Run child processes as different user from a long running process

Question

I've got a long running, daemonized Python process that uses subprocess to spawn new child processes when certain events occur. The long running process is started by a user with super user privileges. I need the child processes it spawns to run as a different user (e.g., "nobody") while retaining the super user privileges for the parent process.

I'm currently using

su -m nobody -c <program to execute as a child>

but this seems heavyweight and doesn't die very cleanly.

Is there a way to accomplish this programmatically instead of using su? I'm looking at the os.set*uid methods, but the doc in the Python std lib is quite sparse in that area.

Answer 1

There is an os.setuid() method. You can use it to change the current user for this script.

One solution is, somewhere where the child starts, to call os.setuid() and os.setgid() to change the user and group id and after that call one of the os.exec* methods to spawn a new child. The newly spawned child will run with the less powerful user without the ability to become a more powerful one again.

Another is to do it when the daemon (the master process) starts and then all newly spawned processes will have run under the same user.

For information look at the manpage for setuid.