Why did chmod 775 work

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Level 1

39 points

Why did chmod 775 work

I recently was asked to look at a friend's Mac mini, which was stuck in the startup screen. That is, it would not progress past the gray screen with the Apple logo and spinning progress wheel.

The first thing I tried was starting in single user mode and running fsck, which took a while and did fix some errors. I ran it again and it returned no more errors.

I then started in verbose mode where it hung up on a repeating line, user-name-mac-pro com.apple.launchd[1] (com.apple.mDNSResponder[xxx]): posix_spawnp(''/usr/sbin/mDNSResponder, ...): No such file or directory

When I did a Google search on this it seemed that there were many people who had a similar issue and they found that performing the command chmod 775 /volume/"Macintosh HD" in Terminal worked. So, I thought I would try it. I didn't use Terminal but I was able to change the permissions for my HD to 775. It was 774. I know that is Read only, and 775 is Read and Execute. When I did this the Mac mini started up and everything worked.

Question: Why did this work? Why was the Mac mini not able to start up as Read only, and why was the mDNSResponder the file that was hanging?

Posted on Jun 22, 2011 7:22 AM

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Answer 1

Niel

Level 10

741,911 points

Jun 22, 2011 10:17 AM in response to plcmms

Allowing the option to read but not execute only makes sense for files. With regards to folders, the execute permission makes the folder searchable, which needs to be enabled for any folder which allows the corresponding read permission.

(58938)

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Answer 2

plcmms Author

Level 1

39 points

Jun 22, 2011 1:17 PM in response to Niel

Thanks Niel,

I'm just learning the reasons for these permissions, and this makes sense to me now. Thanks

I guess the mDNSResponder file must have been the first file that launchd attempted to run but couldn't because of the Read only permissions that the HD had. Is that correct?

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