BUILTIN ENVIRONMENT VARIABLES

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_simp. Others can affect the behavior of either loader_simp 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 115200 unless this was overridden using the BOOT_COMCONSOLE_SPEED variable when loader_simp 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_simp. 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. 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 loader_simp's 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. 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.

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. 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 16; a value of 32 spins half as fast, while a value of 8 spins twice as fast.

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.

ZFS FEATURES

loader_simp supports the following format for specifying ZFS filesystems which can be used wherever loader(8) refers to a device specification:

zfs:pool/filesystem:

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

If /etc/fstab does not have an entry for the root filesystem and vfs.root.mountfrom is not set, but currdev refers to a ZFS filesystem, then loader_simp will instruct kernel to use that filesystem as the root filesystem.