11 Basic Linux Interview Questions and Answers

Theories apart, we are proud to announce a new section on Tecmint, dedicated to Linux Interview. Here we will bring to you Linux Interview Questions and all other aspects of Linux, which is must for a professional in this cut-throat competition world.

A new article in this section (Linux Interview) will be posted on every weekend. The initiative taken by Tecmint is first of it’s kind among other Linux Dedicated websites, along with quality and unique articles.

We will start with Basic Linux Interview Question and will go advance article by article, for which your response is highly appreciated, which put us on a higher note.

Q.1: What is the core of Linux Operating System?

1. Shell
2. Kernel
3. Command
4. Script
5. Terminal

Q.2: What Linus Torvalds Created?

1. Fedora
2. Slackware
3. Debian
4. Gentoo
5. Linux

Q.3: Torvalds, Wrote most of the Linux Kernel in C++ programming Language, do you agree?

The remaining Lines of code 1,972,615 is written in C++, Assembly, Perl, Shell Script, Python, Bash Script, HTML, awk, yacc, lex, sed, etc.

Note : The Number of Lines of codes varies on daily basis and an average of more than 3,509 lines are being added to Kernel.

Q.4: Linux initially was developed for intel X86 architecture but has been ported to other hardware platform than any other Operating System. Do you agree?.

Q.5: Is it legal to edit Linux Kernel?

Q.6: What is the basic difference between UNIX and Linux Operating System.

Q. 7: Choose the odd one out.

1. HP-UX
2. AIX
3. OSX
4. Slackware
5. Solaris

Q.8: Is Linux Operating system Virus free?

Q.9: Linux is which kind of Operating System?

1. Multi User
2. Multi Tasking
3. Multi Process
4. All of the above
5. None of the above

Q.10: Syntax of any Linux command is:

1. command [options] [arguments]
2. command options [arguments]
3. command [options] [arguments]
4. command options arguments

Q.11: Choose the odd one out.

1. Vi
2. vim
3. cd
4. nano

That’s all for now. How much you learned for the above questions? How it helped you in your Interview? We would like to hear all these from you in our comment section. Wait till the next weekend, for new set of questions.

Basic Linux Interview Questions and Answers – Part II

Continuing the Interview Series, we are giving 10 Questions here, in this article. These questions and the questions in the future articles doesn’t necessarily means they were asked in any interview. We are presenting you an interactive learning platform through these kind of posts, which surely will be helpful.

Upon the analysis of comments in different forums on last article 11 Basic Linux Interview Questions of this series, it is important to mention here that to bring up a quality article to our readers. We give our time and money, and in return what we expect from you? Nothing. If you can’t praise our work, please don’t demoralize us from your negative comments.

If you find nothing new in a post, don’t forget that for someone it was helpful, and for that he/she was thankful. We can’t make everyone happy in each of our article. Hope you readers would take pain to understand this.

Q.1: Which command is used to record a user login session in a file?

1. macro
2. read
3. script
4. record
5. sessionrecord

Let’s record the user’s login session with script command as shown.

[root@tecmint ~]# script my-session-record.txt

Script started, file is my-session-record.txt

The content of log file ‘my-session-record.txt’ can be views as:

[root@tecmint ~]# nano my-session-record.txt

script started on Friday 22 November 2013 08:19:01 PM IST
[root@tecmint ~]# ls
^[[0m^[[01;34mBinary^[[0m ^[[01;34mDocuments^[[0m ^[[01;34mMusic^[[0m $
^[[01;34mDesktop^[[0m ^[[01;34mDownloads^[[0m my-session-record.txt ^[[01;34$

Q.2: The kernel log message can be viewed using which of the following command?

1. dmesg
2. kernel
3. ls -i
4. uname
5. None of the above

[root@tecmint ~]# dmesg

Initializing cgroup subsys cpuset
Initializing cgroup subsys cpu
Linux version 2.6.32-279.el6.i686 (mockbuild@c6b9.bsys.dev.centos.org) (gcc version 4.4.6 20120305 (Red Hat 4.4.6-4) (GCC) ) #1 SMP Fri Jun 22 10:59:55 UTC 2012
KERNEL supported cpus:
  Intel GenuineIntel
  AMD AuthenticAMD
  NSC Geode by NSC
  Cyrix CyrixInstead
  Centaur CentaurHauls
  Transmeta GenuineTMx86
  Transmeta TransmetaCPU
  UMC UMC UMC UMC
Disabled fast string operations
BIOS-provided physical RAM map:
...

Q.3: Which command is used to display the release of Linux Kernel?

1. uname -v
2. uname -r
3. uname -m
4. uname -n
5. uname -o

[root@tecmint ~]# uname -r

2.6.32-279.el6.i686

Q.4: Which command is used to identify the types of file?

1. type
2. info
3. file
4. which
5. ls

[root@tecmint ~]# file wtop

wtop: POSIX shell script text executable

Q.5: Which command locate the binary, source and man page of a command?

[root@tecmint ~]# whereis /usr/bin/ftp

ftp: /usr/bin/ftp /usr/share/man/man1/ftp.1.gz

Q.6: When a user login, which files are called for user profile, by default??

[root@tecmint ~]# ls -al
-rw-r--r--.  1 tecmint     tecmint            176 May 11  2012 .bash_profile
-rw-r--r--.  1 tecmint     tecmint            124 May 11  2012 .bashrc

Q.7: The ‘resolv.conf’ file is a configuration file for?

[root@tecmint ~]# cat /etc/resolv.conf

nameserver 172.16.16.94

Q.8: Which command is used to create soft link of a file?

1. ln
2. ln -s
3. link
4. link -soft
5. None of the above

[root@tecmint ~]# ln -s /etc/httpd/conf/httpd.conf httpd.original.conf

Q.9: The command ‘pwd’ is an alias of command ‘passwd’ in Linux?

[root@tecmint ~]# pwd

/home/tecmint

[root@tecmint ~]# passwd
Changing password for user root.
New password:
Retype new password:

Q.10: How will you check pci devices vendor and version on a Linux?

[root@tecmint ~]# lspci

00:00.0 Host bridge: Intel Corporation 5000P Chipset Memory Controller Hub (rev b1)
00:02.0 PCI bridge: Intel Corporation 5000 Series Chipset PCI Express x8 Port 2-3 (rev b1)
00:04.0 PCI bridge: Intel Corporation 5000 Series Chipset PCI Express x8 Port 4-5 (rev b1)
00:06.0 PCI bridge: Intel Corporation 5000 Series Chipset PCI Express x8 Port 6-7 (rev b1)
00:08.0 System peripheral: Intel Corporation 5000 Series Chipset DMA Engine (rev b1)
...

That’s all for now. I hope these above questions might be very helpful to you. In our next weekend we again come-up with some new set of questions.

10 Linux Interview Questions and Answers for Linux Beginners – Part 3

Continuing the Interview Questions series, with a big thanks for the nice feedback on last two articles of this series, we are here presenting 10 questions again for interactive learning.

1. 11 Basic Linux Interview Questions and Answers – Part 1
2. 10 Basic Linux Interview Questions and Answers – Part II

1. How will you add a new user (say, tux) to your system.?

1. useradd command
2. adduser command
3. linuxconf command
4. All of the above
5. None of the above

2. How many primary partition is possible on one drive?

1. 1
2. 2
3. 4
4. 16

3. The default port for Apache/Http is?

1. 8080
2. 80
3. 8443
4. 91
5. None of the above.

4. What does GNU stand for?

1. GNU’s not Unix
2. General Unix
3. General Noble Unix
4. Greek Needed Unix
5. None of the above

5. You typed at shell prompt “mysql” and what you got in return was “can’t connect to local MySQL server through socket ‘/var/mysql/mysql.sock’”, what would you check first.

Note:The above error message can be the result of ill configured my.cnf or mysql user permission. If mysql service starting doesn’t help, you need to see into the above said issues.

6. How to Mount a windows ntfs partition on Linux?

7. From the following which is not an RPM based OS.?

1. RedHat Linux
2. Centos
3. Scientific Linux
4. Debian
5. Fedora

8. Which command can be used to rename a file in Linux.?

1. mv
2. ren
3. rename
4. change
5. None of the Above

9. Which command is used to create and display file in Linux?

1. ed
2. vi
3. cat
4. nano
5. None of the above

10. What layer protocol is responsible for user and the application program support such as passwords, resource sharing, file transfer and network management?

1. Layer 4 protocols
2. Layer 5 protocols
3. Layer 6 protocols
4. Layer 7 protocols
5. None of the above

That’s all for now. I will be writing on another useful topic soon.

15 Basic MySQL Interview Questions for Database Administrators

Prior to This Article, three articles has already been published in ‘Linux Interview‘ Section and all of them were highly appreciated by our notable readers, however we were receiving feedback to make this interactive learning process, section-wise. From idea to action, we are providing you 15 MySQL Interview Questions.

1. How would you check if MySql service is running or not?

root@localhost:/home/avi# service mysql status

/usr/bin/mysqladmin  Ver 8.42 Distrib 5.1.72, for debian-linux-gnu on i486
Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Server version 5.1.72-2
Protocol version 10
Connection Localhost via UNIX socket
UNIX socket /var/run/mysqld/mysqld.sock
Uptime: 1 hour 22 min 49 sec

Threads: 1  Questions: 112138  Slow queries: 1  Opens: 1485  Flush tables: 1  Open tables: 64  Queries per second avg: 22.567.

2. If the service is running/stop how would you stop/start the service?

root@localhost:/home/avi# service mysql stop

Stopping MySQL database server: mysqld.

root@localhost:/home/avi# service mysql start

Starting MySQL database server: mysqld.

Checking for corrupt, not cleanly closed and upgrade needing tables..

3. How will you login to MySQL from Linux Shell?

root@localhost:/home/avi# mysql -u root -p 
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g. 
Your MySQL connection id is 207 
Server version: 5.1.72-2 (Debian) 

Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved. 

Oracle is a registered trademark of Oracle Corporation and/or its 
affiliates. Other names may be trademarks of their respective 
owners. 

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. 

mysql>

4. How will you obtain list of all the databases?

mysql> show databases; 
+--------------------+ 
| Database           | 
+--------------------+ 
| information_schema | 
| a1                 | 
| cloud              | 
| mysql              | 
| phpmyadmin         | 
| playsms            | 
| sisso              | 
| test               | 
| ukolovnik          | 
| wordpress          | 
+--------------------+ 
10 rows in set (0.14 sec)

5. How will you switch to a database, and start working on that?

mysql> use cloud; 
Reading table information for completion of table and column names 
You can turn off this feature to get a quicker startup with -A 

Database changed 
mysql>

6. How will you get the list of all the tables, in a database?

mysql> show tables; 
+----------------------------+ 
| Tables_in_cloud            | 
+----------------------------+ 
| oc_appconfig               | 
| oc_calendar_calendars      | 
| oc_calendar_objects        | 
| oc_calendar_repeat         | 
| oc_calendar_share_calendar | 
| oc_calendar_share_event    | 
| oc_contacts_addressbooks   | 
| oc_contacts_cards          | 
| oc_fscache                 | 
| oc_gallery_sharing         | 
+----------------------------+ 
10 rows in set (0.00 sec)

7. How will you get the Field Name and Type of a MySql table?

mysql> describe oc_users; 
+----------+--------------+------+-----+---------+-------+ 
| Field    | Type         | Null | Key | Default | Extra | 
+----------+--------------+------+-----+---------+-------+ 
| uid      | varchar(64)  | NO   | PRI |         |       | 
| password | varchar(255) | NO   |     |         |       | 
+----------+--------------+------+-----+---------+-------+ 
2 rows in set (0.00 sec)

8. How will you delete a table?

mysql> drop table lookup; 

Query OK, 0 rows affected (0.00 sec)

9. What about database? How will you delete a database?

mysql> drop database a1; 

Query OK, 11 rows affected (0.07 sec)

10. How will you see all the contents of a table?

mysql> select * from engines; 
+------------+---------+----------------------------------------------------------------+--------------+------+------------+ 
| ENGINE     | SUPPORT | COMMENT                                                        | TRANSACTIONS | XA   | SAVEPOINTS | 
+------------+---------+----------------------------------------------------------------+--------------+------+------------+ 
| InnoDB     | YES     | Supports transactions, row-level locking, and foreign keys     | YES          | YES  | YES        | 
| MRG_MYISAM | YES     | Collection of identical MyISAM tables                          | NO           | NO   | NO         | 
| BLACKHOLE  | YES     | /dev/null storage engine (anything you write to it disappears) | NO           | NO   | NO         | 
| CSV        | YES     | CSV storage engine                                             | NO           | NO   | NO         | 
| MEMORY     | YES     | Hash based, stored in memory, useful for temporary tables      | NO           | NO   | NO         | 
| FEDERATED  | NO      | Federated MySQL storage engine                                 | NULL         | NULL | NULL       | 
| ARCHIVE    | YES     | Archive storage engine                                         | NO           | NO   | NO         | 
| MyISAM     | DEFAULT | Default engine as of MySQL 3.23 with great performance         | NO           | NO   | NO         | 
+------------+---------+----------------------------------------------------------------+--------------+------+------------+ 
8 rows in set (0.00 sec)

11. How will you see all the data in a field (say, uid), from table (say, oc_users)?

mysql> select uid from oc_users; 
+-----+ 
| uid | 
+-----+ 
| avi | 
+-----+ 
1 row in set (0.03 sec)

12. Say you have a table ‘xyz’, which contains several fields including ‘create_time’ and ‘engine’. The field ‘engine’ is populated with two types of data ‘Memory’ and ‘MyIsam’. How will you get only ‘create_time’ and ‘engine’ from the table where engine is ‘MyIsam’?

12. mysql> select create_time, engine from xyz where engine="MyIsam";

+---------------------+--------+ 
| create_time         | engine | 
+---------------------+--------+ 
| 2013-12-15 13:43:27 | MyISAM | 
| 2013-12-15 13:43:27 | MyISAM | 
| 2013-12-15 13:43:27 | MyISAM | 
| 2013-12-15 13:43:27 | MyISAM | 
| 2013-12-15 13:43:27 | MyISAM | 
| 2013-12-15 13:43:27 | MyISAM | 
| 2013-12-15 13:43:27 | MyISAM | 
| 2013-12-15 13:43:27 | MyISAM | 
| 2013-10-23 14:56:38 | MyISAM | 
| 2013-10-23 14:56:38 | MyISAM | 
| 2013-10-23 14:56:38 | MyISAM | 
| 2013-10-23 14:56:38 | MyISAM | 
| 2013-10-23 14:56:38 | MyISAM | 
| 2013-10-23 14:56:38 | MyISAM | 
| 2013-10-23 14:56:38 | MyISAM | 
+---------------------+--------+ 
132 rows in set (0.29 sec)

13. How will you show all the records from table ‘xrt’ where name is ‘tecmint’ and web_address is ‘tecmint.com’?

mysql> select  * from xrt where name = "tecmint" and web_address = “tecmint.com”;
+---------------+---------------------+---------------+ 
| Id                  | name                   | web_address | 
+---------------+---------------------+----------------+ 
| 13                 |  tecmint               | tecmint.com  |
+---------------+---------------------+----------------+ 
| 41                 |  tecmint               | tecmint.com  |
+---------------+---------------------+----------------+

14. How will you show all the records from table ‘xrt’ where name is not ‘tecmint’ and web_address is ‘tecmint.com’?

mysql> select * from xrt where name != ”tecmint” and web_address = ”tecmint.com”;

+---------------+---------------------+---------------+ 
| Id            | name                | web_address   | 
+---------------+---------------------+----------------+ 
| 1173          |  tecmint            | tecmint.com   |
+---------------+---------------------+----------------+

15. You need to know total number of row entry in a table. How will you achieve it?

mysql> select count(*) from Tables; 

+----------+ 
| count(*) | 
+----------+ 
|      282 | 
+----------+ 
1 row in set (0.01 sec)

Read Also : 10 MySQL Database Interview Questions Intermediates

That’s all for now. How you feel about this ‘Linux Interview Question‘ section. Don’t forget to provide us with your valuable feedback in our comment section.

25 Apache Interview Questions for Beginners and Intermediates

We are very thankful to All our readers for the response we are getting for our new Linux Interview section. And now we have started section wise learning for Interview questions and continuing with the same today’s article focuses on Basic to Intermediate Apache interview Questions that will help you to prepare yourself.

In this section, we have covered some interesting 25 Apache Job Interview Questions along with their answers so that you can easily understand some new things about Apache that you might never known before.

Before you read this article, We strongly recommend you to don’t try to memorize the answers, always first try to understand the scenarios on a practical basis.

1. What is Apache web server?

2. How to check Apache and it’s version?

[root@tecmint ~]# rpm -qa | grep httpd

httpd-devel-2.2.15-29.el6.centos.i686
httpd-2.2.15-29.el6.centos.i686
httpd-tools-2.2.15-29.el6.centos.i686

[root@tecmint ~]# httpd -v

Server version: Apache/2.2.15 (Unix)
Server built:   Aug 13 2013 17:27:11

3. Apache runs as which user? and location of main config file?.

4. On which port Apache listens http and https both?

[root@tecmint ~]# netstat -antp | grep http

tcp        0      0 :::80                       :::*                        LISTEN      1076/httpd          
tcp        0      0 :::443                      :::*                        LISTEN      1076/httpd

5. How do you install Apache Server on your Linux machine?

[root@tecmint ~]# yum install httpd

[root@tecmint ~]# apt-get install apache2

6. Where you can find all configuration directories of Apache Web Server?

[root@tecmint ~]# cd /etc/httpd/
[root@tecmint httpd]# ls -l
total 8
drwxr-xr-x. 2 root root 4096 Dec 24 21:44 conf
drwxr-xr-x. 2 root root 4096 Dec 25 02:09 conf.d
lrwxrwxrwx  1 root root   19 Oct 13 19:06 logs -> ../../var/log/httpd
lrwxrwxrwx  1 root root   27 Oct 13 19:06 modules -> ../../usr/lib/httpd/modules
lrwxrwxrwx  1 root root   19 Oct 13 19:06 run -> ../../var/run/httpd

[root@tecmint ~]# cd /etc/apache2
[root@tecmint apache2]# ls -l
total 84
-rw-r--r-- 1 root root  7113 Jul 24 16:15 apache2.conf
drwxr-xr-x 2 root root  4096 Dec 16 11:48 conf-available
drwxr-xr-x 2 root root  4096 Dec 16 11:45 conf.d
drwxr-xr-x 2 root root  4096 Dec 16 11:48 conf-enabled
-rw-r--r-- 1 root root  1782 Jul 21 02:14 envvars
-rw-r--r-- 1 root root 31063 Jul 21 02:14 magic
drwxr-xr-x 2 root root 12288 Dec 16 11:48 mods-available
drwxr-xr-x 2 root root  4096 Dec 16 11:48 mods-enabled
-rw-r--r-- 1 root root   315 Jul 21 02:14 ports.conf
drwxr-xr-x 2 root root  4096 Dec 16 11:48 sites-available
drwxr-xr-x 2 root root  4096 Dec  6 00:04 sites-enabled

7. Can Apache be secured with TCP wrappers?

8. How to change default Apache Port and How Listen Directive works in Apache?

Suppose you have multiple IPs assigned to your Linux machine and want Apache to receive HTTP requests on a special Ethernet port or Interface, even that can be done with Listen directive.

To change the Apache default port, please open your Apache main configuration file httpd.conf or apache2.conffile with VI editor.

[root@tecmint ~]# vi /etc/httpd/conf/httpd.conf

[root@tecmint ~]# vi /etc/apache2/apache2.conf

Search for the word ”Listen”, comment the original line and write your own directive below that line.

# Listen 80
Listen 8080

OR

Listen 172.16.16.1:8080

Save the file and restart the web server.

[root@tecmint ~]# service httpd restart

[root@tecmint ~]# service apache2 restart

9. Can we have two Apache Web servers on a single machine?

10. What do you mean by DocumentRoot of Apache?

11. How to host files in different folder and what is Alias directive?

To use Alias directive, Its the part of mod_alias module of Apache. The default syntax of Alias directive is:

Alias /images /var/data/images/

Here in above example, /images url prefix to the /var/data/images prefix that mean clients will query for “http://www.example.com/images/sample-image.png” and Apache will pick up the “sample-image.png” file from /var/data/images/sample-image.png on the server. It’s also known as URL Mapping.

12. What do you understand by “DirectoryIndex”?

The default setting of DirectoryIndex is .html index.html index.php, if you have different names of your first file, you need to make the changes in httpd.conf or apache2.conf for DirectoryIndex value to display that to your client browser.

#
# DirectoryIndex: sets the file that Apache will serve if a directory
# is requested.
#
# The index.html.var file (a type-map) is used to deliver content-
# negotiated documents.  The MultiViews Option can be used for the
# same purpose, but it is much slower.
#
DirectoryIndex index.html index.html.var index.cgi .exe

13. How to disable Directory listing when an index file is missing?

To stop Apache directory listing, you can set the following rule in the main configuration file globally or in .htaccess file for a particular website.

<Directory /var/www/html>
   Options -Indexes
</Directory>

14. What are different log files of Apache Web Server?

15. What do you understand by “connection reset by peer” in error logs?

16. What is Virtual Host in Apache?

You are free to add as many directives you require for your domain, but the two minimal entries for a working website is the ServerName and DocumentRoot. We usually define our Virtual Host section at the bottom of httpd.conf file in Linux machines.

Sample VirtualHost

<VirtualHost *:80>
   ServerAdmin webmaster@dummy-host.example.com
   DocumentRoot /www/docs/dummy-host.example.com
   ServerName dummy-host.example.com
   ErrorLog logs/dummy-host.example.com-error_log
   CustomLog logs/dummy-host.example.com-access_log common
</VirtualHost>

1. ServerAdmin : Its usually the email address of the website owner, where the error or notification can be sent.
2. DocumentRoot : location where the web files are located in the server(Necessary).
3. ServerName : Its the domain name which you want to access from your web browser(Necessary).
4. ErrorLog : Its the location of the log file where all the domain related logs are being recorded.

17. What’s the difference between <Location> and <Directory>?

18. What is Apache Virtual Hosting?

For more information, read on How to Create Name/IP based Virtual Hosts in Apache.

19. What do you understand by MPM in Apache?

20. What is the difference between Worker and Prefork MPM?

1. Basic difference between Worker and MPM is in their process of spawning the child process. In the Prefork MPM, a master httpd process is started and this master process starts manages all other child processes to serve client requests. Whereas, In the worker MPM one httpd process is active, and it uses different threads to serve client requests.
2. Prefork MPM uses multiple child processes with one thread each, where worker MPM uses multiple child processes with many threads each.
3. Connection handling in the Prefork MPM, each process handles one connection at a time, whereas in the Worker mpm each thread handles one connection at a time.
4. Memory footprints Prefork MPM Large memory footprints, where Worker has smaller memory footprints.

21. What’s the use of “LimitRequestBody” and how to put limit on your uploads?

For example: I want to put limits of 100000 Bytes in the folder /var/www/html/tecmin/uploads. So, you need to add following directive in Apache configuration file.

<Directory "/var/www/html/tecmint/uploads">
LimitRequestBody 100000
</Directory>

22. What is mod_perl and mod _php?

23. What is Mod_evasive?

For more information, read the article that guides you how to install and configure mod_evasive in Apache.

24. What is Loglevel debug in httpd.conf file?

25. What’s the use of mod_ssl and how SSL works with Apache?

How SSL works with Apache

Whenever an https requests comes, these three steps Apache follows:

1. Apache generates its private key and converts that private key to .CSR file (Certificate signing request).
2. Then Apache sends the .csr file to the CA (Certificate Authority).
3. CA will take the .csr file and convert it to .crt (certificate) and will send that .crt file back to Apache to secure and complete the https connection request.

These are just most popular 25 questions being asked these days by Interviewers, please provide some more interview questions which you have faced in your recent interview and help others via our Comment section below.

We are also recommend you to read our previous articles on Apache.

1. 13 Apache Web Server Security and Hardening Tips
2. How to Sync Two Apache Web Servers/Websites Using Rsync

10 MySQL Database Interview Questions for Beginners and Intermediates

In our last article, we’ve covered 15 Basic MySQL Questions, again we are here with another set interview questions for intermediate users. As we said earlier these questions can be asked in Job Interviews. But some of our critics on the last article said, that I don’t give response to my critics and the questions are very basic and will never be asked in any Database Administrator Interview.

To them we must admit all the articles and question can not be composed keeping all the flock in mind. We are coming from basic to expert level step by step. Please Co­operate with us.

1. Define SQL?

2. What is RDBMS? Explain its features?

3. What is Data Mining?

4. What is an ERD?

5. What is the difference between Primary Key and Unique Key?

6. How to store picture file in the database. What Object type is used?

7. What is Data Warehousing?

8. What are indexes in a Database. What are the types of indexes?

9. How many TRIGGERS are possible in MySql?

10. What is Heap table?

That’s all for now on MySQL questions, I will be coming up with another set of questions soon. Don’t forget to provide your valuable feedback in comment section.

10 Core Linux Interview Questions and Answers

Again its time to read some serious content in light mood, Yup! Its another article on Interview question and here we are presenting 10 Core Linux Questions, which surely will add to your knowledge.

1. You need to define a macro, a key binding for the existing command. How would you do it?

[root@localhost ~]# bind '"\e[24~":"date"'

Note : Different types of terminals or terminal emulators can emit different codes for the same key.

2. A user is new to Linux and he wants to know full list of available commands, what would you suggest him?

[root@localhost ~]$ compgen -c

l.
ll
ls
which
if
then
else
elif
fi
case
esac
for
select
while
until
do
done
...

3. Your assistant needs to print directory stack, what would you suggest?

[root@localhost ~]# dirs

/usr/share/X11

4. You have lots of running jobs, how would you remove all the running processes, without restarting the machine?

5. What does the command ‘hash’ is used for in bash Shell?

[root@localhost ~]# hash

hits    command
   2    /bin/ls
   2    /bin/su

6. Which built­in Linux command performs arithmetic operation of Integers in Bash?

#! /bin/bash

...

...

let c=a+b

...

...

7. You have a large text file, and you need to see one page at a time. What will you do?

[root@localhost ~]# cat file_name.txt | more

8. Who own the data dictionary?

9. How to know a command summary and useability in Linux?

Assume you came across a command in /bin directory, which you are completely unaware of, and have no idea what it does. What will you do to know its useability?

[root@localhost ~]# whatis zcat

zcat [gzip]          (1)  - compress or expand files

10. What command should you use to check the number of files and disk space used by each user’s defined quotas?

That’s all for now. Provide your valuable Feedback in our comment section. Stay tuned for more Linux and Foss posts.

10 VsFTP (Very Secure File Transfer Protocol) Interview Questions and Answers

FTP stands for ‘File Transfer Protocol‘ is one of the most widely used and standard protocol available over Internet. FTP works in a Server/­Client architecture and is used to transfer file. Initially FTP client were command-­line based. Now most of the platform comes bundled with FTP client and server program and a lot of FTP Client/Server Program is available. Here we are presenting 10 Interview Questions based on Vsftp (Very Secure File Transfer Protocol) on a Linux Server.

1. What is the Difference between TFTP and FTP Server?

Note: Briefly you can say FTP usages port 21 by default when clarification between Data and Control is not required.

2. How to Restrict Users and Disallow browsing beyond their Home Directories? How?

chroot_local_user=YES

3. How would you manage number of FTP clients that connect to your FTP server?

4. How to limit the FTP login attempts to fight against botnet/illegal login attempts?

5. How to enable file upload from anonymous users to FTP Server?

6. How would you disabled downloads from FTP server?

7. How to enable and permit FTP login to local users?

8. Is it Possible to maintain log of FTP requests and responses?

Note: In order to create and maintains logs successfully, the parameter ‘xferlog_std_format’ must be enabled.

9. How to disable the login for few seconds, in case of failed login. How will you achieve this?

10. How to display certain text message before a client connects to FTP server. How would you get this done?

FTP is a very Useful tool and is vast yet very interesting. Moreover it is useful from Interview Point of View. We have taken the pain to bring these questions to you and will cover more of these questions in our future article. Till then stay tuned and connected to Tecmint.

Read Also: 10 Advance VsFTP Interview Questions and Answers – Part II

10 Advance VsFTP Interview Questions and Answers – Part II

We were overwhelmed with the response we’ve received on our last article. Where we’ve presented 10 wonderful question on Very Secure File Transfer Protocol. Continuing VSFTP interview article we are here presenting you yet another 10 Advance Interview Questions which surely will help you.

1. 10 Basic Vsftp Interview Question/Answers – Part I

Please note vsftpd.conf file is used to control various aspects of configuration as specified in this article. By default, the vsftpd searches for the configuration file under /etc/vsftpd/vsftpd.conf. However, the format of file is very simple and it contains comment or directive. Comment lines begins with a ‘#‘ are ignored and a directive line has the following format.

option=value

Before we start the Question and their well explained Answer we would like to answer a question “Who is going to attend FTP Interview?”. Well no one. Perhaps no one would be attending FTP interview. But we are presenting subject wise questions to maintain a systematic approach so that in any Interview, you wont get a new question which you wont be knowing on any of the topics/subjects we covered here.

11. How would you block an IP which is acting malicious on your internal private VSFTP network?

Block IP using host.deny file

Open ‘/etc/hosts.deny’ file.

# vi /etc/hosts.deny

Append the following line at the bottom of the file with the IP address that you want to block access to FTP.

#
# hosts.deny    This file contains access rules which are used to
#               deny connections to network services that either use
#               the tcp_wrappers library or that have been
#               started through a tcp_wrappers-enabled xinetd.
#
#               The rules in this file can also be set up in
#               /etc/hosts.allow with a 'deny' option instead.
#
#               See 'man 5 hosts_options' and 'man 5 hosts_access'
#               for information on rule syntax.
#               See 'man tcpd' for information on tcp_wrappers
#
vsftpd:172.16.16.1

Block IP using iptables rule

To block FTP access to particular IP address, add the following drop rule to iptables INPUT chain.

iptables -A RH-Firewall-1-INPUT -p tcp -s 172.16.16.1 -m state --state NEW -m tcp --dport 21 -j DROP

12. How to allow secured SSL connections to Anonymous users? How would you do?

# Add this line to enable secured SSL connection to anonymous users.
allow_anon_ssl=YES

13. How to allow Anonymous users to create new directory and write to that directory?

# Uncomment this to enable any form of FTP write command.
write_enable=YES

# Uncomment this if you want the anonymous FTP user to be able to create
# new directories.
anon_mkdir_write_enable=YES

14. How to enable Anonymous downloads, but disable permission to write?

# Add this line to enable read only permission to anonymous users.
allow_anon_ssl=YES

15. How to CHMOD all Anonymous uploads automatically. How would you do?

# Add this line to chmod all anonymous uploads automatically.
chmod_enable=YES

16. How to disable directory listing in a FTP server?

# Add this line to disable directory listing.
dirlist_enable=NO

17. How to maintain sessions for logins of VSFTP. How will you do?

# Add this line to maintain session logins.
session_support=YES

18. How to display time in local time zone, when listing the contents of directory?

# Add this line to display directory listing in local time zone.
usr_localtime=YES

19. How will you limit the maximum transfer rate from VSFTP server?

# Add this line to limit the ftp transfer rate.
anon_max_rate=0 # 0 means unlimited

20. How will you timeout the idle session of VSFTP?

# Add this line to set the ftp timeout session.
idle_session_timeout=300

That’s all for now. We will be coming up with next article very soon, till then stay tuned and connected and don’t forget to provide us with your valuable feedback in our comment section.

10 Useful Random Linux Interview Questions and Answers

To a little surprise this time we are not presenting Interview question on any specific subject but on random topics. These question will surely help you in cracking Interviews beside adding to your Knowledge.

1. Let’s say you maintains a backup on regular basis for the company you are working. The backups are maintained in Compressed file format. You need to examine a log, two months old. What would you suggest without decompressing the compressed file?

# zcat ­f phpshell­2.4.tar.gz

2. You need to track events on your system. What will you do?

Running ‘syslogd‘ application in terminal generates log file at the location ‘/var/log/syslog‘. The syslogd application is very useful in troubleshooting Linux sytems. A sample log file looks similar to below.

3. How will you restrict IP so that the restricted IP’s may not use the FTP Server?

Block IP Address

Open ‘/etc/hosts.deny’ file.

# vi /etc/hosts.deny

Add the IP address that you want to block at the bottom of the file.

#
# hosts.deny    This file contains access rules which are used to
#               deny connections to network services that either use
#               the tcp_wrappers library or that have been
#               started through a tcp_wrappers-enabled xinetd.
#
#               The rules in this file can also be set up in
#               /etc/hosts.allow with a 'deny' option instead.
#
#               See 'man 5 hosts_options' and 'man 5 hosts_access'
#               for information on rule syntax.
#               See 'man tcpd' for information on tcp_wrappers
#
vsftpd:172.16.16.1

4. Tell us the difference between Telnet and SSH?

6. You need to stop your X server. When you tries to kill your X server, You got an error message that you cannot quit X server. What will you do?

6. What is the difference between command ‘ping’ and ‘ping6’?

7. You want to search for all the *.tar files in your Home directory and wants to delete all at once. How will you do it?

# find /home/ ­name '*.tar' | xargs rm ­rf

8. What is the difference between locate and slocate command?

9. You need to search for the string “Tecmint” in all the “.txt” files in the current directory. How will you do it?

# find -­name “*.txt” | xargs grep “Tecmint”

10. You want to send a message to all connected users as “Server is going down for maintenance”, what will you do?

# echo please save your work, immediately. The server is going down for Maintenance at 12:30 Pm, sharply. | wall

That’s all for now. Don’t Forget to give your valuable feedback in comment section below.

10 Useful Interview Questions on Linux Services and Daemons

Daemon is a computer program that runs as a background process and generally do not remains under the direct control of user. The parent process of a daemon in most cases are init, but not always.

In Linux, a Service is an application that runs in a background carrying out essential task or waiting for its execution.

Generally, there is no difference between a Daemon and a Service. Daemon is Service but service may be bigger than Daemon. Daemon provide some services and services may contain more than one Daemon.

Here in this series of Interview Article, we would be covering Services and Daemons in Linux.

1. What is Exim Service? What is the purpose of this Service?

2. What is NIS server? What is the purpose of NIS Server?

3. What will you prefer for a reverse proxy in Linux?

4. You are getting following codes (2xx, 3xx, 4xx, 5xx) in Apache, at some point of time. What does this means?

5. You are asked to stop Apache Service through its control Script. What will you do?

# apachectl stop		[On Debian based Systems]
# /etc/inid.t/httpd stop	[On Red Hat based Systems]

6. How is ‘apachectl restart’ different from ‘apachectl graceful’

7. How will you configure the nfs mounts to export it, from your local machine?

8. You are supposed to create a new Apache VirtualHost configuration for the host www.Tecmint.com that is available at /home/Tecmint/public_html/ and maintains log at /var/log/httpd/ by default.

<VirtualHost *:80>
DocumentRoot /home/Tecmint/public_html
ServerName www.Tecmint.com
Server Alias Tecmint.com
CustomLog /var/log/httpd/Tecmint.com.log combined
ErrorLog /var/log/httpd/Tecmint.com.error.log
</VirtualHost>

9. You are supposed to dump all the packets of http traffic in file http.out. What will you suggest?

# tcpdump tcp port 80 -s0 -w http.out

10. How will you add a service (say httpd) to start at INIT Level 3?

chkconfig –level 3 httpd on

That’s all for now. I’ll be here again with another interesting article very soon.

10 Useful SSH (Secure Shell) Interview Questions and Answers

SSH stands for Secure Shell is a network protocol, used to access remote machine in order to execute command-line network services and other commands over a Network. SSH is Known for its high security, cryptographic behavior and it is most widely used by Network Admins to control remote web servers primarily.

Here in this Interview Questions series article, we are presenting some useful 10 SSH (Secure Shell) Questionsand their Answers.

1. SSH is configured on what Port Number, by default? How to change the port of SSH?

We can check port number of SSH by running the below one liner script, directly on terminal.

# grep Port /etc/ssh/sshd_config		[On Red Hat based systems]

# grep Port /etc/ssh/ssh_config		        [On Debian based systems]

To change the port of SSH, we need to modify the configuration file of SSH which is located at ‘/etc/ssh/sshd_config‘ or ‘/etc/ssh/ssh_config‘.

# nano /etc/ssh/sshd_config	[On Red Hat based systems]

# nano /etc/ssh/ssh_config		[On Debian based systems]

Searh for the Line.

Port 22

And replace ‘22‘ with any UN-engaged port Number say ‘1080‘. Save the file and restart the SSH service to take the changes into effect.

# service sshd restart					[On Red Hat based systems]

# service ssh restart					[On Debian based systems]

2. As a security implementation, you need to disable root Login on SSH Server, in Linux. What would you suggest?

To disable SSH root login, open the configuration file located at ‘/etc/ssh/sshd_config‘ or ‘/etc/ssh/ssh_config‘.

# nano /etc/ssh/sshd_config			[On Red Hat based systems]

# nano Port /etc/ssh/ssh_config			[On Debian based systems]

Change the parameter ‘PermitRootLogin‘ to ‘no‘ and restart the SSH service as show above.

3. SSH or Telnet? Why?

4. Is it possible to login to SSH server without password? How

Create ssh-keygen using the command below.

$ ssh-keygen

Copy public keys to remote host using the command below.

$ ssh-copy-id -i /home/USER/.ssh/id_rsa.pub REMOTE-SERVER

Note: Replace USER with user name and REMOTE-SERVER by remote server address.

The next time we try to login to SSH server, it will allow login without asking password, using the keygen. For more detailed instructions, read how to login remote SSH server without password.

5. How will you allows users and groups to have access to SSH Sever?

Here again we need to edit the configuration file of SSH service. Open the configuration file and add users and groups at the bottom as show below and then, restart the service.

AllowUsers Tecmint Tecmint1 Tecmint2
AllowGroups group_1 group_2 group_3

6. How to add welcome/warning message as soon as a user login to SSH Server?

# nano /etc/issue

And add your custom message in this file. See, below a screen grab that shows a custom message as soon as user logged into server.

7. SSH has two protocols? Justify this statement.

Again, we need to open the SSH configuration file and add/edit the lines as shown below.

# protocol 2,1

to

Protocol 2

Save the configuration file and restart the service.

8. Is it possible to trace unauthorized login attempts to SSH Server with date of Intrusion along with their corresponding IP.

# cat /var/log/secure | grep “Failed password for”

Note: The grep command can be tweaked in any other way to produce the same result.

9. Is it possible to copy files over SSH? How?

A dummy SCP command in action is depicted below:

$ scp text_file_to_be_copied Your_username@Remote_Host_server:/Path/To/Remote/Directory

For more practical examples on how to copy files/folders using scp command, read the 10 SCP Commands to Copy Files/Folders in Linux.

10. Is it possible to pass input to SSH from a local file? If Yes! How?

# ssh username@servername < local_file.txt

SSH is a very hot topic from interview point, of all times. The above questions would have surely added to your knowledge.

That’s all for now. I’ll soon be here with another interesting article.

10 Interview Questions and Answers on Various Commands in Linux

Our last article, “10 Useful SSH Interview Questions” was highly appreciated on various Social Networking sites as well as on Tecmint. This time we are presenting you with “10 Questions on various Linux commands“. These questions will prove to be brainstorming to you and will add to your knowledge which surely will help you in day-to-day interaction with Linux and in Interviews.

Q1. You have a file (say virgin.txt). You want this file to be alter-proof so that no one can edit or delete this file, not even root. What will you do?

The Syntax of command chattr, for the above purpose is:

# chattr +i virgin.txt

Now try to remove the file using normal user.

$ rm -r virgin.txt 

rm: remove write-protected regular empty file `virgin.txt'? Y 
rm: cannot remove `virgin.txt': Operation not permitted

Now try to remove the file using root user.

# rm -r virgin.txt 

cannot remove `virgin.txt': Operation not permitted

Q2. If several users are using your Linux Server, how will you find the usage time of all the users, individually on your server?

# apt-get install acct

# ac -p 

(unknown)                     14.18 
server                             235.23 
total      249.42

Q3. Which is preferred tool to create Network Statistics for your server?

# apt-get install mrtg

Q4. It is possible to send query to BIOS from Linux Command Line?

# biosdecode 

# biosdecode 2.11 

ACPI 2.0 present. 
	OEM Identifier: LENOVO 
	RSD Table 32-bit Address: 0xDDFCA028 
	XSD Table 64-bit Address: 0x00000000DDFCA078 
SMBIOS 2.7 present. 
	Structure Table Length: 3446 bytes 
	Structure Table Address: 0x000ED9D0 
	Number Of Structures: 89 
	Maximum Structure Size: 184 bytes 
PNP BIOS 1.0 present. 
	Event Notification: Not Supported 
	Real Mode 16-bit Code Address: F000:BD76 
	Real Mode 16-bit Data Address: F000:0000 
	16-bit Protected Mode Code Address: 0x000FBD9E 
	16-bit Protected Mode Data Address: 0x000F0000 
PCI Interrupt Routing 1.0 present. 
	Router ID: 00:1f.0 
	Exclusive IRQs: None 
	Compatible Router: 8086:27b8 
	Slot Entry 1: ID 00:1f, on-board 
	...
	Slot Entry 15: ID 02:0c, slot number 2

Q5. Most of the Linux Server are headless, i.e., they run in command mode only. No GUI is installed. How will you find hardware description and configuration of your box?

# dmidecode

The output of dmidecode is extensive. It will be a nice idea to redirect its output to a file.

# dmidecode > /path/to/text/file/text_file.txt

Q6. You need to know all the libraries being used and needed by a binary, say ‘/bin/echo’. How will you achieve desirable output?

$ ldd /bin/echo 

linux-gate.so.1 =>  (0xb76f1000) 
libc.so.6 => /lib/i386-linux-gnu/i686/cmov/libc.so.6 (0xb7575000) 
/lib/ld-linux.so.2 (0xb76f2000)

Q7. You are working for the country’s army. You have a file (say “topsecret.txt”) which contains confidential and country’s security Information, Nuclear missiles, etc. What will be your preferred method to delete this file?

# shred -n 15 -z topsecret.txt

shread – overwrite a file to hide its contents, and optionally delete it.

1. -n – Overwrites the files n times
2. -z – Add a final overwrite with zeros to hide shredding.

Note: The above command overwrites the file 15 times before overwriting with zero, to hide shredding.

Q8. Is it possible to mount an NTFS partition on Linux?

For more information, read article on how to monitor an NTFS Partition on Linux.

Q9. What and where you need to edit so that the default desktop at login will be KDE, which at present is GNOME.

DESKTOP=”KDE”
DISPLAYMANAGER=”KDE”

Save the file with above content. Next time when machine boots, it automatically will load KDE as default display manager.

Q10. What does an intrid image file refers to?

That’s all for now. I’ll be here again with another interesting topic, worth knowing.

10 Useful ‘Interview Questions and Answers’ on Linux Shell Scripting

Greeting of the day. The vastness of Linux makes it possible to come up with a unique post every time. 

We have lots of tutorials on Shell Scripting language and Interview Questions for readers of all kind, here are the links to those articles.

1. Shell Scripting Series
2. Interview Question and Answer Series

Adding to the shell scripting posts here, in this article we will be going through questions related to Linux Shell from interview point of view.

1. How will you abort a shell script before it is successfully executed?

For example, create a following shell script as ‘anything.sh‘.

#!/bin/bash
echo "Hello"
exit -1
echo "bye"

Save the file and execute it.

# sh anything.sh

Hello
exit.sh: 3: exit: Illegal number: -1

From the above script, it is clear that the execution went well before exit -1 command.

2. How to remove the headers from a file using command in Linux?

Here it the exact command to remove headers from a file (or first line of a file).

# sed '1 d' file.txt

The only problem with above command is that, it outputs the file on standard output without the first line. In order to save the output to file, we need to use redirect operator which will redirects the output to a file.

# sed '1 d' file.txt > new_file.txt

Well the built in switch ‘-i‘ for sed command, can perform this operation without a redirect operator.

# sed -i '1 d' file.txt

3. How will you check the length of a line from a text file?

A ‘sed –n ‘n p’ file.txt‘, where ‘n‘ represents the line number and ‘p‘ print out the pattern space (to the standard output). This command is usually only used in conjunction with the -n command-line option. So, how to get the length count? Obviously! we need to pipeline the output with ‘wc‘ command.

# sed –n 'n p' file.txt | wc –c

To get the length of line number ‘5’ in the text file ‘tecmint.txt‘, we need to run.

# sed -n '5 p' tecmint.txt | wc -c

4. Is it possible to view all the non-printable characters from a text file on Linux System? How will you achieve this?

How to show non-printable characters in ‘vi‘ editor?

1. Open vi editor.
2. Go to command mode of vi editor by pressing [esc] followed by ‘:’.
3. The final step is to type execute [set list] command, from command interface of ‘vi’ editor.

Note: This way we can see all the non-printable characters from a text file including ctrl+m (^M).

5. You are a Team-Leader of a group of staffs working for a company xyz. The company ask you to create a directory ‘dir_xyz’, such that any member of the group can create a file or access a file under it, but no one can delete the file, except the one created it. what will you do?

# mkdir dir_xyz
# chmod g+wx dir_xyz
# chmod +t dir_xyz

The first line of command create a directory (dir_xyz). The second line of command above allow group (g) to have permission to ‘write‘ and ‘execute‘ and the last line of the above command – The ‘+t‘ in the end of the permissions is called the ‘sticky bit‘. It replaces the ‘x‘ and indicates that in this directory, files can only be deleted by their owners, the owner of the directory or the root superuser.

6. Can you tell me the various stages of a Linux process, it passes through?

Here are the 4 stages of Linux process.

1. Waiting: Linux Process waiting for a resource.
2. Running : A Linux process is currently being executed.
3. Stopped : A Linux Process is stopped after successful execution or after receiving kill signal.
4. Zombie : A Process is said to be ‘Zombie’ if it has stopped but still active in process table.

7. What is the use of cut command in Linux?

For example, extract first 10 columns of a text file ‘txt_tecmint‘.

# cut -c1-10 txt_tecmint

To extract 2nd, 5th and 7th column of the same text file.

# cut -d;-f2 -f5 -f7 txt_tecmint

8. What is the difference between commands ‘cmp’ and ‘diff’?

The ‘diff‘ command reports the changes one should make so that both the files look the same. Whereas ‘cmp‘ command compares the two files byte-by-byte and reports the first mismatch.

9. Is it possible to substitute ‘ls’ command with ‘echo’ command?

10. You might have heard about inodes. can you describe inode briefly?

That’s all for now. We will be coming up with another interesting and knowledgeable Interview questions, in the next article.

Practical Interview Questions and Answers on Linux Shell Scripting

#!/bin/bash 
echo "Hello, $LOGNAME" 
echo "Current date is `date`" 
echo "User is `who i am`" 
echo "Current directory `pwd`"

# chmod 755 userstats.sh 
# ./userstats.sh

Hello, avi 
Current date is Sat Jun  7 13:05:29 IST 2014 
User is avi      pts/0        2014-06-07 11:59 (:0) 
Current directory /home/avi/Desktop

#!/bin/bash 
# The Shebang

if [ $# -ne 2 ] 
# If two Inputs are not received from Standard Input

then 
# then execute the below statements

    echo "Usage - $0   x    y" 
    # print on standard output, how-to use the script (Usage - ./1.sh   x    y )

    echo "        Where x and y are two nos for which I will print sum" 
    # print on standard output, “Where x and y are two nos for which I will print sum ”

    exit 1 
    # Leave shell in Error Stage and before the task was successfully carried out.

fi 
# End of the if Statement.

    echo "Sum of $1 and $2 is `expr $1 + $2`"
    # If the above condition was false and user Entered two numbers as a command Line Argument,   
       it will show the sum of the entered numbers.

# chmod 755 two-numbers.sh

# ./two-numbers.sh

Usage - ./two-numbers.sh   x    y 
        Where x and y are two nos for which I will print sum

$ ./two-numbers.sh 4 5 

Sum of 4 and 5 is 9

#!/bin/bash 
if [ $# -ne 1 ] 
then 
    echo "Usage: $0   number" 
    echo "       I will find reverse of given number" 
    echo "       For eg. $0 0123, I will print 3210" 
    exit 1 
fi 

n=$1 
rev=0 
sd=0 

while [ $n -gt 0 ] 
do 
    sd=`expr $n % 10` 
    rev=`expr $rev \* 10  + $sd` 
    n=`expr $n / 10` 
done 
    echo  "Reverse number is $rev"

# chmod 755 numbers.h

./numbers.sh

Usage: ./numbers.sh  number 
       I will find reverse of given number 
       For eg. ./2.sh 123, I will print 321

$ ./numbers.sh 10572 

Reverse number is 27501

$ echo 7.56 + 2.453 | bc

10.013

# pi 100 

3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342117067

mysql> SELECT VERSION(), DATABASE();

+-------------------------+------------+
| VERSION()               | DATABASE() |
+-------------------------+------------+
| 5.5.34-0ubuntu0.13.10.1 | NULL       |
+-------------------------+------------+
1 row in set (0.06 sec)

mysql> use Tecmint;

Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed

mysql> select VERSION(), DATABASE();

+-------------------------+------------+
| VERSION()               | DATABASE() |
+-------------------------+------------+
| 5.5.34-0ubuntu0.13.10.1 | tecmint    |
+-------------------------+------------+
1 row in set (0.00 sec)

mysql> SELECT * FROM Tecmint WHERE user !=SAM;

+---------------------+---------+---------+---------+---------+-------+ 
| date                | user    | host 	 | root     | local   | size  | 
+---------------------+---------+---------+---------+---------+-------+ 
| 2001-05-14 14:42:21 | Anthony | venus  | barb     | venus   | 98151 | 
| 2001-05-15 08:50:57 | TIM     | venus  | phil     | venus   | 978   | 
+---------------------+---------+---------+---------+---------+-------+

mysql> SELECT * FROM mail WHERE user = SAM AND root = phil

mysql> SELECT * FROM mail WHERE user != SAM OR root != phil

+---------------------+---------+---------+---------+---------+-------+ 
| date                | user    | host    | root    | local   | size  | 
+---------------------+---------+---------+---------+---------+-------+ 
| 2001-05-14 14:42:21 | Anthony | venus   | barb    | venus   | 98151 | 
+---------------------+---------+---------+---------+---------+-------+

mysql> SELECT name, IFNULL(id,'Unknown') AS 'id' FROM taxpayer;

+---------+---------+ 
| name 	  | id      | 
+---------+---------+ 
| bernina | 198-48  | 
| bertha  | Unknown | 
| ben     | Unknown | 
| bill    | 475-83  | 
+---------+---------+

mysql> SELECT * FROM name LIMIT 1;

+----+------+------------+-------+----------------------+------+ 
| id | name | birth      | color | foods                | cats | 
+----+------+------------+-------+----------------------+------+ 
| 1  | Fred | 1970-04-13 | black | lutefisk,fadge,pizza | 0    | 
+----+------+------------+-------+----------------------+------+

mysql> SELECT * FROM profile LIMIT 5;

+----+------+------------+-------+-----------------------+------+ 
| id | name | birth      | color | foods                 | cats | 
+----+------+------------+-------+-----------------------+------+ 
| 1  | Fred | 1970-04-13 | black | lutefisk,fadge,pizza  | 0    | 
| 2  | Mort | 1969-09-30 | white | burrito,curry,eggroll | 3    | 
| 3  | Brit | 1957-12-01 | red   | burrito,curry,pizza   | 1    |   
| 4  | Carl | 1973-11-02 | red   | eggroll,pizza         | 4    | 
| 5  | Sean | 1963-07-04 | blue  | burrito,curry         | 5    | 
+----+------+------------+-------+-----------------------+------+

mysql> SELECT * FROM profile ORDER BY birth LIMIT 1;

+----+------+------------+-------+----------------+------+ 
| id | name | birth      | color | foods          | cats | 
+----+------+------------+-------+----------------+------+ 
| 9  | Dick | 1952-08-20 | green | lutefisk,fadge | 0    | 
+----+------+------------+-------+----------------+------+

mysql> SELECT CURRENT_DATE();

+----------------+
| CURRENT_DATE() |
+----------------+
| 2014-06-17     |
+----------------+

mysql -u USER_NAME –xml -e 'SELECT * FROM table_name' > table_name.xml

mysql> show index from user;
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | 
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 
| user  |          0 | PRIMARY  |            1 | Host        | A         |        NULL |     NULL | NULL   |      | BTREE      |         |               | 
| user  |          0 | PRIMARY  |            2 | User        | A         |           4 |     NULL | NULL   |      | BTREE      |         |               | 
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 
2 rows in set (0.00 sec)

# cat /var/log/messages

OR 

# dmesg

# nano /etc/squid/squid.conf

http_port 3128

# service squid restart

# touch /etc/squid/blacklist

# nano /etc/squid/blacklist

.facebook.com
.twitter.com
.gmail.com
.yahoo.com
...

# nano /etc/squid/squid.conf

acl BLACKLIST dstdom_regex -i “/etc/squid/blacklist”
http_access deny blacklist

# service squid restart

# service squid stop
# rm -rf /var/lib/squid/cache/*<

# squid -z

# nano /etc/squid/squid.conf

acl ALLOW_TIME time M T W H F 16:00-19:00
shttp_access allow ALLOW_TIME

# service squid restart

82.175.219.112

 2005:3200:230:7e:35dl:2874:2190

# ls

# echo *

# echo */

# ls -a

# ls -A

# ls -l

drwxr-xr-x  5 avi tecmint      4096 Sep 30 11:31 Binary

# ls -la

# ls -lA

# ls --author -l

# ls -b

# ls --block-size=M -l
# ls --block-size=K -l

# ls -B

# ls -cl

# ls -ltc

# ls --color=never
# ls --color=auto
# ls --color=always

# ls -d

# ls -a
# nano .bashrc
# ll >> ll.txt
# nano ll.txt

# ls -l

# ls -l --author

# ls -g

# ls -Gl

# ls -hl

# ls -hs

# ls -si

# ls -si -l

# ls -m

# ls -ml

# ls -r

# ls -rl

# ls -R

# ls -S

# ls -Sr

# ls -1

# ls -Q

# ls --group-directories-first

# rpm -qa iptables

iptables-1.4.21-13.el7.x86_64

# yum install iptables-services

# service iptables status			[On CentOS 6/5]
# systemctl status iptables			[On CentOS 7]

---------------- On CentOS 6/5 ---------------- 
# chkconfig --level 35 iptables on
# service iptables start

---------------- On CentOS 7 ---------------- 
# systemctl enable iptables 
# systemctl start iptables 

# lsmod | grep ip_tables

# iptables -L

Chain INPUT (policy ACCEPT)
target     prot opt source               destination         
ACCEPT     all  --  anywhere             anywhere             state RELATED,ESTABLISHED
ACCEPT     icmp --  anywhere             anywhere            
ACCEPT     all  --  anywhere             anywhere            
ACCEPT     tcp  --  anywhere             anywhere             state NEW tcp dpt:ssh
REJECT     all  --  anywhere             anywhere             reject-with icmp-host-prohibited

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         
REJECT     all  --  anywhere             anywhere             reject-with icmp-host-prohibited

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

 
# iptables --flush OUTPUT

# iptables --flush

# iptables -A INPUT -s 192.168.0.7 -j ACCEPT 

# iptables -A INPUT -s 192.168.0.7/24 -j ACCEPT 
# iptables -A INPUT -s 192.168.0.7/255.255.255.0 -j ACCEPT

# iptables -A INPUT -s -p tcp --dport 22 -j ACCEPT 

# iptables -A INPUT -s -p tcp --dport 22 -j REJECT

 
# iptables -A INPUT -s -p tcp --dport 22 -j DENY

 
# iptables -A INPUT -s -p tcp --dport 22 -j DROP

# iptables -A INPUT -s 192.168.0.6 -p tcp -m multiport --dport 21,22,23,80 -j DROP

# iptables -L

Chain INPUT (policy ACCEPT)
target     prot opt source               destination         
ACCEPT     all  --  anywhere             anywhere             state RELATED,ESTABLISHED
ACCEPT     icmp --  anywhere             anywhere            
ACCEPT     all  --  anywhere             anywhere            
ACCEPT     tcp  --  anywhere             anywhere             state NEW tcp dpt:ssh
REJECT     all  --  anywhere             anywhere             reject-with icmp-host-prohibited
DROP       tcp  --  192.168.0.6          anywhere             multiport dports ssh,telnet,http,webcache

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         
REJECT     all  --  anywhere             anywhere             reject-with icmp-host-prohibited

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

# rpm -qa nano
OR
# rpm -qa | grep -i nano

nano-2.3.1-10.el7.x86_64

# vi
# vim

# rpm -qa vim*

vim-minimal-7.4.160-1.el7.x86_64

# rpm -ivh peazip-1.11-1.el6.rf.x86_64.rpm

Preparing...                          ################################# [100%]
Updating / installing...
   1:peazip-1.11-1.el6.rf             ################################# [100%]

# rpm -ql httpd

/etc/httpd
/etc/httpd/conf
/etc/httpd/conf.d
...

# rpm -qa postfix*

postfix-2.10.1-6.el7.x86_64

# rpm -ev postfix-2.10.1-6.el7.x86_64

Preparing packages...
postfix-2:3.0.1-2.fc22.x86_64

# rpm -qa openssh

[root@tecmint tecmint]# rpm -qi openssh
Name        : openssh
Version     : 6.8p1
Release     : 5.fc22
Architecture: x86_64
Install Date: Thursday 28 May 2015 12:34:50 PM IST
Group       : Applications/Internet
Size        : 1542057
License     : BSD
....

# rpm -qc httpd

/etc/httpd/conf.d/autoindex.conf
/etc/httpd/conf.d/userdir.conf
/etc/httpd/conf.d/welcome.conf
/etc/httpd/conf.modules.d/00-base.conf
/etc/httpd/conf/httpd.conf
/etc/sysconfig/httpd

# rpm -qd httpd

/usr/share/doc/httpd/ABOUT_APACHE
/usr/share/doc/httpd/CHANGES
/usr/share/doc/httpd/LICENSE
...

# rpm -qL openssh

/usr/share/licenses/openssh/LICENCE

# rpm -qf /usr/share/alsa/cards/AACI.conf
alsa-lib-1.0.28-2.el7.x86_64

# rpm -qa --last

# rpm -qa --last | grep -i sqlite

sqlite-3.8.10.2-1.fc22.x86_64                 Thursday 18 June 2015 05:05:43 PM IST

# rpm -qa --last | head

# rpm -qa --last | head -n 2

# rpm -qpR gedit-3.16.1-1.fc22.i686.rpm 

/bin/sh
/usr/bin/env
glib2(x86-32) >= 2.40.0
gsettings-desktop-schemas
gtk3(x86-32) >= 3.16
gtksourceview3(x86-32) >= 3.16
gvfs
libX11.so.6
...

# yum repolist
or
# dnf repolist

Last metadata expiration check performed 0:30:03 ago on Mon Jun 22 16:50:00 2015.
repo id                                                                           repo name                                                                                             status
*fedora                                                                           Fedora 22 - x86_64                                                                                    44,762
ozonos                                                                            Repository for Ozon OS                                                                                    61
*updates                                                                          Fedora 22 - x86_64 - Updates   

# yum repolist all
or
# dnf repolist all

Last metadata expiration check performed 0:29:45 ago on Mon Jun 22 16:50:00 2015.
repo id                                                                         repo name                                                                                      status
*fedora                                                                         Fedora 22 - x86_64                                                                             enabled: 44,762
fedora-debuginfo                                                                Fedora 22 - x86_64 - Debug                                                                     disabled
fedora-source                                                                   Fedora 22 - Source                                                                             disabled
ozonos                                                                          Repository for Ozon OS                                                                         enabled:     61
*updates                                                                        Fedora 22 - x86_64 - Updates                                                                   enabled:  5,018
updates-debuginfo                                                               Fedora 22 - x86_64 - Updates - Debug

# yum list available
or
# dnf list available

ast metadata expiration check performed 0:34:09 ago on Mon Jun 22 16:50:00 2015.
Available Packages
0ad.x86_64                               0.0.18-1.fc22                   fedora 
0ad-data.noarch                          0.0.18-1.fc22                   fedora 
0install.x86_64                          2.6.1-2.fc21                    fedora 
0xFFFF.x86_64                            0.3.9-11.fc22                   fedora 
2048-cli.x86_64                          0.9-4.git20141214.723738c.fc22  fedora 
2048-cli-nocurses.x86_64                 0.9-4.git20141214.723738c.fc22  fedora 
....

# yum list installed
or
# dnf list installed

Last metadata expiration check performed 0:34:30 ago on Mon Jun 22 16:50:00 2015.
Installed Packages
GeoIP.x86_64                            1.6.5-1.fc22                     @System
GeoIP-GeoLite-data.noarch               2015.05-1.fc22                   @System
NetworkManager.x86_64                   1:1.0.2-1.fc22                   @System
NetworkManager-libnm.x86_64             1:1.0.2-1.fc22                   @System
aajohan-comfortaa-fonts.noarch          2.004-4.fc22                     @System
....

# yum list
or
# dnf list

Last metadata expiration check performed 0:32:56 ago on Mon Jun 22 16:50:00 2015.
Installed Packages
GeoIP.x86_64                             1.6.5-1.fc22                    @System
GeoIP-GeoLite-data.noarch                2015.05-1.fc22                  @System
NetworkManager.x86_64                    1:1.0.2-1.fc22                  @System
NetworkManager-libnm.x86_64              1:1.0.2-1.fc22                  @System
aajohan-comfortaa-fonts.noarch           2.004-4.fc22                    @System
acl.x86_64                               2.2.52-7.fc22                   @System
....

# yum install nano

# yum groupinstall 'haskell'

# yum update nano

# yum groupupdate 'haskell'

# yum distro-sync      [On CentOS/RHEL]
or
# dnf distro-sync      [On Fedora 20 Onwards]

# yum install deltarpm  python-deltarpm  createrepo

# mkdir /home/$USER/rpm
# cp /path/to/rpm/on/DVD/*.rpm /home/$USER/rpm

# createrepo -v /home/$USER/rpm

cd /etc/yum.repos.d && cat << EOF > abc.repo
[local-installation]name=yum-local
baseurl=file:///home/$USER/rpm
enabled=1
gpgcheck=0
EOF