pi@raspberrypi:/ $ sudo rm -R muddev
pi@raspberrypi:/ $ sudo mkdir muddev
pi@raspberrypi:/ $ ls
bin   dev  home  lost+found  mnt     opt   root  sbin  sys  usr
boot  etc  lib   media       muddev  proc  run   srv   tmp  var
pi@raspberrypi:/ $ cd muddev
pi@raspberrypi:/muddev $ ls
pi@raspberrypi:/muddev $ virtualenv never
Traceback (most recent call last):
  File "/usr/local/bin/virtualenv", line 11, in <module>
    sys.exit(main())
  File "/usr/local/lib/python2.7/dist-packages/virtualenv.py", line 768, in main
    symlink=options.symlink,
  File "/usr/local/lib/python2.7/dist-packages/virtualenv.py", line 1013, in create_environment
    install_python(home_dir, lib_dir, inc_dir, bin_dir, site_packages=site_packages, clear=clear, symlink=symlink)
  File "/usr/local/lib/python2.7/dist-packages/virtualenv.py", line 1214, in install_python
    mkdir(lib_dir)
  File "/usr/local/lib/python2.7/dist-packages/virtualenv.py", line 382, in mkdir
    os.makedirs(at_path)
  File "/usr/lib/python2.7/os.py", line 150, in makedirs
    makedirs(head, mode)
  File "/usr/lib/python2.7/os.py", line 150, in makedirs
    makedirs(head, mode)
  File "/usr/lib/python2.7/os.py", line 157, in makedirs
    mkdir(name, mode)
OSError: [Errno 13] Permission denied: '/muddev/never'
pi@raspberrypi:/muddev $