CONFIG(8)

NAME
config - configuring Minix tasks and servers

DESCRIPTION
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 32-bit mode.

<minix/config.h>
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:

NR_PROCS
    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.

NR_BUFS
    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 user.

ENABLE_CACHE2
    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 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.

ENABLE_AT_WINI
    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. (Several of these "wini" drivers may be enabled, but only one may run as chosen by the hd boot variable.)

ENABLE_BIOS_WINI
    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.

ENABLE_ESDI_WINI
    Enables the ESDI disk driver. Some PS/2 models have this disk.

ENABLE_XT_WINI
    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.

ENABLE_AHA1540_SCSI
    Enables the Adaptec 1540 series SCSI driver.

ENABLE_MITSUMI_CDROM
    Enables the Mitsumi CD-ROM driver. (Proprietary Mitsumi interface, almost extinct. There is no support for IDE/ATAPI CD-ROM yet.)

ENABLE_DOSFILE
    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_DOSFAT
    Enable the "DOS file as disk" driver that interprets a DOS 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.) See dosd(4) for more comments on these two drivers.

ENABLE_SB_AUDIO
    Enable the Soundblaster-16 audio driver.

DMA_SECTORS
    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.

NR_CONSOLES
    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.

ENABLE_NETWORKING
    Master switch to enable networking support. It causes the network server, inet, to be compiled and added to the kernel image, and it enables the network driver in the kernel. See boot(8) for information on configuring network support.

ENABLE_WDETH
    Enable code for the WD8003 and WD8013 cards in the network driver.

ENABLE_NE2000
    Enable code for the NE1000 and NE2000 cards.

ENABLE_3C503
    Enable code for the 3Com Etherlink II (3C503).

NR_PTYS
    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.

NR_RS_LINES
    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 serial lines.

fs/const.h
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:

NR_FILPS
    Maximum number of open file descriptors for all processes combined. A "File table overflow" error might indicate that this number must be increased.

NR_INODES
    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.)

NR_SUPERS
    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 case.

NR_LOCKS
    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.

kernel/bios_wini.c
kernel/dosfile.c
kernel/dosfat.c
The number of disks each of these drivers can handle is specified by:

MAX_DRIVES
    This parameter is set to 4 for the BIOS and DOS "file" drivers, and to 2 for the DOS "FAT" 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/.

inet/buf.c
The number of 512 byte buffers allocated for the TCP/IP server is:

BUF512_NR
    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 has yet to run out.

SEE ALSO
hd(4), dosd(4), usage(8), boot(8).

AUTHOR
Kees J. Bot (kjb@cs.vu.nl)