Starting, stopping, and administration of z/OS UNIX Telnet

The z/OS® UNIX Telnet server is started by inetd for each incoming Telnet connection. When the Telnet session is complete, the z/OS UNIX Telnet server will exit. Each active Telnet session will have a separate instance of the Telnet server which will communicate with the Telnet client.

The z/OS UNIX inetd daemon does not propagate environment variables other than PATH and TZ to its child processes, so the NLSPATH and LANG environment variables cannot be used to point to a different message catalog.

The following standards are supported:

RFC 854 Telnet Protocol Specification
RFC 855 Telnet Option Specification
RFC 856 Telnet Binary Transmission
RFC 857 Telnet Echo Option
RFC 858 Telnet Suppress Go Ahead Option
RFC 859 Telnet Status Option
RFC 860 Telnet Timing Mark Option
RFC 861 Telnet Extended Options - List Option
RFC 885 Telnet End of Record Option
RFC 1073 Telnet Window Size Option
RFC 1079 Telnet Terminal Speed Option
RFC 1091 Telnet Terminal type option
RFC 1096 Telnet X Display Location Option
RFC 1123 Requirements for Internet Hosts -- Application and Support
RFC 1184 Telnet Linemode Option
RFC 1372 Telnet Remote Flow Control Option
RFC 1571 Telnet Environment Option Interoperability Issues
RFC 1572 Telnet Environment Option
RFC 2941 Telnet Authentication Option
RFC 2942 Telnet Authentication: Kerberos Version 5
RFC 2946 Telnet Data Encryption Option
RFC 2952 Telnet Encryption: DES 64 bit Cipher Feedback
RFC 2953 Telnet Encryption: DES 64 bit Output Feedback

When a z/OS UNIX Telnet session is started up, otelnetd sends Telnet options to the client side that indicate a willingness to do the following options:

WILL ENCRYPT
DO ENCRYPT
DO TERMINAL TYPE
DO TSPEED
DO XDISPLOC
DO NEW-ENVIRON
DO ENVIRON
WILL SUPPRESS GO AHEAD
DO ECHO
DO LINEMODE
DO NAWS
WILL STATUS
DO LFLOW
DO TIMING-MARK

The z/OS UNIX Telnet server can enable the following options locally.

WILL BINARY
This option indicates that the client is willing to send 8 bits of data, rather than the normal 7 bits of network virtual terminal data.
WILL ECHO
When the LINEMODE option is enabled, a WILL ECHO or WONT ECHO is sent to the client to indicate the current state of terminal echoing. When terminal echo is not wanted, a WILL ECHO is sent to indicate that Telnet takes care of echoing any data that must be echoed to the terminal, and then nothing is echoed. When terminal echo is wanted, a WONT ECHO is sent to indicate that Telnet is not doing any terminal echoing, so the client can do any terminal echoing that is needed.
WILL LOGOUT
When a DO LOGOUT is received, a WILL LOGOUT is sent in response and the Telnet session is shut down.
WILL SGA
This option indicates that it will not be sending IAC GA, the go ahead command.
WILL STATUS
Indicates a willingness to send the client, upon request, the current status of all Telnet options.
WILL TIMING-MARK
Whenever a DO TIMING-MARK is received, a WILL TIMING-MARK is the response. It is used only in kludge linemode support.
WILL ENCRYPT
Indicates a willingness to encrypt the data stream.

The z/OS UNIX Telnet server can enable the following options remotely.

DO BINARY
Sent to indicate that Telnet is willing to receive an 8-bit data stream.
DO ECHO
If a WILL ECHO is received, a DONT ECHO will be sent in response.
DO ENVIRON
Indicates a desire to be able to request environment variable information. (See RFC 1408.)
DO LFLOW
Requests that the client handle flow control characters remotely.
DO LINEMODE
Supports requests that the client do line-by-line processing.
DO NAWS
Requests that the client inform the server when the window size changes.
DO NEW-ENVIRON
Indicates a desire to be able to request environment variable information. (See RFC 1572.)
DO SGA
Indicates that it does not need to receive IAC GA, the go ahead command.
DO TERMINAL-TYPE
Indicates a desire to be able to request the name of the type of terminal that is attached to the client side of the connection.
DO TERMINAL-SPEED
Indicates a desire to be able to request information about the speed of the serial line to which the client is attached.
DO TIMING-MARK
Only supported if the client responded with WONT LINEMODE. If the client responds with WILL TM, then it is assumed that the client will support kludge linemode. It is not used for any other purposes.
DO XDISPLOC
Indicates a desire to be able to request the name of the X Window System display that is associated with the Telnet client.
DO AUTHENTICATION
Indicates a willingness to receive authentication information for automatic login.
DO ENCRYPT
Indicates a willingness to decrypt the data stream.