1
Under Unix each user belongs to one or more user groups, which allows the organization of their rights.
2
The type file_perm is an alias for the type int.
3
The options and the behavior of this command are not standardized. The given example may not be reproducible.
4
Molière, Le Bourgeois Gentilhome, Acte II, scène 4.

Link

http://www.site-moliere.com/pieces/bourgeoi.htm
5
We recall that the signals are handled in an asynchronous way. So, if two children die one after the other, it is possible that the signal of the first has not been handled.