Simple serial client lk

lk is a simple terminal client over serial line (aka lightweight kermit).

If you are administrating distant unix servers, you propably know this situation: something goes wrong and after upgrading kernel, doing some nontrivial modifications in network configuration, firewall rules or without obvious reason, the computer no more communicates with you. There is no other way than have a walk to the basement. Or, maybe, the computer is in another building, in another street or another city... A simple and cheap solution is to interconnect computers via serial line.

Usage

lk ([line] [+/-/=switch] [name])*

Line format

The line configuration is created by a concatenation of the following parmeters. Not all of them have to be specified.

• device
  Defines the serial device name. With the leading /, a full path to the device must by provided. Otherwise it is searched in the default /dev directory.
• ,
  Separator between device and speed.
• speed
  Device baud rate. Depending on actual architecture, available values are 50, 75, 110, 134, 150, 200, 300, 600, 1200, 1800, 2400, 4800, 9600, 19200, 38400, 57600, 76800, 115200, 153600, 230400, 307200, 460800, 500000, 576000, 921600, 1000000, 1152000, 1500000, 2000000, 2500000, 3000000, 3500000, and 4000000.
• parity
  Defines the character parity checking. Allowed parity types are none (n, N), odd (o, O), and even (e, E).
• bits
  Number of bits per character. Allowed values are 5, 6, 7, and 8.

Switches

Switches controls the behavior of the line. Each switch must be prefixed with one of the marks: + to enable the feature, - to disable the feature, or = to keep untouched.

• cc
  Carrier control (model control lines)
• fci
  Hardware flow control on input (RTS)
• fco
  Hardware flow control on output (CTS)
• fc
  Hardware flow control in both directions (RTS/CTS signals). It is equivalent to setting fci and fco together.
• pc
  Parity check
• ds
  Double stop bits, otherwise one stop bit is used.
• ixon
  Software flow control on output (XON ASCII character)
• ixoff
  Software flow control on input (XOFF ASCII character)
• ix
  Software flow control in both directions (XON/FOFF). It is equivalent to setting ixon and ixoff together.

Options

• -h, --help
  Shows help and exits.
• -v, --verbose
  Enables verbose mode.

User configuration file ~/.tk

Commonly used configurations may get a name and specified here. The syntax of a file is line-oriented, each line starts by a name of configuration followed by a combination of line specification, switches and other configuration names. The final configuration is calculated by applying all the parameters in their order.

Menu

Menu allows to apply special commands during the communication. It is activated by pressing the Ctrl+\ combination, following by the command acronym.

• q
  Quits lk without detaching.
• d
  Detaches lk - hangs up the line and quits.
• h
  Hangups the line.
• b
  Sends the serial break. The serial break is used to access a special menu of the kernel.
• Ctrl+\
  Send the Ctrl+\ command.
• ?
  Shows the help text.

Examples

• ttyS0,9600n8
  Opens the serial line /dev/ttyS0 at 9600 baud rate without parity, with 8 bits per character.
• ttyS0,9600n7 +fc -ix =ds ttyS1
  Opens the serial line /dev/ttyS1 at 9600 baud rate without parity, with 7 bits per character, with full hardware flow control, and without software control flow. The number of stop bits is kept unaffected.

An example of user configuration file describes a common serial parameters "9600n8 -cc -pc +fc" under the name "default" and for all the computers alpha, beta and gama defines the serial port device. There is no flow control for gama.

# Example ~/.tk
default		9600n8 -cc -pc +fc
alpha		default ttyS0
beta		default ttyS1
gama		default ttyS2 -fc

Download

You can download a tarball lk-0.4.tar.gz. Install it by traditional ./configure, make and make install.

Howto

Init getty in respawn mode on one (server) side and run lk on the other (client) side. Have a look at /etc/inittab and add a line:

T0:23:respawn:/sbin/getty -L ttyS0 9600 vt100

Contact

Find a bug, have a comment? Send me an email - the email address is at my home page.