Devices that you are connected to usually need your attention. For the Mac this means having to check the machine from time to time and take steps to ensure it runs optimally. Whether this means cleaning the machine of junk data with the help of a Mac optimization app such as CleanMyMac or by performing disk maintenance depends on the situation you encounter.
A disk check isn't something you'd perform too often, though, unless the system's built-in monitoring utility S.M.A.R.T. sends signals that suggest the hard drive is about to fail or if partitioning a drive gives an error message.
On top of that, macOS has powerful built-in utilities to address issues with the file system. Especially now that Apple has migrated its user base over to its new Apple File System (APFS) after the release of High Sierra, you might want to be assured that everything is fine with your data.
To do that macOS has two powerful utilities: the more user-friendly Disk Utility (which has a nice GUI) and fsck (short for File System Consistency Check), a command-line utility which is only recommended for advanced users comfortable with controlling a Mac using text commands.
Using Disk Utility to Repair a Startup Disk
Thanks to its “Live Verification” feature, Disk Utility can be used to check the Mac's startup disk without starting the computer from another volume. Live Verification works only on MacOS X Extended (Journaled)-formatted (HFS+J) volumes, so if you are trying to verify other volumes then it will only display an error message.
If the utility finds any irregularities then you'll need to start the Mac up from another volume – such as a Mac OS X install DVD – enter macOS Recovery, or start up from Internet Recovery and run Disk Utility to repair the disk. If Disk Utility fails to repair the volume, that’s when you’ll need to run fsck.
Cases When You Need to Run Disk Utility or Fsck
The Mac will signal the use of fsck if it has run into issues and needs your attention to fix them. So if you notice the following symptoms on startup then the Mac has encountered issues with the file system and it needs repairing, with either Disk Utility or fsck. Keep an eye out for these symptoms:
- If the Mac partially starts up and then displays a message prompting you to run fsck, then this usually displays a command-line prompt, indicated by a number sign (#). As the command line suggests, run fsck.
- If the Mac isn't able to reach the login screen after booting.
- If the Mac does reach the login screen but fails to load the desktop after the user has logged in.
How to Fix File System Issues with Disk Utility
There are two ways to fix such serious file system issues. Apple strongly recommends using Disk Utility first, so here is how to address disk faults using this powerful utility:
- Start your Mac in Recovery Mode, or Internet Recovery if you're are running 10.6 or later. Older versions of OS X require an install disk so insert the Superdrive and press C shortly after you hear the boot chime.
- Launch Disk Utility.
- Select your startup disk.
- Run First Aid.
If Disk Utility is unable to fix the issue, proceed with fsck.
How to Fix File System Issues with Fsck
The system utility fsck is a tool for checking the file system consistency in Unix and Unix-like operating systems such as macOS, Linux, and FreeBSD. Fsck is invoked before the file systems are mounted, so you need to mount the boot volume first for write access so you can fix any issues with the file system. To do that, the Mac needs to start in Single-User Mode, an extremely minimal environment with no GUI and no system daemons running. To address the file system issues, do the following:
- Start your Mac in Single-User Mode by holding down the Command + S keys at startup.
- At the command-line prompt type:
- Hit Return and wait for fsck to finish the five ‘phases’ that it needs to go through.
Once this is done the system will highlight the success of the tool, with one of two messages:
- If no issues were found, it will display the following message:
- If it finds issues, it will display the following message:
** The volume [name of volume] appears to be OK.
***** FILE SYSTEM WAS MODIFIED *****
In case the system has found issues then you will need to repeat step 2 above until fsck reports that your volume appears to be OK. Once this is achieved, simply type ‘reboot’ and then press Return to restart the computer.
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