CODEWITHSUNDEEP
shellunix
Haravikk
Haravikk

Reputation: 3290

Reliable IPC With Shell Scripts

Okay, so I have two shell scripts, a server and a client, where the server is always run as root, and the clients can be run as standard users in order to communicate with the server.

The method I've chosen to do this is with a world-accessible directory containing named pipes (fifos), one of which is world-writable (to enable initial connection requests) and the others are created per-user and writable only by them (allowing my server script to know who sent a message).

This seems to work fine but it feels like it may be over-engineered or missing a more suitable alternative. It also lacks any means of determining whether the server is currently running, besides searching for its name in the output of ps. This is somewhat problematic as it means that writing to the connection fifo will hang if the server script isn't available to read from it.

Are there better ways to do something like this for a shell script? Of course I know could use an actual program to get access to more capabilities, but this is really just intended to provide secure access to a root service for non-root users (i.e - it's a wrapper for something else).

Upvotes: 1

Views: 1835

Answers (1)

Kevin
Kevin

Reputation: 30161

You could use Unix domain sockets instead of fifos. Domain sockets can be created with nc -lU /path/to/wherever and connected to with nc -U /path/to/wherever. This creates a persistent object in the filesystem (like a fifo, but different). The server should be able to maintain multiple simultaneous connections over the same socket.

If you're willing to write in C (or some other "real" programming language), it's also possible to pass credentials over Unix domain sockets, unlike fifos. This makes it possible for the server to authenticate its clients without needing to rely on filesystem permissions or other indirect means. Unfortunately, I'm not aware of any widely-supported interface for doing this in a shell script.

Upvotes: 3

Related Questions