We would love to increase your chances of landing your dream job. These are some of the questions you should expect in your JCL interview.
1. Can You Define JCL
JCL is an abbreviation for Job Control Language. It is the standard command language for Multiple Virtual Storage and is mainly used by IBM Mainframe computers as the primary operating system. This scripting language instructs systems on running batch jobs or starting different subsystems. JCL directs how various programs, files, and devices run as a command language. It also informs users when they should skip additional steps.
2. What are the Uses of JCL?
Being a command language, JCL has several uses. It comes in handy when creating and deleting different data sets, VSAM clusters, and GDG’s. It also compares files and PDS members, a function that several developers appreciate. Thirdly, one can use JCL to compile and execute programs and batch programs. Lastly, this command language plays a vital role in merging and sorting file data.
3. How Many Job Control Statements Do You Know?
There are three types of JOB control statements serving different purposes. These are JOB, DD, and EXEC. The job control statements help JCL convey information to VMS. Its primary role, however, is to identify the job. Once identified, the DD job control statement prepares and supplies all the needed I/O files for program execution. Lastly, the EXEC job control statement identifies the program that should be executed. It, therefore, initiates a step within the given job by specifying the name of the program or the procedure that it should run. It works closely with the DD command.
4. How Does JCL Work?
JCL has a pretty simple working mechanism. It first recognizes the program that needs execution, the required inputs, and locations of input and output before relaying such information to the operating system, generally done through the job control statements. Therefore, this control language consists of statements that one code to inform the operating system about the intended work or operation. These statements also notify the operating system on how to process the located inputs and the fate of the resulting output.
5. What are JCL Procedures?
JCL Procedures are an array of statements inside the job control language that exist together and can conduct a given function. They are mainly used for the parallel execution of programs through several input files. These procedures usually contain the fixed part of JCL while the varying part of the job is captured within the language.
6. How Do You Normally Pass Data to a COBOL Program From JCL?
I either use files, PARM parameters, or SYSIN DD statements to pass data from JCL to the COBOL program. The PARM parameter, an optional keyword parameter, allows the passing of data from JCL to a program but with a limitation. It can only pass 100 characters. The last option is a statement in JCL that started an in-stream data set. All these come in handy in different situations.
7. What is DSN?
DSN is an abbreviation for DS NAME, a JCL parameter that is part of the DD statement. It usually comes up with the actual name of a data set. The dataset name determines the name of a given file and is generally referred to as DSN. Other parameters such as the DISP parameter on the DD statements prevent unauthorized or unwanted access to different data sets. This parameter, therefore, manages dataset integrity. They are closely linked, given that they are all part of DD statements.
8. What Makes Up the JCL Statement?
The JCL Statement is made up of four main components. The name field, an optional component, identifies every statement making it easy for other statements and the entire system to refer to it. One must follow a given process or set of steps when coding. The operation field identifies and specifies the statement type for the command statement. Like the name field, it is also coded in a specific way. The operand details the parameters used in operation, beginning from 17 columns up to 72 columns. Lastly, the comments allow information entry in the first three columns and can be achieved by coding //*.
9. What Do You Understand by JCLLIB and STEPLIB in JCL?
The STEPLIB is a DD statement used to create and identify a private library to help the system search for the program in the EXEC statement PGM parameter. The system will only rummage through the system libraries when it cannot locate the program in the provided private library. On the other hand, JOBLIB in JCL is a statement that helps identify the program’s location that needs execution in JCL. It is usually specified after the JOB statement, just before the EXEC statement.
10. What Do You Understand by Catalogued Procedures?
Cataloged procedures are more or less similar to in-stream procedures. They are name sets of job control statements placed/cataloged in partitioned data sets, commonly known as PDS or partitioned data set extended, which make up the procedure library. Thanks to this library, any job can invoke cataloged procedures, usually separated and coded in different data stores, just like the name suggests.
11. COND Can be Coded in the Job Statement or Inside EXEC Statement. What Happens in these Occasions?
The COND parameter in JCL acts as a test on the return code of the previous job steps. When the test comes back as valid or true, the execution of the ongoing job step is bypassed, and instead of terminating the job step, it is only omitted. Coding it in the JOB statement will test the condition for every job step and bypass it along with the given job steps if the condition comes back as true for any job step. Only the tested job step is bypassed when coded inside an EXEC statement and evaluated to be true. Execution, therefore, goes on for the next job step.
12. Do You Know How to Create a Temporary Dataset in JCL? Walk Us Through
I know how to develop a temporary dataset in JCL, thanks to my experience in this field. A temporary dataset only offers storage for the job duration and is deleted shortly after. There are two main ways of provisional data set creation. First, one can either specify the temporary dataset indicator as DSN=&name or by failing to establish any DSName. If the creator intends that the created temporary dataset be used in another job step, it must be referenced as DSN=*. step name.
13. What Do You Understand by SOC4 Error?
The SOC4 error, also known as SOC4 abend, occurs whenever a storage violation error occurs. It is usually caused by several factors but mainly an invalid address caused by an error in the script. Other causes of this error include missing parameters in the subprogram, performing Read/Write attempt in an unopened file, moving data to/from an unopened file, missing SELECT statement, and performing a numeric operation on NON-numeric data.
14. Tell Us How to Access Uncataloged Datasets in JCL
An uncataloged data set is ordinarily unallocated, and the volume on which it resides is unmounted. You should use the VOL and UNIT serial parameters in the DD statement to access this data set. The VOL parameter in JCl identifies the volume in which a given data set resides or is intended to reside. In contrast, the UNIT parameter commands a given system to place a dataset in a device or group of devices or another device as the other dataset.
15. Do You Know the Use of IEBGENER Utility?
The IEBGENER Utility is one of the most lauded copy programs. It has been part of the IBM operating system since it released OS/360. Its primary use is to copy data to and from different sources such as from a physical sequential file to another, a member of a partitioned data set to another physical sequential file, or a physical sequential file to a partitioned data set.
16. Do You Know the Use of a DCB Parameter?
The DCB parameter, fully known as the Data Control Block parameter, has the physical characteristics of a given dataset. It, therefore, offers detailed information on the physical attributes of data sets and is usually required for all data sets recently created in the job steps, making it a valid parameter in the DD statement.
17. Tell Us the Difference Between JES3 and JES2
JES2 is usually considered the functional component of JES. It plays several functions such as receiving the jobs into the OS, scheduling and managing them, spooling, and processing the job output. It, therefore, addresses the job before and after running a program. On the other hand, JES3 controls jobs’ input and output processing. The main difference between these two is that whereas JS3 assigns datasets to all the steps before job scheduling, JES2 only assigns the required datasets before executing a given step.
18. Can One Code Instream Data Inside a PROC?
No. It is entirely impossible to perform such an operation. This is a rule that every developer or JCL user must adhere to. Alternatively, you can code a dummy statement inside the PROC before overriding the step’s DD statement from the JCL and finally executing it.
19. Tell Us about How In-Stream Procedures are Built
In-built procedures are built by coding different statements and stationing them after the JOB statement. However, they must appear before the EXEC statements. They usually begin with a PROC statement and end with a PEND statement. It is worth noting that a single job can contain up to 15 in-stream procedures, which can be invoked severally within a given job. These procedures can also use symbolic parameters just like their cataloged counterparts.
20. Do You Know What an Operation Exception Error Is?
An exception operation error is a clear sign that an operation code hasn’t been assigned. It may also indicate that the set operations can’t be found in a specific computer model, and therefore the mother device cannot run the operations or instructions used. Thirdly, the operation error can result from trying to read an unopened file or a misspelled DD statement.
21. Explain What Notcat Is
Notcat is an MVS message signifying that there is a copy catalog entry. It is one of the most common errors in JCL. The open and write function would go through, pushing the system to try and record it in the system catalog, thus causing a duplication. This error can be fixed quickly by deleting or cataloging the first data set. This is usually achieved by cataloging the volume holding the new dataset.
22. Do You Know How JCL Acts on a Code?
JCL acts as a link between the application programs such as Assembler and the Mainframe OS, which can be MVS or Z/OS, made possible by its nature as a set of commands that offer the correct specifications to run a given application program. It is also worth noting that this process is made possible by many divisions such as the identification, environment, data, and procedure division. The identification division is the introductory part of JCL containing the date, author, and program, while the procedure division has the actions conducted on files.
23. Can You Tell Us What // Is?
// is one of the most important symbols for JCL statements, as all JCL statements must start with it. Every developer must follow this rule for the execution of JCL statements or will run into an error since JCL has an execution system that checks for it at the beginning of every statement. It acts as an identifier. It helps avoid runtime exceptions.
24. What Do You Understand by a Job Control Language?
A job control language is a set of statements that facilitate the operation of a job step. The job runs in the background in the absence of user interaction, while the operating system manages every user request with its presence, thereby initiating what needs to be done. Some of the statements that should be accessed using the job control language are the input data sets.
25. Can You Tell Us about Positional Parameters
A positional parameter in JCL is part of its job statements. Parameters are generally used to create a clear path line on how the jobs should run. They decide the class of the job, its priority, the accounting information for every job, the required maximum CPU time, and many others. They allow a fixed position and usually cone in fixed defined orders.
26. What are Keyword Parameters?
Keyword parameters are pretty different from positional parameters, and one shouldn’t confuse one for the other. They do not usually require a fixed position meaning that you can’t get an error if you don’t stick to a given order. The most critical keyword parameters include NOTIFY, PRTY, REGION, TYPRUN, TIME, MSGCLASS, and MSGLEVEL.
27. What Role Does a DISP Parameter Serve?
The DISP Parameter, fully known as the disposition parameter, is one of the most crucial keyword parameters. It describes the data set status in JCL and specifies the disposition of the data set. It also tells the OS the fate of the dataset after the termination of JOB/STEP. This data status is usually specified at the start of the particular step, its successful execution, and during any abnormal execution of the given stage. This parameter is generally called for two dispositions provided that the status is also included.
28. Tell Us about Addressing Mode in JCL
The addressing mode is part of the instruction set architecture in several central processing unit designs. It directs on how the effective memory address of an errand can be calculated through the information found in different registers. There are different addressing modes in JCL, such as AMODE(24) indicating 24-bit addressing in the memory located below the line, AMODE(31), which signifies 31-bit handling in the memory located above, and below the line, and finally, AMODE representing either 24 or 31-bit addressing techniques.
29. Do You Know about DISP=mod
DISP=mod allows for easy addition of data to a sequential dataset’s end. It is programmed to change from MOD to NEW in the absence of the data set, which won’t happen if the VOL parameter asks for a specific volume. The stem terminates the step if it can’t locate a data set once VOL has been coded. On the other hand, MOD extends data sets into many direct access volumes.
30. Define PRTY in JCL
PRTY refers to the priority perimeter in JCL. It is an optional keyword that assigns priorities to a set of jobs of a given class. It, therefore, plays a significant role when deciding the order in which the jobs should be executed. Thus, it controls the job execution.
Was our article insightful? I hope that we equipped you with some of the essential concepts of JCL that you should know ahead of your interview. Ensure that you don’t ignore other aspects, such as giving an excellent first impression during the interview and answering questions confidently.