nullshell

do nothing but print keep alive characters, can be used for login shell

This is a minimal program that does nothing but print some characters (namely version information and time&date string) 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 (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.