comp.unix.sco Technical FAQ (3/3)

comp.unix.sco Technical FAQ (3/3)

Post by Stephen M. Du » Wed, 03 Dec 1997 04:00:00



   OK ... now the FAQ has grown again, and instead of being in _two_
pieces, it's in _three_.

Revision Information
--------------------
Version:  3.28a
Date:     30 October 1997
Author:   Stephen M. Dunn
          step...@bokonon.ussinc.com
New Features:  Minor clarifications

NOTE:  All lines that have been added or modified since the previous
       version are marked with ** at the start of the line.  All new
       questions are indicated in the Table of Contents with * at the
       start of the line.

DISCLAIMER:  I try to keep this information correct, up-to-date, and useful.
  From time to time, errors and oversights will occur.  While this group
  is read by numerous SCO staff and other experts, and they tend to catch
  any mistakes I make, there is no guarantee that the information below is
  100% right.

THANKS:  I can't do this without the help of a number of other people.
  You know who you are.  Thank you.

Table of Contents
-----------------
One Bit of Administrivia (All Three Parts)

How Do I Ask A Question?

Questions and Answers Common to Unix, Xenix and ODT (Part 1)
-How do I stop banners from printing?
-Are there any screen savers?
-Is tar/cpio a good backup program?
-How do I compress my backups?
-What are some third-party backup/recovery products?
-I don't like being restricted to 14 character filenames
-How do I get a copy of adb?
-I can't find crypt
-What do I need to compile programs?
-What does the NCALL kernel parameter affect?
-How do I reset the root password if I forget it?  (part 1)
-How do I reset the root password if I forget it?  (part 2)
-How do I reset the root password if I forget it?  (part 3)
-How do I crash out of the install script?
-Why can't fsck find my lost+found directory?
-I want more space in my lost+found directory
-How do I find out serial numbers of my various components?
-How do I solve an "arglist too long"?
-What versions/configurations am I using?
-I have a bad block on my hard drive
-My system is slow
-Why did my region table overflow?
-How do I solve "fork failed: no more processes"?
-How are minor device numbers assigned by mkdev hd?
-I need fax software.  Who makes it?
-How much swap space do I need?
-Can I add more swap space?
-Do haltsys and reboot do a sync()?
-How can I get more than 64k inodes?
-Where do I get zmodem?
-Where do I get kermit?
-I get messages saying "stat() failed:  /tmp/croutPPGa00288:  no such file"
-Does SCO support my hardware?
-How do I get a file off my distribution diskettes?
-Will I have problems upgrading my hardware?
-I typed in the wrong serial number!
-Why does fsck want a scratch file?
-What books are there about SCO systems?
-How can I boot multiple operating systems?
-How do I set disk space quotas?
-How do I find out what IP address a user logged in from?
-My ANSI terminal emulator doesn't work properly
-What is Skunkware?
-Can I replace csh with tcsh?

Questions and Answers Specific to OpenServer Release 5 (Part 2)
-Graphical characters don't work
-sar doesn't work
-My emergency floppies don't have enough inodes
-I'm having trouble with licensing and registration
-sysadmsh is missing
-Will Release 5 run my older binaries?
-I loaded a patch but it didn't take effect
-What patches should I use?
-What patches are on my system?
-What's this free copy of SCO Unix I keep hearing about?
-I'm having trouble using my ATAPI CD-ROM
-My >2GB hard drive doesn't work with OSR5
-My floppy drive doesn't work reliably
-People log out but still show up in who
-Can I perform an in-place upgrade?

Questions and Answers Specific to Unix/ODT (Part 2)
-I have a system memory dump in my swap space; how do I delete it?
-How do I save kernel panic dumps to tape?
-At boot time, the "Enter the root password or ^D" message doesn't work!
-My pre-EAFS filesystem gives errors on filenames greater than 14 chars
-I just upgraded to 3.2v4 but I still can't use long filenames
-The permissions on /usr/adm/sa and its children are wrong
-I get an error "Cannot obtain database information on this terminal"
-I need help configuring MMDF
-What is the new "low" security level in 3.2v4?
-My AHA154x/174x isn't being detected
-How do I upgrade from an n-user licence?
-How do I get MMDF to send one copy of a message to many people?
-My system is slow or hangs when sizing memory
-My system doesn't recognize files starting with #!
-Where do I get POP binaries?
-What is Everest?
-How do I fix a kernel trap 0x00000006?
-How do I configure an EIDE drive to work on 3.2v4.x?
-How do I change my SCSI host adapter?
-My machine had a panic.  How do I find out why?
-How do I find out the names of BTLDs on a BTLD diskette?
-My keyboard locks up
-My machine locks up at boot time
-How can I use a PC Card with Unix?
-How much RAM can my system use?

Questions and Answers about TCP/IP and NFS (Part 2)
-telnet doesn't work properly
-How do I know if I have enough streams buffers for TCP/IP and/or NFS?
-TCP/IP gives messages like "Notice: TCP SUM: SRC 89270107  SUM 0000D7AD"
-How do I get /etc/issue to print for telnet sessions?
-What does "WARNING: tcp_dequdata" mean?
-Ping is really slow

Questions and Answers about Serial Communications and UUCP (Part 3)
-My serial connections are losing characters
-What do the terms UART, 8250, 16450 and 16550 mean?
-How do I adjust my 16550's trigger level?
-I can transfer small files via UUCP but large ones won't go
-I can transfer small files via UUCP but large ones go really slowly
-How do I get better UUCP throughput?
-How do I change uucico's window size?
-I increased my window size but nothing changed
-I increased my window size and UUCP broke!
-UUCP frequently has to resend packets
-How do I change uucico's packet timeout?
-What special considerations are there regarding my Telebit modem?
-What are all the V.something codes, MNP, HST, etc.?
-How do I maximize serial throughput?
-My data-compressing modem doesn't work much faster than my old modem
-A BSD-based machine can't connect to mine via UUCP
-Where can I get more information on UUCP protocols?
-I edited my gettydefs and things broke
-I can't get shared dial-in and dial-out working
-What are some common settings for my modem?
---------------------------------------------------------------------------

One Bit of Administrivia
------------------------
   There are two different FAQ lists that periodically get posted here.
This is the technical one.  If you have a question regarding net.etiquette,
the administration of these mailing lists/newsgroups, how to contact
SCO, where to look on the net for SCO ports of software, or how to
download files from SCO's systems, please look for the Administrative
FAQ.  It will probably answer your question.  These two FAQs are posted
at the same time, at intervals of roughly two weeks.

   Note in particular that if you require instructions on how to
contact SCO, download SLSes, or look at various anonymous archive
sites, you should look in the Administrative FAQ.

   I should also note that you may see references to TAs (Technical
Articles), or to their old name IT Scripts, in various places in
the FAQ.  These are SCO's documents on various technical issues
with SCO products.  They are generally available in searchable
form on www.sco.com, and the sysops of SCO Forum on CompuServe
also have access to them and may post them there.  Each TA has a
unique number; you should be able to search for this number for
more information.  The URL for the searchable library is
http://www.sco.com/Support/ssl.html.  If you wish to search for
a particular TA by number, replace nnnnnn in the example below with
that number:
http://www5.sco.com/cgi-bin/ssl_reference?nnnnnn
         --------------------Beginning of Part Three-------------------

Questions and Answers about Serial Communications and UUCP
----------------------------------------------------------
My serial connections are losing characters
  Here are three possibilities.  First, check the NCLIST kernel parameter.
  This governs how many CLIST structures are allocated; these are used
  to buffer input and output.  If this is too low, then at times of
  high serial I/O demands, your system will run out of CLIST structures
  and start discarding characters.  Note that there is a limit as to how
  many CLIST structures may be allocated to an individual process,
  regardless of how many are available systemwide.  This is done to
  prevent one misbehaving program from monopolizing all of the CLIST
  structures.  Look for the tunable parameter TTHOG (only available in
  newer Unix systems), which controls this limit.

  The next possibility is that you may have an old UART (8250 or 16450).
  See the next answer for more info.

  And you may also have flow control problems.  The devices at either
  end of a serial cable must agree on what flow control is being used
  or else you can end up with data loss, unexplained pauses in the
  data stream, etc.  See the man pages for stty and termio for more
  information on the available settings.

What do the terms UART, 8250, 16450 and 16550 mean?
  UART means Universal Asynchronous Receiver/Transmitter.  This is a
  chip which receives and transmits data serially; each serial port you
  have will use one, though it is possible that several may be
  integrated into one chip.

  8250, 16450 and 16550 are all common types of UARTs.  The 8250 is an
  old chip which cannot run at high speed.  The 16450 is similar to the
  8250 except that it supports data communications at higher speeds.
  Both of these chips generate an interrupt for every character that is
  sent or received, which basically tells the CPU either "Here is some
  data for you" or "Feed me!"  This is all very well, except that at
  high speed, the number of interrupts (nearly 4000 per port per second
  at 38 400 bps) can overwhelm a CPU, bringing system performance way
  down.  Also, if the CPU is busy servicing another interrupt at the
  time, the serial port's interrupt may not be serviced in time, which
  will cause a character to be lost.

  The 16550 is pin-compatible with the 16450 and, by default, runs in
  16450 mode.  This makes it compatible with software which is not
  16550-aware.  If your software is 16550-aware, it can turn on a
  special mode in which the 16550 buffers all data with 16-byte internal
  buffers.  This not only allows the CPU to deal with far more bytes at
  a time, increasing efficiency, but also means that if the CPU can't
  service the interrupt before the next character comes in, there's
  still space in the buffer for it.

  16550 support was introduced in Xenix 2.3.4, ODT 1.1 and Unix 3.2.2.
  If you have these, or later, versions, your operating system will
  automatically detect 16550-equipped ports and will enable their
  buffering.  A third-party serial driver called FAS includes 16550
  awareness in its feature set; you may wish to investigate this as
  well.  FAS can be found on ftp.fu-berlin.de in the directory
  /pub/unix/driver/fas.

  Note that the above is not really applicable to intelligent multiport
  serial cards.  While these cards may well use 16550s, it is the
  processor on the serial card which is responsible for dealing with the
  serial ports it controls, and the main CPU has nothing to do with
  the UARTs.

How do I adjust my 16550's trigger level?
  The answer is different for Unix and Xenix, but much of the
  information is the same, so it's been grouped together here.  We will
  deal with the common information first, and the specific details for
  Xenix and Unix.

  By default, Xenix and Unix set the 16550's trigger level to 14.  This
  means that once fourteen characters have been received, the 16550 will
  generate an interrupt (it will also generate an interrupt if the
  buffer is not full but serial data flow has stopped, so the system
  doesn't always have to wait until the trigger level is reached).  This
  give the system two character times in which to begin to clear the
  buffer; at high speed on a highly loaded system, this may not be
  enough, and you may still lose characters even though you have a
  16550.  On the other hand, this value should generally be set as high
  as possible to reduce the number of interrupts generated; servicing an
  interrupt is quite costly in terms of CPU time.

  There is an array in the kernel called sio_fifoctl[].  It is a 16-byte
  array with control values for different minor numbers.  To find which
  array element will be used for a particular serial port, AND the minor
  number of the port with 0x0F (for example, /dev/tty2A has a minor number
  of 136 and /dev/tty2a of 8; either one ANDed with 0x0F yields 8, so
  sio_fifoctl[8] controls this port).

  There are four different values you may wish to use for the entries in
  sio_fifoctl[].  A value of 0x0F sets the trigger value to 1; 0x4F sets
  it to 4; 0x8F sets it to 8; 0xCF sets it to 14 (these values are
  determined by the 16550 itself, not by SCO, and other values will not
  set the trigger level to intermediate values).

  In Xenix, this parameter is set by patching the disk image of the
  kernel (/xenix) using adb (the info on how to find adb is elsewhere in
  this FAQ).  The following is a sample adb session to change the
  trigger level of /dev/tty2A to 8 from 14 (the line numbers in
  parentheses are for the explanation below); the asterisks are
  adb's prompt and should not be typed in:

  (1)   cp /xenix /xenix.save
  (2)   adb -w /xenix -
  (3)   * sio_fifoctl+8/x
  (4)   sio_fifoctl+0x8:        0xcfcf
  (5)   * sio_fifoctl+0x8/w 0xcf8f
  (6)   sio_fifoctl+0x8:        0xcfcf= 0xcf8f
  (7)   * $q

  Line 1 makes a backup, and line 2 runs adb in write mode.  Line 3
  tells adb to print the current value of sio_fifoctl[8].  Line 4 is
  adb's reply, which includes two bytes from this array (the rightmost
  one is the value for sio_fifoctl[8], and the leftmost is for
  sio_fifoctl[9]).  You must look at these carefully, as one half will
  have to be changed while the other will have to be left alone.  In
  line 5, we write 0xCF8F into this location; note that the value for
  sio_fifoctl[9] is left unchanged at 0xCF.  Line 6 is adb's reply
  giving the old and new values.  Line 7 quits adb.

  For Unix, there is a table at the end of the text file
  /etc/conf/pack.d/sio/space.c which gives the same array.  It is
  formatted in the same manner (to find the appropriate value, AND the
  minor device number with 0x0F).

  If you run Unix, check the man page for the sar command to see if
  you have the -g option to check for serial I/O overruns.  If so, try
  running it.  If you see overruns, this indicates that your trigger
  level is set too high and the system doesn't have adequate time to
  service the 16550.  The cure is to turn the trigger level down one
  notch and try again.

  The information for Xenix in this answer is taken from the
  comp.unix.xenix.sco FAQ, maintained by Chip Rosenthal.  The
  copyright for that document reads:
  This collection is Copyright 1992-1994, Unicom Systems Development, Inc.
  All rights reserved.  Permission granted to reproduce and distribute this
  document provided this notice remains intact and any changes to the document
  are clearly marked.  We have tried to review all information, but cannot
  guarantee it for any particular purpose.  We do not offer any warranties or
  representations, nor do we accept any liability for any damage resulting
  from the use or misuse of information or procedures in this document.

I can transfer small files via UUCP but large files won't go
I can transfer small files via UUCP but large ones go really slowly
  This may indicate a flow control problem.  uucico, the program that
  actually performs UUCP transfers, turns off all hardware and software
  flow control on the port it is using (prior to 3.2v4.0, which allows
  you to specify what it should use).  If your modem's buffers are
  too small, then the stream of data involved in a large file transfer
  may overflow them, causing transmission errors.  This may just cause
  your throughput to go way down, or it may result in a total inability
  to transfer larger files.  Run uucico with debugging (you may find
  /usr/lib/uucp/uutry to be useful) and watch for "alarm" messages.
  If you see these, it's an indication that some characters are
  likely being dropped during transmission.

  If you are using a serial port on a multiport serial card such as
  one from Equinox or Digi, your board may have shipped with a
  utility that lets you permanently set flow control on your port.
  Another alternative is to reduce uucico's window size.

  Under 3.2v4.0, uucico does not turn off flow control; it is left at
  whatever setting the dialer used.  If you are using a compiled dialer
  and have the source and the development system, you can write in
  whatever stty settings you desire.  Under 3.2v4.1, if you are using
  atdialer, you can specify stty settings in /etc/default/atdial*.
  Note that it has been reported that cu, even under 3.2v4.x, turns on
  XON/XOFF flow control and, in doing so, disables hardware flow
  control.

  In 3.2v4.x, a new stty setting has been added to perform bidirectional
  RTS/CTS flow control.  This is CRTSFL.  CTSFLOW and RTSFLOW do not
  perform proper bidirectional flow control; they allow the modem to
  signal the computer to stop sending, but not vice versa.  Depending on
  what modem you have, you may need CRTSFL if your system can't accept
  characters as quickly as your modem can produce them.

How do I get better UUCP throughput?
  You may or may not be able to.  Here are some rules of thumb which
  may or may apply to your situation:

  If you and the remote site both use Telebit modems, enable UUCP
  spoofing.  This enables the modems to maintain the UUCP protocol
  between them, and means that your CPU's response time to individual
  UUCP packets is not as critical.  Some sites can achieve higher
  throughput with a Telebit link than with a direct connection at
  the same baud rate.

  If you and the remote site are both running versions of UUCP which
  allow you to specify different protocols (the only such version from
  SCO is found in Unix 3.2v4), look through your release notes to find
  the highest-performing protocol that's applicable to your situation.
  For example, the standard g protocol has its own error detection and
  correction logic.  If you are running over a guaranteed error-free
  link, this is unnecessary overhead, and eliminating it by selecting
  a protocol that relies on an error-free link can speed up transfers.
  Be careful that you don't specify such a protocol for a non-error-free
  link, or else your transmissions will occasionally be corrupted.  Note
  that just because you are using error-correcting modems does not
  guarantee that your data will be error-free; there is a possibility
  of lost characters and flow control problems in the serial ports at
  both ends of the connection.  While the link between the modems may
  well be error-free, the end-to-end link from one uucico to another
  may not.

  If you are running over a link that uses MNP, V.42 or V.42bis, set
  your window size as high as possible to ensure that the modems
  have as much data to work with as possible.  For further tips on
  high-speed modems, see the section on maximizing serial throughput
  below.  For information on changing uucico's window size, see below.

  If the site with which you are communicating sometimes drops packets,
  try adjusting your packet delay to a lower number.  If you are operating
  over a link with high latency (i.e. it takes a long time for a packet
  to get from one site to the other - an example would be a satellite
  link), you may need to increase your packet delay.  For more details,
  see below.

  See the note below on how to get the UUCP Internals FAQ.

How do I change uucico's window size?
  For OpenServer Release 5, see the man page for configuration(F).
  For earlier versions, read on.

  You need to have adb or _fst to do this.  See the information on
  getting these which can be found elsewhere in this FAQ.
  First, make a backup copy of /usr/lib/uucp/uucico!  This is very
  important.  Also, note its ownership and permissions.
  To change the window size to 7, run the following command from the
  Bourne shell:
--------------------8<--------(cut here)--------->8-------------------
adb -w /usr/lib/uucp/uucico - << EOF
$d
_windows/w 7
$q
EOF
--------------------8<--------(cut here)--------->8-------------------
  When you have done this, reset the ownership and permissions to what
  they were originally; this process will change them on you.

  Note that specifying a window size greater than seven may break
  uucico, as the g protocol is designed for a window size of no more
  than seven.  Also, the documentation and/or scopatches that ship with
  some SCO products list the second line of the above as "%d".  This,
  at least on the copy of adb I have, will fail; $d is correct.  If
  you are using Unix 3.2v4, leave the underscore off the symbol name.

  On Xenix 2.3.4, you may be tempted to use the scopatch command to
  make this change.  Don't bother; there are at least three bugs in
  the short script which does this work, and it's just as easy to
  do it manually as it is to fix the script.

I increased my window size but nothing changed
  When UUCP is negotiating a connection, each side will tell the other
  what window size to use when sending.  Therefore, if your window size
  is 7 and the remote uses 3, you will be sending files using a window
  size of 3, but the other side may send with a window size of up to
  7.  Note that the UUCP on the other side may not support the window
  size you specify, and may send with a smaller window than you
  requested.  While this should not cause problems, it may provide
  lower performance than you'd like.

  If your connection does not have data compression, error correction,
  or long transmission delays, and the two sites involved have
  sufficient CPU power to respond quickly to incoming packets, a window
  size of 2 or 3 should be sufficient to achieve streaming data flow.
  In this case, a larger window size will not provide any benefit.

  If you have a Telebit modem, see the Telebit notes below.

I increased my window size and UUCP broke!
  If your modem, or the modem on a remote site, has small data buffers,
  a large window size may cause the modem's buffers to overrun.  If
  the site that broke polls your system, you may wish to create a
  separate copy of uucico with a smaller window size, and specify it
  as the login shell in /etc/passwd.  If you are the polling site,
  you may have to restore your original uucico.  Alternatively, you
  could try a window size of 4, then 5, then 6, then 7, and see at
  what point UUCP stops working.  You will then know the maximum
  window size you can use.  You may also wish to ask the sysadmin
  at the remote site if there is anything they can do, such as
  forcing flow control to be used on their modem, that may remedy
  the problem.  You may, however, have no choice but to return to
  using a window size of 3.  If you have a Telebit modem, see the notes
  below relating to Telebit modems.

UUCP frequently has to resend packets
  If you are using a modem with error correction and/or data
  compression, or if you are making a long-distance connection,
  there are delays inherent in your connection which may cause UUCP
  to timeout and resend packets.  You may need to increase the
  packet timeout.

  See also the section above on problems in which UUCP can transfer
  small files but not larger ones.

How do I change uucico's packet timeout?
  For OpenServer Release 5, see the man page for configuration(F).
  For earlier versions, read on.

  This is very similar to changing the window size; once again, you
  will need to have a copy of adb, and you must first make a backup
  copy of uucico.  Then run the following Bourne shell command:
--------------------8<--------(cut here)--------->8-------------------
adb -w /usr/lib/uucp/uucico - << EOF
$d
_pktime/w 5
$q
EOF
--------------------8<--------(cut here)--------->8-------------------
  Obviously, replace 5 with the desired number of seconds.  Note that
  you should set this parameter to the smallest value that works
  reliably.  If you specify too large a value, it will reduce throughput
  if you encounter a bad line or other conditions that require packets
  to be resent.  If you are running Unix 3.2v4, leave the underscore
  out of the symbol.  Once again, restore the permissions and
  ownership once you're done.

What special considerations are there regarding my Telebit modem?
  If you are using Telebit UUCP spoofing (S111=30), the modem spoofing
  firmware will only negotiate a 3-window connection, so changing the
  window size to 7 will not do anything for spoofed connections.  It
  will, however, be effective for non-spoofed connections (i.e. if you
  connect to a site which is not using a Telebit modem).

  Some people have reported problems with Telebit modems and UUCP-g
  spoofing when they change their window and/or packet sizes.
  Apparently, Telebits can handle requests for increased window sizes
  without error (though they will only use a maximum window size of 3),
  but will not work correctly with large packets (probably above the SCO
  default of 64 bytes).

  There is a bug in version LA 5.00W of the Telebit Worldblazer firmware
  that causes uucico to fail in startup when the answering uucico is set
  for windows=7.

What are all the V.something codes, MNP, HST, etc.?
  Here are the most common data modem signalling standards.  Note that
  the descriptions are not complete technical descriptions, and only
  cover the major feature of the standard (i.e. no discussion is made of
  fallback data rates etc.)

  Bell 103 - North American 0-300 bps
  Bell 212A - North American 1200 bps
  V.22 - International 1200 bps; not generally used in North America
  V.22bis - 2400 bps
  V.32 - 4800 & 9600 bps
  V.32bis - 4800 - 14 400 bps
  V.32terbo - Vendor standard (no formal recognition), 16.8 & 19.2 kbps
  V.FC - Vendor standard (no formal recognition), up to 28.8 kbps
**V.34 - International standard, up to 28.8 kbps; this has been
**       extended to 33.6 kbps
  HST - USRobotics' proprietary High-Speed Transfer, 9600 - 16 800 bps
  PEP - Telebit's proprietary standard; also Turbo PEP
**X2 - USRobotics' asymmetrical high-speed modulation; up to 56 kbps
**     downstream (limited to 53.3 kbps by legislation), V.34 upstream.
**     See http://x2.usr.com/
**K56flex - same idea as X2, different implementation

  There are also numerous standard for error correction and data
  transmission.  MNP (Microcom Networking Protocol) is a family of
  protocols with various levels.  MNP levels 1 through 4 denote error
  correction schemes of increasing sophistication.  MNP level 4 is the
  most common MNP error correction level; while there are higher levels,
  they are not terribly widespread.  You may never see your modem report
  an MNP level 4 connection if you have data compression enabled; it will
  report level 5 instead.  MNP level 5 is usually considered a
  2:1 compressor, meaning that it will generally compress your data by
  up to a factor of 2 (though it can exceed this on some data and not
  reach it on other data).  Note that it does not check to ensure that it
  can actually compress the data; if you send precompressed data through
  it, it will actually increase the amount of data which must be
  transferred between modems.

  V.42 is another error correction standard; unlike MNP, it is
  non-proprietary.  Its primary error-control protocol is called
  LAP-M.  It also includes a provision for falling back to MNP level 4
  error correction should the remote modem not support V.42. V.42bis is
  the corresponding data compression standard.  It is both more
  efficient than MNP level 5, providing up to a 4:1 rate (even higher on
  particularly repetitive data), and more intelligent, in that it will
  recognize whether or not it can compress data.

  For further information on modems, see the newsgroup comp.dcom.modems.

How do I maximize serial throughput?
  This answer assumes that you have an error-correcting and/or
  data-compressing modem.  The rule of thumb here is to feed data to the
  modem as fast as you can.  The more data it has to work with, the more
  efficiently it can compress it.  Not only that, but there is a
  more-or-less fixed overhead involved in bundling data into packets,
  which is how the modems transmit it, so when error correction and/or
  data compression is in use, you can reduce this overhead to a minimum
  by ensuring that the modem has as much data as possible to put into
  each packet.  The usual rule of thumb is to feed the modem four times
  faster than the fastest connection rate it supports.  If you have a
  V.32 modem, which supports connections of up to 9600 bps, you should
  communicate with it at 38 400 bps (assuming your hardware supports
  this rate).  If you are using error correction but not data
  compression, the next speed up (19 200 bps, in this case) is generally
  sufficient.

  The modem will have an internal data buffer of some size; it could be
  as large as a couple of kilobytes on better modems.  If you are
  sending it data faster than it can transmit it (which you should be),
  this buffer will fill up over time.  You will need to have handshaking
  between the modem and the computer so that the modem can signal to the
  computer to stop sending when the buffer is nearly full, and to start
  sending again once there is room in the buffer.  This can be done in
  software (usually using the ASCII XON and XOFF characters), or in
  hardware (usually using the RS-232 CTS and RTS lines).  The use of
  software handshaking requires less wires between the computer and the
  modem, but will interfere with the transmission of binary data.  The
  use of hardware handshaking requires additional wiring, but will not
  interfere with binary data.  There are advocates of both methods; I
  personally prefer hardware handshaking.  Whichever method you choose,
  you must make sure that you configure both the modem and the computer
  (via stty settings) to use the same protocol.

My data-compressing modem doesn't work much faster than my old modem
  There are a couple of possible reasons for this.  Firstly, you may
  be transferring data that has already been compressed and is therefore
  not compressible (compressed news batches, for example).  If your
  modem connects to the remote site using V.42bis data compression,
  this will not adversely affect throughput.  If, however, you are
  using an MNP level 5 connection, you will actually lose
  throughput when sending compressed data.  If the majority of your
  transfers are already compressed, you should disable MNP level 5
  data compression.  Note that using MNP level 3 or 4 error correction,
  or V.42 error correction, without any compression will increase
  throughput regardless of the type of data being transmitted.

  Also, due to the way data compression and error correction in modems
  work, there are delays involved while the two modems agree on whether
  or not each packet of data was received correctly.  If possible, you
  and the remote site should try to increase uucico's window size; this
  will cause more data to be transmitted at once, which will not only
  improve the efficiency of your modem's data compression, but will also
  often mean that the response to a previous packet arrives before the
  window has expired.  I'm afraid a complete discussion of packetization
  and sliding window protocols is beyond the scope of this FAQ; just trust
  me on this one if you don't quite follow me.  Further discussion can
  often be found in the newsgroup comp.mail.uucp.

A BSD-based machine can't connect to mine via UUCP
  BSD-based UUCP sends data with even parity; SCO expects no parity.  Add
  "" P_ZERO to the chat script in the BSD machine's Systems or L.sys
  file.  For example:
        xnxbox Any uucp 19200 5553333 "" P_ZERO "" \r in:--in: nuucp

Where can I get more information on UUCP protocols?
  If you get the Usenet news group comp.mail.uucp, there is a FAQ posted
  there approximately monthly which goes into a good deal of detail on
  the format of UUCP files, the handshake process at the start of a
  connection, what some of the debugging output from uucico -x? means,
  and the internals of numerous UUCP protocols including the common g
  protocol and several others.

  If you do not get this group, anonymous ftp to rtfm.mit.edu
  and look around /pub/usenet/alt.answers.  If you do not
  have anonymous ftp access, send email to mail-ser...@rtfm.mit.edu;
  include the words "help" and "index" in separate lines in the body of
  your message.

I edited my gettydefs and things broke
  You can check gettydefs using /etc/getty -c /etc/gettydefs ... this
  command will print out everything you could possibly want to know, and
  then some. Common mistakes include not leaving a blank line between
  entries or having a cycle of settings but forgetting to close the loop
  (e.g. if 1 fails, use 2; if 2 fails, use 3; if 3 fails, you forgot to
  tell it to go back to 1).

I can't get shared dial-in and dial-out working
  Here are a few things to keep in mind.  Under Unix, the entries in
  /etc/inittab and /usr/lib/uucp/Devices must match exactly; if one says
  "ttyi3" while the other says "/dev/ttyi3", getty won't consider them
  to be the same port, and your modem will not be sent the undialer
  string.  This is usually only a problem on multiport serial cards.

  Serial ports to be used by UUCP (or even just initialized with an
  undialer) should generally be owned by user uucp and group uucp.
  If you set it this way but it keeps being put back to something else,
  chances are you're suffering from the problem mentioned above.

  If you have several entries in /usr/lib/uucp/Devices for a port
  (specifying different dialers for different speeds or whatever), only
  the first one will actually be used to reset the port.  Make sure the
  first one listed is the one you want - that's usually marked ACU, but
  local customs may vary.

What are some common settings for my modem?
  For the real answers, read your modem's manual.  If you want to
  discuss modems, see comp.dcom.modems.  Having said that, here are some
  common setup strings for various features on many modems; see your
  manual to determine which one(s) apply to your modem.  Note that not
  all modems will accept the following commands; even the manual for one
  modem is too large to fit, let alone all possible modems.

  Locked DTE rate - this causes your modem to always talk to your serial
  port at the same rate, regardless of the data transfer rate between
  modems.  Try AT\J0, AT&Qn (n is a number which depends on other
  settings as well), or AT&B1.

  Hardware flow control - this uses out-of-band signalling on the RTS
  and CTS lines to perform flow control and will not interfere with the
  transmission of binary data, as software flow control will.  Try AT&K3
  or AT&E4.

  Software flow control - particularly on interactive (cu) connections,
  you may wish to use software flow control in some cases.  This is
  usually done with the same command as hardware flow control, but with
  a different number (e.g. AT&K4).  One disadvantage is that if you get
  garbage characters (due to line noise, modem disconnection, etc.),
  you will sometimes get a flow control character as part of the garbage;
  the system doesn't know it's garbage and so it may appear to hang
  the port.

  Correct use of carrier detect - the DCD line is used to indicate to
  the computer that the modem has established carrier.  This setting is
  almost universally done with AT&C1.

  Error control - this feature, if negotiated between modems, causes the
  modems to take care of retransmitting data when errors crop up on the
  phone line.  Try AT&Qn (again, n depends on other settings), AT\Nn
  (ditto), or AT&E1.  See the discussion elsewhere in this FAQ to help
  determine what, if any, error control you should use.  Generally,
  though not always, you will want to enable all error control methods
  your modem supports, in order to be able to negotiate connections with
  other modems, but may need adjustment in some circumstances.

  Data compression - this feature, if negotiated between modems, causes
  the modems to attempt to compress the data before sending, improving
  throughput.  Try AT&Qn (n depends on other settings) and AT%C1; some
  modems also use registers such as S36 to fine-tune this.  See the
  discussion elsewhere in this FAQ for more information on when you
  might or might not want to use data compression.

  Correct use of DTR - the DTR line, when dropped by the computer,
  should cause the modem to hang up (and, according to some opinions,
  reset entirely).  This feature is almost universally done with AT&Dn,
  but the supported values of n may vary from modem to modem.  Try AT&D2
  to hang up and AT&D3 to hang up and reset.

  Writing settings - Two cautions first.  First, you do NOT want to do
  this every time you initialize the modem.  The EEPROMs used in most
  modems to store this information have a lifetime of something like
  10 000 writes.  At 30 reinitializations a day, you'll burn out your
  EEPROM in around a year.  Second, if you use this to do the initial
  setup of the modem, DOCUMENT YOUR SETTINGS somewhere so that if your
  modem does die, you'll have the settings you used somewhere (I'd
  recommend in a comment in your Dialers file).  See AT&W; some modems
  have several settings available, written to with AT&W0, AT&W1, etc.
  See AT&Y on some modems to determine which settings are used upon
  reset, and ATZn for resetting the modem.

  To Echo or Not To Echo - you can configure your modem to echo commands
  back, or not to echo commands back, with ATE1 and ATE0, respectively.
  You can control the sending of result messages with ATQ1 and ATQ0;
  some modems also use ATQ2 to disable result codes on incoming
  connections.

  Enabling busy detection - ATXn controls both the range of result codes
  the modem sends (such as enabling the display of connect speed rather
  than simply CONNECT) and what phone company signals the modem detects
  (e.g. busy, dialtone).  Most people use ATX4; check your manual for
  other options.

  Auto-answer - use ATS0=n, where n is the number of rings to allow to
  pass before answering.  ATS0=0 disables auto-answer.  You may wish to
  disable auto-answer while calling out or at other times when you don't
  wish the modem to answer.

  Escape code - most modems use a pause, followed by three plus signs,
  followed by a pause, as a signal from the computer that the modem
  should go into command mode while on-line.  This may cause problems in
  some cases.  To disable this escape sequence, use ATS2=128.
         --------------------End of Part Three-------------------
--
Stephen M. Dunn (SD313), CNE, ACE                  ste...@bokonon.ussinc.com
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