LOADER(7) Standards, Environments, and Macros LOADER(7)

NAME

loader - kernel bootstrapping final stage

DESCRIPTION

The loader is the final stage of illumos's kernel bootstrapping
process. The actual name for the stage depends on the platform. On
IA32 (i386) architectures with BIOS firmware, it is a BTX client and
named loader. It is linked statically to libstand and usually located
in the directory /boot.

loader supports booting from ZFS, UFS, PCFS, HSFS and NFS file systems.
Additionally, loader can load files from the TFTP file service. The
NFS and TFTP based boot is enabled via pxeboot(7). The loader also
does support uncompressing gzip files while reading. The uncompression
will happen automatically if the compressed file is stored without .gz
suffix or if the file is accessed by leaving out the .gz suffix from
the name. If the file is referred by full name, including .gz suffix,
then the file content is read as is and the uncompression is not
performed.

loader provides a scripting language that can be used to automate
tasks, do pre-configuration or assist in recovery procedures. This
scripting language is roughly divided in two main components. The
smaller one is a set of commands designed for direct use by the casual
user, called "builtin commands" for historical reasons. The main drive
behind these commands is user-friendliness. The bigger component is an
ANS Forth compatible Forth interpreter based on FICL, by John Sadler.

During initialization, loader will probe for a console and set the
console variable, or set it to serial console ("ttya" - "ttyd") if the
previous boot stage used that. If multiple consoles are selected, they
will be listed separated by commas. Then, devices are probed, currdev
and loaddev are set, and screen-#cols, screen-#rows, and ISADIR are
set. Next, FICL is initialized, the builtin words are added to its
vocabulary. The inner interpreter loader will use with FICL is then
set to interpret, which is FICL's default. After that, /boot/loader.rc
is processed if available. These files are processed through the
include command, which reads all of them into memory before processing
them, making disk changes possible.

At this point, if an autoboot has not been tried, and if autoboot_delay
is not set to "NO" (not case sensitive), then an autoboot will be
tried. If the system gets past this point, prompt will be set and
loader will engage interactive mode. Please note that historically
even when autoboot_delay is set to "0" user will be able to interrupt
autoboot process by pressing some key on the console while kernel and
modules are being loaded. In some cases such behaviour may be
undesirable, to prevent it set autoboot_delay to "-1", in this case
loader will engage interactive mode only if autoboot has failed.

Builtin Commands

In loader, builtin commands take parameters from the command line. If
an error condition occurs, an exception will be generated, which can be
intercepted using ANS Forth exception handling words. If not
intercepted, an error message will be displayed and the interpreter's
state will be reset, emptying the stack and restoring interpreting
mode.

The builtin commands available are:

autoboot [seconds [prompt]]
Proceeds to bootstrap the system after a number of seconds, if
not interrupted by the user. Displays a countdown prompt
warning the user the system is about to be booted, unless
interrupted by a key press. The kernel will be loaded first if
necessary. Defaults to 10 seconds.

bcachestat
Displays statistics about disk cache usage. For debugging
only.

boot
boot kernelname [...]
boot -flag ...
Immediately proceeds to bootstrap the system, loading the
kernel if necessary. Any flags or arguments are passed to the
kernel, but they must precede the kernel name, if a kernel name
is provided.

WARNING: The behavior of this builtin is changed if
loader.4th(7) is loaded.

chain device
Chain load another boot loader from the specified device.
Device can be either disk name, partition or file name. In
case of x86 BIOS boot, the file must be copy of MBR or PBR.
For UEFI boot, the file is efi application.

echo [-n] [<message>]
Displays text on the screen. A new line will be printed unless
-n is specified.

heap Displays memory usage statistics. For debugging purposes only.

help [topic [subtopic]]
Shows help messages read from /boot/loader.help. The special
topic index will list the topics available.

include file [file ...]
Process script files. Each file, in turn, is completely read
into memory, and then each of its lines is passed to the
command line interpreter. If any error is returned by the
interpreter, the include command aborts immediately, without
reading any other files, and returns an error itself (see
ERRORS).

load [-t type] file ...
Loads a kernel or file of opaque contents tagged as being of
the type type. Kernel and modules can be either in a.out or
ELF format. Any arguments passed after the name of the file to
be loaded will be passed as arguments to that file.

ls [-l] [path]
Displays a listing of files in the directory path, or the root
directory if path is not specified. If -l is specified, file
sizes will be shown too.

lsdev [-v]
Lists all of the devices from which it may be possible to load
modules. In addition to disks and partitions, ZFS pools are
also listed. If -v is specified, more details are printed.
For ZFS pools the output resembles zpool status output.

lsmod [-v]
Displays loaded modules. If -v is specified, more details are
shown.

lszfs filesystem
A ZFS extended command that can be used to explore the ZFS
filesystem hierarchy in a pool. Lists the immediate children
of the filesystem. The filesystem hierarchy is rooted at a
filesystem with the same name as the pool.

more file [file ...]
Display the files specified, with a pause at each screen-#rows
displayed.

read [-t seconds] [-p prompt] [variable]
Reads a line of input from the terminal, storing it in variable
if specified. A timeout can be specified with -t, though it
will be canceled at the first key pressed. A prompt may also
be displayed through the -p flag.

reboot [-f]
Immediately reboots the system. On a UEFI system, if the -f
flag is set, or the BOOT_TO_FW_UI environment variable exists,
and the firmware supports this feature, the system will
automatically enter the firmware setup after reboot.

set variable
set variable=value
Set loader's environment variables.

show [variable]
Displays the specified variable's value, or all variables and
their values if variable is not specified.

unload Remove all modules from memory.

unset variable
Removes variable from the environment.

? Lists available commands.

ZFS Features

loader supports the following format for specifying ZFS filesystems
which can be used wherever loader refers to a device specification:

zfs:pool/filesystem:

where pool/filesystem is a ZFS filesystem name as described in zfs(8).

Builtin Environment Variables

The loader has actually two different kinds of `environment' variables.
There are ANS Forth's environmental queries, and a separate space of
environment variables used by builtins, which are not directly
available to Forth words. It is the latter type that this section
covers.

Environment variables can be set and unset through the set and unset
builtins, and can have their values interactively examined through the
use of the show builtin. Their values can also be accessed as
described in BUILTIN PARSER.

Notice that these environment variables are not inherited by any shell
after the system has been booted.

A few variables are set automatically by loader. Others can affect the
behavior of either loader or the kernel at boot. Some options may
require a value, while others define behavior just by being set. Both
types of builtin variables are described below.

autoboot_delay
Number of seconds autoboot will wait before booting. If this
variable is not defined, autoboot will default to 10 seconds.

If set to "NO", no autoboot will be automatically attempted
after processing /boot/loader.rc, though explicit autoboot's
will be processed normally, defaulting to 10 seconds delay.

If set to "0", no delay will be inserted, but user still will
be able to interrupt autoboot process and escape into the
interactive mode by pressing some key on the console while
kernel and modules are being loaded.

If set to "-1", no delay will be inserted and loader will
engage interactive mode only if autoboot has failed for some
reason.

boot_ask Will set kernel(8) -a option.

boot_debug
Will set kernel(8) -d option.

boot_kmdb
Will set kernel(8) -k option.

boot_reconfigure
Will set kernel(8) -r option.

boot_single
Will set kernel(8) -s option.

boot_verbose
Will set kernel(8) -v option.

boot-args
Will set custom arguments for the kernel. If set in loader
configuration, the loader startup will parse the boot-args
value to set boot prefixed variables listed above, any
unrecognized options are added to kernel command line
verbatim.

bootfile The name of the kernel.

chain_disk
If set, contains the device or file name used with chain
command and will cause chain command menu entry to appear on
loader main menu. The alternate method to use chain loader
is to add menu entries into menu.lst(5) file.

console Defines the current console or consoles. Multiple consoles
may be specified. In that case, the first listed console
will become the default console for the kernel(8).

currdev Selects the default device. Syntax for devices is odd.

interpret
Has the value "ok" if the Forth's current state is
interpreting.

screen-#rows
Define the number of lines on the screen, to be used by the
pager.

module_path
Sets the list of directories which will be searched for
modules named in a load command or implicitly required by a
dependency. The default value for this variable is
"/platform/i86pc/${ISADIR}"

prompt Value of loader's prompt. Defaults to "${interpret}". If
variable prompt is unset, the default prompt is `>'.

os_console
If set, the value is used to set kernel(8) console property.

twiddle_divisor
Throttles the output of the `twiddle' I/O progress indicator
displayed while loading the kernel and modules. This is
useful on slow serial consoles where the time spent waiting
for these characters to be written can add up to many
seconds. The spinner is updated only once every
twiddle_divisor operations. The default value for
twiddle_divisor is 16.

Other variables are used for loader or to set kernel properties or for
informational purposes.

Builtin Parser

When a builtin command is executed, the rest of the line is taken by it
as arguments, and it is processed by a special parser which is not used
for regular Forth commands.

This special parser applies the following rules to the parsed text:

1. All backslash characters are preprocessed.

+o \b , \f , \r , \n and \t are processed as in C.

+o \s is converted to a space.

+o \v is converted to ASCII 11.

+o \z is just skipped. Useful for things like "\0xf\z\0xf".

+o \0xN and \0xNN are replaced by the hex N or NN.

+o \NNN is replaced by the octal NNN ASCII character.

+o \" , \' and \$ will escape these characters, preventing them
from receiving special treatment in Step 2, described below.

+o \\ will be replaced with a single \ .

+o In any other occurrence, backslash will just be removed.

2. Every string between non-escaped quotes or double-quotes will be
treated as a single word for the purposes of the remaining steps.

3. Replace any $VARIABLE or ${VARIABLE} with the value of the
environment variable VARIABLE.

4. Space-delimited arguments are passed to the called builtin
command. Spaces can also be escaped through the use of \\ .

An exception to this parsing rule exists, and is described in Builtins
And FORTH.

Builtins And FORTH

All builtin words are state-smart, immediate words. If interpreted,
they behave exactly as described previously. If they are compiled,
though, they extract their arguments from the stack instead of the
command line.

If compiled, the builtin words expect to find, at execution time, the
following parameters on the stack:
addrN lenN ... addr2 len2 addr1 len1 N
where addrX lenX are strings which will compose the command line that
will be parsed into the builtin's arguments. Internally, these strings
are concatenated in from 1 to N, with a space put between each one.

If no arguments are passed, a 0 must be passed, even if the builtin
accepts no arguments.

While this behavior has benefits, it has its trade-offs. If the
execution token of a builtin is acquired (through ' or [']), and then
passed to catch or execute, the builtin behavior will depend on the
system state at the time catch or execute is processed! This is
particularly annoying for programs that want or need to handle
exceptions. In this case, the use of a proxy is recommended. For
example:
: (boot) boot;

FICL

FICL is a Forth interpreter written in C, in the form of a forth
virtual machine library that can be called by C functions and vice
versa.

In loader, each line read interactively is then fed to FICL, which may
call loader back to execute the builtin words. The builtin include
will also feed FICL, one line at a time.

The words available to FICL can be classified into four groups. The
ANS Forth standard words, extra FICL words, extra FreeBSD words, and
the builtin commands; the latter were already described. The ANS Forth
standard words are listed in the STANDARDS section. The words falling
in the two other groups are described in the following subsections.

FICL Extra Words

.env

.ver

-roll

2constant

>name

body>

compare This is the STRING word set's compare.

compile-only

endif

forget-wid

parse-word

sliteral This is the STRING word set's sliteral.

wid-set-super

w@

w!

x.

empty

cell-

-rot

Loader Extra Words

$ (--) Evaluates the remainder of the input buffer, after having
printed it first.

% (--) Evaluates the remainder of the input buffer under a catch
exception guard.

.# Works like . but without outputting a trailing space.

fclose (fd --)
Closes a file.

fkey (fd -- char)
Reads a single character from a file.

fload (fd --)
Processes a file fd.

fopen (addr len mode -- fd)
Opens a file. Returns a file descriptor, or -1 in case of
failure. The mode parameter selects whether the file is to
be opened for read access, write access, or both. The
constants O_RDONLY, O_WRONLY, and O_RDWR are defined in
/boot/forth/support.4th, indicating read only, write only,
and read-write access, respectively.

fread (fd addr len -- len')
Tries to read len bytes from file fd into buffer addr.
Returns the actual number of bytes read, or -1 in case of
error or end of file.

heap? (-- cells)
Return the space remaining in the dictionary heap, in cells.
This is not related to the heap used by dynamic memory
allocation words.

inb (port -- char)
Reads a byte from a port.

isvirtualized? (-- addr len flag | flag)
Returns true and string with virtualization engine name or
false.

key (-- char)
Reads a single character from the console.

key? (-- flag)
Returns true if there is a character available to be read
from the console.

ms (u --)
Waits u microseconds.

outb (port char --)
Writes a byte to a port.

seconds (-- u)
Returns the number of seconds since midnight.

tib> (-- addr len)
Returns the remainder of the input buffer as a string on the
stack.

Loader Extra Framebuffer Words

fb-bezier (x1 y1 x2 y2 x3 y3 width --)
Draws a quadratic Bezier curve in the current foreground
color using the three provided points and specified line
with.

fb-drawrect (x1 y1 x2 y2 fill --)
Draws a rectangle to the screen with the top left at (x1,y1)
and the bottom right at (x2,y2) , using the current
foreground color. If fill is true then the rectangle will be
filled in.

fb-line (x1 y1 x2 y2 width --)
Draws a line from (x1,y1) to (x2,y2) in the current
foreground color and with the specified width.

fb-putimage (flags x1 y1 x2 y2 addr len -- flag)
Outputs an image to the screen. Returns true if the image
was able to be written and false otherwise. Only truecolor
PNG images are supported and the path to the file must be
provided through the addr and len arguments on the stack.
The image will be displayed in the rectangular screen region
with the top left at (x1,y1) and the bottom right at (x2,y2)

Either x2 or y2 can be set to "0" which causes it to be
calculated to maintain the aspect ratio of the image. If
both are "0" then the native resolution of the image will be
used.

If x1 is "0", then the image will be placed as far over to
the right of the screen as possible. Similarly, if y1 is
"0", then the image will be placed as far down the screen as
possible.

Flags is a bitfield; the following bits are defined:

1 Draw a single pixel border around the image in
the current foreground color.

2 Do not scroll the image with the rest of the
screen.

128 Output diagnostic information (for debugging).

fb-setpixel (x y --)
Colors the pixel at (x,y) with the current foreground color.

term-drawrect (x1 y1 x2 y2 --)
Draws a rectangle with rounded corners using terminal
coordinates and the current foreground color.

Loader Defined Environmental Queries

arch-i386
TRUE if the architecture is IA32.

loader_version
loader version.

Errors

The following values are thrown by loader:

100 Any type of error in the processing of a builtin.

-1 Abort executed.

-2 Abort" executed.

-56 Quit executed.

-256 Out of interpreting text.

-257 Need more text to succeed -- will finish on next run.

-258 Bye executed.

-259 Unspecified error.

FILES

/boot/defaults/loader.conf
/boot/conf.d/*
/boot/loader.conf
/boot/loader.conf.local loader configuration files, as described in
loader.conf(5).
/boot/loader.help Loaded by help. Contains the help
messages.
/boot/loader.rc loader bootstrapping script.
/boot/forth/loader.4th Extra builtin-like words.
/boot/forth/support.4th loader.conf processing words.
/boot/loader loader itself.

EXAMPLES

Boot in single user mode:

boot -s

Load the kernel, a boot_archive, and then autoboot in five seconds.
Notice that a kernel must be loaded before any other load command is
attempted.

load /platform/i86pc/kernel/amd64/unix
load -t rootfs /platform/i86pc/amd64/boot_archive
autoboot 5

Set the default device used for loading a kernel from a ZFS filesystem:

set currdev=zfs:rpool/ROOT/knowngood:

NOTES

Although setting the currdev as shown in the example above is
supported, it is advisable to use loader beadm command or boot
environment menu instead. The reason is, the beadm or menu selection
will also instruct loader to clean up the currently set configuration
and load configuration from the new boot environment.

SEE ALSO

btxld(1onbld), loader.conf(5), menu.lst(5), boot(8)

STANDARDS

For the purposes of ANS Forth compliance, loader is an ANS Forth System
with Environmental Restrictions, Providing .(, :noname, ?do, parse,
pick, roll, refill, to, value, \, false, true, <>, 0<>, compile, ,
erase, nip, tuck and marker from the Core Extensions word set,
Providing the Exception Extensions word set, Providing the Locals
Extensions word set, Providing the Memory-Allocation Extensions word
set, Providing .s, bye, forget, see, words, [if], [else] and [then]
from the Programming-Tools extension word set, Providing the Search-
Order extensions word set.

illumos March 30, 2023 illumos