Category Archives: OS X

One-liner: Check the five, most important SMART parameters on a disk.

A while ago, Backblaze published a report on what they consider to be the most reliable SMART parameters for determining whether a disk is failing. These include:

  • 5 – Reallocated_Sector_Ct
  • 187 – Uncorrectable_Error_Cnt
  • 188 – Command_Timeout
  • 197 – Current_Pending_Sector_Count
  • 198 – Offline_Uncorrectable

For a complete description of these parameters, take a look at the Wikipedia article on SMART.

While our sample of failing disks is no where near as large as Backblaze’s, our results have, unsurprisingly, correlated pretty strongly to theirs.

Note that not all of these parameters are supported by the drive manufacturers and that we typically don’t see many of these parameters on the hard disks supplied in Apple hardware. Additionally, note that SMART is not supported on some drives.

Assuming you’ve got smartmontools installed, this one-liner will very quickly give you a snapshot of the key values we look for as strong indicators that a drive needs to be replaced:

smartctl -a disk0 | egrep "^( 5|187|188|197|198)"



is the disk you’re testing. To get the disks available to test, run

diskutil list

You’ll get back output that looks like this:

   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *256.1 GB   disk0
   1:                        EFI                         209.7 MB   disk0s1
   2:                  Apple_HFS Macintosh HD                 255.2 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.1 GB   disk1
   1:                        EFI                         209.7 MB   disk1s1
   2:                  Apple_HFS Storage                 499.8 GB   disk1s2

In the example above, there are two disks to choose from,




Assuming the drive supports all five SMART parameters, you’ll get back something that looks like this:

  5 Reallocated_Sector_Ct   0x0033   100   100   010    Pre-fail  Always       -       0
187 Reported_Uncorrect      0x0032   100   100   001    Old_age   Always       -       0
188 Command_Timeout         0x0032   100   100   001    Old_age   Always       -       0
197 Current_Pending_Sector  0x0032   100   100   001    Old_age   Always       -       0
198 Offline_Uncorrectable   0x0030   100   100   001    Old_age   Offline      -       0

Those trailing zeros are what we like to see. Positive values in the last column mean that the drive probably needs to be replaced.

10.8/10.9 Security Update 2015-004 & broken SSL.

After updating a couple of 10.8 Macs with Security Update 2015-004, we observed problems with iTunes and App Store. Attempting to update apps in iTunes yielded messages like this:

Screen Shot 2015-04-15 at 12.33.50 PM

It took some digging, but we stumbled onto this post that suggested that it may be a problem with Verisign SSL certificates.

When we opened the login keychain, we found two “VeriSign Class 3 Public Primary Certification Authority – G5” certificates. The cert expiring in 2036, with serial number beginning in

18 DA D1

is the certificate you want to keep.

Removing the other certificate immediately resolved the issue.

On affected Macs, problems also appear in Safari and Chrome.  It does seem to be intermittent; we’re not hearing that this is widespread.

On the surface, it appears that this is related to changes Apple made in the certificate trust policy.