Having an issue as well with updating on a Mac running OS X 10.10.4.
In the bottom right of screen, I get the little notifications about it downloading, preparing, etc., but when it gets to the “restarting Sonarr to apply update”, nothing seems to happen. I have restarted the computer to see if it kicks it along with no success.
Not sure if it is the same problem as the OP, but here is what it says in the Update log:
15-7-29 15:58:55.0|Info|UpdateApp|Starting Sonarr Update Client
15-7-29 15:58:55.0|Info|UpdateApp|Updating Sonarr to version 2.0.0.3357
15-7-29 15:58:55.1|Debug|UpdateApp|NzbDrone process ID: 346
15-7-29 15:58:55.1|Debug|UpdateApp|Arguments:
15-7-29 15:58:55.1|Debug|UpdateApp| 346
15-7-29 15:58:55.1|Debug|UpdateApp| /var/folders/33/c69hc0_54xv003q5wl_96fmw0000gp/T/nzbdrone_update
15-7-29 15:58:55.1|Debug|UpdateApp| /Applications/Sonarr.app/Contents/MacOS/NzbDrone.exe
15-7-29 15:58:55.1|Debug|UpdateApp|Using executing application: /Applications/Sonarr.app/Contents/MacOS/NzbDrone.exe
15-7-29 15:58:55.1|Debug|UpdateApp|Executable location: /Applications/Sonarr.app/Contents/MacOS/NzbDrone.exe
15-7-29 15:58:55.1|Info|UpdateApp|Starting update process. Target Path:/Applications/Sonarr.app/Contents/MacOS
15-7-29 15:58:55.1|Info|InstallUpdateService|Verifying requirements before update…
15-7-29 15:58:55.1|Debug|ProcessProvider|Finding process with Id:346
15-7-29 15:58:55.1|Warn|ProcessProvider|Unable to find process with ID 346
15-7-29 15:58:55.1|Fatal|UpdateApp|An error has occurred while applying update package.
System.ArgumentException: Process with ID doesn’t exist 346
at NzbDrone.Update.UpdateEngine.InstallUpdateService.Verify (System.String targetFolder, Int32 processId) [0x000c3] in m:\BuildAgent\work\6c3239faf2b92630\src\NzbDrone.Update\UpdateEngine\InstallUpdateService.cs:75
at NzbDrone.Update.UpdateEngine.InstallUpdateService.Start (System.String installationFolder, Int32 processId) [0x00000] in m:\BuildAgent\work\6c3239faf2b92630\src\NzbDrone.Update\UpdateEngine\InstallUpdateService.cs:79
at NzbDrone.Update.UpdateApp.Start (System.String[] args) [0x00020] in m:\BuildAgent\work\6c3239faf2b92630\src\NzbDrone.Update\UpdateApp.cs:59
at NzbDrone.Update.UpdateApp.Main (System.String[] args) [0x00042] in m:\BuildAgent\work\6c3239faf2b92630\src\NzbDrone.Update\UpdateApp.cs:43