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name: ibm-mainframe description: Use when working with IBM z/OS mainframe systems — JCL (Job Control Language) syntax and patterns, dataset types (sequential/PDS/PDSE/VSAM), IDCAMS utility, DFSORT/ICETOOL, ISPF navigation, TSO/REXX scripting, system utilities (IEBCOPY/IEBGENER/IEFBR14), RACF security basics, GDG (Generation Data Groups), SMS (Storage Management Subsystem), and z/OS fundamentals. Part of the ibm-mainframe skill family. family: ibm

IBM z/OS Mainframe Fundamentals

For enterprise Python connectors to mainframe systems (Zowe SDK, ibm_db, EBCDIC handling) see: python-enterprise-connectors.

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Reference Files

Detailed code examples, patterns, and configuration are in the reference files below. Read the relevant file when working on that area.

File	Covers
datasets-idcams-dfsort.md	dataset types (sequential, PDS, PDSE, VSAM), IDCAMS utility, and DFSORT/ICETOOL
ispf-rexx-racf-patterns.md	ISPF navigation, TSO/REXX scripting, system utilities, RACF security, SMS storage management, and practical JCL patterns
zos-jcl.md	z/OS fundamentals, JCL syntax and patterns (JOB, EXEC, DD statements, procedures, conditional execution, GDGs)

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Anti-Patterns

Anti-Pattern	Why It Fails	Correct Approach
Submitting JCL without testing with TYPRUN=SCAN	Syntax errors consume job queue slots and waste batch window time before failing	Always validate JCL syntax with TYPRUN=SCAN or JCL checker before production submission
Using default SPACE allocation without growth estimates	Under-allocated datasets get B37/D37 abends mid-job; over-allocated wastes DASD across the complex	Calculate space from record length, volume, and growth; use RLSE to return unused space
Hardcoding dataset names without high-level qualifier substitution	Jobs break when migrated between LPAR/environments; manual editing of DSNs is error-prone	Use symbolic parameters and system symbols for HLQ; parameterize environment-specific DSNs
Not running IDCAMS VERIFY after abnormal job termination	VSAM datasets left in an inconsistent state; subsequent jobs get locked-out or corrupt data	Always run IDCAMS VERIFY on VSAM clusters after abend recovery before restarting dependent jobs
Ignoring return codes and condition codes in JCL	COND parameter misuse causes steps to run (or skip) unexpectedly; silent data corruption	Use IF/THEN/ELSE/ENDIF for clear condition handling; check RC after every step in multi-step jobs

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Related Skills

Topic	Skill
Python connectors to z/OS (Zowe SDK, ibm_db, EBCDIC)	python-enterprise-connectors
DB2 for z/OS administration	db2-mainframe
Lineage-grade reading: deterministic COBOL+JCL+EXEC SQL → OpenLineage data lineage (DSN/DDNAME bind, PROC/symbol expansion, host-var→column)	mainframe-lineage-parsers
Reverse-engineer COBOL/flat-file record layouts + inferred DDL (byte offsets, REDEFINES, OCCURS)	structure-recovery
Queryable symbol graph over COBOL/DataStage/JCL (call graph, copybook impact)	legacy-code-intel