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

       config - configuring MINIX 3 tasks and servers

       MINIX  3 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 3 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.

       This is the main configuration file for the MINIX 3.  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 user.

              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

              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

              Enables the Adaptec 1540 series SCSI driver.

              Enable  the  "DOS file as disk" driver that is used when MINIX 3
              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 3  disk  driver  is  a  better
              choice  then the previous driver.  (And it works when MINIX 3 is
              not started from MS-DOS.)  This is the last driver that needs to
              be assigned to a controller task.

              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

              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

              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.

       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 be increased.

              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 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
       server is:

              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  3  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 (