In output of ps -elf command in linux, we can recognize that process flag of 4 and 1, and process flag of 5, (sum of 1 and 4), but what is meaning of process flag 0 ?
unfortunately, man does not help us completely...
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Flags are represented by the bitwise OR of their numeric value; this is called a mask. As long as the flags are incompatible, adding them gives the same result, but reasoning in terms of additions obscures the way to find flag values from the mask.
4 means “used super-user privileges”, and 1 means “forked but didn't exec”, as indicated in the manual. 5 means that both flags apply. 0 means that neither flag applies. 0 always means that none of the flags are set.