What Really Sets Linux Apart from Unix? Key Differences Explained

Linux is not Unix, though it is derived from Unix and is a Unix‑like operating system. This article lists several noticeable differences between the two.

1. Bash is not the standard shell

On all Unix systems the default shell is sh, not Bash. The POSIX standard describes the language used by sh. Many Linux systems make sh a symlink to Bash, allowing use of Bash features that are not portable to other systems.

2. Unix does not include long options

Unix commands support short options (single dash) and long options (double dash). Short options are usually abbreviations, while long options are full words. GNU tools often provide long options (e.g., grep --count), but other systems such as BSD may not support them; the standard getopts utility and the getopt C function only handle short options.

3. Make differs from GNU make

The POSIX version of make is more limited than GNU make. Many aspects of the specification are incomplete, especially logical or conditional operators. Workarounds include moving logic to a configure script that generates another Makefile. BSD’s syntax also differs from GNU’s, but on macOS and Linux you can safely rely on GNU features.

4. C compiler differs from GCC

When invoking a C compiler in Makefiles, use the variable $(CC) and for C++ use $(CXX). Most BSD systems now default to Clang and may not provide a gcc executable. Outside Makefiles, the commands cc and c++ work across all systems.

5. GNU differs from Linux

GNU interfaces are not guaranteed to appear on every Linux distribution. For example, Alpine Linux uses the musl C library and BusyBox instead of GNU tools. Using portable interfaces is advisable even when targeting Linux only.

6. Unix differs from UNIX

Unix and UNIX are not identical; the latter is a trademark requiring certification by The Open Group. macOS is a certified UNIX system, and most Unix‑like systems (including BSD and GNU tools) strive to follow the UNIX specifications.