Yearly Archives: 2017

Create a .tar file with different compression methods

 in Bash / GNU/Linux  tagged bz2 / gz / tar / tgz / xz by

The following commands will create .tar archives  and compress them using the different methods that are available. We provide multiple solutions, each one for a different type of .tar archive depending on the compression method that is desired.

For .tar archives

tar -c -f archive.tar $FILES_TO_ARCHIVE;

For .tar.bz2 archives

tar -c -j -f archive.tar.bz2 $FILES_TO_ARCHIVE;

For .tar.xz archives

tar -c -J -f archive.tar.xz $FILES_TO_ARCHIVE;

For .tar.gz and .tgz archives

tar -c -z -f archive.tar.gz $FILES_TO_ARCHIVE;

tar Parameters Legend

  • -z or --gzip instructs tar to filter the archive through gzip
  • -j or --bzip2 filters the archive through bzip2
  • -J or --xz filters the archive through xz
  • -f or --file=OUTPUT uses the archive file OUTPUT
  • -c or --create a new archive

Bonus Example: Create a tar.xz archive using the current date in the archive name

The following command will create an archive out of the folders Folder1 and Folder2 and then it will compress it to the .tar.xz format.
The filename of the archive will contain the current date in the format YYYY-MM-DD.

tar -c -J  -f archive.`date +%F`.tar.xz Folder1 Folder2;

The above command will result in something similar to:

archive.2017-06-04.tar.xz
 in Funny by | Open »

Studies have shown that an increased amount of birthdays correlates with an increased risk of death.

How To Install on GNU/Linux CentOS 7 the LAMP stack (Apache, MySQL, PHP) + phpMyAdmin

 in GNU/Linux  tagged apache / CentOS / centos 7 / GNU / lamp / linux / mysql / php / phpmyadmin by

Following you will find the commands to perform the installation of the LAMP stack (Apache, MySQL, PHP) and phpMyAdmin on a GNU/Linux CentOS 7.
In this guide we kept the information to the bare minimum about what is what.

Installation

To perform the installation, please execute the following as a user with administrative rights:


#Update your system
sudo yum update -y;
#Install Apache, MariaDB (MySQL), PHP (with MySQL support and phpMyAdmin which is a free software tool written in PHP, intended to handle the administration of MySQL over the Web)
sudo yum install httpd mariadb-server mariadb php php-mysql phpmyadmin -y;
#Start Apache (PHP will start with Apache as module)
sudo systemctl start httpd;
#Enable Apache to start on boot
sudo systemctl enable httpd;
#Start MariaDB(MySQL)
sudo systemctl start mariadb;
#Enable MariaDB(MySQL) to start on boot
sudo systemctl enable mariadb;

Configuration of MariaDB (MySQL)

By now, your system should have all necessary packages installed and the services up and running.
Now it is best to configure your MariaDB (MySQL) in a way to disable some test data and test accounts and assign a password to your root user.
Execute the following to do so:


sudo mysql_secure_installation;

This tool will ask you for your current database root password. Since you just installed MariaDB (MySQL) you should not have one, so leave the field empty and press enter.
We recommend to answer with Y (Yes) in all of the security questions of this tool and set a strong password for your root user.


sudo mysql_secure_installation;

Following is the output we got from this tool:

NOTE: RUNNING ALL PARTS OF THIS SCRIPT IS RECOMMENDED FOR ALL MariaDB
 SERVERS IN PRODUCTION USE!  PLEASE READ EACH STEP CAREFULLY!

In order to log into MariaDB to secure it, we'll need the current
 password for the root user.  If you've just installed MariaDB, and
 you haven't set the root password yet, the password will be blank,
 so you should just press enter here.

Enter current password for root (enter for none):
 OK, successfully used password, moving on...

Setting the root password ensures that nobody can log into the MariaDB
 root user without the proper authorisation.

Set root password? [Y/n] Y
 New password:
 Re-enter new password:
 Password updated successfully!
 Reloading privilege tables..
 ... Success!

By default, a MariaDB installation has an anonymous user, allowing anyone
 to log into MariaDB without having to have a user account created for
 them.  This is intended only for testing, and to make the installation
 go a bit smoother.  You should remove them before moving into a
 production environment.

Remove anonymous users? [Y/n] Y
 ... Success!

Normally, root should only be allowed to connect from 'localhost'.  This
 ensures that someone cannot guess at the root password from the network.

Disallow root login remotely? [Y/n] Y
 ... Success!

By default, MariaDB comes with a database named 'test' that anyone can
 access.  This is also intended only for testing, and should be removed
 before moving into a production environment.

Remove test database and access to it? [Y/n] Y
 - Dropping test database...
 ... Success!
 - Removing privileges on test database...
 ... Success!

Reloading the privilege tables will ensure that all changes made so far
 will take effect immediately.

Reload privilege tables now? [Y/n] Y
 ... Success!

Cleaning up...

All done!  If you've completed all of the above steps, your MariaDB
 installation should now be secure.

Thanks for using MariaDB!

Configuration of the firewall

Executing the following will enable access to your web-server from the network for http and https.


sudo firewall-cmd --permanent --zone=public --add-service=http;
sudo firewall-cmd --permanent --zone=public --add-service=https;
sudo firewall-cmd --reload;

Location of files / Where to upload your website

In CentOS 7, the directory where the website pages are located is at /var/www/html/.
You can place your html and php code there.

Configuration of phpMyAdmin

phpMyAdmin should be available at http://<IP of the web server>/phpmyadmin
The access to phpMyAdmin is controlled by the Apache Virtual Host File for phpMyAdmin that is found here /etc/httpd/conf.d/phpMyAdmin.conf.
By default, this configuration file only allows access to phpMyAdmin from the localhost (127.0.0.1).
In case you want to access it from another machine, you need to modify this file.
Before doing any changes, make a backup of the original file first:

 sudo cp /etc/httpd/conf.d/phpMyAdmin.conf /etc/httpd/conf.d/phpMyAdmin.conf.original;

To enable access only for a specific IP

Edit the Apache Virtual Host File for phpMyAdmin (/etc/httpd/conf.d/phpMyAdmin.conf) and change every reference of 127.0.0.1 with the IP address of the machine you want to give access to.

There should be four lines that you need to change.
In our installation it was the following lines:

  1. 17 – Require ip 127.0.0.1
  2. 25 – Allow from 127.0.0.1
  3. 34 – Require ip 127.0.0.1
  4. 42 – Allow from 127.0.0.1

Then restart the Apache service to apply the changes:


sudo systemctl restart httpd;

To enable access to any IP

Delete the existing file and create a new one.


sudo rm /etc/httpd/conf.d/phpMyAdmin.conf;
sudo touch /etc/httpd/conf.d/phpMyAdmin.conf;

Using the editor of your choice add the following content and save it:

Alias /phpMyAdmin /usr/share/phpMyAdmin
Alias /phpmyadmin /usr/share/phpMyAdmin

<Directory /usr/share/phpMyAdmin/>
 AllowOverride None
 Options None
 Allow from All
 Require all granted
</Directory>

Then restart the Apache service to apply the changes:


sudo systemctl restart httpd;

Following is the original content of our Apache Virtual Host File for phpMyAdmin (/etc/httpd/conf.d/phpMyAdmin.conf)

[download id=”3647″]

$ cat /etc/httpd/conf.d/phpMyAdmin.conf
 # phpMyAdmin - Web based MySQL browser written in php
 #
 # Allows only localhost by default
 #
 # But allowing phpMyAdmin to anyone other than localhost should be considered
 # dangerous unless properly secured by SSL

Alias /phpMyAdmin /usr/share/phpMyAdmin
Alias /phpmyadmin /usr/share/phpMyAdmin

<Directory /usr/share/phpMyAdmin/>
 AddDefaultCharset UTF-8

 <IfModule mod_authz_core.c>
  # Apache 2.4
  <RequireAny>
   Require ip 192.168.0.20
   Require ip ::1
  </RequireAny>
 </IfModule>
 <IfModule !mod_authz_core.c>
  # Apache 2.2
  Order Deny,Allow
  Deny from All
  Allow from 192.168.0.20
  Allow from ::1
  </IfModule>
</Directory>

<Directory /usr/share/phpMyAdmin/setup/>
 <IfModule mod_authz_core.c>
  # Apache 2.4
  <RequireAny>
   Require ip 192.168.0.20
   Require ip ::1
  </RequireAny>
 </IfModule>
 <IfModule !mod_authz_core.c>
  # Apache 2.2
  Order Deny,Allow
  Deny from All
  Allow from 192.168.0.20
  Allow from ::1
 </IfModule>
</Directory>

# These directories do not require access over HTTP - taken from the original
# phpMyAdmin upstream tarball
#
 <Directory /usr/share/phpMyAdmin/libraries/>
  Order Deny,Allow
  Deny from All
  Allow from None
 </Directory>

<Directory /usr/share/phpMyAdmin/setup/lib/>
  Order Deny,Allow
  Deny from All
  Allow from None
</Directory>

<Directory /usr/share/phpMyAdmin/setup/frames/>
 Order Deny,Allow
 Deny from All
 Allow from None
</Directory>

# This configuration prevents mod_security at phpMyAdmin directories from
# filtering SQL etc.  This may break your mod_security implementation.
#
#<IfModule mod_security.c>
#    <Directory /usr/share/phpMyAdmin/>
#        SecRuleInheritance Off
#    </Directory>
#</IfModule>

[download id=”3647″]

C++: How to print an unsigned character (unsigned byte – uint8_t) using cout 1

 in C++  tagged ADL / Argument-dependent name lookup / cout / static_cast / uint8_t / unary + operator by

When you try to print an unsigned 8-bit (1 byte – uint8_t) integer through cout, you will notice that instead of getting the arithmetic value of the variable on the output, you will get its character representation of the ASCII table. This issue occurs due to the fact that there is no data type for unsigned 8-bit integer in C++ and the uint8_t is nothing more than a typedef of the unsigned char data type. When cout tries to print the uint8_t it will call the ostream& operator<< (ostream& os, unsigned char c); which will insert the character representation of the character variable c to the os.

Below we propose a few methods to resolve this issue.

Method A: Convert the variable to an unsigned int before printing it

The following example will convert the value of the variable to an unsigned int before printing it so that cout will call the ostream& operator<< (unsigned int val); and it will print it as a number.


//For unsigned characters
cout << unsigned(c) << endl;
//For signed characters
cout << int(c) << endl;

Method B: Static cast the variable to an unsigned int before printing it

The following example will use static_cast to cast the value of the variable to an unsigned int before printing it so that cout will call the ostream& operator<< (unsigned int val); and it will print it as a number.


//For unsigned characters
cout << static_cast<unsigned int>(c) << endl;
//For signed characters
cout << static_cast<int>(c) << endl;

Method C: Cast the variable to an unsigned int before printing it

The following example will cast the value of the variable to an unsigned int before printing it so that cout will call the ostream& operator<< (unsigned int val); and it will print it as a number.


//For unsigned characters
cout << (unsigned int) c << endl;
//For signed characters
cout << (int) c << endl;

Method D: Add a unary + operator before the variable to create an arithmetic operation that does not affect the value and print its result

The following example will add a unary + operator before the variable so that it will produce an arithmetic result and print that one so that cout will treat the result as a number.


cout << +c << endl;

Method E: Use Argument-dependent name lookup (ADL)

Argument-dependent name lookup, applies to the lookup of an unqualified function name depending on the types of the arguments given to the function call.
Reference: http://en.wikipedia.org/wiki/Argument-dependent_name_lookup

In the following example we change the behavior of cout using a custom namespace to achieve the goal of printing and char as an 8-bit integer.
Specifically, we overload the inline std::ostream &operator<<(std::ostream &os, const char c); for cases where we the variable is not defined to be signed or not, to check if the input char variable is signed or unsigned and then perform a static_cast to the proper type.
Also, inline std::ostream &operator<<(std::ostream &os, const signed char c); and inline std::ostream &operator<<(std::ostream &os, const unsigned char c); are also overloaded to perform the correct static_cast immediately when the the type of the variable is known.


#include <iostream>

namespace bytes {
    inline std::ostream &operator<<(std::ostream &os, const char c) {
        return os << (std::is_signed<char>::value
                ? static_cast<int>(c)
                : static_cast<unsigned int>(c));
    }

    inline std::ostream &operator<<(std::ostream &os, const signed char c) {
        return os << static_cast<int>(c);
    }

    inline std::ostream &operator<<(std::ostream &os, const unsigned char c) {
        return os << static_cast<unsigned int>(c);
    }
}

using namespace std;

int main() {

    const uint8_t c = 64;

    {
        using namespace bytes;
        cout << c << endl;
    }
    {
        cout << c << endl;
    }

    return 0;
}