Joomla version view file

Joomla 1.7.x
root\librairies\joomla\version.php:
the version is mentioned in the lines var $RELEASE (for the release version)
and var $DEV_LEVEL (for the maintenance version).
root\template\system\css\system.css:
the version is not clearly mentioned, but you know that you are running 1.7 version
thanks to this line: @version $Id: system.css 21322 2011-05-11 01:10:29Z dextercowley $.
If you do not have a FTP access, you can also open the system.css file in your browser.
root\languages\en-GB\en-GB.ini:
the version is not clearly mentioned, but you know that you are running
1.7.1 thanks to the 1st line of this .ini file ; $Id: en-GB.ini 20990 2011-03-18 16:42:30Z infograf768 $,
1.7.3 if the 1st line is ; $Id: en-GB.ini 22183 2011-09-30 09:04:32Z infograf768 $,
1.7.5 if the 1st line is ; $Id: en-GB.ini 22183 2011-09-30 09:04:32Z infograf768 $.

Joomla 2.5.x
By FTP, go to root\librairies\cms\version\version.php:
the version is mentioned in the lines public $RELEASE (for the release version)
and public $DEV_LEVEL (for the maintenance version).
By FTP, go to root\template\system\css\system.css:
the version is not clearly mentioned, but you know that you are running
2.5 thanks to this line: Copyright (C) 2005 – 2014 Open Source Matters, Inc.
If you do not have a FTP access, you can also open the system.css file in your browser.
By FTP, go to root\languages\en-GB\en-GB.xml: the version is mentioned in the file, in the version tag.
For Joomla < 3.8.x: root\libraries\cms\version\version.php

For Joomla >= 3.8.x: root\libraries\src\Version.php