Making the iOS Simulator case sensitive

Posted on March 08, 2013

In Dave Koziol’s iOS Debugging session at CocoaConf, he pointed out that the iOS Simulator does not have a case sensitive file system. As the actual device does have a case sensitive file system, this allows bugs to enter your application unnoticed.

Here’s a few scripts to create and mount a RAM disk in place of the iOS Simulator directory. Please close the simulator completely before running these scripts, and note that this will reset your simulator. You could persist the data if you wanted, but I notice that the simulator gets wonky after too long anyhow.

Mounting Simulator on RAM-disk:

pushd ~/Library/Application\ Support
diskutil erasevolume hfsx "Simulator" `hdiutil attach -nomount ram://2314836`
rm -rf iPhone\ Simulator
ln -s /Volumes/Simulator/ iPhone\ Simulator

Returning to normal:

pushd ~/Library/Application\ Support
rm -rf iPhone\ Simulator
hdiutil detach /Volumes/Simulator

Don’t take my word for it:

int main(int argc, char *argv[])
    @autoreleasepool {
        NSFileManager *fileMan = [NSFileManager defaultManager];
        NSURL *docs = [fileMan URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask][0];

        NSURL *lowercaseDocUrl = [docs URLByAppendingPathComponent:@"lowercase.txt"];
        NSURL *uppercaseDocUrl = [docs URLByAppendingPathComponent:@"LOWERCASE.TXT"];

        assert(![fileMan fileExistsAtPath:lowercaseDocUrl.path]);
        assert(![fileMan fileExistsAtPath:uppercaseDocUrl.path]);
        assert([@"Hello" writeToURL:lowercaseDocUrl atomically:YES encoding:NSASCIIStringEncoding error:nil]);
        assert([fileMan fileExistsAtPath:lowercaseDocUrl.path]);
        assert(![fileMan fileExistsAtPath:uppercaseDocUrl.path]); // will crash on case-insensitive filesystem

        NSLog(@"All assertions passed. We're case sensitive.");

        return 0;