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PHP uses a hash algorithm for password encryption. For this, PHP has a variety of methods - 

• md5()
• crypt()
• password_hash()

MD5 algorithm is a one-way encryption algorithm and generates a 32-bit characters string which is also called hash hexadecimal number for any word the user puts in the input. The md5() function calculates the respective hash for a given string. The function is md5(string, parameter), where the string is the input given by the user and the parameter is optional value to pass. 

The crypt algorithm generates the password without the salt. The salt is a random string used in modifying the password hash. The salt string distinguishes between two passwords if different users possess the same password. The function is crypt($string, $salt) that does hashing and returns the hashed string using Blowfish, MD5, or DES algorithm.

The password_hash() function creates a strong password using one way hash function. One way hash function validates the hashed output only if the result is matched with the value returned after passing the original value to the algorithm. The function syntax is password(string, algorithm, options) where the string is the required string that needs to be encrypted, algorithm it is using, and options is the associative array that contains options.

A trigger is a set of SQL statements that are automatically invoked in response to any insertion, update, or deletion that occurs in the database tables. For example, when a database table is inserted, updated, or deleted 1000 times, then 1000 times the trigger program will be invoked.

Repairing a table in MySQL is done with REPAIR command. 

• REPAIR TABLE <table_name> QUICK - Repair of the index tree only.
• REPAIR TABLE <table_name> EXTENDED - create the index row-by-row.

The nl2br() function is used to insert line breaks in a strong when needed. For example, nl2br("Welcome to UltraGenius") will give you the output - Welcome to UltraGenius.

Following are the key linux command that every freelance LAMP developer must use.

• cd
• ls
• mv
• rm
• cp
• rmdir
• mkdir
• chown
• chmod
• locate
• updatedb
• tar
• cat
• locate
• less
• grep
• reboot
• passwd
• du
• hal

SQL injection can be prevented by the following ways - 

• Using stored procedure - Stored procedure helps in preventing the SQL injection, because input arguments are treated as true value of the text rather than command. Stored procedure are SQL commands that are saved in the database in order to reuse them multiple times.
• Using Prepared Statements - Prepared Statements prevent changing the commands during the SQL injection attacks. Prepared Statements are the pre-compiled instructions that are stored in a program and can be used over multiple times. Prepared Statements have binded parameters which are considered as plain values.
• Using Object Relational Mapping (ORM) -  ORM is a  programming model in which the database is converted into an object that represents the database structure. ORM makes the developers easily communicate with the database using the UPDATE, INSERT, SEARCH, and DELETE.
• Input Validation - Input Validation is extremely necessary before submission by the server. The inputs which are doubtful are filtered before only. 
• Least Validation - The developer must use only the least number of privileges to potentially reduce the SQL injection attacks. You can grant the privileges as per your need.
• Character Escaping - Character escaping allows pa programmer to treat some special characters like "/_" as an SQL injection attack. It tells programmers that these characters should be treated as a string instead of a command.
• Using sqlmap - Scanning the SQL injections manually includes lots of work. To use sqlmap is an effective and efficient option when searching SQL injection attacks in thousands of lines of code. Run the sqlmap in the command line and pass the targeted URL which generates the result that is inserted into a log file where the possible points of attacks can be analyzed. The development team then takes the mandatory actions , for example, code patching or code refactoring.
• Using firewall for web application - A Web Application Firewall is used to protect your website by filtering the SQL injection patterns in an HTTP requests. The most common known WAFs are - 
• NGINX WAF - NGINX WAF is an audit logging UI ModSecurity tool which is used by the system adminstrators to monitor system.

Apache runs as nobody or apache by default. It shows ps aux  |  egrep ' (apache|httpd)'

All the Apache configuration files are located in /etc/httpd/conf directory. 

The Apache HTTP server is responsible for serving HTTP requests and supplies only the static content like HTML text, audio, images, and videos in response while Tomcat is a servlet container that provides the dynamic content in response to Java servlet requests.