Sync Checker is a diagnostic application which can check if two folders or disks are perfectly synchronized, i.e. if they have exactly the same contents. When creating backup copies of valuable files, or when making sure that two computers or mobile devices work on the same set of data, the status of being “in perfect sync” can be very important. In order to be safe and to prevent loss of data, you can let Sync Checker verify whether a pair of file collections are matching exactly or not.
In other situations, it might be interesting to find differences between file sets. For example, you might like to know which files have changed on your computer, comparing a Time Machine backup of last Friday with one of last Tuesday. It could also be interesting to find out where exactly two macOS system installations of two computers are differing. The latter task is also known as “sysdiffing”, a technical term derived from a utility used on Windows platforms to perform similar operations.
After performing a sync check, Sync Checker will either confirm that all files are identical, or it will present all detected mismatches. You can browse through the differing items, analyzing exactly where a mismatch occurred, and if the differences are critical or negligible. Filter tools help you to navigate through large sets of mismatching objects. Ignore lists assist you to exclude objects in advance, based on their names or file system locations. You can also create a textual report of the results which can be printed or exported.
It is even possible to analyze the results offline: You can save the mismatch report as document into a file and evaluate it, perhaps on some other computer, at a later time. When working with an offline document, the results will be presented in the same fashion as if you had performed a sync check online.
You can also save an offline scan of a hierarchy of folders for later use. With certain restrictions, such an archived snapshot of file system objects can be used as a complete substitute for “real” files when performing a sync check. For example, you could scan files on a different computer, transfer the scan result to your computer, and use it as a virtual source of data to check if a specific set of files match. This method can also be used to compare the state of files at different points in time, even if you don’t have access to a backup: Scan the contents of a folder and use the archived data later to perform a sync check with live data from the same folder. The results will show you exactly what has changed.
Sync Checker can compare any files in folders which can be accessed by macOS via “disk-like” devices. Here are some examples:
The main task of Sync Checker is to verify if two file sets are in sync. This means the two collections of files should have at least some similarities. It does not make sense to compare two folders which have nothing in common. Otherwise, the resulting list of differences would be so large that you can no longer handle it.
In addition to this natural restriction, there is also a technical reason why it should be avoided that the number of differences becomes too high: Sync Checker will present the list of differences after the check has been completed, so it has to store all details about the mismatching objects temporarily in memory. A high number of differences will need a large amount of memory which could overload small computers. To avoid technical problems that could arise if a sync check would need too much memory, Sync Checker automatically limits the number of differences which can be evaluated.
When using Sync Checker, you can select in advance how many mismatching objects you like to accept during the compare operation. The maximum number of mismatches you can preselect is 100,000. There are no limits regarding the number of objects you can compare. For example, you can check an entire system disk containing 2 million files with a Time Machine backup of this disk which should also contain almost 2 million files.
To use Sync Checker, you’ll need a computer which has one of the following operating systems installed:
Sync Checker is constantly evolving, adapting to new features in the latest versions of macOS. New versions are released as (usually free) updates from time to time. To check manually if a new version of Sync Checker is available for download, select the menu item Sync Checker > Check for updates. For automatic checks in regular intervals when you are launching the application, set a check mark at the menu item Sync Checker > Automatic Update Checks.