Linux interview technical questions

lest start with some Linux interview technical questions :

Basic Level 1 for freshers or < 2 yr exp..

Expert Level for lateral 

1.            What is Linux 

2.            Diff Linux & Unix 

3.            Diff RHEL 5/6 

4.            What's new in RHEL 7

5.            Linux boot process in brief 

6.            Port numbers on FTP 

7.            Port number of telnet, smtp, dns, dhcp, ntp, http, https

8.            How to check/edit other users cron entries

9.            What is user shell

10.          How to check available shells

11.          How to change your current shell 

12.           

DNS:

1.            What is DNS 

2.            How DNS works 

3.            Types of DNS

4.            Types of records in DNS 

5.            How to check DNS lookup 

6.            How to update DNS zone without service restart

7.            How to check any error in zone file

8.            What & Why NS record in DNS

9.            Master and slave how it's working 

10.          How to ensure updates send to slaves

11.          Static vs Dynamic DNS zones

12.          How to update dynamic zones & usages 

13.          Fields in zone file 

14.          reload for specifiz domain zone 

CRONTAB:

1.            What is crontab

2.            Fields in crontab

3.            Where is user specific cron file

4.            What is system specific cron, where are they defined  

5.            Use of /etc/crontab file 

6.            Eg. Schedule a script run every day at 11:00pm
      Schedule a script run every 2 minutes

Backup:

1.            Any backup tools you know?

2.            What is diff tar and zip 

3.            gzip pack and unpack 

4.            cat gzip file 

5.            bazip2 pack and unpack 

6.            cat bazip2 file 

7.            extract without effecting current file 

8.            extract to specific dir 

Yum & rpm:

   yum: 

1.            yum package name 

2.            Find current available repos

3.            Install from specific repo

4.            Install local rpm

5.            Find all available version of package

6.            Find when package was installed 

7.            Install a specific version of package 

8.            Check package integrity 

9.            Clear yum cache, required in which case example .

10.          Find package all files 

11.          How to setup YUM server 

12.          How to setup yum client

13.          How to setup yum proxy

    rpm:

1.            rpm package name 

2.            install/update/remove etc 

3.            Find when package last updated

4.            Find package info, files, dependencies 

5.            What is rpmdb

6.            how to re-build

Mail Server:

Do you have experience on any mail server ?

Postfix: 

1.            How Postfix or any mail server works 

2.            What is configuration file

3.            PORT Number 

4.            Check service running or not and listening on which IP

5.            How to send a test mail 

6.            Log file path

7.            Check mailq 

8.            Flush mailq

9.            Resend, force retry all mails in queue 

10.          How to handle maillog rotation 

11.          Listen on localhost why ?

12.          Listen is specific IP why ?

13.          Diff master and client setup basic 

14.          What is master.cf 

15.          Filter any specific user mail -> DISCARD

16.          Mail to specific user -> DISCARD 

17.          Allow mail sent to specific domain only 

18.          Allow only specific set of users to send mail 

19.          Allow mail form a specific subnet

20.          Minimum requirement to setup postfix mail server

21.          Sent mail lost troubleshooting steps .

Specification:

1.            Find Physical or Virtual

2.            Find System vendor name i,e Manufacturer name 

3.            Find total RAM  

4.            Find total swap

5.            Find total socket, Core, CPU's on server

6.            Find System serial number 

7.            Find HBA cards

Troubleshooting:

1.            Total current Load on server, how to check 

2.            What is load average, how and where to find and statics interval

3.            Total cpu utilization on server how to calculate

4.            Total memory utilization

5.            Total swap utilization 

6.            Add additional swap? how ?

7.            Which process consuming more CPU

8.            Which process consuming more RAM

9.            Which process consuming more SWAP

10.          Which process consuming more no of process 

11.          How to find total number of process thread initiated by a process 

12.          What is i/o on system, how to find 

13.          Which process causing high i/o

14.          Diff paging and caching 

15.          What is cpu steal time 

16.          What is memory over-commit

17.          Find troubleshoot memory leak

18.          How to enter in single user mode 

19.          diff single user and emergency mode 

20.          How to recover boot grub password 

21.          How to clear cache, why its required and what would be impact of this 

Boot level :

1.            How to set grub password

2.            How to set default kernel to boot 

3.            How to change kernel parameters during boot 

4.            How to repair FS 

5.            What is GRUB 

6.            Size of MBR, fields in MBR, PT size in MBR

7.            What is rescue mode 

8.            How to enter in rescue mode and why required example 

9.            Take MBR backup and repair 

Networking:

1.            How to assign IP address

2.            How to assign  virtual IP address

3.            How to assign temporary IP address

4.            How to change hostname permanent

5.            How to assign temporary hostname 

6.            What is Gateway

7.            How to assign Gateway 

8.            What is domainname 

9.            TCP vs UDP with example of each 

10.          OSI layer 

11.          How many virtual IP you can assign to a single interface .

12.          What is route table 

13.          How to update route table temporary 

14.          How to update route table permanent

15.          What is bonding

16.          How to setup network bonding for 2 interface 

17.          Mode of bonding 

18.          Steps of bonding 

19.          Check current status of bond interface 

20.          Check members of bond

21.          Bonding vs Bridging in Linux

22.          What is ARP

23.          What is network boot

24.          What is iptables

25.          Tables in iptables

26.          Write iptable to block use of sshd service via port 22 from outside of range 192.168.8.10-192.168.8.50

27.          What is tcpdump 

28.          tcpdump take dump of all packets coming from host1 and host 2 on port 3030 on ethernet eth2 and write to file /tmp/a.pcap

29.          Read tcpdump file 

30.          What is ip_forwarding 

Setup:

1.            How to install Linux RHEL/CentOS OS 

2.            Types of installation 

3.            What is PXE boot 

4.            What is network boot 

5.            Rapid Kickstart installation 

6.            Any other installation method you know 

Volume Management ( LVM ) :

1.            What is LVM 

2.            What is File system 

3.            Advantage of ext4 over ext3

4.            Advantage of xfs over ext4

5.            What are the fields in /etc/fstab

6.            Ex: create a LV of 5GB and mount of /test
Disk1: /dev/sda
Disk1: /dev/sdb
VG to create: VG01 with above 2 disk
LV: mytestlv
Mount with both dump & pass enabled ? What are these fields ?

7.            How to extend LV

8.            how to reduce LV

9.            How to extend VG

10.          how to reduce VG 

11.          How to take snap of LV

12.          How to destroy LV, VG, PV 

13.          Find number of PV's in VG

14.          Find free available size in VG

15.          Create LV with all availabel free size in VG

16.          Change VG parameters .  

Scripting:

1.            Do you have experience on any scripting language

2.            Bash shell scripting ?

3.            What is first line of script eg. "#! /bin/bash" and why it's there

4.            How to pass arguments in script 

5.            How to read arguments in script 

6.            How to define array 

7.            How to define float value

8.            How to define string

9.            How to print no of arguments passed in script 

10.          What is echo $#

11.          What is echo $@

12.          Print 1 to 10 in reverse order

13.          Synatx of for loop

14.          Syntax of while loop

15.          Syntax of if else

16.          Syntax of neted if else

17.          Syntax of case statement

18.          What is getopts

19.          What AWK stands

20.          AWK to print 3rd column

21.          Using grep find how many times word "HELLO" appear in file1

22.          Using egrep find if file1 contains HELLO1 and HELLO2

23.          Diff grep and egrep 

24.          Use sed to replace "hello" to "sello" in file

Others:

1.            USe of ip_farwording

2.            Where is config file of sshd service.

3.            What is tunnel

4.            What is mutt

5.            Fields in top command meanings

6.                1>load average 2> %id     3> Mem: 4> SWAP

7.            What is the use of swap partition

8.            Can we increase swap partition size how

9.            Syntax of for loop in bash

10.          Can we change vsftpd default directory location

11.          Can we change Default Directory in apache

12.          Can we use index.php insted of index.html as default page in apache how .

13.          visudo command will open file?

14.          Diff RHEL & Centos

15.          Diff LILO GRUB

16.          Advantages of GRUB

17.          What is iptables, Firewall, netfilter ..?

18.          What is cluster & virtualizaton just basic, what you understand by term..