今天在使用ps -aux的时候，发现有一句提醒
Warning: bad syntax, perhaps a bogus '-'? See /usr/share/doc/procps-3.2.8/FAQ
使用man ps发现下面一段话
Note that "ps -aux" is distinct from "ps aux". The POSIX and UNIX
standards require that "ps -aux" print all processes owned by a user
named "x", as well as printing all processes that would be selected by
the -a option. If the user named "x" does not exist, this ps may
interpret the command as "ps aux" instead and print a warning. This
behavior is intended to aid in transitioning old scripts and habits. It
is fragile, subject to change, and thus should not be relied upon.