List of usefull command line (updated)

* Last reboot time
      last reboot;

* Searching command
      greb filename;

* Searching for file in the computer
      tree -fa | grep filename;

* Real internet ip

     curl ifconfig.me;

     curl icanhazip.com;

* Real-time view of a running system.
     top
http://www.tecmint.com/12-top-command-examples-in-linux/

* vcgencmd

     vcgencmd measure_temp     vcgencmd measure_clock arm
     vcgencmd measure_volts core

http://elinux.org/RPI_vcgencmd_usage
http://www.maketecheasier.com/finding-raspberry-pi-system-information/

*Change mode of file
     chmod u=rwx,g=rx,o=r myfile

*testing PHP file
    php -f filename.php


*php information function

   <?php phpinfo();

*The sudo command can be used to obtain the privileges of other users too. I've installed the Apache web server, and the user www-data is automatically created during this process. If I want to edit a file using www-data's permissions, I can use the -u option:
  
   sudo -u www-data nano /var/www/somefile.txt

* Helpful sites
http://www.makeuseof.com/tag/15-useful-commands-every-raspberry-pi-user-should-know/

http://www.tecmint.com/command-line-tools-to-monitor-linux-performance/

http://www.tecmint.com/linux-performance-monitoring-tools/

http://www.stuffaboutcode.com/p/raspberry-pi.html