config - configuring Minix tasks and servers
Minix has a number of configuration files containing parameters that can
be changed to enable or disable a device driver, to change the number of
times a resource can be used, or to tune the performance of the system.
We will name the file that contains the parameter, the name of the
parameter, and the values it can be set to. Some comments are prefixed
by "8086" for Minix running in 16-bit real mode, "286" for 16-bit
protected mode, and "386" for 32-bit protected mode. Configuration file
names can be <file.h> for a file in /usr/include/, or a simple file name
for a file in /usr/src/.
There may be several definitions for a parameter with only one that is
active. Which one this is is easy to find if you know that
(CPU == INTEL) is true, and _WORD_SIZE equals 2 in 16-bit mode, and 4 in
This is the main configuration file for the Minix. It contains lots of
boolean variables to enable or disable drivers and a number of parameters
that specify the sizes of system data structures:
The number of slots in the process table, and thus the maximum
number of processes that can be run concurrently. Should be
increased from the default 32 if networking is enabled (add 8 for
deamons), and if more users are using the system (add 4 for each
active session). There are a lot of loops in the kernel scanning
the process table, so setting NR_PROCS too high will slow things
down a little bit, so don't overdo it.
The number of disk buffers in the file system server. It is used to
keep frequently used disk blocks in memory. 8086 & 286: The
default is 40, and that's about as high as it can be set. 386: The
default is 80, which is best increased to 1024 if you can spare the
memory. More will help, but the effect won't be as pronounced as
1024 is more than enough to contain the working set of one active
Number of tasks used for disk or tape controllers. By default 2,
maximum 4. You need a controller task for each device class to be
handled through a /dev/cn* set of devices.
If set to 1 allows the RAM disk to be used as a second level file
system cache. Any block that is evicted from the normal cache is
both written to disk (if dirty), and copied to the second level
cache. If it is needed again then the block is reloaded from the
RAM disk if it is still there. 8086: Forget it, you don't have any
memory for it. 286: Turn it on and set the boot environment
variable ramsize to 512 if you have the memory. That's enough to
contain the working set of one active user, and is also the maximum
FS can handle. 386: The installation scripts sets ramsize to 1024
if there is enough memory. Your first point of call is to compile a
new kernel with ENABLE_CACHE2 off, NR_BUFS set to a large value, and
ramsize set back to zero. A normal block cache works much better
than a two level arrangement.
Enables the AT or IDE disk driver. (The IDE interface grew out of
the old AT disk interface.) Any run of the mill PC needs this
driver. You need to assign a driver like this one to a controller
task using one of the cn boot variables. See boot(8).
Enables the BIOS disk driver. The BIOS driver uses the system BIOS
to read or write disk blocks. 8086: The preferred disk driver for
XT class machines. 286 & 386: Use a native driver if possible to
avoid switching back to real mode to make BIOS calls. Especially on
the 286 this is a painful affair.
Enables the ESDI disk driver. Some PS/2 models have this disk.
Enables the XT disk driver. Useful for early IBM/AT machines that
have XT disks. In real mode it is best to use the BIOS driver.
Enables the Adaptec 1540 series SCSI driver.
Enable the "DOS file as disk" driver that is used when Minix is run
from MS-DOS to access a large file as a disk.
Enable the "FAT file as disk" driver that interprets a FAT file
system to find a large file to use as a disk. This driver combined
with a fast native Minix disk driver is a better choice then the
previous driver. (And it works when Minix is not started from MS-
DOS.) This is the last driver that needs to be assigned to a
Enable the Soundblaster-16 audio driver.
Enable the Printer driver.
The size of the DMA buffer for drivers that use DMA or other drivers
that can only do I/O to a single chunk of memory. (BIOS, ESDI, XT,
DOSFILE.) Choose a number between 1 and 128 for the sector size of
this buffer. The memory cost is twice this amount, because of
trouble getting it aligned in memory properly. A value of 16 is the
minimum to work well, choose 64 if you have enough memory.
Number of virtual consoles. By default 2, so you can have two login
sessions that can be switched to by ALT-F1, ALT-F2 or ALT-
left/rightarrow. If you have an EGA screen then you can specify up
to 4 virtual consoles, for VGA you can have 8. It is best to choose
one less to leave some video memory to keep text scrolling fast.
You really should read console(4) on this. Note also the console
boot variable, you can use it to put more characters on the screen,
at the cost of video memory.
Master switch to enable the network drivers. They are required by
the network server, inet. See boot(8) for information on
configuring network support.
Enable code for the WD8003 and WD8013 cards in the network driver.
Enable code for the NE1000 and NE2000 cards.
Enable code for the 3Com Etherlink II (3C503).
Number of pseudo terminals supported, by default 0, which disables
the driver. Pseudo terminals are used for incoming network logins
by telnet or rlogin. One pty is needed per session.
Number of RS-232 lines supported. By default 2 for a normal kernel,
but 0 for a tiny kernel used for XT installation. You can save a
bit of memory by setting this parameter to zero if you don't need
This file contains most of the parameters used by the file system code.
Most of these cannot be changed, with the exception of these four:
Maximum number of open file descriptors for all processes combined.
A "File table overflow" error might indicate that this number must
Maximum number of in-use files for all processes combined. Like
above a "File table overflow" error may also indicate that this
number should be increased. In cases like these one usually doubles
both parameters. (If one table runs out then the other one is
likely to run out also anyway.)
Number of file systems that can be mounted. Again a "file table
overflow" error is given if this table is full, but it will be
produced by the mount command, so you know what's wrong in this
Number of active file locks by fcntl(2). These locks are often used
by programs that update a shared file, like mail programs do with
mail boxes. A "no locks available" error indicates that this table
has run out.
The number of disks each of these drivers can handle is specified by:
This parameter is set to 4 for the BIOS and "DOS file" drivers, and
to 2 for the "FAT file" driver. It can be set as high as you need
to allow for more disks, or files as disks. (The "FAT" driver needs
quite some memory per disk, which is why it by default only allows 2
disks.) You will need to run MAKEDEV(8) to create the extra disk
devices in /dev/.
The maximum number of TCP/IP networks is:
Sets the maximum number of networks that can be defined in
/etc/inet.conf. 8086, 286: By default 2. 386: By default 4.
The number of 512 byte buffers allocated for data within the TCP/IP
These buffers are a shared resource used by the server for any data
it wants to play with. For incoming data this number of buffers
determines the time packets are kept around, with each new packet
evicting an old packet. It's no big deal if packets get lost before
a user process reads them, packets get lost all the time. The only
real problem is outgoing TCP data. The default setting for
BUF512_NR allows up to four backlogged TCP streams, i.e. when data
is output faster then it is read. If more buffers are needed then
one of the TCP connections is shut down. When this happens you will
see a "not enough buffers left" error. This could happen for
instance if a Minix web server is assaulted by a browser that likes
to open several connections to the server simultaneously. The fix
is to increase BUF512_NR to allow more slow outgoing TCP streams.
86: The default of 32 buffers can be increased up to 64. (The "TCP
window size" has been limited in 16-bit mode to keep the buffer use
by TCP down.) 386: The default of 128 can be increased to any
value you like, but 512 seems to be more than enough. Minix-vmd
uses 512 by default, and it seems happy that way.
controller(4), usage(8), boot(8), MAKEDEV(8).
Associated with drivers there are device files to access the devices
controlled by the drivers that may have to be created. Let's simplify
this sentence: Type ls /dev, note that there are only c0* and c1*
devices, and only for two disks each. Some devices, like the audio
devices, are not even present. So if you enable a driver, or increase
some limits, you also need to use MAKEDEV(8) in /dev to allow programs to
talk to the drivers.
Kees J. Bot (email@example.com)