[SOLVED] `exec` hangs when command is executed from Java/Groovy

LXD
1

Problem:

The following command never finishes when executed from Java: (example using in Groovy)

println "lxc exec example-test -- echo Hi".execute().text

What I have tested:

  • Java Runtime.getRuntime().exec() also halts when using process.waitFor().
  • Any other command like: lxc info example-test, etc. has not problem
  • "echo Hi".execute().text returns ‘Hi’ as expected.
  • Running the same command from bash returns immediately.
  • Interestingly, running it inside perl, the code won’t return unless I press enter.

Checking the Java native source code (java.io), it seems that BufferedInputStream.readBytes its waiting for a termination character that is never returned. However I can see in the buffer the value: “Hi\n” (followed by zeros) just before waiting forever.

Any suggestions on how to debug or make it work?

2

That’s probably because that environment provides some bogus stdin which causes lxc to hang during read from stdin.

Did you try using -n, -T or --mode non-interactive? Chances are that one of those will make this work.

3

Thanks for your reply, I really appreciate it.

Yes, -n did the trick. This is the command I applied:

lxc exec example-test -n -- echo 'Hi'

Thanks!