git: 9873c807dac1 - main - loader: Create loader_simp(8) to document simple version of loader

[Warner Losh]

The branch main has been updated by imp:

URL: https://cgit.FreeBSD.org/src/commit/?id=9873c807dac1f8b83b9f7bc9a8d4e318ea295b55

commit 9873c807dac1f8b83b9f7bc9a8d4e318ea295b55
Author:     Warner Losh <imp at FreeBSD.org>
AuthorDate: 2021-07-14 22:43:25 +0000
Commit:     Warner Losh <imp at FreeBSD.org>
CommitDate: 2021-07-14 22:59:51 +0000

    loader: Create loader_simp(8) to document simple version of loader
    
    loader_simp is a much simplified version of loader that will process a
    linear sequence of commands from loader.rc. It has neither Forth nor Lua
    built in and is much smaller. Document it. This is largely copied from
    loader.8 since it implements those built-in commands. Future revisions
    will fix this duplication.
    
    Sponsored by:           Netflix
---
 stand/man/Makefile      |   1 +
 stand/man/loader_simp.8 | 762 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 763 insertions(+)

diff --git a/stand/man/Makefile b/stand/man/Makefile
index d5e7ad791ffb..5523908b6814 100644
--- a/stand/man/Makefile
+++ b/stand/man/Makefile
@@ -5,6 +5,7 @@
 M.${MK_EFI}+=		boot1.efi.8
 M.yes+=			loader.8
 M.${MK_EFI}+=		loader.efi.8
+M.yes+=			loader_simp.8
 
 MAN=${M.yes}
 
diff --git a/stand/man/loader_simp.8 b/stand/man/loader_simp.8
new file mode 100644
index 000000000000..689996f244fd
--- /dev/null
+++ b/stand/man/loader_simp.8
@@ -0,0 +1,762 @@
+.\" Copyright (c) 1999 Daniel C. Sobral
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\" $FreeBSD$
+.\"
+.Dd July 14, 2021
+.Dt LOADER 8
+.Os
+.Sh NAME
+.Nm loader
+.Nd kernel bootstrapping final stage
+.Sh DESCRIPTION
+The program called
+.Nm
+is the final stage of
+.Fx Ns 's
+kernel bootstrapping process.
+On IA32 (i386) architectures, it is a
+.Pa BTX
+client.
+It is linked statically to
+.Xr libstand 3
+and usually located in the directory
+.Pa /boot .
+.Pp
+It 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
+.Tn ANS
+Forth compatible Forth interpreter based on FICL, by
+.An John Sadler .
+.Pp
+During initialization,
+.Nm
+will probe for a console and set the
+.Va console
+variable, or set it to serial console
+.Pq Dq Li comconsole
+if the previous boot stage used that.
+If multiple consoles are selected, they will be listed separated by spaces.
+Then, devices are probed,
+.Va currdev
+and
+.Va loaddev
+are set, and
+.Va LINES
+is set to 24.
+After that,
+.Pa /boot/loader.rc
+is processed if available.
+These files are processed through the
+.Ic include
+command, which reads all of them into memory before processing them,
+making disk changes possible.
+.Pp
+At this point, if an
+.Ic autoboot
+has not been tried, and if
+.Va autoboot_delay
+is not set to
+.Dq Li NO
+(not case sensitive), then an
+.Ic autoboot
+will be tried.
+If the system gets past this point,
+.Va prompt
+will be set and
+.Nm
+will engage interactive mode.
+Please note that historically even when
+.Va autoboot_delay
+is set to
+.Dq Li 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
+.Va autoboot_delay
+to
+.Dq Li -1 ,
+in this case
+.Nm
+will engage interactive mode only if
+.Ic autoboot
+has failed.
+.Sh BUILTIN COMMANDS
+In
+.Nm ,
+builtin commands take parameters from the command line.
+Presently,
+the only way to call them from a script is by using
+.Pa evaluate
+on a string.
+If an error condition occurs, an exception will be generated,
+which can be intercepted using
+.Tn 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.
+.Pp
+The builtin commands available are:
+.Pp
+.Bl -tag -width Ds -compact
+.It Ic autoboot Op Ar seconds Op Ar 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.
+.Pp
+.It Ic bcachestat
+Displays statistics about disk cache usage.
+For debugging only.
+.Pp
+.It Ic boot
+.It Ic boot Ar kernelname Op Cm ...
+.It Ic boot Fl flag Cm ...
+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.
+.Pp
+.It Ic echo Xo
+.Op Fl n
+.Op Aq message
+.Xc
+Displays text on the screen.
+A new line will be printed unless
+.Fl n
+is specified.
+.Pp
+.It Ic heap
+Displays memory usage statistics.
+For debugging purposes only.
+.Pp
+.It Ic help Op topic Op subtopic
+Shows help messages read from
+.Pa /boot/loader.help .
+The special topic
+.Em index
+will list the topics available.
+.Pp
+.It Ic include Ar file Op Ar
+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 ) .
+.Pp
+.It Ic load Xo
+.Op Fl t Ar type
+.Ar file Cm ...
+.Xc
+Loads a kernel, kernel loadable module (kld), disk image,
+or file of opaque contents tagged as being of the type
+.Ar 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
+.Li md_image
+type to make the kernel create a file-backed
+.Xr md 4
+disk.
+This is useful for booting from a temporary rootfs.
+Currently, argument passing does not work for the kernel.
+.Pp
+.It Ic load_geli Xo
+.Op Fl n Ar keyno
+.Ar prov Ar file
+.Xc
+Loads a
+.Xr geli 8
+encryption keyfile for the given provider name.
+The key index can be specified via
+.Ar keyno
+or will default to zero.
+.Pp
+.It Ic ls Xo
+.Op Fl l
+.Op Ar path
+.Xc
+Displays a listing of files in the directory
+.Ar path ,
+or the root directory if
+.Ar path
+is not specified.
+If
+.Fl l
+is specified, file sizes will be shown too.
+.Pp
+.It Ic lsdev Op Fl v
+Lists all of the devices from which it may be possible to load modules,
+as well as ZFS pools.
+If
+.Fl v
+is specified, more details are printed, including ZFS pool information
+in a format that resembles
+.Nm zpool Cm status
+output.
+.Pp
+.It Ic lsmod Op Fl v
+Displays loaded modules.
+If
+.Fl v
+is specified, more details are shown.
+.Pp
+.It Ic lszfs Ar filesystem
+A ZFS extended command that can be used to explore the ZFS filesystem
+hierarchy in a pool.
+Lists the immediate children of the
+.Ar filesystem .
+The filesystem hierarchy is rooted at a filesystem with the same name
+as the pool.
+.Pp
+.It Ic more Ar file Op Ar
+Display the files specified, with a pause at each
+.Va LINES
+displayed.
+.Pp
+.It Ic pnpscan Op Fl v
+Scans for Plug-and-Play devices.
+This is not functional at present.
+.Pp
+.It Ic read Xo
+.Op Fl t Ar seconds
+.Op Fl p Ar prompt
+.Op Va variable
+.Xc
+Reads a line of input from the terminal, storing it in
+.Va variable
+if specified.
+A timeout can be specified with
+.Fl t ,
+though it will be canceled at the first key pressed.
+A prompt may also be displayed through the
+.Fl p
+flag.
+.Pp
+.It Ic reboot
+Immediately reboots the system.
+.Pp
+.It Ic set Ar variable
+.It Ic set Ar variable Ns = Ns Ar value
+Set loader's environment variables.
+.Pp
+.It Ic show Op Va variable
+Displays the specified variable's value, or all variables and their
+values if
+.Va variable
+is not specified.
+.Pp
+.It Ic unload
+Remove all modules from memory.
+.Pp
+.It Ic unset Va variable
+Removes
+.Va variable
+from the environment.
+.Pp
+.It Ic \&?
+Lists available commands.
+.El
+.Ss BUILTIN ENVIRONMENT VARIABLES
+The
+.Nm
+has actually two different kinds of
+.Sq environment
+variables.
+There are ANS Forth's
+.Em 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.
+.Pp
+Environment variables can be set and unset through the
+.Ic set
+and
+.Ic unset
+builtins, and can have their values interactively examined through the
+use of the
+.Ic show
+builtin.
+Their values can also be accessed as described in
+.Sx BUILTIN PARSER .
+.Pp
+Notice that these environment variables are not inherited by any shell
+after the system has been booted.
+.Pp
+A few variables are set automatically by
+.Nm .
+Others can affect the behavior of either
+.Nm
+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.
+.Bl -tag -width bootfile
+.It Va autoboot_delay
+Number of seconds
+.Ic autoboot
+will wait before booting.
+Configuration options are described in
+.Xr loader.conf 5 .
+.It Va boot_askname
+Instructs the kernel to prompt the user for the name of the root device
+when the kernel is booted.
+.It Va boot_cdrom
+Instructs the kernel to try to mount the root file system from CD-ROM.
+.It Va boot_ddb
+Instructs the kernel to start in the DDB debugger, rather than
+proceeding to initialize when booted.
+.It Va boot_dfltroot
+Instructs the kernel to mount the statically compiled-in root file system.
+.It Va boot_gdb
+Selects gdb-remote mode for the kernel debugger by default.
+.It Va boot_multicons
+Enables multiple console support in the kernel early on boot.
+In a running system, console configuration can be manipulated
+by the
+.Xr conscontrol 8
+utility.
+.It Va 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
+.Xr conscontrol 8
+utility.
+.It Va boot_pause
+During the device probe, pause after each line is printed.
+.It Va boot_serial
+Force the use of a serial console even when an internal console
+is present.
+.It Va 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.
+.It Va boot_verbose
+Setting this variable causes extra debugging information to be printed
+by the kernel during the boot phase.
+.It Va bootfile
+List of semicolon-separated search path for bootable kernels.
+The default is
+.Dq Li kernel .
+.It Va 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
+.Va BOOT_COMCONSOLE_SPEED
+variable when
+.Nm
+was compiled.
+Changes to the
+.Va comconsole_speed
+variable take effect immediately.
+.It Va 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
+.Va BOOT_COMCONSOLE_PORT
+variable during the compilation of
+.Nm .
+Setting the
+.Va comconsole_port
+variable automatically set
+.Va hw.uart.console
+environment variable to provide a hint to kernel for location of the console.
+Loader console is changed immediately after variable
+.Va comconsole_port
+is set.
+.It Va 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
+.Li 'bus:device:function[:bar]' ,
+where all members must be numeric, with possible
+.Li 0x
+prefix to indicate a hexadecimal value.
+The
+.Va bar
+member is optional and assumed to be 0x10 if omitted.
+The bar must decode i/o space.
+Setting the variable
+.Va comconsole_pcidev
+automatically sets the variable
+.Va comconsole_port
+to the base of the selected bar, and hint
+.Va hw.uart.console .
+Loader console is changed immediately after variable
+.Va comconsole_pcidev
+is set.
+.It Va 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.\& from
+.Xr init 8 ) .
+.It Va currdev
+Selects the default device to loader the kernel from.
+The syntax is:
+.Dl Ic loader_device:
+or
+.Dl Ic zfs:dataset:
+Examples:
+.Dl Ic disk0p2:
+.Dl Ic zfs:zroot/ROOT/default:
+.It Va dumpdev
+Sets the device for kernel dumps.
+This can be used to ensure that a device is configured before the corresponding
+.Va dumpdev
+directive from
+.Xr rc.conf 5
+has been processed, allowing kernel panics that happen during the early stages
+of boot to be captured.
+.It Va init_chroot
+See
+.Xr init 8 .
+.It Va init_exec
+See
+.Xr init 8 .
+.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 .
+.It Va init_script
+See
+.Xr init 8 .
+.It Va init_shell
+See
+.Xr init 8 .
+.It Va interpret
+Has the value
+.Dq Li OK
+if the Forth's current state is interpreting.
+.It Va LINES
+Define the number of lines on the screen, to be used by the pager.
+.It Va 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
+.Dq Li /boot/kernel;/boot/modules .
+.It Va 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
+.Va root_disk_unit .
+.It Va prompt
+Value of
+.Nm Ns 's
+prompt.
+Defaults to
+.Dq Li "${interpret}" .
+If variable
+.Va prompt
+is unset, the default prompt is
+.Ql > .
+.It Va root_disk_unit
+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.
+.It Va rootdev
+By default the value of
+.Va currdev
+is used to set the root file system
+when the kernel is booted.
+This can be overridden by setting
+.Va rootdev
+explicitly.
+.El
+.Pp
+Other variables are used to override kernel tunable parameters.
+The following tunables are available:
+.Bl -tag -width Va
+.It Va 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.
+.It Va hw.physmem
+Limit the amount of physical memory the system will use.
+By default the size is in bytes, but the
+.Cm k , K , m , M , g
+and
+.Cm 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.
+.It Va 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).
+.It Va 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.
+.It Va kern.maxusers
+Set the size of a number of statically allocated system tables; see
+.Xr 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.
+.It Va 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.
+.It Va kern.ipc.nsfbufs
+Set the number of
+.Xr sendfile 2
+buffers to be allocated.
+Overrides
+.Dv NSFBUFS .
+Not all architectures use such buffers; see
+.Xr sendfile 2
+for details.
+.It Va 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.
+.Pp
+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.
+.Pp
+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
+.Va kern.ipc.nmbclusters .
+Modifies kernel option
+.Dv VM_SWZONE_SIZE_MAX .
+.It Va 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.
+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
+.Va kern.ipc.nmbclusters .
+Note that
+the NBUF parameter will override this limit.
+Modifies
+.Dv VM_BCACHE_SIZE_MAX .
+.It Va 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
+.Dv MSGBUF_SIZE .
+.It Va machdep.disable_mtrrs
+Disable the use of i686 MTRRs (x86 only).
+.It Va net.inet.tcp.tcbhashsize
+Overrides the compile-time set value of
+.Dv TCBHASHSIZE
+or the preset default of 512.
+Must be a power of 2.
+.It Va twiddle_divisor
+Throttles the output of the
+.Sq 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.
+.It Va vm.kmem_size
+Sets the size of kernel memory (bytes).
+This overrides the value determined when the kernel was compiled.
+Modifies
+.Dv VM_KMEM_SIZE .
+.It Va vm.kmem_size_min
+.It Va 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
+.Dv VM_KMEM_SIZE_MIN
+and
+.Dv VM_KMEM_SIZE_MAX .
+.El
+.Ss ZFS FEATURES
+.Nm
+supports the following format for specifying ZFS filesystems which
+can be used wherever
+.Xr loader 8
+refers to a device specification:
+.Pp
+.Ar zfs:pool/filesystem:
+.Pp
+where
+.Pa pool/filesystem
+is a ZFS filesystem name as described in
+.Xr zfs 8 .
+.Pp
+If
+.Pa /etc/fstab
+does not have an entry for the root filesystem and
+.Va vfs.root.mountfrom
+is not set, but
+.Va currdev
+refers to a ZFS filesystem, then
+.Nm
+will instruct kernel to use that filesystem as the root filesystem.
+.Sh SECURITY
+Access to the
+.Nm
+command line provides several ways of compromising system security,
+including, but not limited to:
+.Pp
+.Bl -bullet
+.It
+Booting from removable storage.
+.Pp
+One can prevent unauthorized access
+to the
+.Nm
+command line by booting unconditionally in
+.Pa loader.rc .
+In order for this to be effective, one should also configure the firmware
+(BIOS or UEFI) to prevent booting from unauthorized devices.
+.Sh FILES
+.Bl -tag -width /boot/loader_simp -compact
+.It Pa /boot/loader_simp
+.Nm
+itself.
+.It Pa /boot/loader.rc
+The script run by
+.Nm
+on startup.
+.Sh EXAMPLES
+Boot in single user mode:
+.Pp
+.Dl boot -s
+.Pp
+Load the kernel, a splash screen, and then autoboot in five seconds.
+Notice that a kernel must be loaded before any other
+.Ic load
+command is attempted.
+.Bd -literal -offset indent
+load kernel
+load splash_bmp
+load -t splash_image_data /boot/chuckrulez.bmp
+autoboot 5
+.Ed
+.Pp
+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.
+.Bd -literal -offset indent
+set root_disk_unit=2
+boot /boot/kernel/kernel
+.Ed
+.Pp
+Set the default device used for loading a kernel from a ZFS filesystem:
+.Bd -literal -offset indent
+set currdev=zfs:tank/ROOT/knowngood:
+.Ed
+.Pp
+.Sh ERRORS
+The following values are thrown by
+.Nm :
+.Bl -tag -width XXXXX -offset indent
+.It 100
+Any type of error in the processing of a builtin.
+.It -1
+.Ic Abort
+executed.
+.It -2
+.Ic Abort"
+executed.
+.It -56
+.Ic Quit
+executed.
+.It -256
+Out of interpreting text.
+.It -257
+Need more text to succeed -- will finish on next run.
+.It -258
+.Ic Bye
+executed.
+.It -259
+Unspecified error.
+.El
+.Sh SEE ALSO
+.Xr libstand 3 ,
+.Xr loader.conf 5 ,
+.Xr tuning 7 ,
+.Xr boot 8 ,
+.Xr btxld 8
+.Sh HISTORY
+The
+.Nm
+first appeared in
+.Fx 3.1 .
+.Sh AUTHORS
+.An -nosplit
+The
+.Nm
+was written by
+.An Michael Smith Aq msmith at FreeBSD.org .