OSX and "Necessary Permissions"

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OSX and "Necessary Permissions"

Post by therealorion » Fri Jan 08, 2016 12:00 pm

I am trying to migrate (slowly) from OSX to Mint, which in large part involves having access to the same data (old documents and videos, mostly), but when I try to access my OSX drive from inside Mint, I see almost all of the folders with X's in the corners, and only a few without them. When I click on the X'd folders, I get this:
You do not have the permissions necessary to view the contents of [directory]

When I click on the few other folders, I can read them. I cannot write to the drive at all.

So: a) how do I get permissions (within OSX?), and b) is there a way to write to these drives?
- The Real Orion

Mint 17.3, Mackbook 5,1 (2009)

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Re: OSX and "Necessary Permissions"

Post by cholq » Mon Jan 11, 2016 11:03 am

Have you turned on File Sharing on your Mac (System Preferences -> Sharing -> check "File Sharing" checkbox)? It should default to giving your mac ID read/write permission.

I tried doing this, and I was able to see my shared folder on the Mac from Mint file manager. When I click on the folder, I had to enter my Mac's ID and Password, but at that point I could see all the directories located within my Mac login's home directory (documents, downloads, music, etc...). I was able to create a file on my mac from Mint.

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Re: OSX and "Necessary Permissions"

Post by srs5694 » Mon Jan 11, 2016 10:07 pm

Assuming you're talking about a dual-boot configuration, the issue is that your user IDs (UIDs) don't match between OS X and Ubuntu. More background: Unix-like systems, including both OS X and Linux, use numeric UID values to identify files' owners. These numbers are then "translated" to (and from) usernames by system tools. In Linux, the mappings are stored in /etc/passwd for a basic configuration, or in various other places (including network servers) for more advanced setups. The default first UID number in most Linux distributions, including Mint, is 1000. You can check this in various ways, such as by typing "id":

Code: Select all

$ id
uid=1000(rodsmith) gid=1000(rodsmith) groups=1000(rodsmith),4(adm),8(mail),24(cdrom),27(sudo),30(dip),46(plugdev),108(lpadmin),124(sambashare),133(mythtv),136(libvirtd)
This example shows the current UID to be 1000, plus a bunch more information, much of it system-specific.

Under OS X, the default first UID is 501. Again, you can type "id" in a Terminal to check this.

If your UIDs are not syncronized across the two OSes, the files you create under OS X will seem to be owned by another (possibly non-existent) user in Mint, and vice-versa. You can make this work if you set permissions very loosely, but this tends to fall down pretty easily, and for security reasons, it's better to synchronize your UID (and perhaps GID) values. This is a little easier to do in Linux than in OS X, but you can do it in either OS. For complete instructions, see:
There are, of course, other pages that describe how to do it in both OSes. Googling "{OS name} change UID" will turn up lots of hits. Be aware that there are perils to making such changes; if you miss something critical you can end up unable to log in or with any manner of bizarre malfunctions. You should change it in just one OS -- set your UID in Mint to 501 or set your UID in OS X to 1000 (assuming you've got the default UIDs in both OSes).

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