Running ps aux just gave me the following output:
...
www-data 26254 0.0 0.7 27304 3544 ? S 15:07 0:00 /usr/sbin/apache2 -k start
1001 25807 0.8 0.8 48444 4332 ? Sl Sep03 1330:24 ./ts3server_linux_x86
...www-data is the apach2 user. That's okay, it's what I expected with -u, but what is 1001?
5 Answers
It means that user id is 1001 but that id has no name assigned. This can happen for example a command running in a chroot with a user defined in that chroot will not necessarily have a name assigned outside the chroot.
This can happen if the username is longer than 8 characters.
1This is most like user's id (uid) for a user which was removed after the process was started. Or perhaps there was some kind of failure resolving username from uid.
It is a uid for users whose name is unknown (e.g. an uid missing in /etc/passwd) or perhaps with strange spelling (like maybe Debian-exim, or a user with a long enough user-name, or for a bad entry in /etc/passwd)
It's the user ID. There are cases where Linux doesn't display usernames (this can be a permissions issue). Check out this thread:
