'fseventsd' error messages in system logs

Periodically people will find various "fseventsd" related log entries such as an "out of sync" error in their system logs, and will wonder what is going on and whether or not the errors pose a problem.

Apple Discussion poster "Gerard James" writes:

"It seems that every time I connect a USB drive or FireWire drive to my iMac lately, I get a message like this in the console system log:

Apr 7 21:01:03 fseventsd39: event logs in /Volumes/250GB Drive/.fseventsd out of sync with volume. destroying old logs. (346 0 4864943)

Apr 7 21:01:03 fseventsd39: log dir: /Volumes/250GB Drive/.fseventsd getting new uuid: 43341D60-7F10-4DDE-8474-C726E1B1DE42

The drives work perfectly but I just don't understand the error messages."

Fseventsd is a low-level file system "events" notifier that can be used for logging changes in the file system. It runs as a daemon that launches very early at boot, which can be tapped for file system events by various programs, instead of having developers create their own event notification processes, each of which would have to be loaded early in the boot process and run continuously.

This daemon is used by Spotlight and Time Machine, since the fsevents daemon will help keep track of what has changed on the file system, and does this on a per-directory basis. Events are logged in the hidden ".fseventsd" directory at the root of the drive, and as such can be read by other software at any time, instead of having to actively scan the file system for changes all the time.

When there are error messages with the file system events, many times they will clear by themselves while the fsevents daemon "catches up" to and properly logs the changes in the file system. However, it can also occur from problems with the directory structure on the hard drive. If this is the case, there are several things you can do to check the drive's data structure; however, if not then more than likely the messages will go away after a while.

Possible fixes:

1. Disable and reenable journaling

Journaling may affect how fsevents interacts with data on the disk, so toggling it off and on for a specific disk may help. This can be done on both external and internal disks using Disk Utility. Launch the program and select the volume of the drive you wish to toggle journaling on. Then press the options key and from the "File" menu select "Disable Journaling." You may have to restart to complete this, but when journaling is disabled select the volume again and click the green "Enable Journaling" button in the Disk Utility toolbar.

2. Run disk verification

There are several ways to run directory verifications. The first is to use "Disk Utility" to verify and repair the drive. If you are doing this on the boot drive you will need to boot off the OS X installation disk and run Disk Utility from the "Utilities" menu there.

Alternatively, you can run the "fsck" utility on the drive. For non-boot drives, open the terminal and type "fsck -fy " (including the space after the command). Then drag the drive to the terminal window to complete the path to the drive's mount point, and press enter. For the boot drive, reboot the computer and hold the command and "S" keys simultaneously to get into "Single User" mode. From here, enter "fsck -fy /" at the command prompt and press enter. When it is completed enter "shutdown -r now" to reboot the system normally.

Beyond the tools that come with OS X, you can also try third-party utilities such as "Disk Warrior," "Drive Genius," "Tech Tool Pro," and "Drive Tools" to clear any potential disk problems.

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