Difference Between Linux and UNIX
UNIX is copyrighted name only big companies are allowed to use the UNIX copyright and name, so IBM AIX and Sun Solaris and HP-UX all are UNIX operating systems. The Open Group holds the UNIX trademark in trust for the industry, and manages the UNIX trademark licensing program.
Linux is a UNIX Clone
But if you consider Portable Operating System Interface (POSIX) standards then Linux can be considered as UNIX. To quote from Official Linux kernel README file:Linux is a Unix clone written from scratch by Linus Torvalds with assistance from a loosely-knit team of hackers across the Net. It aims towards POSIX compliance.However, "Open Group" do not approve of the construction "Unix-like", and consider it misuse of their UNIX trademark.
Linux Is Just a Kernel
Linux is just a kernel. All Linux distributions includes GUI system + GNU utilities (such as cp, mv, ls,date, bash etc) + installation & management tools + GNU c/c++ Compilers + Editors (vi) + and various applications (such as OpenOffice, Firefox). However, most UNIX operating systems are considered as a complete operating system as everything come from a single source or vendor.As I said earlier Linux is just a kernel and Linux distribution makes it complete usable operating systems by adding various applications. Most UNIX operating systems comes with A-Z programs such as editor, compilers etc. For example HP-UX or Solaris comes with A-Z programs.
Common Things Between Linux & UNIX
Both share many common applications such as:- GUI, file, and windows managers (KDE, Gnome)
- Shells (ksh, csh, bash)
- Various office applications such as OpenOffice.org
- Development tools (perl, php, python, GNU c/c++ compilers)
- Posix interface