Application Support Engineer

1) LVM (Logical Volume Management) is basically a tool that provides logical volume management for the Linux kernel. It is being introduced simply to make physical storage device management easier. 

2) It also includes allocating disks, striping, mirroring, resizing logical volumes. Its main advantages are increased abstraction, flexibility, and control. 

3) It simply allows for flexible disk space management. It is especially required to resize the size of the file system online. 

4) In Linux, the size of the LVM partition can be extended using “lvextend” command and can be reduced using “lvreduce” commands, respectively.

Proc file system is a pseudo or virtual file system that provides an interface to the kernel data structure. It generally includes useful information about processes that are running currently. It can also be used to change some kernel parameters at runtime or during execution. It is also regarded as a control and information center for the kernel. All files under this directory are named virtual files.

By using "df" command in UNIX. For example "df -h ." will list how full your current drive is.

grep -i july *
The option i make the grep command to treat the pattern as case insensitive.

The 644 represents permission 110 for the owner, permission 100 for the group, and 100 for others which means read + write for an owner who creates that file, and read-only permission for the group and others.

You can use the lsof (list open files) command to find out the process which has a file handle on the particular file. It's a very useful command to check which process is reading a file. You can use the lsof command as shown below to find out all the processes :

$ lsof /home/someuser/somefile

This will list all the process which has opened this file. you can see the command, PID, user, and full file path to find out the process.

Linux operating system basically consists of 3 components. They are:

1) Kernel: This is considered as the core part and is responsible for all major activities of the Linux operating system. Linux Kernel is considered as free and open-source software that is capable of managing hardware resources for the users. It consists of various modules and interacts directly with the underlying hardware.


2) System Library: Most of the functionalities of the operating system are implemented by System Libraries. These act as a special function using which application programs accesses Kernel’s features.


3) System Utility: These programs are responsible for performing specialized, individual-level tasks.

1) Install crontab : crontab -a filename
2) Edit the crontab : crontab -e
3) Command to view crontab entries of current user : crontab -l
4) To remove your crontab tasks : crontab -r
5) Command to execute a cron after every 5 minutes : */5* * * * * /scripts/script.sh

General Syntax for cron : minute(s) hour(s) day(s) month(s) weekday(s) command(s) "Argument1" "Argument2"
If you don't have parameter put star(*) 

Description of Cron fields : 

minute(0-59) : The exact minute that the command sequence executes
hour (0-23) : The hour of the day that the command sequence executes
day(1-31) : The day of the month that the command sequence executes
month(1-12) : The month of the year that the command sequence executes
weekday(0-6) : The day of the week that the command sequence executes (Sunday = 0, Monday = 1, Tuesday = 2, and so forth)
command(s) : File Path Absolute path CronFile
Argument : Argument (IF you want to pass an argument)


Example : 0 5 * * mon /scripts/script.sh ==> Cron scheduler command helps you to execute the task on every Monday at 5 AM.

The pipe is generally a connection among two or more processes that are interrelated to each other. It is a mechanism that is used for inter-process communication using message passing. One can easily send information such as the output of one program process to another program process using a pipe. It can be used when two processes want to communicate one-way i.e., inter-process communication (IPC).

1) ls -> Lists files in current directory
2) cd -> Change directory to tempdir
3) mkdir -> Make a directory called graphics
4) rmdir -> Remove directory (must be empty)
5) cp -> Copy file into directory

These are file management commands. These are used for :

chmod - It changes the permission set of a file
chown - It changes the ownership of the file.
chgrp - It changes the group of the file.

Example :
$ chmod g+w test
It changes permission for a user group to write.

$ chown adas1923 testfile
It changes the owner of testfile to adas1923.

$ chgrp moderators testfile
It changes a group of testfile to moderators.

A database cursor is a control structure that allows for the traversal of records in a database. Cursors, in addition,
facilitates processing after traversal, such as retrieval, addition, and deletion of database records. They can be
viewed as a pointer to one row in a set of rows.

Working with SQL Cursor:

1) DECLARE a cursor after any variable declaration. The cursor declaration must always be associated with a
SELECT Statement.

2) Open cursor to initialize the result set. The OPEN statement must be called before fetching rows from the result
set.

3) FETCH statement to retrieve and move to the next row in the result set.

4) Call the CLOSE statement to deactivate the cursor.

5) Finally use the DEALLOCATE statement to delete the cursor definition and release the associated resources.

Approach : Sort the distinct salary in descend order and then utilize the LIMIT clause to get the second highest salary.

Query :

SELECT DISTINCT Salary
FROM Employee
ORDER BY Salary DESC
LIMIT 1 OFFSET 1;

DROP command is a DDL command which is used to drop/delete the existing table, database, index or view from the
database.

The major difference between DROP, TRUNCATE and DELETE commands are :

DROP and TRUNCATE commands are the DDL commands which are used to delete tables from the database and
once the table gets deleted, all the privileges and indexes that are related to the table also get deleted. These 2
operations cannot be rolled back and so should be used only when necessary.

DELETE command, on the other hand, is a DML Command which is also used to delete rows from the table and this
can be rolled back.

Normalization is a process of reducing redundancy by organizing the data into multiple tables. Normalization leads to
better usage of disk spaces and makes it easier to maintain the integrity of the database.


Denormalization is the reverse process of normalization as it combines the tables which have been normalized into a
single table so that data retrieval becomes faster. JOIN operation allows us to create a denormalized form of the data
by reversing the normalization.

Method 1 – Taking a Backup of a MySQL Table Using INSERT INTO

CREATE TABLE table_backup;
INSERT INTO table_backup SELECT * FROM table;

This method creates the structure of the table including indexes and then loading the data in via one statement.


Method 2 – Taking a Backup of a MySQL Table Using mysqldump

mysqldump -u{backup_user} -p{backup_password} from_db_name table_to_backup > backup_file.sql

The backup is taken using mysqldump and can be directed to a location of choice. Disk space is therefore not a
consideration for the data drive, rather it is necessary just for the location being backed up to.

Tip : For an experienced professional seeking a change, this is a common question. The easiest method to respond
to this question is to state that you are leaving your current work in order to advance your career. Make sure you don't
criticize or speak poorly about the company where you now work

If you get this question, it's an opportunity to choose the most compelling information to share that is not obvious from
your resume.

Example :

Strength -> I believe that my greatest strength is the ability to solve problems quickly and efficiently, which makes me
unique from others.

Ability to Handle Pressure -> I enjoy working under pressure because I believe it helps me grow and become more
efficient .


Tip : Emphasize why you were inspired to apply for the job. You can also explain that you are willing to invest a great
deal of energy if hired.

These are generally very open ended questions and are asked to test how quick wit a candidate is. So there is
nothing to worry about if you have a good command over your communication skills and you are able to propagate
your thoughts well to the interviewer.