Интерактивная система просмотра системных руководств (man-ов)
>> loader (8) ( FreeBSD man: Команды системного администрирования )
- kernel bootstrapping final stage
The program called
is the final stage of
Fx Ns 's
kernel bootstrapping process.
On IA32 (i386) architectures, it is a
It is linked statically to
and usually located in the directory
It provides a scripting language that can be used to
automate tasks, do pre-configuration or assist in recovery
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
Forth compatible Forth interpreter based on FICL, by
An John Sadler .
will probe for a console and set the
variable, or set it to serial console
if the previous boot stage used that.
If multiple consoles are selected, they will be listed separated by spaces.
Then, devices are probed,
are set, and
is set to 24.
is initialized, the builtin words are added to its vocabulary, and
is processed if it exists.
No disk switching is possible while that file is being read.
The inner interpreter
will use with
is then set to
is processed if available, and, failing that,
is read for historical reasons.
These files are processed through the
command, which reads all of them into memory before processing them,
making disk changes possible.
At this point, if an
has not been tried, and if
is not set to
(not case sensitive), then an
will be tried.
If the system gets past this point,
will be set and
will engage interactive mode.
Please note that historically even when
is set to
user will be able to interrupt autoboot process by pressing some key
on the console while kernel and modules are being loaded.
cases such behaviour may be undesirable, to prevent it set
in this case
will engage interactive mode only if
builtin commands take parameters from the command line.
the only way to call them from a script is by using
on a string.
If an error condition occurs, an exception will be generated,
which can be intercepted using
Forth exception handling
If not intercepted, an error message will be displayed and
the interpreter's state will be reset, emptying the stack and restoring
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.
Displays statistics about disk cache usage.
For debugging only.
boot kernelname [...
boot -flag ...
Immediately proceeds to bootstrap the system, loading the kernel
Any flags or arguments are passed to the kernel, but they
must precede the kernel name, if a kernel name is provided.
The behavior of this builtin is changed if
Displays text on the screen.
A new line will be printed unless
Displays memory usage statistics.
For debugging purposes only.
help [topic [subtopic]
Shows help messages read from
The special topic
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
Sx ERRORS ) .
Loads a kernel, kernel loadable module (kld), or file of opaque
contents tagged as being of the 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.
Currently, argument passing does not work for the kernel.
Displays a listing of files in the directory
or the root directory if
is not specified.
is specified, file sizes will be shown too.
Lists all of the devices from which it may be possible to load modules.
is specified, more details are printed.
Displays loaded modules.
is specified, more details are shown.
more file [file ...
Display the files specified, with a pause at each
Scans for Plug-and-Play devices.
This is not functional at present.
Reads a line of input from the terminal, storing it in
A timeout can be specified with
though it will be canceled at the first key pressed.
A prompt may also be displayed through the
Immediately reboots the system.
set variable = value
Set loader's environment variables.
Displays the specified variable's value, or all variables and their
is not specified.
Remove all modules from memory.
from the environment.
Lists available commands.
BUILTIN ENVIRONMENT VARIABLES
has actually two different kinds of
There are ANS Forth's
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
builtins, and can have their values interactively examined through the
use of the
Their values can also be accessed as described in
Sx 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
Others can affect the behavior of either
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.
Unset this to disable automatic loading of the ACPI module.
Number of seconds
will wait before booting.
If this variable is not defined,
will default to 10 seconds.
If set to
will be automatically attempted after processing
will be processed normally, defaulting to 10 seconds delay.
If set to
no delay will be inserted, but user still will be able to interrupt
process and escape into the interactive mode by pressing some key
on the console while kernel and
modules are being loaded.
If set to
no delay will be inserted and
will engage interactive mode only if
has failed for some reason.
Instructs the kernel to prompt the user for the name of the root device
when the kernel is booted.
Instructs the kernel to try to mount the root file system from CD-ROM.
Instructs the kernel to start in the DDB debugger, rather than
proceeding to initialize when booted.
Instructs the kernel to mount the statically compiled-in root file system.
Selects gdb-remote mode for the kernel debugger by default.
Enables multiple console support in the kernel early on boot.
In a running system, console configuration can be manipulated
All console output is suppressed when console is muted.
In a running system, the state of console muting can be manipulated by the
During the device probe, pause after each line is printed.
Force the use of a serial console even when an internal console
Prevents the kernel from initiating a multi-user startup; instead,
a single-user mode will be entered when the kernel has finished
Setting this variable causes extra debugging information to be printed
by the kernel during the boot phase.
List of semicolon-separated search path for bootable kernels.
The default is
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
Otherwise it is set to 9600 unless this was overridden using the
Changes to the
variable take effect immediately.
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. from
Selects the default device.
Syntax for devices is odd.
If set to a valid directory in the root file system, it causes
to perform a
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
Sets the list of binaries which the kernel will try to run as the initial
The first matching binary is used.
The default list is
If set to a valid file name in the root file system,
to run that script as the very first action,
before doing anything else.
Signal handling and exit code interpretation is similar to
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
process (PID 1).
Defines the shell binary to be used for executing the various shell scripts.
The default is
It is used for running the
if set, as well as for the
The value of the corresponding
variable is evaluated every time
calls a shell script, so it can be changed later on using the
In particular, if a non-default shell is used for running an
it might be desirable to have that script reset the value of
back to the default, so that the
script is executed with the standard shell
Has the value
if the Forth's current state is interpreting.
Define the number of lines on the screen, to be used by the pager.
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
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
is unset, the default prompt is
If the code which detects the disk unit number for the root disk is
confused, e.g. by a mix of SCSI and IDE disks, or IDE disks with
gaps in the sequence (e.g. no primary slave), the unit number can
be forced by setting this variable.
By default the value of
is used to set the root file system
when the kernel is booted.
This can be overridden by setting
Other variables are used to override kernel tunable parameters.
The following tunables are available:
Limit the amount of physical memory the system will use.
By default the size is in bytes, but the
k , K , m , M , g
are also accepted and indicate kilobytes, megabytes and gigabytes
An invalid suffix will result in the variable being ignored by the
hw.pci.host_start_mem , hw.acpi.host_start_mem
When not otherwise constrained, this limits the memory start
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
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.
Set the size of a number of statically allocated system tables; see
for a description of how to select an appropriate value for this
When set, this tunable replaces the value declared in the kernel
compile-time configuration file.
Set the number of mbuf clusters to be allocated.
The value cannot be set below the default
determined when the kernel was compiled.
Set the number of
buffers to be allocated.
Not all architectures use such buffers; see
Limits the amount of KVM to be used to hold swap
meta information, which directly governs the
maximum amount of swap the system can support.
This value is specified in bytes of KVA space
and defaults to 32MBytes on i386 and amd64.
Care should be taken
to not reduce this value such that the actual
amount of configured swap exceeds 1/2 the
The default of 32MB allows
the kernel to support a maximum of ~7GB of swap.
this parameter if you need to greatly extend the
KVM reservation for other resources such as the
buffer cache or
Modifies kernel option
Limits the amount of KVM reserved for use by the
buffer cache, specified in bytes.
The default maximum is 200MB.
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
the NBUF parameter will override this limit.
Disable the use of i686 MTRRs (x86 only).
Overrides the compile-time set value of
or the preset default of 512.
Must be a power of 2.
Sets the size of kernel memory (bytes).
This overrides the value determined when the kernel was compiled.
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.
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:
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
\z is just skipped.
Useful for things like
\0xN and \0xNN are replaced by the hex N or NN.
\NNN is replaced by the octal NNN
\" , \' 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.
Every string between non-escaped quotes or double-quotes will be treated
as a single word for the purposes of the remaining steps.
with the value of the environment variable
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
Sx 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:
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
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
and then passed to
the builtin behavior will depend on the system state
at the time
Ef This is particularly annoying for programs that want or need to
In this case, the use of a proxy is recommended.
: (boot) boot
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
each line read interactively is then fed to
which may call
back to execute the builtin words.
will also feed
one line at a time.
The words available to
can be classified into four groups.
Forth standard words, extra
Fx words, and the builtin commands;
the latter were already described.
Forth standard words are listed in the
The words falling in the two other groups are described in the
FICL EXTRA WORDS
This is the STRING word set's
This is the STRING word set's
FREEBSD EXTRA WORDS
Evaluates the remainder of the input buffer, after having printed it first.
Evaluates the remainder of the input buffer under a
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
fopen (addr len mode -- fd
Opens a file.
Returns a file descriptor, or -1 in case of failure.
parameter selects whether the file is to be opened for read access, write
access, or both.
O_RDONLY , O_WRONLY
are defined in
indicating read only, write only, and read-write access, respectively.
(fd addr len -- len'
Tries to read
bytes from file
Returns the actual number of bytes read, or -1 in case of error or end of
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
if there is a character available to be read from the console.
ms (u --
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
FREEBSD DEFINED ENVIRONMENTAL QUERIES
if the architecture is IA32.
Fx version at compile time.
configuration files, as described in
Contains the help messages.
Boot in single user mode:
Load the kernel, a splash screen, and then autoboot in five seconds.
Notice that a kernel must be loaded before any other
command is attempted.
For the purposes of ANS Forth compliance, loader is an
ANS Forth System with Environmental Restrictions, Providing
Ef Bf Li
parse, pick, roll, refill, to, value, \, false, true,
compile, , erase, nip, tuck
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
Ef Bf Li
bye, forget, see, words,
from the Programming-Tools extension word set, Providing the
Search-Order extensions word set.