The restricted shell

There are different ways to what a user can do on a system and there are a lot of reasons why we would restrict a user's ability to interact with a system: maybe we want a user just to be able to copy a file to and from the system or to have a simple home where they can work on their tasks without peeking around the system. Anyway, whatever is our goal we can start working with a restrict shell.

Bash itself offers an additional layer of security using the following options:

• rbash
• --restricted
• -r

Invoking rbash or simply bash with the --restricted or -r options spins a Bash instance that trims down what the users will be able to do on such an environment:

• The user cannot change the directory using the cd builtin. The user will be prevented to set or unset the values for the following environment variables:
  • BASH_ENV
  • ENV
  • SHELL
  • PATH
• The user will not be able to specify command names with slashes and this means no command names with absolute paths.No filenames containing a slash can...