As400 Interview Questions Part 1

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Here is a solid set of 20 intermediate/advanced IBM i (AS400 / RPGLE / CL) interview questions.
I’ll answer them one by one, clearly and concisely:

1. Which library gets loaded first when we login to IBM i?

  • QSYS library is always the first loaded because it contains essential IBM-supplied objects and system commands.

  • Then comes user profile’s job description library list (like QGPL, QTEMP, and user libraries).

2. How to see all the objects in library and its size?

  • Use: DSPOBJD LIB(MYLIB) OBJ(*ALL) DETAIL(*ALL) → shows all objects.

  • For library size: DSPLIB LIB(MYLIB) OUTPUT(*PRINT) or WRKLIB MYLIB (F11 = size).

3. How to check all members of a file?

  • Command: WRKMBRPDM FILE(MYLIB/MYFILE) or

  • DSPFD FILE(MYLIB/MYFILE) TYPE(*MBRLIST).

4. How to see all record formats used in a file?

  • Command: DSPFD FILE(MYLIB/MYFILE) TYPE(*RCDFMT).

  • It shows all record formats defined in PF/LF.

5. How to change the record size of a PF?

  • Use: CHGPF FILE(MYLIB/MYFILE) with MAXMBRS, LVLCHK, REUSEDLT, etc.

  • If DDS change is required: Update DDS → CHGPF or CRTPF with FILE(MYLIB/MYFILE).

6. Why we use USROPN keyword in RPGLE?

  • USROPN = User Open.

  • File will not be automatically opened at program start; programmer must explicitly OPEN and CLOSE.

  • Useful for performance and conditional opening of files.

7. Why we use EXTMBR keyword in RPGLE?

  • EXTMBR('MBRNAME') is used when PF has multiple members.

  • It lets RPGLE program access a specific member instead of default *FIRST.

8. What is the purpose of using Varying?

D Var1  S  10A Varying
/Free
  Var1 = 'HELLO';
/End-Free

  • VARYING means storage allocated only for actual length + 2 bytes (to store length).

  • Saves memory and allows dynamic string manipulation.

9. What is CPF4131?

  • CPF4131 = Record Lock Error.

  • Raised when program tries to update/delete a record locked by another job.

10. Difference between CRTDUPOBJ and CPYF command?

  • CRTDUPOBJ: Duplicates object (programs, files, data areas, etc.) definition; optionally with data.

  • CPYF: Copies records between files; structure must exist.

11. Mandatory keywords for subfile?

  • SFL → Defines subfile format.

  • SFLCTL → Subfile control record format.

  • SFLSIZ (size) and SFLPAG (page size) required.

  • SFLDSP, SFLDSPCTL, SFLCLR, SFLEND commonly used.

12. Difference between PLIST and KLIST?

  • PLIST: Defines parameter list (used in CALL/PARM).

  • KLIST: Defines key list (used in CHAIN/SETLL with multiple fields).

13. Difference between *INLR = *ON and RETURN?

  • *INLR = *ON: Last record indicator, closes files and releases storage.

  • RETURN: Exits program but doesn’t necessarily close files.

  • Using both ensures program ends cleanly.

14. Effective use and side effects of *INLR? How to overcome?

  • Side effect: Files remain open, causing record locks if *INLR not set.

  • Solution: Use CLOSE or activation groups (in ILE).

  • Example: In service programs, avoid *INLR; use RETURN and CLOSE explicitly.

15. What operations we can perform on Indicators?

  • Turn ON or OFF.

  • Used for conditions (IF), record operations (CHAIN, READ), controlling display fields, conditioning opcodes.

16. How to check if a record is locked in RPGLE?

  • Use CHAIN(E) or READ(E).

  • E (Error/Lock) extender sets %ERROR or indicator ON if record is locked.

  • %STATUS = 1218 indicates lock.

17. How can we execute a CL command from within RPG program without calling a CL program?

  • Use QCMDEXC API:

C     CALL 'QCMDEXC'
C     PARM  CMDstring
C     PARM  CMDlength

18. Can we use a file with same file and record format name in RPGLE?

  • Yes, but not recommended.

  • To resolve, use RENAME keyword in F-spec:
    FMYFILE IF E K DISK RENAME(MYREC:NEWREC).

19. What are those commands which can only be executed in CL program but not in RPG program?

  • Examples: OVRDBF, DLTF, SBMJOB, RTVJOBA, RTVMBRD, etc.

  • These are CL-specific commands (RPG can run them via QCMDEXC, but not natively).

20. How to retrieve RRN value of the file record in RPGLE?

  • Use function %RRN(fileName) after CHAIN/READ.

  • Example:

C     READ FILE1
C           Eval rrn = %RRN(FILE1)

AS400 interview questions - Part 2

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