Screen sharing not working in mountain lion

Well, finally after almost a year of pain I have figured out the problem. The application firewall was blocking the requests (observed in /var/log/ does not automatically reload the plist. You have to delete/rename /Library/Preferences/com.apple.alf.plist

The file with the current settings is /usr/libexec/ApplicationFirewall/com.apple.alf.plist, but it is only loaded if

/Library/Preferences/com.apple.alf.plist is missing. The /Library version is binary and cannot be edited.

Deleted the file, rebooted, and VNC worked fine.

Thank you. Wow. I tried all until I got to your advice nothing worked.

I have the same problem after updating ARD on my 2008 Xserve running OS 10.7, and the same on my MacPro running 10.9!! I cant access the screen, but it shows me available but connecting fails. What can I do? Its very annoying. Fortunately I can shut down the Xserve with Apple Remote Desktop. I were happily if someone has an answer, because I need it every day at work.

Deleting /Library/Preferences/com.apple.alf.plist worked for me on an iMac host, which had been successfully Screen Sharing on the home LAN to a Macbook Air and a Macbook Pro, all using OSX 10.8.5, until the iMac had its video card replaced by Apple. An additional clue was that Screen Sharing would also work if System Preferences/Security/Firewall was turned off.

I too have experienced a recent problem with screen sharing on 10.8.5.

At first I thought it was an incomapatibility between my 10.9 machine & ML. Tried most of the fixes here (sorry haven't read all 12 pages). What worked for me (think it was point 2 mainly):

1. Manually installed Apple Remote Desktop Client 3.7 (dated 22 Oct 2013)

2. After a reboot, respond to prompt "do you want 'screensharingd' to accept incoming connections?"

It would appear that the issue was a Firewall problem, and re-installation reset this to 'Prompt' rather than an explicit Allow/Deny.

I suggest that this may also be the reason the logout/login of BTMM works?

Hope this helps.

Removing /Library/Preferences/com.apple.alf.plist and rebooting solved my problem after installing OS X Update 10.8.5. Everything was working fine on all 3 of my systems until I applied this update tonight - Apple, time to validate your patches before releasing them; standard ITIL procedure.... Thanks PK Tjo o Tjim for posting - great find!

Yes, I have the same problem. Removing /Library/Preferences/com.apple.alf.plist and rebooting solves the problem for a while, but OS-X 10.8.5 eventaully recreates the file and blocks screen sharing again.

And the problem is back...

After a reboot (for unrelated reasons) the problem has reoccurred.

I note that in the Firewall Preference panel, both Screen Sharing & Remote Management are listed 'above the line' and cannot be changed. Both have a Green traffic light.

For some reason 'screensharingd' was also listed below the line, and had a Red traffic light.

I have removed the item (rather than changing it) & temporarily diabled the Firewall.

Screen Sharing is working again.

awhittall wrote:

And the problem is back...

After a reboot (for unrelated reasons) the problem has reoccurred.

I note that in the Firewall Preference panel, both Screen Sharing & Remote Management are listed 'above the line' and cannot be changed. Both have a Green traffic light.

For some reason 'screensharingd' was also listed below the line, and had a Red traffic light.

I have removed the item (rather than changing it) & temporarily diabled the Firewall.

Screen Sharing is working again.

Problem back for me too. Not sure at what point it resurfaced, I don't access the Mac Pro from my MBPro daily. I've tried my old fix of removing the sharing preferences on the Mac Pro, closing Preferences and reopening and resetting them back. No luck. The Mac Pro also cannot share the screen of the MBPro anymore either, but that was done very infrequently so I have no idea when that started. I have Intego NetBarrier & VirusBarrier, tried to access the settings the other day and the app went into a state where it caused a Force Quit. Am going to uninstall and reinstall as soon as I can. NetBarrier does set "Allow-Deny" for various apps. I even tried setting it to "Protection Off" and same results - no screen sharing; although that doesn't rule it out. Can share network disks, no problem; just the screen sharing is not working. Did recently upgraded my ISP, got a new high speed modem which has its own firewall. So there is an OS X firewall, the modem firewall and my NetBarrier. Never had a problem with them conflicting before, and I'm not sure if screen sharing was good before the modem upgrade. Frustrating...

Tom

For me, removing /Library/Preferences/com.apple.alf.plist and rebooting always works.

This is OK for me and my wife, since the host iMac stays on for weeks at a time.

I have seen a user comment that suggests changing the status of scrrensharingd (below the line in security/firewall settings) to allow.

I wil try that next time.

chesters wrote:

For me, removing /Library/Preferences/com.apple.alf.plist and rebooting always works.

This is OK for me and my wife, since the host iMac stays on for weeks at a time.

I have seen a user comment that suggests changing the status of scrrensharingd (below the line in security/firewall settings) to allow.

I wil try that next time.

I didn't find that preference. Did find the security/firewall screensharing deny (below the line), which I deleted; it didn't have an option to allow. So I added the Core Services Screen Sharing. I also did an uninstall/reinstall of NetBarrier. All to no avail. Still no access to my Mac Pro from my MBPro on my home network. Small inconvenience but irritating. I have a hunch it is something small causing it since I do have access to all my disks on the network still.

Tom

This issue has plaguing me since upgrading to 10.8.5 on my MBA, and I found no proper solution, but looks like it is an ARD issue. This issue has been fixed (at least for me) since I downloaded the latest update for ARD to 3.7.1 (via App Store updates), sweet!

Ah, thank PK Tjo o Tjim. Renaming /Library/Preferences/com.apple.alf.plist did the trick!

What I find when I delete /Library/Preferences/com.apple.alf.plist, and then reboot, the Firewall turns off, which could be why screensharing works again, but upon reboot again, the problem returns. I didn't try renaming it, so perhaps that works. Updating ARD to 3.7.1 resolves the issue for me.

I followed your instructions and successfully connected to the first machine I set up on :5900, then proceeded to map all the other machines :5901...:5905 but have not been able to connect to any machines accept the :5900.

Any thoughts on where to troubleshoot?

Thanks