Use the LOGON command to identify yourself to the system when your installation requires operators to log on before issuing commands.
The LOGON command enables an operator to access the SMCS console. An installation can indicate that this command be mandatory. It is suggested that if an SMCS console session can be established from outside a secure area, logging on should be mandatory.
and HMCS
consoles, use the CLEAR key or the PA2 key.
For SMCS consoles, the prompt cannot be cleared from the screen until
the console is successfully logged on. To restore the prompt enter: LOGON [userid]
The LOGON command restores the logon prompt display.
The userid is an 8-character field where you enter your operator userid. The userid parameter is optional; the system will prompt you for it. Issuing the LOGON or LOGON userid command results in the LOGON prompt being displayed. The LOGON prompt is presented in the Syntax section of the LOGON command.
As of z/OS® V1R10, the LOGON command has been architected such that all keywords and keyword values appear in the same position when the LOGON command is issued. All LOGON commands are now issued as if they were issued from a typical console that is 80 columns wide. For the architected LOGON mapping which is mapped by CNZMYLGN, see the z/OS MVS™ Data Areas book in the z/OS Internet library.
Note that the system does not substitute text for system symbols specified in the LOGON command.