Before editing the kernel configuration file, it is recommended to perform an inventory of the machine's hardware. On a dual-boot system, the inventory can be created from the other operating system. For example, Microsoft®'s Device Manager contains information about installed devices.

If FreeBSD is the only installed operating system, use dmesg(8) to determine the hardware that was found and listed during the boot probe. Most device drivers on FreeBSD have a manual page which lists the hardware supported by that driver. For example, the following lines indicate that the psm(4) driver found a mouse:

psm0: <PS/2 Mouse> irq 12 on atkbdc0
psm0: [GIANT-LOCKED]
psm0: [ITHREAD]
psm0: model Generic PS/2 mouse, device ID 0

Since this hardware exists, this driver should not be removed from a custom kernel configuration file.

If the output of dmesg does not display the results of the boot probe output, instead read the contents of /var/run/dmesg.boot.

Another tool for finding hardware is pciconf(8), which provides more verbose output. For example:

% pciconf -lv
ath0@pci0:3:0:0:        class=0x020000 card=0x058a1014 chip=0x1014168c rev=0x01 hdr=0x00
    vendor     = 'Atheros Communications Inc.'
    device     = 'AR5212 Atheros AR5212 802.11abg wireless'
    class      = network
    subclass   = ethernet

This output shows that the ath driver located a wireless Ethernet device.

The -k flag of man(1) can be used to provide useful information. For example, to display a list of manual pages which contain the specified word:

# man -k Atheros

ath(4)                   - Atheros IEEE 802.11 wireless network driver
ath_hal(4)               - Atheros Hardware Access Layer (HAL)

Once the hardware inventory list is created, refer to it to ensure that drivers for installed hardware are not removed as the custom kernel configuration is edited.