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 nullshell
 =========
 
-do nothing but print asterisks, can be used for login shell
+**do nothing but print asterisks, can be used for login shell**
+
+This is a minimal program that does nothing but print asteriks every now
+and then. It is intended to be used for login shell with accounts
+accessible via secure shell that are used for secure tunneling but
+should not allow to execute commands.
+
+Requirements
+------------
+
+To compile and run `nullshell` you need:
+
+* nothing (this is plain C)
+* [markdown](http://daringfireball.net/projects/markdown/) (HTML documentation)
+
+Additionally it is expected to have `make` and a C compiler around to
+successfully compile.
+
+Build and install
+-----------------
+
+Building and installing is very easy. Just run:
+
+> make
+
+followed by:
+
+> make install
+
+This will place an executable at `/usr/bin/nullshell`.
+
+Usage
+-----
+
+To create a new user `user` with `nullshell` as login shell just run:
+
+> useradd -s /usr/bin/nullshell user
+
+Or to make `nullshell` the login shell for an existing user `user`:
+
+> usermod -s /usr/bin/nullshell user
+
+Make sure `/usr/bin/nullshell` is listed in `/etc/shells` if your system
+expects this.