose=""	# -v: Causes extra debugging information to be printed
 #init_path="/sbin/init:/sbin/oinit:/sbin/init.bak:/rescue/init:/stand/sysinstall"
 			# Sets the list of init candidates
+#init_shell="/bin/sh"	# The shell binary used by init(8).
+#init_script=""		# Initial script to run by init(8) before chrooting.
+#init_chroot=""		# Directory for init(8) to chroot into.
 
 
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