LOADXX in IPL-优快云博客

本文链接：https://blog.youkuaiyun.com/astro_boy/article/details/84089904

本文介绍了系统启动时操作员如何通过系统控制台输入参数，并详细解释了如何在SYS1.IPLPARM中指定参数值，以及这些参数如何影响系统的初始化过程。文章还探讨了PARMLIB和IEASYM成员的选择方式及其在系统启动过程中的作用。

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When the system is up, operators can type parameters in the system consol, which is connected to the processor. In another way, operators can write the values of the parameters in SYS1.IPLPARM (SYS*.IPLPARM). Those values are stored in members LOADXX. Operators can specify IODF, IEASYM, PARMLIB, SYSCAT, SYSPLEX, etc.
As LOADXX is read, system can know which PARMLIB to use. In a system, operators can specify 10(15?) PARMLIB at most. But system would add SYS1.PARMLIB at the end of the list, so the maximum is 11(16?). If we specify PARMLIB as following:
SYS1.IVAN.PARMLIB     VOL001
SYS1.BACKUP.PARMLIB  VOL002
SYS1.TEST.PARMLIB     SYS500
Then, system would add SYS1.PARMLIB behind SYS1.TEST.PARMLIB, so the list will contain 4 PARMLIB.
If the first one doesn’t exist, the IPL process would look for the next.
LOADXX also specify IEASYM parameters. Using this, systems can know which IEASYM members to use when IPL. Operators can specify more than one IEASYM members by writing there suffixes. IPL process would read them from left to right. If the IEASYM members specified in the right have some duplicated parameters, they would be used by the system and the left ones would be discarded.
After these parameters are specified, system would know what values to be used, which libraries are used and which volumes they reside on. Then IPL process would read these libraries and continue the initialization.