What is sudo?

Many first-time users of IOTstack get into difficulty by misusing the sudo command. The problem is best understood by example. In the following, you would expect ~ (tilde) to expand to /home/pi. It does:

$ echo ~/IOTstack
/home/pi/IOTstack

The command below sends the same echo command to bash for execution. This is what happens when you type the name of a shell script. You get a new instance of bash to run the script:

$ bash -c 'echo ~/IOTstack'
/home/pi/IOTstack

Same answer. Again, this is what you expect. But now try it with sudo on the front:

$ sudo bash -c 'echo ~/IOTstack'
/root/IOTstack

Different answer. It is different because sudo means "become root, and then run the command". The process of becoming root changes the home directory, and that changes the definition of ~.

Any script designed for working with IOTstack assumes ~ (or the equivalent $HOME variable) expands to /home/pi. That assumption is invalidated if the script is run by sudo.

Of necessity, any script designed for working with IOTstack will have to invoke sudo inside the script when it is required. You do not need to second-guess the script's designer.

Please try to minimise your use of sudo when you are working with IOTstack. Here are some rules of thumb:

1. Is what you are about to run a script? If yes, check whether the script already contains sudo commands. Using menu.sh as the example:

   $ grep -c 'sudo' ~/IOTstack/iotstack-menu.sh
   2
   

   A non-zero count means the designer thought about when sudo was needed.

   Technically, iotstack-menu.sh does not use sudo at all. The first of those two hits is actually a check for whether you have launched the menu using sudo, in which case the menu refuses to run. Absent this check, running the menu with sudo would just create a mess. The second hit is where the menu displays a command that you can copy/paste to install bash autocompletions, if you choose to do that.

2. Did the command you just executed work without sudo? Note the emphasis on the past tense. If yes, then your work is done. If no, and the error suggests elevated privileges are necessary, then re-execute the last command like this:

   $ sudo !!
   

It takes time, patience and practice to learn when sudo is actually needed. Over-using sudo out of habit, or because you were following a bad example you found on the web, is a very good way to find that you have created so many problems for yourself that will need to reinstall your IOTstack. Please err on the side of caution!

Configuration

To edit sudo functionality and permissions use: sudo visudo

For instance, to allow sudo usage without prompting for a password:

# Allow members of group sudo to execute any command without password prompt
%sudo   ALL=(ALL:ALL) NOPASSWD:ALL

For more information: man sudoers