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Install, Configure, and Troubleshoot Linux Web Server (Apache)

By on 14 Ağustos 2019 in GNU/Linux İpuçları

In this tutorial, we will talk about Linux web server or Apache web server specifically and how to install it and configure it to serve your content to others. A web server is a system that manipulates requests via HTTP protocol, you request a file from the server and it responds with the requested file, which might give you an idea that web servers are only used for the web. Actually, web servers can also be found embedded in devices such as printers, routers, when you open your router configuration page, there is a web server behind it. When you open the printer configuration page, there is also a web server behind it serving your requests, so web servers are important today because they are used everywhere. First, your browser sends a request to the server.

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How Web server Works

First, your browser sends a request to the server.

The server takes the requested file or page from you and maps it to the corresponding file from the server. The server sends the file back to the browser with some information such as its MIME type, the length of the content and some other useful information.

Sometimes the requested file is a static page like HTML pages or dynamic pages like PHP, Java, Perl or any other server-side language.

For example, when you type www.yourDomain.com, the browser queries the DNS server about the IP address of the computer: www.yourDomain.com. Once the browser gets the response from the DNS, it starts a TCP connection on port 80 and asks for the default web page, then this page is sent to you and that’s all.

Linux Web server Implementations

There are many Linux web server implementations available for you to use:

  • Apache server
  • Nginx
  • Lighttpd
  • Apache Tomcat
  • Monkey HTTP Daemon (used especially for embedded systems)

There are more Linux web servers, but this list is the most used web servers.

The most used web servers are Apache and Nginx.

In this post, we will use Apache server for several reasons:

  • It is stable.
  • It is flexible.
  • It is secure.

We’ll install and configure Apache server on Linux, but at first, let’s review some of the basics of HTTP protocol basics.

Understanding HTTP

When you request a file or a page from a web server, the client at first connects to the server on port 80. After successful connection, the client then sends HTTP commands (also methods) to the server. This command includes a request header which includes information about the client.

To view these request headers in chrome, open chrome devtools, then open network panel and visit google.com and check the request headers, you should see something like this:

Linux Web Server Request Header

The request header also includes information about the client, like the user agent and the accepted formats.

Additional information may be sent with the request header. For example, if you click on a link that will open another website, the header will include the referral site.

After receiving the request header completely, the server responds with the requested file or page along with a response header.

The response header includes information about the received content, its type, and other information.

Response header

You can check the response headers from the browser network panel.

Install Apache Web server

You can install Apache server on Red Hat based distros using the following command:

dnf -y httpd

Or if you are using a Debian-based distro, you can install it like this:

apt-get -y install apache2

The Apache web server service is called httpd on Red Hat based distros like CentOS, while it is called apache2 in Debian based distros.

If you are using a firewall like iptables, you should add a rule for port 80.

iptables -I INPUT 1 -m state --state NEW -m tcp -p tcp --dport 80 -j ACCEPT

Or if you are using firewalld, you can use the following command:

firewall-cmd --add-port=80/tcp

To start your service and enable it on boot:

systemctl start httpd
systemctl enable httpd

You can check if your service is running or not, using the following command:

systemctl status httpd

Now open your browser and visit http://localhost or http://[::1]/ if you are using IP v6 and if your installation goes well, you should see your HTML homepage.

Configuring Apache Web server

You can add files to Apache in the /var/www/html directory for top-level pages.

Just remember to make sure that any files or directories placed in that directory are world-readable.

The default index page is index.html.

The Apache configuration files are in /etc/httpd/conf/ directory.

On Debian based systems like Ubuntu, you may find it at /etc/apache2/apache2.conf file.

We can’t discuss every option for Apache on a single post, but we will discuss the most important options.

You call them options or directives.

ServerRoot Option

This option specifies the configuration folder for Apache web server. On Red Hat based distros, the ServerRoot option is /etc/httpd/ directory. On Debian distros the ServerRoot option is /etc/apache2/.

ServerRoot /etc/httpd

Listen Option

This is the port that Apache web server will use to wait for incoming connections.

The default value for this option is 80 for nonsecure connections and 443 for secured connections.

If you have multiple IP addresses on your server, you can assign which IP should listen for connection using Listen option.

You can specify a different port other than 80, just make sure that it’s not in use.

You can run many HTTP servers on the same hardware every one on a unique port.

When a server runs on a non-standard port such as port 8080, it will require the port number to be explicitly stated like this:

www.example.com:8080

Listen 80

ServerName Option

This option specifies the hostname of the web server that appears to the visitors.

ServerName FQDN

DocumentRoot Option

This defines the path that will contain your files that will be served.

The default path is /var/www/html .

DocumentRoot /var/www/html

MaxRequestWorkers Option

This option sets the maximum number of concurrent connections that the server will receive.

LoadModule Option

This option is used to load modules into Apache web server.

There are a lot of Apache modules like these:

mod_cgid: This module is used to run CGI scripts using Apache web server.

mod_ssl: Provides secure connections via SSL and TLS protocols.

mod_userdir: This module allows you to serve content from users specific directories.

If you want to disable loading a specific module, you can comment the Load module line that contains that module.

Or if you use Debian based distros like Ubuntu, you can use these commands:

a2enmod modulename

This command to enable the module.

a2dismod modulename

This command to disable the module.

All these commands do is create a symlink under /etc/apache2/mods-enabled directory with the file that contains the module you want to enable. All files under this directory are included in Apache configuration by default, so any file will exist in this directory will be included.

And if you use a2dismod, the symlink will be removed.

If you enable or disable a module, you have to reload or restart Apache web server.

LoadModule mod_cgid.so

Include Option

This option allows you to include other configuration files.

You can store all the configuration for different virtual domains, and Apache will include them at runtime.

Include filePath

UserDir option

This option specifies the directory that will contain the files that will be accessible via the web server. This directory is usually named public_html and its location in user’s home directory.

For example, if you have a user adam who wants to make his web content available via Apache web server.

First, we make a public_html folder under his home directory.

Then set the permission for the public_html folder:

chmod 644 public_html

Now if we put an index.html file, it will be accessible via the browser like this:

http://YOURHOSTNAME/~adam

UserDir public_html

Alias Option

This option specifies the location of the files that are outside the DocumentRoot location and need to be served by the Apache web server.

Like you have files outside DocumentRoot and you want them to be available to the visitors.

Alias URL_Path Actual_Path

ErrorLog Option

This option specifies the error log file for Apache web server.

ErrorLog /var/log/httpd/error_log

VirtualHost Option

This option allows you to host multiple websites on the same server.

The idea is that the content is served based on the requested hostname.

To setup a virtual host for the host www.example.com. First, create a VirtualHost option in /etc/httpd/conf/httpd.conf file.

And specify the DocumentRoot and ServerName like this:

<VirtualHost www.example.com>
ServerAdmin admin@example.com
DocumentRoot /home/adam/public_html
ServerName www.example.com
ErrorLog /var/log/users/adam/error_log
</VirtualHost>

Keep in mind that the ServerName option must be resolvable via DNS.

These are the most used Apache options.

Virtual Host Types

There are two types of virtual hosts that you can define in Apache web server:

  • Name-based virtual hosts
  • IP-based virtual hosts

The NameVirtualHost directive defines which addresses can be virtual hosts; the asterisk (*) means any name or address on this server. You can write them like this:

NameVirtualHost
<VirtualHost *>
ServerName www.example.com
DocumentRoot “/home/user1/public_html/”
</VirtualHost>
<VirtualHost *>
ServerName www.example2.com
DocumentRoot “/ home/user2/public_html/”
</VirtualHost>

If you have more than one IP address and you want to use SSL certificate, the website must be on a dedicated IP address. You can write IP-based virtual hosts like this:

<VirtualHost 192.168.1.2>
ServerName www.example.com
DocumentRoot “/home/user1/public_html/”
</VirtualHost>
<VirtualHost 192.168.1.3>
ServerName www.example2.com
DocumentRoot “/ home/user2/public_html/”
</VirtualHost>

Apache Process Ownership

We know from the Linux process management that each process inherits its permissions from its parent process.

This fact is true for all processes except for applications with the SETUID bit set, they inherit permissions from the owner, not the parent process. A good example is the /bin/su.

If a normal user runs /bin/su program, it does not inherit the permission from adam, but it acts as a root user running it.

Since Apache web server needs to bind port 80, and this needs root privileges.

After binding to port 80, Apache can run as a normal user and only read files that have permissions to read them.

Based on the Linux distro you use, the user could be one of the following:

nobody, www, apache, www-data, or daemon.

I delayed introducing two more options for apache till reaching that point.

User Option

This specifies the user ID which the web server will use to answer requests.

User www-data

Group Option

This specifies the group that Apache web server will use to read files.

Group www-data

Security is very important for sites that use executable scripts such as CGI or PHP scripts.

The user you will use will have the permission to read and write the content of all sites on the server. But we want to ensure that only the members of a particular site can read their own site only.

This is very important because if a site got compromised, the attacker will be able to read all files since the apache user has permission to do that.

So how to solve this problem?

suEXEC Support

A popular method is to use suEXEC. suEXEC is a program that runs with root permissions and makes CGI programs run as the user and group IDs of a specific user, not the Apache server user.

You can specify the user on each virtual host like this:

<VirtualHost www.example.com>
SuExecUserGroup adam adamGroup
</VirtualHost>

Just that simple.

Apache Authentication

You may want to restrict some parts to specific visitors. It’s like a password protected directory.

In Apache, you can store authentication information file called .htpasswd file.

You can use the htpasswd command to do that.

First, create the .htpasswd file using the htpasswd command:

htpasswd -c /home/adam/.htpassswd myuser

The -c option is needed the first time you run htpasswd, but when you need to add more users you shouldn’t use -c because it will overwrite the file.

Then create a .htaccess file in the public_html folder and write the following:

<Location /vip>
AuthName “test”
AuthType Basic
AuthUserFile /home/adam/.htpasswd
Order deny,allow
require valid-user
</Location>

AuthName is required, you can use any string you want.

AuthType Basic says that you’re using htpasswd style user file.

AuthUserFile points to the file that contains the generated password from htpasswd command.

The Order line indicates that Apache must deny access by default, and only allow access for users specified in the htpasswd file.

The require directive means any user in the .htpasswd file is allowed.

Troubleshooting Apache Web server

If you modify the httpd.conf file and restart or reload Apache web server and it did not work, then you have typed a wrong configuration, however, this is not the only case that you need to troubleshoot Apache, you may look at the apache logs to see how the service works so you can diagnose the problem and solve it.

The two main log files for apache are error_log and access_log files.

You can find these files in /var/log/httpd/ directory in Red Hat based distros, or in /var/log/apache2/ directory if you are using Debian based distros.

The access_log file contains every request to Apache web server with the details about client requested that resource.

The error_log file contains errors of Apache web server.

You can use tail command to watch the log file:

tail -f /var/log/httpd/error_log

I recommend you to review the Linux syslog server to know more about logging.

I hope you find working with Apache web server easy and interesting. Keep coming back.

Thank you.

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Doxygen 1.8.16 duyuruldu

By on 9 Ağustos 2019 in Ofis

C++, C, Java, Objective-C, Python, IDL, PHP, C#, Fortran, VHDL, Tcl ve bir dereceye kadar D dilleri için online/offline dokümantasyon hazırlamayı sağlayan bir dokümantasyon sistemi olan Doxygen‘in 1.8.16 sürümü duyuruldu. Kaynak kodlarının içinde herhangi ek bir IDE’ye yada programa ihtiyaç duymaksızın gezinmeyi sağlayan Doxygen; HTML, RTF (MS-Word), PostScript, hyperlinked PDF, compressed HTML, Unix man şeklinde çıktıları destekliyor. Projelere ait dokümantasyon hazırlarken zaman bakımından büyük bir kazanç sağlayan yazılım, Mac OS X ve Linux altında geliştirilmiş, ancak oldukça taşınabilir bir platform olarak ayarlanmıştır. Doxygen ayrıca hepsi otomatik olarak üretilen bağımlılık grafiklerini, kalıtım şemalarını ve işbirliği şemalarını kullanarak çeşitli elemanlar arasındaki ilişkileri görselleştirebilir. Doxygen’i normal belgeler oluşturmak için de kullanabilirsiniz. Doxygen 1.8.16 hakkında ayrıntılı bilgi edinmek için değişiklikler sayfasını inceleyebilirsiniz.

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Doxygen 1.8.16 edinmek için aşağıdaki linkten yararlanabilirsiniz.

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Cast or Convert an Array to Object Using PHP (Hydrator Pattern)

By on 30 Temmuz 2019 in GNU/Linux İpuçları

In this post, we will convert an array to object using PHP hydrator pattern. This method is so simple, it’s about transferring data from one place to another. We will define a class that will take an array and an object as inputs and search for all set() methods in the object and fills it with values from the array. First, we will determine the object class using get_class() function then we will use get_class_methods() to get the class methods. Keep in mind that we use PHP 7 coalescing operator (??), in case you are not using PHP 7, you can use ternary operator instead. We use substr then we concatenate because if we have lowerCamelCase member variables like $firstName.

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class Converter
{
public static function toObject(array $array, $object)
{
$class = get_class($object);

$methods = get_class_methods($class);

foreach ($methods as $method) {

preg_match(' /^(set)(.*?)$/i', $method, $results);

$pre = $results[1] ?? '';

$k = $results[2] ?? '';

$k = strtolower(substr($k, 0, 1)) . substr($k, 1);

If ($pre == 'set' && !empty($array[$k])) {

$object->$method($array[$k]);
}
}
return $object;
}
}

To test this converter class, we need to create a class with properties and methods (getters & setters) and see how to convert an array to object using PHP in action.

Let’s assume that we have an employee class like this:

class Employee
{
protected $name;

protected $phone;

protected $email;

protected $address;

public function getName()
{
return $this->name;
}

public function getPhone()
{
return $this->phone;
}

public function getEmail()
{
return $this->email;
}

public function getAddress()
{
return $this->address;
}

public function setName($name)
{
$this->name = $name;
}

public function setPhone($phone)
{
$this->phone = $phone;
}

public function setEmail($email)
{
$this->email = $email;
}

public function setAddress($address)
{
$this->address = $address;
}
}

Convert Array To Object

Now let’s create an array that will hold the data that will be transferred to the class.

$arr['name'] = "Adam";

$arr['phone'] = "123456";

$arr['email'] = "adam@mail.com";

$arr['address'] = "U.S";

Great, let’s convert the array data to the class.

$obj = Converter::toObject($arr, new Employee());

var_dump($obj);

Look at the result:

Cool!!

You can convert an array to object using PHP hydrator pattern.

Convert Object to Associative Array

What about converting the object to an associative array, it’s the same concept, we are going to create a new function that does the opposite.

Our function will search for all get() functions the same way as the previous function like this:

public static function toArray($object)
{
$array = array();

$class = get_class($object);

$methods = get_class_methods($class);

foreach ($methods as $method) {

preg_match(' /^(get)(.*?)$/i', $method, $results);

$pre = $results[1] ?? '';

$k = $results[2] ?? '';

$k = strtolower(substr($k, 0, 1)) . substr($k, 1);

If ($pre == 'get') {

$array[$k] = $object->$method();
}
}
return $array;
}

Add this function to our converter class and call it with a passed object like this:

var_dump(Converter::toArray($obj));

Note that the passed $obj here is the generated object from the array to object conversion process.

The output shows the associative array as expected.

I hope you find the post useful. Keep coming back.

Thank you.

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Process Large Files Using PHP

By on 29 Temmuz 2019 in GNU/Linux İpuçları

If you want to process large files using PHP, you may use some of the ordinary PHP functions like file_get_contents() or file() which has a limitation when working with very large files. These functions rely on the memory_limit setting in php.ini file, you may increase the value but these functions still are not suitable for very large files because these functions will put the entire file content into memory at one point. Any file that has a size larger than memory_limit setting will not be loaded into memory, so what if you have 20 GB file and you want to process it using PHP? Another limitation is the speed of producing output. Let’s assume that you will accumulate the output in an array then output it at once which gives a bad user experience. For this limitation, we can use the yield keyword to generate an immediate result.

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SplFileObject Class

In this post, we will use the SplFileObject class which is a part of Standard PHP Library.

For our demonstration, I will create a class to process large files using PHP.

The class will take the file name as input to the constructor:

class BigFile
{
protected $file;
public function __construct($filename, $mode = "r")
{
if (!file_exists($filename)) {
throw new Exception("File not found");
}
$this->file = new SplFileObject($filename, $mode);
}
}

Now we will define a method for iterating through the file, this method will use fgets() function to read one line at a time.

You can create another method that uses fread() function.

Read Text Files

The fgets() is suitable for parsing text files that include line feeds while fread() is suitable for parsing binary files.

protected function iterateText()
{
$count = 0;
while (!$this->file->eof()) {
yield $this->file->fgets();
$count++;
}
return $count;
}

This function will be used to iterate through lines of text files.

Read Binary Files

Another function which will be used for parsing binary files:

protected function iterateBinary($bytes)
{
$count = 0;
while (!$this->file->eof()) {
yield $this->file->fread($bytes);
$count++;
}
}

Read in One Direction

Now we will define a method that will take the iteration type and return NoRewindIterator instance.

We use the NoRewindIterator to enforce reading in one direction.

public function iterate($type = "Text", $bytes = NULL)
{
if ($type == "Text") {
return new NoRewindIterator($this->iterateText());
} else {
return new NoRewindIterator($this->iterateBinary($bytes));
}
}

Now the entire class will look like this:

class BigFile
{
protected $file;
public function __construct($filename, $mode = "r")
{
if (!file_exists($filename)) {
throw new Exception("File not found");
}
$this->file = new SplFileObject($filename, $mode);
}
protected function iterateText()
{
$count = 0;
while (!$this->file->eof()) {
yield $this->file->fgets();
$count++;
}
return $count;
}
protected function iterateBinary($bytes){
$count = 0;
while (!$this->file->eof()) {
yield $this->file->fread($bytes);
$count++;
}
}
public function iterate($type = "Text", $bytes = NULL)
{
if ($type == "Text") {
return new NoRewindIterator($this->iterateText());
} else {
return new NoRewindIterator($this->iterateBinary($bytes));
}
}
}

Parse large Files

Let’s test our class:

$largefile = new BigFile("file.csv");
$iterator = $largefile->iterate("Text"); // Text or Binary based on your file type
foreach ($iterator as $line) {
echo $line;
}

This class should read any large file without limitations Great!!

You can use this class in your Laravel projects by autoloading your class and add it to composer.json file.

Now you can parse and process large files using PHP easily.

Keep coming back.

Thank you.

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How to prevent SQL injection attacks?

By on 25 Temmuz 2019 in GNU/Linux İpuçları

Before we talk about how to prevent SQL injection, we have to know the impact of SQL Injection attack which is one of the most dangerous attacks on the web. The attacker can steal your data or even worse, the whole web server can be stolen from one SQL injection vulnerability. I wrote this post to show you how to prevent SQL injection. If you need to know more about SQL injection itself and its types and all other stuff, you can do a simple search on google if you want. The solution is to clean the request parameters coming from the user . Keep in mind that the solution that I’ll share with you is not like the most solutions on the web that go to every SQL statement and clean the request variables one by one.

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My solution is preventing SQL injection without messing with your CMS files. Well, maybe someone who is using PHP would say that is easy, it is just using a function like mysql_real_escape_string or mysqli_real_escape_string. But that works only on a single dimensional array, what about a multi-dimensional array? Well, we need to iterate over array items recursively. So what we will do is preventing SQL injection against a multidimensional array.

Solution

This code does the magic for both single and multidimensional arrays using PHP:

if (!function_exists("clean")) {
//Gets the current configuration setting of magic_quotes_gpc if on or off
if (get_magic_quotes_gpc()) {
function magicquotes_Stripslashes(&$value, $key) {
$value = stripslashes($value);
}
$gpc = array(&$_COOKIE, &$_REQUEST);
array_walk_recursive($gpc, 'magicquotes_Stripslashes');
}
function clean(&$value, $key) {
//here the clean process for every array item
// use mysqli_real_escape_string instead if you use php 7
$value = mysql_real_escape_string($value);
}
}
$req = array(&$_REQUEST);
array_walk_recursive($req, 'clean');

The PHP function used to walk through the request multidimensional array is array_walk_recursive.

Just put this code on the top of your site or header file right after connecting to the database, your file could be up.php or header.php or something similar.

Because if you use this code before the connection occurs, it will show an error because you are using mysql_real_escape_string function which needs a SQL connection.

If you are using PHP 7, you’ll notice that MySQL extension is removed, so in order to make the above code working, you need to replace the function mysql_real_escape_string with mysqli_real_escape_string.

One final thing I have to mention regarding your code, you should keep your SQL parameters on all of your pages between quotes like this:

mysql_query("select * from users where email='$email' order by id");

Notice how the variable $email is quoted.

Without quoting your input like the above statement, SQL injection prevention won’t work.

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Apache NetBeans IDE 11.1 duyuruldu

By on 22 Temmuz 2019 in Programlama

Apache NetBeans IDE’nin 11 döngüsünün LTS sürümünün Apache NetBeans 11.0 olduğu belirtilirken, 11.1 sürümünün, LTS sürümü kadar ağır olarak test edilmediği belirtiliyor. Bu nedenle sürümün daha az kararlı olabileceği ifade ediliyor. Nisan 2020’de yayınlanması planlanan bir sonraki LTS sürüm için geri bildirim sağlamak üzere 11.1 sürümünün kullanılmasının önemli olduğu belirtilirken, ilgili sürümü indirmek isteyen kullanıcıların buradan yararlanabilecekleri söyleniyor. The Apache Software Foundation,  Apache NetBeans IDE 11.1 hakkında ayrıntılı bilgi edinmek için sürüm duyurusunu inceleyebilirsiniz.

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Apache NetBeans IDE 11.1 edinmek için aşağıdaki linkten yararlanabilirsiniz.

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cURL 7.65.3 duyuruldu

By on 19 Temmuz 2019 in İnternet

cURL ve liburl adlı iki kısımdan oluşan, özgür ve açık kaynak kodlu bir yazılım olan cURL‘un 7.65.3 sürümü duyuruldu. cURL’un yeni sürümünün arabalar, televizyonlar, yönlendiriciler, yazıcılar, ses ekipmanları, cep telefonları, tabletler, set üstü kutular, medya oynatıcıları gibi platformlarda kullanılan ve milyarlarca insanı her gün etkileyen binlerce yazılım uygulaması için internet üzerinden aktarma omurgası işlevi gören bir yazılım olduğu hatırlatıldı. cURL kütüphanesi; curl_init(), curl_setopt(), curl_exec(), curl_close(), curl_getinfo() gibi fonksiyonlara sahiptir. cURL; FTP , FTPS, HTTP, HTTPS, TELNET, DICT, FILE ve LDAP gibi protokolleri destekler. Pek çok platformda çalışmak üzere tasarlanmış olan libcurl ise ücretsiz , hızlı, IPv6 uyumlu , ve daha pek çok zengin özelliğe sahip olan bir kütüphanedir. cURL; RedHat , Debian , FreeBSD gibi pek çok sistemle birlikte ön tanımlı olarak gelmektedir. cURL 7.65.3 hakkında ayrıntılı bilgi edinmek için değişiklikler sayfasını inceleyebilirsiniz.

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cURL 7.65.3 edinmek için aşağıdaki linkten yararlanabilirsiniz.

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