TERM

Section: User Commands (1)
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NAME

term - server for multiple communication channels on a serial link

SYNOPSIS

term [-s speed] [-n on|off] [-c on|off] [-r] [-f arg] [-w arg] [-t arg] [-o] [-a] [-d lev] [-l file] [-v file] [-1]

DESCRIPTION

Term and its clients support multiple, compressed, and error-corrected communication channels over a regular serial link, typically a modem connection. The clients can set up channels to run an interactive shell on the other system similarly rlogin(1), to execute commands on the other system similarly rsh(1), to transfer files in either direction, to redirect X-server connections from one system to the other, or to redirect any network port connection from one system to a port on the other. Any of these can occur simultaneously, and in either direction.

To support these multiple clients, a term daemon on each system takes control of the device connected to the modem. So you must compile term and the clients on both systems. Source is available by anonymous ftp from tartarus.uwa.edu.au:/pub/oreillym/term/term???.tar.z and nic.funet.fi:/pub/OS/Linux/BETA/term???.tar.z

DEFINITION

Due to the fact that anything term and its clients can initiate from one end of the link they will just as happily initiate from the other, the following frame of reference will be used throughout this documentation. The remote system refers to the system at the other end of the modem link, and the local host refers to the machine you are typing on, typically the user's home system.

USAGE

Term is run as a daemon which accepts connections from its clients and establishes channels for each client's data. Term must be run on both ends. On the remote system, execute something like

term -r -n off

Then, on the local system, either exit your comm program and type

term -v /dev/tty?? [-n off] &

where tty?? is the device name for your modem or serial port. You may be able to start the local term from within your comm program, e.g. for xcomm type

control-A x "$ term"

Once the term daemons are running at both ends they handle the transmission of data over the link. These clients connect to a local term daemon which establishes a communication channel with the remote daemon and/or remote processes. The clients are discussed in detail in term_clients(1). Briefly, trsh runs an interactive shell or commands on the remote system, tupload transfers files from the local system to the remote, tredir redirects connections from a port on the local system to a port on the remote system, txconn redirects X-server connections from the local system to the remote, and tmon monitors client statistics.

OPTIONS

Term accepts a number of command-line options which override settings established by the termrc file (see below):

-c off: Turns off compression. Still does error correction. Consider this option if you have hardware compression (ie. v.32.bis) or are transferring compressed files. The default is to have compression on.
-n on|off: Turns on line noise echoing. Talk requests, writes, and biffs to the login which is running term will then appear. This is a useful option to use on the local end (the end you are sitting at). Without this, you will never see any talk requests directed to your remote login. Default is on.
-f <number>: Makes term send XON at specified interval. Zero is no flow control emulation, 10 is a single XON every 10 characters. The default is zero. 100 is a reasonable value.
-s <number>: Specifies a maximum number of bits per second (baudrate) term will try to send over the serial link. Term will avoid sending characters at a higher data rate than this. This overrides the BAUDRATE environment variable. The default is 2400. This option is needed as most systems will buffer the data sent to the serial port. Unfortunately this (unknown) buffering can interfere with term's packet timeout mechanism. During setup and tuning it is better to have <number> be too small rather than too large. For high speed links ( > 9600), making it unlimited is probably advantageous. This is achieved by setting the number to zero. Term will then rely solely on the packet windows to do flow control.
-w <number>: Sets the transmission window size, that is, the number of unacknowledged packets that term may send. Lower numbers may lead to better interactive response times. Higher numbers may lead to better throughput, particularly if the serial link latencies are large and the timeout length is set large. Higher numbers can also improve efficiency on noisy lines. Default is 3. This will be too low for higher speed links. A reasonable value is 10 with a timeout (see below) of 150 for 14.4Kbps link.
-t <number>: Timeout length in 20ths of a second. This specifies how long term will wait for an acknowledgement before retransmitting a packet. Default is 50, maximum 200. Increasing both the window size and timeout can lead to improved throughput, but at the expense of greater latencies for interactive work and during noise recovery.
-r: Use this on the remote term so that client numbers won't clash.
-a: Turns on seven bit line mode. Use only if you have a seven bit line, as determined by linecheck.
-l <filename>: Output all log/noise/debugging to the file <filename>
-v <filename>: Set the modem device to be <filename>. Appropriate usage is something like "-v/dev/ttys1"
-1: Use stdout instead of stdin as the modem port. This is ignored if a -v is also present.
-d <number>: This sets the debuging level. This is useful for monitoring packet timeout conditions and other things. Level 64 is suggested, 478 is verbose. Read debug.h and the other source files to find out what the levels do. If you are not familiar with packet protocols and pouring through source code, then this option is unlikely to help you.
-o: Turns on packet send forcing. Re-transmits oldest packet if nothing to send. Default off. Of dubious utility. Not properly debugged. Very bad idea if speed is unlimited.

INITIALIZATION FILE

The file termrc in the .term directory in your home directory may be used to specify default settings for a user. These settings are overruled by values set in the command line, but several options can only be set in this file. Blank lines and lines beginning with '#' are comments, other lines must begin with one of the options, and, if an argument is required, it must be separated from the option by exactly one space. Legal options are:

escape <number>: This is one of the most important options for term. Usage is either 'escape <some decimal number>' or 'escape <start of range>-<end of range>'. This tells term to never transmit the character or characters in the range. This is essential for serial lines that aren't fully transparent. For example, lines that use software flow control will want to do 'escape 17' and 'escape 19'. If you only have a seven-bit link, DO NOT use 'escape 128-255', see the termrc 'sevenbit' option below. See also the linecheck program, and term_setup(1).
ignore <number>: This tells term to silently strip this character if it is received over the serial link. Its use should correspond to 'escape' options used by the term on the other system. E.g. if you use 'escape 126' on one end, you should use 'ignore 126' on the other.
compress [on|off].: Turns the default compression mode on or off. The default is 'compress on'. With this on, all data will be compressed by term before sending over the serial line, and then un-compressed at the other end. If you are sending already compressed data, it is recommended that you turn compression off. Similarly, if your modem already does compression you may consider leaving it off. You can turn compression on and off on a client-by-client basis with the '-c' option for clients. See term_clients(1).
baudrate <number>.: This is used to limit the rate at which term sends data. Set this to the minimum of your modem speed, and the computer-to-modem baud rate. Values that are too high shouldn't hurt too much, as long as timeout is not set too low. Default is 2400.
timeout <number>.: Set the number of 1/20th of a second to wait before re-sending packets that haven't been acknowledged. Low values will provide faster recovery from line noise, but higher values are required if the latencies in your link are large. Values between 50 and 120 are typical. The default value is 70.
window <number>: The size of the packet window. Default value is 3. Increase this if your latencies (and timeout) are large.
noise on: If this is set, then term will send anything it doesn't understand to the standard error or the -l file. This is where talk requests, mail biffs, writes, and corrupted packets will end up. This is recommended for the local end.
remote: Sets this to the remote side. It should always be specified on one, and only one end of the link. This prevents client number clashes.
sevenbit: Use this if your line is a sevenbit line. Use this instead of 'escape 128-255'.
breakout <number>: The value of breakout character. Default is 48 ('0'). If either 'term' daemon receives five breakout characters in a row from the link, outside a packet, it will exit.
chdir <path>: Sets the home directory for the term daemon. This will be the directory for processes started started by this daemon for remote trsh clients. And it will be used by a remote tupload when relative paths are used.
denyrsh on: If this is set, any trsh request from the other end will be rejected. This is to provide better security, especially when run as root. You can set this on both ends separately, allowing access on one end and denying on the other.
chroot <directory>: Runs term in a chroot environment (see chroot(2), ftpd(8)). If term is run as root, a tupload from the other side could clobber every file on the system. To avoid this, a chroot environment can be set up to give access only to specific directories. It accordingly restricts the commands that can be used by trsh. The chroot takes place after every file access in the initialisation process, in particular after the server socket is opened.

ENVIRONMENT VARIABLES

BAUDRATE: Used to set the speed. Overridden by termrc or command line setting.
SHELL: Default shell for trsh.
DISPLAY: Used by txconn to determine which X-server port to use.
TERMDIR: Where to make the .term directory (which contains the socket for term itself). Default is HOME.

DIAGNOSTICS

The -d option provides debugging output. See term_setup(1), linecheck(1), or linerem(1) for further diagnostic information.

BUGS

If a remote client stops consuming its input but leaves the channel open, the local term daemon will continue to resend unacked packets. Term by default requires a line which passes through all ascii values from 0 to 255. Xyplex-type terminal servers may require the use of set session passall to work correctly.

AUTHOR

Michael O'Reilly, oreillym@tartarus.uwa.edu.au.

This document was created by man2html, using the manual pages.
Time: 20:08:19 GMT, December 23, 2022