Optimal way to set and read variables

Question

I need to set 6 variables which are used by several services and applications in Linux. I have so far been using the environment variables, but find it very complicating to modify these variables throughout multiple users. At the same time I wish that all users are able to modify these variables that are used globally.

My solution so far has been to use SQLite instead, but seems to be a bit of a mess when I want to set the variables within a service daemon.

So the question is, is it possible or even realistic to use global environment variables that can be altered by any user or should I consider a database solution such as SQLite?

E.g. if i have a variable IP_RECIPIENT, this variable has to be accessed and set by all users in the system. If it is altered, all users should be able to read the changes, in other words it has to be global even when altered and not just local.

Also whats the best-practice for using global environment variables within Arch Linux ARM.

Answer 1

A simple solution might be to have these variables set in a file, making that file world-writeable and sourcing it from /etc/bash.bashrc. That way, the variables would be available to all users, any change in the sourced file would be kept after reboot and would also be available to any new shells started. Note that any open shells will not have their values updated.

1. Create the file with the variable definitions and make it world readable

   printf "%s=%s\n%s=%s\n" "var1='foo'" "var2='bar'" | sudo tee /etc/variables
   sudo chmod a+w /etc/variables
   

   That will create a file called /etc/variables with the following contents:

   var1='foo'
   var2='bar'
   

2. Edit /etc/bash.bashrc to make it source that file

   sudo printf "\n## Source global variables\n. /etc/variables\n" | 
       sudo tee -a /etc/bash.bashrc
   

Now, any changes in that file will be reflected in any new interactive non-login shells.

---

If you need this to be immediately inherited even by open shells, you could use bash's PROMPT_COMMAND variable:

   PROMPT_COMMAND
          If set, the value is executed as a command prior to issuing each
          primary prompt.

Edit /etc/profile and add this line:

PROMPT_COMMAND='. /etc/variables'

Once you have done this, any changes in the /etc/variables file will be immediately available to all shells since the file will be sourced before every prompt is shown. Note that this will only take effect after your users have logged back in since they will need to read /etc/profile again.