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?


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.


This 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)

  • +1 for "long enough"; ps has a strange default limit. – grawity Dec 22 '11 at 19:37

It's the user ID. There are cases where Linux doesn't display usernames (this can be a permissions issue). Check out this thread:


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