What does aux mean in `ps aux`?
a = show processes for all users
u = display the process's user/owner
x = also show processes not attached to a terminal
By the way,
man psis a good resource.
Historically, BSD and AT&T developed incompatible versions of
ps. The options without a leading dash (as per the question) are the BSD style while those with a leading dash are AT&T Unix style. On top of this, Linux developed a version which supports both styles and then adds to it a third style with options that begin with double dashes.
In the comments, you say you are using Apple MacOS (OSX, I presume). The OSX man page for
psis here and it shows support only for AT&T style.
According to my manual page (MacOS), u means "Display the processes belonging to the specified usernames"
@jordanm In this manual page, there is not any explained option without leading dash, I am afraid.
@HowardGuo I have updated the answer to reflect the differences between the GNU (Linux) version of `ps` and the Apple OSX version. This question is currently tagged "Linux". If you are asking also about MacOS, you might want to update the tags.
Thanks very much. I just checked manual page of ps in Linux and it has information regarding `aux`, MacOS' manual page does not have such information, it might be a document bug.
OSX man page for `ps` does say "... `ps aux` still works as it did in Tiger" under "Legacy Description" section.
@dev the whole paragraph reads: _The biggest change is in the interpretation of the -u option, which now displays processes belonging to the specified username(s). Thus, "ps -aux" will fail (unless you want to know about user "x"). As a convenience, however, "ps aux" still works as it did in Tiger._
I have to object to the comment that "`man ps` is a good resource on mac OSX. The man page, only at the very end, notes that `ps aux` is maintained as a convenience, but there is absolutely no hint that options may be specified without leading hyphens before the end, the man page is long and richly complex, and a reader can spend a lot of time questioning his/her sanity before giving up and googling for this stackexchange question.