Unix Background process STOPPED abnormally

There are several ways a process running in the background can be stopped. All of them involve one of these signals:

• SIGSTOP
• SIGTSTP
• SIGTTOU
• SIGTTIN

SIGSTOP is severe. It's unblockable, unignorable, unhandlable. It stops the process as surely as SIGKILL would kill it. The others can be handled by the background process to prevent stopping.

• A signal was sent by another process using kill(2), or by the process to itself using raise(3) or kill(2)
• The process attempted to write to the terminal, and the terminal option tostop is enabled (see output of stty -a). This generates SIGTTOU.
• The process attempted to change the terminal modes with tcsetattr(3) or an equivalent ioctl. (These are the same modes shown by stty.) This generates SIGTTOU regardless of the current state of the tostop flag.
• The process attempted to read from the terminal. This generates SIGTTIN.

This list is probably very incomplete.

Are you using tcsh by any chance? Tcsh actually comes with a built-in nohup command that I've had lots of problems with before, seeing the exact behavior you're seeing.

Try using /usr/bin/nohup directly if that is the case.