Repair Disk Permissions ./usr?

Question

This is the second time I've seen this after running my Repair Disk Permissions. Does anyone know what this means?
Group differs on ./usr, should be 0, group is 80
Owner and group corrected on ./usr
Permissions corrected on ./usr
I've had my Mac for 2 years and run my Repair Disk Permissions regularly - I've only seen this once before a few months ago and now.
Also, where would I find ./usr
Thanks for any help or info.
BJArt

Answer 1

I'm the only one that uses my Mac....
The operating system is made up of many small applications called processes. Each of these processes has a user (owner) and a group associated with it. Open the Activity Monitor in the Utilities folder and select All Processes in the drop down menu. You are not alone! You should see yourself running applications (processes) and at least root and nobody listed as users. You may be the only login user on your computer but the operating system contains many non-login users that control different processes. The root user primarily controls the operating system. In OS X the root user is a non-login user unless you make root a login user.
Who am I?
Every user has a primary group associated with that user. Let me do the "heavy lifting" from within the Terminal application. Of course you can try the command to see the ---text_output---. I'll use the command id to see who I am:
[purplehaze:~] fred% id
---text_output---
uid=501(fred) gid=501(fred) groups=501(fred), 79(appserverusr), 80(admin), 81(appserveradm)
I'm user 501(uid) whose shortname is fred. My primary group(gid) is 501 or fred. I belong to 4 groups. Because I belong to the group admin, I can install system software and perform tasks only the root user can do.
Who are they?
Let's look at the id for the root user:
[purplehaze:~] fred% id root
---text_output---
uid=0(root) gid=0(wheel) groups=0(wheel), 1(daemon), 2(kmem), 3(sys), 4(tty), 5(operator), 20(staff), 31(guest), 80(admin)
root's primary group (gid) is 0 or wheel. You can express users and groups in words or numbers. The root user belongs to many groups tied to running the operating system. Let's query the netinfo database for all the users on my computer showing the uid and gid in numbers, their shortname, where their home folder is, and their realname:
[purplehaze:~] fred% nireport . /users uid gid name home realname
---text_output---
-2 -2 nobody /var/empty Unprivileged User
0 0 root /var/root System Administrator
1 1 daemon /var/root System Services
99 99 unknown /var/empty Unknown User
25 25 smmsp /private/etc/mail Sendmail User
26 26 lp /var/spool/cups Printing Services
27 27 postfix /var/spool/postfix Postfix User
70 70 www /Library/WebServer World Wide Web Server
71 71 eppc /var/empty Apple Events User
74 74 mysql /var/empty MySQL Server
75 75 sshd /var/empty sshd Privilege separation
76 76 qtss /var/empty QuickTime Streaming Server
77 6 cyrus /var/imap Cyrus User
78 78 mailman /var/empty Mailman user
79 79 appserver /var/empty Application Server
501 501 fred /Users/fred Mark Jalbert
502 502 saraswati /Users/saraswati saraswati
Users above 500 are login users. User 501 was created when I installed my system software . User 502 is another login user on my system that I created. I have the ability to create other users because I belong to the group admin (80) Remember- only the root user or users who belong to the group admin can perform changes to the OS. Users below 500 where created by the operating system during installation and are responsible for running processes tied to the OS.
Hopefully, I haven't lost you in to much techno babble. You are not the root user but you are a member of the group admin. This allows you to take on the role of the root user and make changes to the operating system. As I said before- It's not a big deal whether the /usr folder has the group admin associated with it. If repairing permissions will not permanently change the group to 0 (wheel) then I suspect you may have some file corruption. From the Finder > Go menu > Go to Folder... type /usr and click to Go button to see inside the /usr folder.