2023's Most Common JCL Interview Questions - IQCode
What is JCL (Job Control Language)?
Job Control Language (JCL) is a scripting and command language used on IBM mainframe computers, mainly with the MVS (Multiple Virtual Storage) and Z/OS operating systems. When using these systems, the user must provide instructions to the operating system on what tasks they want to be performed and how they want the output to be produced. JCL acts as an interface between the user's application programs (such as COBOL and PL/1) and the mainframe operating system.
JCL consists of job control statements, such as JOB, EXEC, and DD statements, that tell the operating system how to run a job or application program. These statements give the OS information about the user, the resources the job needs, the programs required, and the data sets needed by the job.
In a mainframe environment, programs can be executed either in batch or online mode. JCL can be used for executing a series of programs or jobs without manual intervention, known as batch mode.
JCL Interview Questions for Freshers:
1. What are the benefits of using JCL?
Types of Job Control Statements in JCL
JCL (Job Control Language) is a scripting language used to define and execute jobs on IBM mainframe computers. It consists of job control statements that specify the job requirements, such as input/output files, program name, run-time, and more. There are different types of job control statements used in JCL:
This statement defines the start of a job and assigns a job name and job ID. It also specifies the accounting information, such as account number, department number, and programmer's name.
This statement defines the start of a job step and specifies the program to be executed. It also includes the input and output files for the program.
This statement defines the input and output devices used by the job step. It specifies the device type, device name, and data set name.
//IF, //THEN, //ELSE statements
These statements are used for job control flow and conditional processing. They allow you to specify whether a job step should be executed or not based on a certain condition.
This statement allows you to include another JCL file within the current JCL file. It is useful for reusing common job steps and reducing JCL duplication.
This statement defines a symbolic parameter that can be used within the JCL file. It makes the JCL file more flexible and easier to modify.
Understanding the different types of job control statements in JCL is essential for creating and executing mainframe jobs efficiently.
Difference between Positional Parameter and Keyword Parameter in JCL
In JCL (Job Control Language), positional parameters are defined by their position in the parameter field and are not explicitly named. On the other hand, keyword parameters are specified with their name or keyword followed by a value.
In simpler terms, positional parameters rely on the order in which they are entered, while keyword parameters depend on the names assigned to them. For example, a positional parameter in JCL might be the input file to be processed, while a keyword parameter could be an optional flag to modify the behavior of a particular program or utility being executed.
Parameters for Data Definition (DD) Statement
A DD statement is used to define the input and output files in a JCL job. The parameters used in a DD statement are:
- DDNAME: The name of the DD statement that is used to identify the file in the job
- DSNAME: The name and location of the data set or file
- DISP: Specifies how the operating system handles the data set after the job completes. Options include KEEP, CATLG, DELETE, and MOD
- UNIT: Specifies the device type for the data set. For example, TAPE or DASD
- SPACE: Specifies the amount of space required for the data set
- DCB: Defines the attributes of the data set. This includes information such as the record format, block size, and organization
- DUMMY: Specifies that a temporary data set is being used. This is useful for testing and debugging purposes.
The parameters used in a DD statement are specific to the system being used. It is important to consult the system documentation for the correct syntax and options for DD statements.
When you use the EXEC statement in programming, you may need to include parameters to customize the action being executed. Here are some of the commonly used parameters:
The PARM parameter allows you to pass one or more values to the program being executed. This is useful when you need to customize the behavior of the program based on certain input values.
The PGM parameter specifies the name of the program to be executed. This can be a program that is already compiled, or it can be a program that is created dynamically at runtime.
The COND parameter allows you to specify a condition that must be true in order for the program to be executed. This can be used to create more sophisticated control flow in your programs.
The TIME parameter specifies how much CPU time is allocated to the program being executed. This can be useful for controlling the performance of your programs and preventing them from using too many system resources.
The REGION parameter specifies how much memory is allocated to the program being executed. This is useful for preventing programs from running out of memory and crashing.
//Example of EXEC statement with parameters EXEC PGM=MYPROG, PARM='VALUE1 VALUE2', COND=(4,LT), TIME=(100,10), REGION=2048K
Difference between JOBLIB and STEPLIB statements
In JCL (Job Control Language), JOBLIB and STEPLIB statements are used tO specify the location of load libraries containing executable programs or subroutines used by the job or a job step, respectively.
JOBLIB statement provides a list of data sets that are searched in the order specified to locate the program or subroutine to be executed. It is used when the program or subroutine is used by a number of steps or the entire job.
On the other hand, the STEPLIB statement is used to specify the load library for a specific step in the job. It provides a list of data sets that are searched sequentially to locate the program or subroutine used by that step only.
In summary, JOBLIB is for the entire job, while STEPLIB is only for a specific step within the job.
Explanation of Generation Data Group (GDG)
A Generation Data Group (GDG) is a set of related files that have the same name and are distinguished by a relative generation number. The first file in the group is given a generation number of 0, the second file is given a generation number of 1, and so on.
GDGs are commonly used in mainframe environments to manage versions of files. The use of GDGs allows multiple versions of a file to be stored and easily accessed, without the need for unique names for each version. GDGs can also be used for backup and restore processes, data archiving, and audit trails.
Symbolic Parameters and Their Importance
Symbolic parameters are variables that are used to represent values within a system. They provide a way to modify the behavior of a system without changing its underlying structure. By using symbolic parameters, the user can easily adjust the system's parameters without requiring any code changes, making it more flexible and customizable.
Symbolic parameters are important because they allow the user to fine-tune the behavior of a system and make it better suited for their needs. For example, in a machine learning model, symbolic parameters can be used to adjust the learning rate, the number of hidden layers, and the number of neurons in each hidden layer. These adjustments can have a significant impact on the accuracy and performance of the model.
In summary, symbolic parameters are a powerful tool for customizing systems and optimizing their behavior. They allow for easy modification of a system's parameters without requiring any code changes, making it more versatile and adaptable to changing needs.
What is a Temporary Dataset in JCL and how to create one?
In JCL, a temporary dataset is a file that is created for a specific job and is deleted after the job is complete. It is used to store intermediate data that is only required for a short period of time and does not need to be saved for future use.
To create a temporary dataset in JCL, we can use the DD statement with a special dataset name of "SYSUT1", "SYSUT2", "SYSUT3", etc. These names indicate that the dataset is temporary and will be automatically deleted when the job is complete.
For example, to create a temporary dataset in JCL, we can use the following DD statement:
//SYSUT1 DD DISP=(NEW,DELETE,DELETE),UNIT=SYSDA,
In this example, we have specified a temporary dataset named "SYSUT1" with a size of 10 tracks and a secondary size of 5 tracks. The dataset will be deleted after the job is complete.
Overall, temporary datasets are useful in JCL for storing intermediate data and conserving storage space on the system.
Understanding Time Parameter in JCL and Time=1440
In JCL (Job Control Language), the time parameter controls the amount of CPU time allocated to execute a job. The format for specifying the time parameter is time=mm or time=hhmm.
The time parameter is optional, but if specified, it should be set to a value that is sufficient to complete the job execution. If the time parameter is omitted, the default value is one hour (time=0600).
For instance, time=1440 means the job can run for 1440 minutes, which is equivalent to 24 hours. If the job execution is not finished within the allocated time, the job will be terminated with a time-out message. It's essential to set the time parameter accurately as the system resources are limited, and it affects the execution of other jobs. Therefore, it's necessary to coordinate with the system operator and establish guidelines for time allocation in the production environment.
Explanation of MSGLEVEL Parameter and Its Significance
The MSGLEVEL parameter is used to specify the level of messages that need to be logged in the system log data set. The parameter is typically used in the JCL (Job Control Language) of mainframe systems.
The MSGLEVEL parameter accepts a value between 0 and 99, where 0 indicates that no messages need to be logged while 99 indicates that all messages need to be logged.
The significance of the MSGLEVEL parameter lies in its ability to help system administrators identify and troubleshoot issues in the mainframe environment. By setting the MSGLEVEL parameter appropriately, administrators can ensure that only the necessary messages are logged, thereby reducing the amount of data that needs to be analyzed.
In addition, the MSGLEVEL parameter allows administrators to control the amount of system resources that are consumed by system logging. By logging only the necessary messages, administrators can reduce the CPU and I/O overhead associated with logging and improve the overall performance of the system.
Overall, the MSGLEVEL parameter is a crucial tool for efficient system management and troubleshooting in mainframe environments.
Converting FB File to VB File using SORT Program
To convert a Fixed Block (FB) file to Variable Block (VB) file using a SORT program, we can follow the below steps:
1. Define SORTIN and SORTOUT files DDnames and specify the input and output files.
2. Define an OUTFIL statement with VTOF option which will convert the FB file to VB file.
The SORT Control Statement will look something like this:
//SORTJOB JOB ... //STEP01 EXEC PGM=SORT //SORTIN DD DSN=FB_FILE,DISP=SHR //SORTOUT DD DSN=VB_FILE,DISP=(NEW,CATLG,DELETE), // SPACE=(CYL,(X,Y)),UNIT=XXXXXXXX //SYSIN DD * SORT FIELDS=COPY OUTFIL REMOVECC, VTOF, TRAILER1=('VB file created') /*
In the above SORT control statement, we have specified the DDname of the input FB file as SORTIN and the output VB file as SORTOUT.
The VTOF (Variable-to-Fixed) option in the OUTFIL statement is used to convert the FB file to VB file. It removes the leading record length field from the fixed-length records and replaces it with a variable-length record header.
Once the SORT program is executed, the input FB file will be converted to output VB file, which we have specified in the SORTOUT DD statement.
Name JCL Statements that are not allowed in Procedures
In JCL procedures, certain JCL statements cannot be used. These include:
- JOBPARM statement is used for giving information and associating particular variables with a job, it cannot be used in procedures.
- EXEC statement specifies the program or procedure to be executed, it cannot be used in procedures.
- DD statement is used to specify input/output/dummy files for a program, it cannot be used in procedures.
- SYSIN statement specifies standard input for a job or a program, it cannot be used in procedures.
- SORTIN DD identifies the input file(s) for a sort step, it cannot be used in procedures.
//SORTOUT, //SORTWK, //SORTWKnn
- These are DD statements, used for sorting in a job step and not allowed in procedures as they are not part of job or exec statement.
Understanding JCL Hierarchy Levels
JCL (Job Control Language) has 3 hierarchy levels: JOB, EXEC, and DD. These levels determine the flow of the job execution and the specific instructions for each step:
- This is the highest level and represents the entire job. It includes information such as the job name, the accounting information, and the time to start the job.
- This level represents a step within the job. It includes information such as the name of the program to execute, any input or output files, and any required resources.
- This level represents the input and output files that are associated with a step. It includes information such as the file name, the file type, and the location of the file.
Understanding the hierarchy levels is essential for creating and managing JCL jobs effectively. It helps ensure that jobs run smoothly and efficiently.
Understanding DISP=OLD and DISP=SHR
In JCL (Job Control Language), DISP is a keyword used to specify the status of a data set that is being opened. DISP=OLD means that the data set being opened is old, meaning it is an existing data set. If the user specifies DISP=OLD and the data set does not exist, the job will fail.
On the other hand, DISP=SHR means that the data set is being opened for shared access. This allows multiple jobs or steps to read the data set simultaneously.
Overall, DISP=OLD is used when the user wants to open an existing data set and DISP=SHR is used when multiple jobs or steps need to access the data set at the same time.
JCL Interview Questions for Experienced
16. What does the use of "//" symbol signify in JCL?
symbol is used in JCL to indicate the beginning of a new job or a step in the job. It is mandatory to use "//" symbol to indicate job name and optional to use for indicating step name. It is used to differentiate comments in JCL from executable statements.
Condition Checking in JCL
Condition checking in JCL refers to the capability of JCL to check for and act upon specific conditions that occur during the job execution. This is done using condition code parameters, which are defined as three-digit numeric values that are set based on the status of the previous step or condition. These codes can then be used to guide the flow of the job and perform specific actions based on the outcome of each step or condition.
What is the Effect of Including COND in both a JOB Statement and an EXEC Statement?
When COND is specified in both a JOB statement and an EXEC statement, the condition is tested twice. The first test is performed before the job is executed, and the second test is performed before the specific EXEC statement is executed. If both tests evaluate to true, the job step is bypassed. However, if only one test is evaluated to true, the job step runs as usual. It is not recommended to include COND in both a JOB statement and an EXEC statement, as it can sometimes result in unexpected job behavior.
Explanation of "COND=EVEN" and "COND=ONLY"
"COND=EVEN" is a syntax used in JCL (Job Control Language) to specify that a particular job step should be executed only on even-numbered nodes in a parallel sysplex. In contrast, "COND=ONLY" specifies that the job step should be executed only on a specific node, as specified in the job definition.
Explanation of Utilities in JCL
In JCL (Job Control Language), utilities are used to perform various tasks such as copying, comparing, merging, sorting, deleting, or renaming files. These utilities can help in managing datasets and jobs more efficiently. Some commonly used JCL utilities include:
- IEBGENER: This utility is used for copying datasets from one location to another.
- IEFBR14: This is a utility program that is used to create a dataset or delete a dataset.
- IEFBR14: This is a utility program that is used to create a dataset or delete a dataset.
- IEFBR14: This is a utility program that is used to create a dataset or delete a dataset.
- IKJEFT01: This is a utility that allows a user to enter TSO (Time Sharing Option) commands from a batch job.
- ICETOOL: This is a powerful utility that is used for sorting, merging, and copying datasets.
These utilities can be included in JCL scripts to automate tasks, save time, and improve overall efficiency in working with mainframe systems.
Usage of Coding Class Parameters in JCL
In JCL (Job Control Language), coding class parameters are used to specify the level of priority for the execution of a batch job. These parameters determine the order in which batch jobs are executed based on their criticality.
The coding class parameters are defined using the JOB card statement in JCL and are specified as a single character from A to Z. The higher the priority level, the lower the character value assigned. For example, a job with a coding class parameter of A is the most critical job and is executed first, while a job with a coding class parameter of Z is the least critical job.
Here is an example syntax of the JOB card statement with the coding class parameter:
//JOBNAME JOB (ACCOUNT),'JOB DESCRIPTION',CLASS=class
Where the CLASS parameter specifies the coding class. It is optional, and if it is not specified, the default value is A.
This feature is particularly useful in mainframe systems where numerous batch jobs are executed daily, and execution order plays a vital role in ensuring the smooth workflow of the system.
In the mainframe environment, a PROC is a piece of JCL code that defines a set of processing steps for a job to be executed. It can be used as a template to streamline job execution and eliminate the need to rewrite the same JCL code for multiple jobs.
An instream PROC is a type of PROC that resides within the JCL code of a job and is not stored separately. It is used for one-time execution and is not saved for reuse.
On the other hand, a catalogued PROC is stored externally in a system library and can be accessed from multiple jobs. It can be updated and maintained separately, ensuring consistency in processing steps for all jobs that use it.
In summary, a PROC is a powerful tool in mainframe computing that helps streamline job execution, and there are two types: instream and catalogued PROCs.H3. Coding Instream Data in PROC
Yes, it is possible to code instream data in PROC within SAS programming language. Instream data refers to the data that is included in the SAS code itself, rather than reading it from a separate data file.
Here's an example of how to code instream data in PROC:
proc print data = /* Instream data begins here */ datalines; Bob 25 Sue 32 Tom 19 /* Instream data ends here */ run;
In the above example, `datalines` is a keyword that indicates the start of the instream data. The data values are then listed below until the keyword `run;` is reached, indicating the end of the data.
Overall, using instream data can be a useful way to quickly input data for testing and small-scale projects without needing to create a separate data file.
What are ABENDS in JCL and Examples of Different JCL ABEND Codes?
In the context of JCL, an ABEND refers to an abnormal termination of a program or job. When a job or program ends abnormally, an error message is produced and an ABEND code is assigned to indicate the reason for the abnormal termination. Here are some examples of ABEND codes in JCL:
- S0C1 - This is a common ABEND code that occurs when there is a protection exception or an attempt to execute an instruction that is not valid for the current program status.
- S0C4 - This ABEND code is usually caused by a data exception, such as an attempt to reference a storage area beyond its limits.
- S0C7 - This ABEND code typically occurs when there is a numeric data exception, such as an attempt to divide by zero.
- S0CB - This ABEND code indicates that an attempt was made to execute a program that was built for an unsupported operating system or hardware configuration.
- S222 - This ABEND code is a system completion code that is usually caused by a failure to allocate a required resource.
These are just a few examples of the many ABEND codes that can occur in JCL. When an ABEND occurs, it is important to review the associated error message and ABEND code to determine the root cause of the error and take appropriate corrective action.Sorry, as an AI language model, I don't have the context to understand what "NOTCAT 2- GS" refers to. Can you please provide more information or context so I can better assist you?
Usage of INCLUDE Statement in JCL
The INCLUDE statement in JCL (Job Control Language) is used to include common JCL statements or procedures in a job stream. It helps to reduce redundant code and improves the readability of JCL. This statement refers to an external file that contains JCL statements and can be used multiple times in one or more jobs. We can specify multiple include statements in a job, and the order of the statements is significant as it determines the order in which JCL statements or procedures will be included in the job stream.
For example, if we have a common set of DD statements or procedures that are used frequently in multiple jobs, we can define these statements or procedures in a separate JCL file and include this file in our jobs using the INCLUDE statement. This approach saves time and effort in creating and maintaining similar JCL code across jobs.
In the above example, the INCLUDE statement is used to include the JCL code from member DD1 in dataset JCLLIB.
Ways to Pass Data to a COBOL Program from JCL
In COBOL, there are different ways to pass data from a JCL to a COBOL program. Some of these methods include:
- Using input/output files: Data can be passed to a COBOL program using input/output files specified in the JCL.
- Using parameters: Parameters can be passed to a COBOL program using the PARM parameter in the JCL.
- Using environment variables: Data can be passed to a COBOL program using environment variables defined in the JCL.
- Using control cards: Data can be passed to a COBOL program using control cards specified in the JCL.
- Using system symbols: System symbols can be used to pass data to a COBOL program by defining them in the JCL.
It is important to choose the method that best suits the specific requirements of the COBOL program being executed.
Explanation of DISP=(NEW,PASS,DELETE)
In mainframe systems, "DISP" is a parameter used in the Job Control Language (JCL) to specify the disposition of data sets used or created by a job.
DISP=(NEW,PASS,DELETE) is a common specification used when creating and using temporary data sets.
- NEW - specifies that a new data set will be allocated if it does not already exist.
- PASS - specifies that the data set will not be deleted when the job ends, but will be available to any subsequent jobs that specify DISP=OLD or DISP=MOD.
- DELETE – specifies that the data set will be deleted at the end of the job execution.
The combination of NEW, PASS, and DELETE ensures that the data set will be allocated as a new empty data set, will persist for as long as necessary during the job, and will be deleted when the job is complete.
JCL Scenario-Based Interview Question:
Can you explain how to check the syntax of a JCL without running it?
To check the syntax of JCL without running it, we can use the JCLCHECK utility provided by IBM. We can follow these steps: 1. Create a job that invokes the IEBEDIT utility and specify the input as the JCL that we want to check. 2. Specify the output as the JCLCHECK utility. 3. Submit the job. 4. Check the JES output to verify whether the JCL syntax is correct or not. If there are any syntax errors in the JCL, JCLCHECK will generate a report that highlights the errors. We can also use the JSCAN command provided by JES2 or the JESJCL command provided by JES3 to check the syntax of JCL. Both of these commands check the syntax of the JCL without executing it.
Does JCL Support Automatic Start? If Yes, Then Explain How.
JCL (Job Control Language) does support automatic start using the initiator parameter. The initiator parameter specifies the subsystem that automatically starts a job.
To use automatic start, you need to specify the initiator parameter in the EXEC statement in the JCL code. The syntax for the initiator parameter is as follows:
// EXEC PGM=program-name, // INITIATOR=init-subsystem
The init-subsystem is the name of the subsystem that is used to start the job automatically. Once the initiator parameter is defined in the JCL, the job is automatically started when the subsystem starts.
Using automatic start can save time and resources as it eliminates the need for manual intervention to start the job. It is particularly useful for batch processing and production jobs that need to be executed at specific times.
Understanding Job Time-Out and How to Overcome It
Job time-out refers to the amount of time a program or script has to complete a certain task before the system interrupts or terminates it. This is typically done to prevent the system from hanging or freezing due to a runaway or malfunctioning process.
To overcome job time-out, you can try the following approaches:
- Optimize your code to make it run faster and more efficiently.
- Break the task down into smaller, more manageable chunks that can be completed within the time-out limit.
- Adjust the time-out limit setting if possible, to allow for more time to complete the task.
By using these methods, you can avoid job time-out and ensure that your programs and scripts run smoothly and efficiently.
Explanation of DISP=(NEW,CATLG,KEEP)
The statement DISP=(NEW,CATLG,KEEP) is used in JCL (Job Control Language) for allocating datasets. Here is the meaning of each parameter:
- NEW - Allocate a new dataset.
- CATLG - Catalog the dataset so that it can be easily found and reused.
- KEEP - Keep the dataset even if the job abnormally terminates.
Therefore, DISP=(NEW,CATLG,KEEP) means that a new dataset should be allocated and cataloged, and it should be kept even if the job abnormally terminates.
DUMMY DD DUMMY,DISP=(NEW,CATLG,KEEP)
H3. Explanation of DISP=(NEW,CATLG,KEEP) for a DSN
The DISP parameter specifies what should happen to a data set after the job has finished executing. In this case, DISP=(NEW,CATLG,KEEP) means that a new data set should be created, cataloged, and retained after the job completes.
- "NEW" means that a new data set should be created. - "CATLG" means that the new data set should be cataloged. - "KEEP" means that the new data set should be kept after the job completes.
This DISP parameter is often used when creating new output files that need to be retained for future reference.If you have seven tasks to complete and you want to do one of them simultaneously, how can you achieve this?
Checking for Empty Files in JCL
In JCL, the best way to check if a file is empty is by using a conditional statement in the Job Control Language. This can be accomplished by including an IF statement before the step where the empty file is being processed.
Here is an example IF statement that checks if a file is empty:
//STEP1 EXEC PGM=IEFBR14
//INFILE DD DSN=MY.INPUT.FILE,DISP=SHR
//OUTFILE DD DSN=MY.OUTPUT.FILE,DISP=(NEW,CATLG,DELETE),
//SYSIN DD *
IF (INFILE,GT,0) THEN
//STEP2 EXEC PGM=MYPROG
//INDD DD DSN=MY.INPUT.FILE,DISP=SHR
//OUTDD DD DSN=MY.OUTPUT.FILE,DISP=(MOD),UNIT=SYSDA,
In this example, the IF statement checks if the input file INFILE has a record count greater than 0. If it does, the JCL job will proceed to execute STEP2, where the file will be processed. If the file is empty, the IF statement will evaluate to false, and the JCL job will skip over STEP2 and continue processing subsequent steps, if any.
This method allows you to avoid processing empty files, which can save time and resources.