Well, the processes aren't going one-after-another, they're started one-after-another, and then all run at the same time, and either one can finish before the other even begins to run ...

Anyway what you posted has typos as "dev/null" is not "/dev/null"

also cwd could be anything so you should make sure its what you want/need it to be

web UI is giving error that 'No data Received'.

Study the following things :) Proc::Background, Highlander: one instance at a time (Oct 00), Watching long processes through CGI (Aug 02), Re: ERROR on CGI script:The timeout specified has expired