Mainframe Interview Questions and Answers in 2025 (100+ Q&A)

Mainframe Tech Architect

Ques:- What could be the disposition parameter that i would have to use in the jcl if i have a file that has to be created newly for every successful run of the program ,but at the same time it should retain the old data if my program abend in the middle and res

Asked In :-

Right Answer:
Use the disposition parameter `DISP=(NEW,CATLG,DELETE)` for the dataset in the JCL.

Mainframe Tech Architect

Ques:- What is a GDG? How is it referenced? How is it defined? What is a MODELDSCB? GDG stands for generation data group. It is a dataset with versions that can be referenced absolutely or relatively. It is defined by an IDCAMS define generation datagroup execut

Asked In :-

Right Answer:
A GDG (Generation Data Group) is a dataset that contains multiple versions (generations) of data. It is defined using the IDCAMS utility with the command `DEFINE GDG`. GDGs can be referenced absolutely using the full dataset name or relatively using the generation number (e.g., `GDG(+1)` for the most recent generation). A MODELDSCB is a data set control block that defines the attributes of the GDG's generations.

Mainframe Team Lead/ Tech Lead

Ques:- How do you override a specific DDNAME/SYSIN in PROC from a JCL?

Asked In :- Magma HDI General Insurance,

Right Answer:
To override a specific DDNAME/SYSIN in a PROC from a JCL, you can specify the DD statement with the same DDNAME in the JCL that calls the PROC. For example:

```
//STEPNAME EXEC PGM=YOURPROGRAM
//SYSIN DD DSN=YOUR.INPUT.DATASET,DISP=SHR
```

This will override the SYSIN DDNAME defined in the PROC with the specified dataset in the JCL.

Mainframe Team Lead/ Tech Lead

Ques:- What is S322 abend ?

Asked In :-

Right Answer:
S322 abend occurs when a task is trying to access a resource that is not available, typically due to a timeout waiting for a resource that is not being released.

Mainframe Team Lead/ Tech Lead

Ques:- What does the TIME parameter signify ? What does TIME=1440 mean ?

Asked In :- i&m bank,

Right Answer:
The TIME parameter specifies the maximum amount of CPU time that a job or step can use. TIME=1440 means the job can run for a maximum of 1440 minutes, which is equivalent to 24 hours.

Mainframe Team Lead/ Tech Lead

Ques:- What is NOTCAT 2 ?

Asked In :-

Right Answer:
NOTCAT 2 is a type of dataset in IBM's mainframe environment used for storing and managing data in a specific format, primarily associated with the processing of non-cataloged datasets.

Mainframe Team Lead/ Tech Lead

Ques:- What does IEBGENER do?

Asked In :- TCS NextStep,

Right Answer:
IEBGENER is a utility in IBM's z/OS operating system used for copying data sets, generating reports, and performing data manipulation tasks. It can read from and write to various types of data sets, including sequential and partitioned data sets.

Mainframe Team Lead/ Tech Lead

Ques:- A PROC has five steps. Step 3 has a condition code. How can you override/nullify this condition code?

Asked In :-

Right Answer:
You can override/nullify the condition code of Step 3 by using the `COND` parameter in the subsequent steps. Set `COND=(0,LE)` for the steps that follow Step 3 to ensure they execute regardless of the condition code from Step 3.

Mainframe Team Lead/ Tech Lead

Ques:- How do you check the syntax of a JCL without running it?

Asked In :-

Right Answer:
You can check the syntax of a JCL without running it by using the JCL CHECK command or by submitting the JCL to a utility like IEBGENER with the SYSOUT parameter set to a dataset, which will validate the syntax without executing the job.

Mainframe Team Lead/ Tech Lead

Ques:- What is a S0C4 error ?

Asked In :-

Right Answer:
A S0C4 error occurs in a mainframe environment when a program tries to access an invalid memory address, typically due to a pointer or address being incorrect or uninitialized.

Mainframe Team Lead/ Tech Lead

Ques:- How do you send the output of a COBOL program to a member of a PDS?

Asked In :-

Right Answer:
To send the output of a COBOL program to a member of a PDS, you can use the following steps:

1. Define the output dataset in the JCL with the DSN pointing to the PDS member, using the `DISP` parameter appropriately.
2. In the COBOL program, use the `OUTPUT` statement to write to the defined dataset.
3. Ensure that the PDS member is created or updated by specifying the correct member name in the DSN.

Example JCL snippet:
```
//STEP01 EXEC PGM=YOURCOBOLPROGRAM
//SYSPRINT DD SYSOUT=*
//OUTPUT DD DSN=YOUR.PDS(MEMBERNAME),
// DISP=(NEW,CATLG,DELETE),
// SPACE=(TRK,(1,1)),
// DCB=(RECFM=FB,LRECL=80,BLKSIZE=800)
//SYSIN DD *
```
Make sure to replace `YOURCOBOL

Mainframe Team Lead/ Tech Lead

Ques:- What is COND=EVEN ?

Asked In :-

Right Answer:
COND=EVEN is a condition code used in JCL (Job Control Language) that indicates the job step should always execute, regardless of the condition codes from previous steps. It allows the step to run even if previous steps completed with a non-zero return code.

Mainframe Team Lead/ Tech Lead

Ques:- How do you skip a particular step in a proc/JOB?

Asked In :-

Right Answer:
You can skip a particular step in a PROC or JOB by using the `COND` parameter in the JOB statement or the `IF` statement in the PROC. For example, you can set `COND=(0,LT,STEPNAME)` to skip the step if the specified condition is met. Alternatively, you can use the `SKIP` parameter in the step definition to bypass it.

Mainframe Team Lead/ Tech Lead

Ques:- What is 'S0C7' abend?

Asked In :-

Right Answer:
S0C7 abend is a type of error in IBM mainframe systems that occurs when a program tries to use invalid data, typically due to a data exception like a non-numeric character in a numeric field.

Mainframe Team Lead/ Tech Lead

Ques:- What are SD37, SB37, SE37 abends?

Asked In :-

Right Answer:
SD37, SB37, and SE37 are types of abends (abnormal ends) in mainframe systems related to dataset handling:

- **SD37**: Occurs when a program tries to write to a dataset that is full (out of space).
- **SB37**: Happens when a dataset is full and cannot accommodate more data during a batch job.
- **SE37**: Indicates that a program has attempted to write to a dataset that is not allocated or does not exist.

Mainframe Team Lead/ Tech Lead

Ques:- What are common DLI functions?

Asked In :-

Right Answer:
Common DLI functions include:

1. **Get Unique (GU)** - Retrieves a single record.
2. **Get Next (GN)** - Retrieves the next record in a sequence.
3. **Insert (IS)** - Adds a new record to the database.
4. **Update (UPD)** - Modifies an existing record.
5. **Delete (DL)** - Removes a record from the database.
6. **Get First (GF)** - Retrieves the first record in a dataset.
7. **Get Last (GL)** - Retrieves the last record in a dataset.

Mainframe System Security Engineer

Ques:- Describe the DD statement, its meaning, syntax and keywords

Asked In :-

Right Answer:
The DD (Data Definition) statement in JCL (Job Control Language) is used to define the data sets that a job will use. It specifies the attributes of the data sets, such as their names, types, and other characteristics.

**Syntax:**
```
DD statement
//ddname DD keyword1=value1, keyword2=value2, ...
```

**Keywords:**
- `DSN=`: Specifies the data set name.
- `DISP=`: Indicates the status of the data set (e.g., NEW, SHR).
- `SPACE=`: Defines the space allocation for the data set.
- `UNIT=`: Specifies the device type (e.g., SYSDA).
- `LABEL=`: Defines the label for the data set.
- `DCB=`: Specifies the Data Control Block parameters for the data set.

These keywords help in defining how the job interacts with the specified data sets.

Mainframe Team Lead/ Tech Lead

Ques:- How do you calculate record size of an alternate cluster? Give your values for both unique and non-unique.

Asked In :-

Right Answer:
To calculate the record size of an alternate cluster, you can use the following formulas:

1. **For Unique Records:**
Record Size = (Length of Key + Length of Data + Length of Control Information)

2. **For Non-Unique Records:**
Record Size = (Length of Key + Length of Data + Length of Control Information + Length of Duplicate Indicator)

Make sure to substitute the actual lengths based on your specific data definitions.

Mainframe System Security Engineer

Ques:- Why we use export-import over repro?

Asked In :-

Right Answer:
We use export-import over repro because it allows for more flexibility in transferring data between different environments, supports selective data movement, and can handle complex dependencies better than repro.

Mainframe System Security Engineer

Ques:- What is DISP=(NEW,PASS,DELETE)?

Asked In :-

Right Answer:
DISP=(NEW,PASS,DELETE) is a JCL (Job Control Language) parameter that specifies the disposition of a dataset. It indicates that a new dataset should be created (NEW), that it should be passed to subsequent steps in the job (PASS), and that it should be deleted after the job completes (DELETE).

The Mainframe category on takluu.com is designed for IT professionals preparing for interviews related to mainframe computing environments. Mainframes are large, powerful computers that handle vast amounts of data and support critical business operations with exceptional uptime and performance.

This category covers key mainframe components and technologies including z/OS operating system, JCL (Job Control Language), COBOL programming, CICS transaction processing, DB2 databases, VSAM files, TSO/ISPF interfaces, and system utilities. Understanding how these components work together to manage batch processing, online transaction processing, and data storage is crucial for many enterprise jobs.

Candidates will find interview questions focusing on job scheduling, debugging batch jobs, dataset management, system commands, performance tuning, and security protocols. Real-time problem-solving scenarios and practical tips for efficient mainframe operations are also included to help you prepare thoroughly.

Mainframe roles often demand knowledge of legacy systems combined with the ability to integrate with modern IT infrastructure, including cloud technologies and automation tools. Whether you are a fresher entering the mainframe domain or an experienced professional upgrading your skills, this category offers comprehensive resources to boost your confidence and technical knowledge.

At Takluu, we provide well-structured content, detailed explanations, and mock interview questions tailored to the demands of mainframe job interviews. Our goal is to help you demonstrate your expertise and secure your dream role in industries that rely heavily on mainframe computing.

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