Q&A: MacFixIt Answers

MacFixIt Answers is a feature in which I answer Mac-related questions e-mailed in by our readers.

This week, readers asked about the necessity of running regular permissions fix routines, how to prevent Time Machine from backing up over VPN, and resizing PDF files in QuickLook.

I welcome contributions from readers, so if you have any suggestions or alternative approaches to these problems, please post them in the comments!

Question: The necessity and utility of running regular permissions fix routines
MacFixIt reader Jim asks:

I was taught it was a good idea to occasionally do a "repair permission" periodically, and I also do this when experiencing some little glitch in the Mac's performance. Is this a necessary step?

Answer:
Repairing permissions won't hurt anything, but it won't necessarily help, either. If there are slowdowns and access errors, this can help, but if not, it won't do a thing to speed the system up and keep it running nicely.

Permissions on files are a complex matter, but overall the file simply needs to be readable, optionally executable, or writable by the appropriate user or system process. There are numerous permissions settings that allow this for any given file, but in the permissions fix routine the files are only tested for one specific permissions setup. Therefore when you run the permissions fix you will likely see a number of "errors" that show up, but in the vast majority of cases these errors reflect a subtle change that has no effect on access to the files.

Apple's permissions database contains settings that are "known to work," but are by no means the only settings that will work.

Question: Preventing Time Machine from backing up over VPN
MacFixIt reader Francis asks:

While I'm at work I often VPN to my home network; Time Machine sees my Open NAS server and starts the backup. However since the bandwidth is somewhat limited, I would like to prevent Time Machine from running backups while I'm at work. Is there an automated way of doing that? The only way I have found so far is to turn off Time Machine in the System Preferences and turn it back on when I get home.

Answer:
There is no way to do this with Apple's built-in settings, but tools like Time Machine Scheduler will override Apple's settings with their own scheduling options and can limit networked Time Machine backups to a given Wi-Fi network name and SSID. You can also use them to turn off backups during a time range such as when you will be at work.

Question: Resizing PDF files in QuickLook so they appear in full-width instead of full-page view
MacFixIt reader Gon asks:

Is there a way to use QuickLook for a PDF file in full-width view instead of as a full page onscreen?

Answer:
By default QuickLook will show you as much of the PDF as it can, so it will present at full-page view. However, you can zoom in once the PDF is displayed by pinch-zooming until the PDF is the desired size.

If you do not have a multitouch trackpad, then you can hold the Option key and scroll up and down to change the zoom level of the QuickLook view.

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