Other Mainframe related questions which attracts you and there is no suitable Forum you find for it and related FAQs.
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Is there some document which can explain in detail and in an easy way the practical flow of IPL in mainframe? And also explain the order in which subsystems of zOS get started; subsystems like, JES, TSO, DB2 CICS etc.?
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Google is your friend. Googling z/os ipl
returned about 272,000 hits and one of them on the first page has a link to http://www-03.ibm.com/support/techdocs/ ... ex/PRS3699
which has a PDF describing the IPL process in some detail. Whether or not it is "easy" to understand is a different issue -- the entire topic of z/OS IPLs is a complex issue and parts of it simply cannot be understood without doing some thinking and research.
To a large degree, the order the subsystems come up during the IPL is site-dependent. If a required predecessor is not up when a given subsystem starts, it issues a console message and waits for the predecessor to be available (for example, TSO cannot come up until TCP/IP and Unix System Services are running). There is a SYS1.PARMLIB member that contains the commands executed during the IPL, and most of the subsystem start commands will be located there (but some sites use other data sets with commands as well).