Cold starts and warm starts

When you start a CICS® region automatically, CICS starts up in one of the following ways, depending upon how the region terminated previously:

Cold start

The region has not previously been started. When you specify that a CICS region is to be cold started, no attempt is made to recover any previously running transactions, and any data that is stored in the transient data queues and temporary storage queues is lost. That is, the region starts as if for the first time.

Warm start

The previous run of the CICS region terminated normally. CICS retains any data that is stored in the transient data queues and temporary storage queues. On a warm start, any changes that are made through the CEMT transaction or the EXEC CICS SET command are not restored.

Emergency start

The previous run of the CICS region terminated abnormally, for example, with an immediate shutdown or a hardware error. CICS performs any necessary recovery processing and retains any data that is stored in the recoverable transient data queues and temporary storage queues, but discards data that is in the nonrecoverable queues. On an emergency start, any changes that are made through the CEMT transaction or the EXEC CICS SET command are not restored.

The first time you start a region after creating it, you must use a cold start to ensure correct region initialization. When the cicscp start region command is used, the command checks whether it is the first time the region is being started. If it is the first time the region is started, the cicscp command always performs a cold start, regardless of the setting for the RD attribute StartType. If the region has ever been started before, the cicscp command performs only a warm start, regardless of the setting for the RD attribute StartType, to ensure data integrity.

You can start only one CICS region at a time. You can start as many CICS regions as you like; however, the performance of the CICS regions depends on the overall system load.

If you want to run a region with a specific locale, you can set up the locale in the region's environment file, which is in /var/cics_regions/regionName/environment.

After CICS initialization is complete, before CICS allows users to sign onto the region, CICS automatically runs any user-written post-initialization programs.