Miscellaneous Options

The following options are a potpourri of basic configuration instructions:

machine

i386

You must tell config(8) the architecture, or hardware platform, the kernel is intended to run on. This absolutely must be correct; you cannot boot, say, a Sparc kernel on an i386! You do this with the machine keyword.

maxusers

32

The maxusers setting affects a variety of in-kernel memory structure sizes, such as the maximum number of processes that can be run and the maximum number of files that can be open at any given time. (For those of you who read code, take a look at param.c in the kernel configuration directory for the full gory details on how maxusers affects these values.) What's more, these values trickle down throughout the kernel to set a variety of hard limits. The default of 32 is sensible for most occasions.

Many of these characteristics can be altered via sysctls, rather than changing maxusers. For example, the maximum number of files that can be open at one time is shown in kern.maxfiles, while the maximum number of processes is in kern.maxproc.

config

bsd

swap generic

The kernel needs to understand where its root device is, where it will swap, and where it will dump. You can specify all of this with the config keyword. The default config statement covers almost any circumstance, using standardized routines to figure out where each of these components will be.

You can do some very strange things with it if you desire, as discussed in config(8). You simply specify the disk device where you want each of the root, swap, and dump partitions. You can use the word "and" to concatenate multiple instances of one device. In the following example, we explicitly tell the kernel that the root partition is on the device sd3a (SCSI disk three, partition a):

 config   bsd   root on sd3a 

We don't tell the kernel anything about the dump or swap partitions, so it doesn't know anything about them. In most cases, your system can find its swap partitions through /etc/fstab, and it will dump automatically to a swap partition.

In this example (shown in the GENERIC kernel configuration, but commented out), we explicitly list the root partition, the swap partition, and the dump device:

 config   bsd   root on wd0a swap on wd0b and vnd0c dumps on wd0b 

For most cases you can just let the kernel figure everything out — I've never had a problem with the generic routines the OpenBSD kernel uses.