Manual Pages  — LOADER

loader – kernel bootstrapping final stage

DESCRIPTION BUILTIN COMMANDS BUILTIN ENVIRONMENT VARIABLES ZFS FEATURES BUILTIN PARSER BUILTINS AND FORTH FICL FICL EXTRA WORDS FREEBSD EXTRA WORDS FREEBSD DEFINED ENVIRONMENTAL QUERIES SECURITY MD FILES EXAMPLES ERRORS SEE ALSO STANDARDS HISTORY AUTHORS BUGS

In loader, builtin commands take parameters from the command line. Presently, the only way to call them from a script is by using evaluate on a string. 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(8) is loaded.
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, kernel loadable module (kld), disk image, 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. Use the md_image type to make the kernel create a file-backed md(4) disk. This is useful for booting from a temporary rootfs. Currently, argument passing does not work for the kernel.
load_geli
	[-n keyno] prov file Loads a geli(8) encryption keyfile for the given provider name. The key index can be specified via keyno or will default to zero.
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, as well as ZFS pools. If -v is specified, more details are printed, including ZFS pool information in a format that resembles zpool 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 LINES displayed.
pnpscan [-v]
	Scans for Plug-and-Play devices. This is not functional at present.
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
	Immediately reboots the system.
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.
amp;?	Lists available commands.

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. Configuration options are described in loader.conf(5).
boot_askname
	Instructs the kernel to prompt the user for the name of the root device when the kernel is booted.
boot_cdrom
	Instructs the kernel to try to mount the root file system from CD-ROM.
boot_ddb
	Instructs the kernel to start in the DDB debugger, rather than proceeding to initialize when booted.
boot_dfltroot
	Instructs the kernel to mount the statically compiled-in root file system.
boot_gdb
	Selects gdb-remote mode for the kernel debugger by default.
boot_multicons
	Enables multiple console support in the kernel early on boot. In a running system, console configuration can be manipulated by the conscontrol(8) utility.
boot_mute
	All kernel console output is suppressed when console is muted. In a running system, the state of console muting can be manipulated by the conscontrol(8) utility.
boot_pause
	During the device probe, pause after each line is printed.
boot_serial
	Force the use of a serial console even when an internal console is present.
boot_single
	Prevents the kernel from initiating a multi-user startup; instead, a single-user mode will be entered when the kernel has finished device probing.
boot_verbose
	Setting this variable causes extra debugging information to be printed by the kernel during the boot phase.
bootfile
	List of semicolon-separated search path for bootable kernels. The default is "kernel".
comconsole_speed
	Defines the speed of the serial console (i386 and amd64 only). If the previous boot stage indicated that a serial console is in use then this variable is initialized to the current speed of the console serial port. Otherwise it is set to 9600 unless this was overridden using the BOOT_COMCONSOLE_SPEED variable when loader was compiled. Changes to the comconsole_speed variable take effect immediately.
comconsole_port
	Defines the base i/o port used to access console UART (i386 and amd64 only). If the variable is not set, its assumed value is 0x3F8, which corresponds to PC port COM1, unless overridden by BOOT_COMCONSOLE_PORT variable during the compilation of loader. Setting the comconsole_port variable automatically set hw.uart.console environment variable to provide a hint to kernel for location of the console. Loader console is changed immediately after variable comconsole_port is set.
comconsole_pcidev
	Defines the location of a PCI device of the 'simple communication' class to be used as the serial console UART (i386 and amd64 only). The syntax of the variable is 'bus:device:function[:bar]', where all members must be numeric, with possible 0x prefix to indicate a hexadecimal value. The bar member is optional and assumed to be 0x10 if omitted. The bar must decode i/o space. Setting the variable comconsole_pcidev automatically sets the variable comconsole_port to the base of the selected bar, and hint hw.uart.console. Loader console is changed immediately after variable comconsole_pcidev is set.
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 userland output (e.g.amp; from init(8)).
currdev
	Selects the default device to loader the kernel from. The syntax is:     loader_device: or     zfs:dataset: Examples:     disk0p2:     zfs:zroot/ROOT/default:
dumpdev
	Sets the device for kernel dumps. This can be used to ensure that a device is configured before the corresponding dumpdev directive from rc.conf(5) has been processed, allowing kernel panics that happen during the early stages of boot to be captured.
init_chroot
	See init(8).
init_exec
	See init(8).
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 "/sbin/init:/sbin/oinit:/sbin/init.bak:/rescue/init".
init_script
	See init(8).
init_shell
	See init(8).
interpret
	Has the value "OK" if the Forth's current state is interpreting.
LINES
	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 "/boot/kernel;/boot/modules".
num_ide_disks
	Sets the number of IDE disks as a workaround for some problems in finding the root disk at boot. This has been deprecated in favor of root_disk_unit.
prompt
	Value of Ns prompt. Defaults to "${interpret}". If variable prompt is unset, the default prompt is ‘>’.
root_disk_unit
	If the code which detects the disk unit number for the root disk is confused, e.g.amp; by a mix of SCSI and IDE disks, or IDE disks with gaps in the sequence (e.g.amp; no primary slave), the unit number can be forced by setting this variable.
rootdev
	By default the value of currdev is used to set the root file system when the kernel is booted. This can be overridden by setting rootdev explicitly.

Other variables are used to override kernel tunable parameters. The following tunables are available:

efi.rt.disabled
	Disable UEFI runtime services in the kernel, if applicable. Runtime services are only available and used if the kernel is booted in a UEFI environment.
hw.physmem
	Limit the amount of physical memory the system will use. By default the size is in bytes, but the k, K, m, M, g and G suffixes are also accepted and indicate kilobytes, megabytes and gigabytes respectively. An invalid suffix will result in the variable being ignored by the kernel.
hw.pci.host_start_mem, hw.acpi.host_start_mem
	When not otherwise constrained, this limits the memory start address. The default is 0x80000000 and should be set to at least size of the memory and not conflict with other resources. Typically, only systems without PCI bridges need to set this variable since PCI bridges typically constrain the memory starting address (and the variable is only used when bridges do not constrain this address).
hw.pci.enable_io_modes
	Enable PCI resources which are left off by some BIOSes or are not enabled correctly by the device driver. Tunable value set to ON (1) by default, but this may cause problems with some peripherals.
kern.maxusers
	Set the size of a number of statically allocated system tables; see tuning(7) for a description of how to select an appropriate value for this tunable. When set, this tunable replaces the value declared in the kernel compile-time configuration file.
kern.ipc.nmbclusters
	Set the number of mbuf clusters to be allocated. The value cannot be set below the default determined when the kernel was compiled.
kern.ipc.nsfbufs
	Set the number of sendfile(2) buffers to be allocated. Overrides NSFBUFS. Not all architectures use such buffers; see sendfile(2) for details.
kern.maxswzone
	Limits the amount of KVM to be used to hold swap metadata, which directly governs the maximum amount of swap the system can support, at the rate of approximately 200 MB of swap space per 1 MB of metadata. This value is specified in bytes of KVA space. If no value is provided, the system allocates enough memory to handle an amount of swap that corresponds to eight times the amount of physical memory present in the system. Note that swap metadata can be fragmented, which means that the system can run out of space before it reaches the theoretical limit. Therefore, care should be taken to not configure more swap than approximately half of the theoretical maximum. Running out of space for swap metadata can leave the system in an unrecoverable state. Therefore, you should only change this parameter if you need to greatly extend the KVM reservation for other resources such as the buffer cache or kern.ipc.nmbclusters. Modifies kernel option VM_SWZONE_SIZE_MAX.
kern.maxbcache
	Limits the amount of KVM reserved for use by the buffer cache, specified in bytes. The default maximum is 200MB on i386, and 400MB on amd64 and sparc64. This parameter is used to prevent the buffer cache from eating too much KVM in large-memory machine configurations. Only mess around with this parameter if you need to greatly extend the KVM reservation for other resources such as the swap zone or kern.ipc.nmbclusters. Note that the NBUF parameter will override this limit. Modifies VM_BCACHE_SIZE_MAX.
kern.msgbufsize
	Sets the size of the kernel message buffer. The default limit of 96KB is usually sufficient unless large amounts of trace data need to be collected between opportunities to examine the buffer or dump it to a file. Overrides kernel option MSGBUF_SIZE.
machdep.disable_mtrrs
	Disable the use of i686 MTRRs (x86 only).
net.inet.tcp.tcbhashsize
	Overrides the compile-time set value of TCBHASHSIZE or the preset default of 512. Must be a power of 2.
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 default is 1 (full speed); a value of 2 spins half as fast, and so on.
vm.kmem_size
	Sets the size of kernel memory (bytes). This overrides the value determined when the kernel was compiled. Modifies VM_KMEM_SIZE.
vm.kmem_size_min vm.kmem_size_max
	Sets the minimum and maximum (respectively) amount of kernel memory that will be automatically allocated by the kernel. These override the values determined when the kernel was compiled. Modifies VM_KMEM_SIZE_MIN and VM_KMEM_SIZE_MAX.

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.
   • \b , \f , \r , \n and \t are processed as in C.
   • \s is converted to a space.
   • \v is converted to ASCII 11.
   • \z is just skipped. Useful for things like "\0xf\z\0xf".
   • \0xN and \0xNN are replaced by the hex N or NN.
   • \NNN is replaced by the octal NNN ASCII character.
   • \" , \' and \$ will escape these characters, preventing them from receiving special treatment in Step 2, described below.
   • \\ will be replaced with a single \ .
   • 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.

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: 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 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.

.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

amp;$ (--)	Evaluates the remainder of the input buffer, after having printed it first.
amp;% (--)	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/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.
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.
trace! (flag --)
	Activates or deactivates tracing. Does not work with catch.

arch-i386
	TRUE if the architecture is IA32.
FreeBSD_version
	FreeBSD version at compile time.
loader_version
	loader version.

/boot/loader	loader itself.
/boot/loader.4th	Additional FICL initialization.
/boot/defaults/loader.conf /boot/loader.4th
	Extra builtin-like words.
/boot/loader.conf /boot/loader.conf.local
	loader configuration files, as described in loader.conf(5).
/boot/loader.rc	loader bootstrapping script.
/boot/loader.help	Loaded by help. Contains the help messages.
/boot/support.4th	loader.conf processing words.
/usr/share/examples/bootforth/
	Assorted examples.

Boot in single user mode:

    boot -s

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

load kernel
load splash_bmp
load -t splash_image_data /boot/chuckrulez.bmp
autoboot 5

Set the disk unit of the root device to 2, and then boot. This would be needed in a system with two IDE disks, with the second IDE disk hardwired to ada2 instead of ada1.

set root_disk_unit=2
boot /boot/kernel/kernel

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

set currdev=zfs:tank/ROOT/knowngood:

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.

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<>, compileamp;, , 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 amp;.s, bye, forget, see, words, amp;[if], amp;[else] and [then] from the Programming-Tools extension word set, Providing the Search-Order extensions word set.

The loader first appeared in FreeBSD 3.1 .

The loader was written by Michael Smith <msmith@FreeBSD.org>.

FICL was written by John Sadler <john_sadler@alum.mit.edu>.

The expect and accept words will read from the input buffer instead of the console. The latter will be fixed, but the former will not.