"No space left on device" error makes Safari unusable.

Thank you all for helpful suggestions. I finally got so fed up (and as a software developer myself, have infinite patience with software) that I called Apple Support (first time!). The person on the other line was really helpful, and seems to have fixed the issue for me. Here was my experience with the tech support.

Problem : While tech support was on the line (and had remote access to my machine), I Googled "Safari "No space left on device". I tried to navigate to several of the search results. Virtually all of them gave me the same "Safari can't open the page" error.

What appears to have fixed the problem : Safari->Preferences->Websites. Then scroll down left pane to "Pop-up Windows". The Apple technical support had me select "allow" for all websites I had previously set to "block and notify". What may have really been the trick, though was to select "allow" "When visiting other websites". I then restarted Safari, and tried the same Google search. I was able to navigate to all sites that had previously failed.

I am hopeful that this fixed the problem, but will report back. One mystery is that this issue was fairly sporadic. Sometimes a website would load fine, other times not. Are websites - even those visited regularly, so bloated with random pop-ups that they can load one day, and fail the next?

BTW, I had IP tracking off already, so that didn't seem to be the issue. Also, it doesn't seem that it is a DNS failure, or a cache issue.

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I believe I have found the source of this error. I had been running the "Cisco Anyconnect Secure Mobility client" VPN app along with the "Cisco Anyconnect socket filter" app. Although we had switch VPN at my university several months (maybe even a year?) previously, I discovered in network preferences that the Cisco socket filter was still running. I removed the filter from Network preferences and haven't had the error since.

I did the following (although in retrospect, my approach was probably overkill) :

• Moved the whole Cisco Anyconnect app to the trash. (this was probably a bit drastic - I could have used the Cisco uninstaller).
• In /Library/LaunchAgents, I removed the file `com.cisco.anyconnect.gui.plist` (again the uninstaller might have done this for me)
• In network preferences, I removed the running socket filter.
• In Activity Monitor, I Force Quit the running instance of the socket filter.

At least in my particular situation, am 99.9% sure the Cisco VPN app was the culprit.

Mac Jim ID :

It seems that it is related to pop-up windows (see my reply below). But I will look into EtreCheck - always good to have more diagnostic tools.

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Update on "allowing pop-up windows" : This solution only worked for a few hours. Then the Safari error came back. See my solution above (get rid of Cisco Anyconnect).