Dear Manikandan,

Please accept our sincere apologies for the delay in response.

Below are the answers of your queries:

(i) What is DNS record type?

Ans : DNS stands for Domain Name System, which is the largest digital database in the world, containing information about every web site on the internet. DNS records are basically mapping files that tell the DNS server which IP address each domain is associated with, and how to handle requests sent to each domain. When someone visits a web site, a request is sent to the DNS server and then forwarded to the web server provided by a web hosting company, which contain the data contained on the site. Various strings of letters are used as commands that dictate the actions of the DNS server, and these strings of commands are called DNS syntax.  Various strings of letters are used as commands that dictate the actions of the DNS server, and these strings of commands are called DNS syntax. 
(ii) What you means by Linux Bootup Process.

Linux Bootup process is the multi-stage initialization process performed during booting a Linux installation. It is in many ways similar to the BSD and other Unix-style boot processes, from which it derives.  Booting a Linux installation involves multiple stages and software components, including firmware initialization, execution of a boot loader, loading and startup of a Linux kernel image, and execution of various startup scripts and daemons. For each of these stages and components there are different variations and approaches; for example, GRUB, LILO, SYSLINUX or Loadling can be used as boot loaders, while the startup scripts can be either traditional init-style, or the system configuration can be performed through modern alternatives such as system or Upstart.

(iii) What is sync command in Linux and why it is used?

Sync writes any data buffered in memory out to disk. This can include  modified superblocks, modified inodes, and delayed reads and writes. This must be implemented by the kernel. 
The kernel keeps data in memory to avoid doing disk reads and writes. This improves performance, but if the computer crashes, data may be lost or the filesystem corrupted as a result. Sync ensures that everything in memory is written to disk.

What is the use for fuser?

fuser displays the PIDs of processes using the specified files or file systems. It returns a non-zero return code if none of the specified files is accessed or in case of a fatal error. If at least one access has been found, fuser returns zero. In the default display mode, each file name is followed by a letter denoting the type of access:

c    current directory

e    executable being run

f     open file. f is omitted in default display mode

r     root directory

(v) What are the methods to check the linux server is healthy or not?

Ans: Below are the Commands which are used to Monitor the Linux Servers:

(a) Top - Linux Process Monitoring

Linux Top command is a performance monitoring program which is used frequently by many system administrators to monitor Linux performance and it is available under many Linux/Unix like operating systems. The top command used to display all the running and active real-time processes in ordered list and updates it regularly. It display CPU usage, Memory usage, Swap Memory, Cache Size, Buffer Size, Process PID, User, Commands etc.

(b) VmStat – Virtual Memory Statistics

Linux VmStat command used to display statistics of virtual memory, kernerl threads, disks, system processes, I/O blocks, interrupts, CPU activity and much more. By default vmstat command is not available under Linux systems you need to install a package called sysstat that includes a vmstat program.

(c) Lsof – List Open Files

Lsof command used in many Linux/Unix like system that is used to display list of all the open files and the processes. The open files included are disk files, network sockets, pipes, devices and processes. One of the main reason for using this command is when a disk cannot be unmounted and displays the error that files are being used or opened. With this command you can easily identify which files are in use.

(d) Tcpdump – Network Packet Analyzer

Tcpdump one of the most widely used command-line network packet analyzer or packets sniffer program that is used capture or filter TCP/IP packets that received or transferred on a specific interface over a network. It also provides a option to save captured packages in a file for later analysis. tcpdump is almost available in all major Linux distributions.

(e)  Netstat – Network Statistics

Netstat is a command line tool for monitoring incoming and outgoing network packets statistics as well as interface statistics. It is very useful tool for every system administrator to monitor network performance and troubleshoot network related problems

(f)  Htop – Linux Process Monitoring

Htop is a much advanced interactive and real time Linux process monitoring tool. This is much similar to Linux top command but it has some rich features like user friendly interface to manage process, shortcut keys, vertical and horizontal view of the processes etc.

(vi) Explain gzip. is it splittable?

Ans: gzip  command compresses the file and replaces it with the compressed version named "<File Name>.gz". The ".gz" file extension is commonly used by the compression programgzip, which is the counter part of gunzip. No, gzip is not Splittabel however BZIP2, LZO and LZ4 are Splittable.

(vii) What is CAP Theorem?
This theorem states that it is impossible for a distributed computer system to simultaneously provide all three of the following guarantees:
  • Consistency - It means that all nodes see the same data at the same time across the cluster, so you can read or write to/from any node and get the same data.
  • Availability - It means the ability to access the cluster even if a node in the cluster goes down. Every request receives a response about whether it succeeded or failed.
  • Partition tolerance - It means that the cluster continues to function even if there is a "partition" (communications break) between two nodes (both nodes are up, but can't communicate).

(viii) Explain about ACID in RDBMS

Ans: A transaction is a very small unit of a program and it may contain several low level tasks. A transaction in a database system must maintain Atomicity, Consistency, Isolation, and Durability, commonly known as ACID properties ,in order to ensure accuracy, completeness, and data integrity.

Atomicity − This property states that a transaction must be treated as an atomic unit, that is, either all of its operations are executed or none. There must be no state in a database where a transaction is left partially completed.

Consistency − The database must remain in a consistent state after any transaction. No transaction should have any adverse effect on the data residing in the database. If the database was in a consistent state before the execution of a transaction, it must remain consistent after the execution of the transaction as well.

Durability − The database should be durable enough to hold all its latest updates even if the system fails or restarts. If a transaction updates a chunk of data in a database and commits, then the database will hold the modified data. If a transaction commits but the system fails before the data could be written on to the disk, then that data will be updated once the system springs back into action.

Isolation − In a database system where more than one transaction are being executed simultaneously and in parallel, the property of isolation states that all the transactions will be carried out and executed as if it is the only transaction in the system. No transaction will affect the existence of any other transaction.
(xi) MSCK repair,
Ans: Hive stores a list of partitions for each table in its metastore. If, however, new partitions are directly added to HDFS (say by using hadoop fs -put command), the metastore (and hence Hive) will not be aware of these partitions unless the user runs ALTER TABLE table_name ADD PARTITION commands on each of the newly added partitions.
However, users can run a metastore check command with the repair table option:


which will add metadata about partitions to the Hive metastore for partitions for which such metadata doesn't already exist.

(x) CRUD operation

Ans: The CRUD cycle describes the elemental functions of a persistent database. CRUD stands for Create, Read, Update and Delete

Create or insert operations add new documents to a collection. If the collection does not currently exist, insert operations will create the collection.

The Read procedure reads the table records based on the primary key specified in the input parameter.

The Update procedure performs an UPDATE statement on the table based on the primary key for a record specified in the WHERE clause of the statement. Same as the Create procedure it has one parameter for every column in the table:

he Delete procedure deletes a row specified in the WHERE clause.

I hope this answers your query.

Please feel free to revert if you need any further help.