Changing configuration information

If you want to change the TCP/IP configuration without stopping and starting the TCP/IP address space, you can dynamically change many of the TCP/IP configuration options established by the PROFILE.TCPIP data set. To make dynamic changes, put the changed configuration statements in a separate data set and process it with the VARY TCPIP,,SYNTAXCHECK and VARY TCPIP,,OBEYFILE commands.

VARY TCPIP,,SYNTAXCHECK
The VARY TCPIP,,SYNTAXCHECK command checks the syntax of statements in the data set but does not apply any changes to the active configuration.
VARY TCPIP,,OBEYFILE
The VARY TCPIP,,OBEYFILE command checks the syntax of statements in the data set and also applies changes to the active configuration.

Statements in a VARY TCPIP,,OBEYFILE data set that are coded with syntax errors might not be applied to the active configuration as expected; activating a profile data set that contains syntax errors can lead to unscheduled outages.

Guideline: Use the VARY TCPIP,,SYNTAXCHECK command to check for syntax errors in a profile data set before activating it as the initial profile or activating it with the VARY TCPIP,,OBEYFILE command.

Result: Changes that are applied to the active configuration with the VARY TCPIP,,OBEYFILE command remain in effect only until you stop the stack. You can retain these configuration changes by integrating them into the initial profile, or by using the VARY TCPIP,,OBEYFILE command each time you start TCP/IP.

For more information about VARY TCPIP commands, see z/OS Communications Server: IP System Administrator's Commands. For information about dynamically changing settings for a particular configuration statement, see the Modifying information under each configuration statement in z/OS Communications Server: IP Configuration Reference.

Guideline: If you attempt to edit the PROFILE.TCPIP data set while TCP/IP is active, and PROFILE.TCPIP is defined in the TCPIP PROC as a sequential data set (for example, //PROFILE DD DISP=SHR,DSNAME=TCPIP.PROFILE.TCPIP), the Data set in use message might be displayed. To avoid this situation, specify FREE=CLOSE, as shown in the following example:

//PROFILE  DD DISP=SHR,DSNAME=TCPIP.PROFILE.TCPIP,FREE=CLOSE

Specifying FREE=CLOSE enables you to edit the profile while TCP/IP is active. Typically, when TCP/IP starts, it keeps the profile allocated and does not release the allocation until the end of the step (in this case, the end of the job). When you specify FREE=CLOSE, the release occurs after the data set is read, and MVS™ releases the enqueue on the profile so that you can edit it.

If the profile is a member of a partitioned data set (PDS), such as SYS1.TCPPARMS(PROFILE), FREE=CLOSE is not needed.