run spawns a single child process, then waits for it and all descendants to complete, while reaping zombie processes and forwarding Unix signals to the entire process group.

Years ago, when the concept of the "cloud" was just emerging, I imagined it as a collection of networked Linux computers, each fully set up, and with a service manager I could configure to run my software. It turned out I was wrong: Docker containers run only one process, and cloud providers essentially charge us per each process we start. Not a good state of affairs, but I cannot change the world. All I want is to run inside my container something as simple as:

/bin/run sh -c 'service1 & service2 & service3 &'

and reduce my cloud bill by two-thirds.

▶ ./run -h
Usage:
  run [-qset] cmd [args...]
  run [-hv]

Start `cmd`, then wait for it and all its descendants to complete.

Options:
  -q       Reduce logging level (may be given more than once).
  -s SIG   Send signal SIG to all remaining processes when one terminates;
           SIG can be any of: INT, TERM, KILL, QUIT, HUP, USR1, USR2.
  -e CODE  Minimal process exit code to trigger the above signal (default: 0).
  -t N     Wait N seconds before sending KILL signal to all remaining processes.
  -h       Show this help and exit.
  -v       Show version and exit.

With no options run simply starts the given command and waits for it and all descendants to complete, otherwise:

• With -s option it sends the given signal to the entire process group when any process terminates. Note: Linux shells typically block INT and QUIT signals.
• With -e option the above signal is sent only when a process exits with a code greater or equal to the one specified.
• With -t option KILL signal is sent to all the remaining processes after the specified timeout.

Options -e and -t are meaningless without -s. In practice -s and -t are usually set to reflect Docker defaults: -s SIGTERM -t 10.

Exit code from run is that of the first process terminated with non-zero code, or 0 if all completed successfully.

git clone https://github.com/maxim2266/run.git
cd run
make image

The last command builds an image according to the provided dockerfile. The compiled binary in the container is statically linked with musl library.

Other targets:

• make test to run all tests in a container;
• make to build the program locally.

At the moment the program does the intended job reasonably well, but there are other features that would be nice to have in the future:

• Ability to launch multiple services without a shell.
• Collect STDOUT and STDERR from each service individually, to make sure they don't share the same Unix pipe.
• Service management, able (at least) to restart a process without shutting down the whole container.
• setuid, although this is likely to (massively) complicate the code.

I don't know if anything of the above will ever be implemented.

BSD-3-Clause