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BOOT_CONFIG(8) System Manager's Manual BOOT_CONFIG(8)

boot_config — how to change kernel configuration at boot

BOOT_CONFIG is a kernel option that makes it possible to change the configuration at boot time. The same interface is available from userland, using the -e argument to config(8).

The boot time configuration is invoked by passing the -c option, either from the firmware prompt or, depending on the architecture, when the bootstrap loader prompts for a kernel to boot:

>> OpenBSD/i386 BOOT 3.26
boot> boot -c
booting hd0a:/bsd: ...
...
real mem  = 1073086464 (1023MB)
avail mem = 1043189760 (994MB)
User Kernel Config
UKC>

Changes made can be saved for the next reboot, by using config(8).

dev
Add a device through copying another.
8 | |
Change the base of numbers displayed and entered.
devno | dev
Modify one or more devices.
devno | dev
Disable one or more devices.
devno | dev
Enable one or more devices.
Continue boot.
devno | dev
Find one or more devices.
Give a short summary of all commands and their arguments.
Show all known devices, a screen at a time.
[count]
Set the number of rows per page.
Continue boot.
[attr [val]]
Show all devices for which attribute attr has the value val.
Toggle the autoconfig verbose variable.

The Ethernet card is not detected at boot because the kernel configuration does not match the physical hardware configuration, e.g. wrong IRQ in OpenBSD/i386. The Ethernet card is supposed to use the ne(4) driver.

UKC> find ne
24 ne0 at isa0 port 0x240 size 0 iomem 0xd8000 iosiz 0 irq 9 drq -1 drq2 -1 flags 0x0
25 ne1 at isa0 port 0x300 size 0 iomem -1 iosiz 0 irq 10 drq -1 drq2 -1 flags 0x0
26 ne* at isapnp0 port -1 size 0 iomem -1 iosiz 0 irq -1 drq -1 flags 0x0
27 ne* at pci* dev -1 function -1 flags 0x0
28 ne* at pcmcia* function -1 irq -1 flags 0x0
UKC>

ne1 seems to match the configuration except it uses IRQ 5 instead of IRQ 10. So the irq on ne1 should be changed via the change command. The device can be specified by either name or number.

UKC> change ne1
25 ne1 at isa0 port 0x300 size 0 iomem -1 iosiz 0 irq 10 drq -1 drq2 -1 flags 0x0
change (y/n) ? y
port [0x300] ?
size [0] ?
iomem [-1] ?
iosiz [0] ?
irq [10] ? 5
drq [-1] ?
drq2 [-1] ?
flags [0] ?
25 ne1 changed
25 ne1 at isa0 port 0x300 size 0 iomem -1 iosiz 0 irq 5 drq -1 drq2 -1 flags 0x0
UKC>

The show command is useful for finding which devices have a certain attribute. It can also be used to find those devices with a particular value for an attribute.

UKC> show slot
  2 ahc* at eisa0 slot -1 flags 0x0
 10 uha* at eisa0 slot -1 flags 0x0
 12 ep0 at eisa0 slot -1 flags 0x0
 17 ep* at eisa0 slot -1 flags 0x0
102 ahb* at eisa0 slot -1 flags 0x0
103 fea* at eisa0 slot -1 flags 0x0
UKC> show port 0x300
 25 ne1 at isa0 port 0x300 size 0 iomem -1 iosiz 0 irq 10 drq -1 drq2 -1 flags 0x0
 72 we1 at isa0 port 0x300 size 0 iomem 0xcc000 iosiz 0 irq 10 drq -1 drq2 -1 flags 0x0
 75 el0 at isa0 port 0x300 size 0 iomem -1 iosiz 0 irq 9 drq -1 drq2 -1 flags 0x0
 77 ie1 at isa0 port 0x300 size 0 iomem -1 iosiz 0 irq 10 drq -1 drq2 -1 flags 0x0
UKC>

It is possible to add new devices, but only devices that were linked into the kernel. If a new device is added, following devices will be renumbered.

UKC> find ep
 11 ep0 at isa0 port -1 size 0 iomem -1 iosiz 0 irq -1 drq -1 drq2 -1 flags 0x0
 12 ep0 at eisa0 slot -1 flags 0x0
 13 ep0 at pci* dev -1 function -1 flags 0x0
 14 ep* at isapnp0 port -1 size 0 iomem -1 iosiz 0 irq -1 drq -1 flags 0x0
 15 ep* at isa0 port -1 size 0 iomem -1 iosiz 0 irq -1 drq -1 drq2 -1 flags 0x0
 16 ep* at eisa0 slot -1 flags 0x0
 17 ep* at pci* dev -1 function -1 flags 0x0
 18 ep* at pcmcia* dev -1 irq -1 flags 0x0
UKC> add ep1
Clone Device (DevNo, 'q' or '?') ? 13
Insert before Device (DevNo, 'q' or '?') 14
 14 ep1 at pci* dev -1 function -1
UKC> change 14
 14 ep1 at pci* dev -1 function -1
change (y/n) ? y
dev [-1] ? 14
function [-1] ?
flags [0] ? 18
 14 ep1 changed
 14 ep1 at pci* dev 14 function -1 flags 0x12
UKC>

When configuration is completed, booting can proceed by issuing the quit or exit commands.

UKC> quit
Continuing...
mainbus0 (root)

config(8)

Mats O Jansson <moj@stacken.kth.se>

The add command is rather restricted, and might be expanded in the future.

September 6, 2019 OpenBSD-6.8