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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?

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migrated from Dec 22 '11 at 16:46

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up vote 2 down vote accepted

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.

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This can happen if the username is longer than 8 characters.

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Quote man ps under NOTES section: "If the length of the username is greater than the length of the display column, the numeric user ID is displayed instead." – Ciro Santilli 巴拿馬文件 六四事件 法轮功 Nov 15 '13 at 16:07

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.

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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)

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+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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