Why does Mathematica stop when run in the background in command line mode?

Question

If I try to start a Mathematica script in the background from the command line, like this:

math -script someFile.m &

then the process gets automatically suspended. Here's a terminal transcript for clarifications:

This happens both on Linux and OS X. Other programs don't typically stop when run in the background.

• Why does this happen?

• What can I do to prevent this?

Answer 1

Mathematica for unknown reasons is waiting for input. Possible solution

echo | math -script someFile.m &

Answer 2

This is because your shell doesn't allow background processes to print to the console. For instance tcsh has this behavior by default:

% echo "a"&
[1] 26502
% 
[1]  + Suspended (tty output)        echo a
% fg
echo a
a

In pretty much all shells you should be able to disable this behavior with stty -tostop

% stty -tostop
% echo "a" &
[1] 26539
a
%
[1]    Done                          echo a

Re-enable the behavior with stty tostop

You could also redirect the output so it never hits stdout at all:

% echo "a" > /dev/null &