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I am trying to edit my hosts file on Mac OS X Lion 10.7.4. I've tried all the Terminal trickery I can, but I always get "Operation not permitted" when attempting to modify the file. I've tried:

sudo chmod 777 /etc/hosts
sudo chmod nouchg /etc/hosts
sudo cp ~/hosts /etc/hosts

All fail with "operation not permitted" messages. Here's the output of ls -lO@e /etc/hosts:

-rw-r--r--  1 root  wheel  uappnd,nodump,opaque 2073 Sep 22  2010 /etc/hosts

Unfortunately, I have no idea how to read most of that. Any tips?

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up vote 4 down vote accepted

The user append-only flag is set. Run

sudo chflags nouappnd /etc/hosts

and you should be able to edit and save the file as the superuser.

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And for that matter, why are the nodump and opaque flags set? – Gordon Davisson Jul 21 '12 at 3:47

Do not change any permissions to hosts.

To use vi to edit the file:

sudo vi /etc/hosts

Enter your password and you can edit and save.

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That won't work. The uappend flag only allows the file to be appended to. Even root cannot overwrite the file when this flag is set. – Kyle Jones Jul 21 '12 at 18:19
It works with 10.6.8. Is the uappend flag new to 10.7? – broomdodger Jul 22 '12 at 6:18
No, those file flags are very old. They were inherited from FreeBSD, which inherited them from 4.4BSD. Probably the earliest Mac OS X releases had them, certainly 10.4-10.7 do. The question is why uappend was set on /etc/hosts. It isn't set on my 10.7.4 Lion (Server) installation. Neither it nor opaque nor nodump make sense there, except perhaps in a virtual machine context. – Kyle Jones Jul 22 '12 at 17:36

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