File Extensions in Linux

Understanding File Extensions in Linux
Extensions are file name suffixes that start with a period. Usually, they are two or three letters long. 

Linux can read many file extensions used by other platforms, such as 

jpg for a graphic file, or .html for a web file. It can also use 
them for mime types. However, Linux does not always use extensions to identify file types. 

Often, the directory where a file is placed is a better indication of what type of file it is. 

However, Linux does use a few regular extensions.

Extensions Used in Linux

Extension	File Type
.bz2	A file compressed using bzip2 .
.c	A file written in the C programming language.
.conf	A configuration file. In some cases, "conf" is used in a file name, but not as an extension.
.deb	A Debian package for installing software.
.lock	A lock file that prevents the use of another file.
.rpm	A Red Hat package file. Although you can sometimes use .rpm s in Debian, doing so can have unexpected results and is not generally recommended. You can also convert packages using the alien utility .
.so	A shared object (a library or module).
.src	A source code file. Written in plain text, a source file must be compiled to be used.
.tar	A single file made of a collection of files archived using the tar command.
.tar.gz	A single file made of a collection of files archived using the tar command, then compressed used the gzip command.
.tgz	A single file made of a collection of files archived using the tar command, then compressed used the gzip command.
.gz	A file compressed using the gzip command.
.txt	a plain ASCII text file
.ps	a PostScript file; formatted for printing
.au	an audio file
.wav	an audio file
.xpm	an image file
.jpg	a graphical or image file, such as a photo or artwork
.gif	a graphical or image file
.pdf	an electronic image of a document
.a	an archive file
.h	a C or C++ program language header file
.cpp	a C++ program language source code file
.o	a program object file
.php	a PHP Script
.sh	a Shell Script
.png	a graphical or image file
.tcl	a TCL script
.pl	a Perl script
.html/.htm	an HTML file