It seems when su executes in a shell scripts, there is a timing race, sometimes, su will receive a SIGTTOU when parent su tries to set child su's process group as foreground group, and su will be stopped unexpectly, ignoring SIGTTOU fixes the problem.
It seems when su executes in a shell scripts, there is a timing race,
sometimes, su will receive a SIGTTOU when parent su tries to set child
su's process group as foreground group, and su will be stopped unexpectly,
ignoring SIGTTOU fixes the problem.

Noticed by: fjoe

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