Manage time machine backups

Some times you get some errors saying that your time machine's disk is full and Time Machine could not complete the backup so you need to  manually delete old backups.

tmutil provides methods of controlling and interacting with Time Machine, as well as examining and manipulating Time Machine backups. Common abilities include restoring data from backups, editing exclusions, and comparing backups.

tmutil latestbackup

Will output the path to the most recent backup and

tmutil listbackups

will list all existing backups, if you use the same backup disk for multiple machines, you can get just the backups from your machine with:

tmutil listbackups | grep "$(scutil --get ComputerName)"

The following command will delete the backups from a mac named old_mac_name:

sudo tmutil delete /Volumes/drive_name/Backups.backupdb/old_mac_name

If you want to be safe, you can pick one snapshot to delete first to be sure the command works as intended. This is nice since it could take hours to clean up some larger backup sets and you want to leave the Mac confident it's deleting the correct information store.

You can use the tmutil tool to delete backups one by one.

sudo tmutil delete /Volumes/drive_name/Backups.backupdb/mac_name/YYYY-MM-DD-hhmmss

Since tmutil was introduced with Lion, this will not work on earlier OS versions.

The tmutil delete command only removes the backup from the sparse bundle. It doesn’t actually free the disk space. To do that, you have to go a little deeper.

On your Mac is a mount point called /Volumes. You can examine the contents of this mount point with ls:

cd /Volumes
ls -1

Should output something like:

Macintosh HD
Recovery HD
Time Machine Backups
TimeMachine

These are the names of all the mounted disks (or things that look like disks) on your Mac. Notice two likely candidates for your actual TimeMachine volume. Yours may be named slightly differently, but the one you want is the one that actually shows files of type .sparsebundle . In my case, it is the volume TimeMachine:

sudo ls -l TimeMachine/

and you should see something similar to:

...
drwxr-x---@ 1 root wheel 264 Jul 25 08:21 sysadmin’s MacbookPro.sparsebundle
...

Notice that you don’t actually own the file. (Had I not used the sudo command with ls I could not have listed the contents of /Volumes/TimeMachine)

That .sparsebundle file for your Mac is where all your backup sets live. TimeMachine manages the contents of this file, but doesn’t do anything automatically to reduce its size. Luckily there is another tool for that, but you’ll have to be root to run it:

sudo su -
hdiutil compact /Volumes/TimeMachine/YourBackup.sparsebundle

Sample output:

Starting to compact…
Reclaiming free space…
...................................................
Finishing compaction…
Reclaimed 3.1 GB out of 304.1 GB possible.

That’s it! In this example I reclaimed 3.1GB of actual disk space on my TimeMachine volume. 

The following bash script will remove the oldest backup and reclaim the free space:

COMPUTER_NAME=$(/usr/sbin/scutil --get ComputerName)
NBACKUPS=$(/usr/bin/tmutil listbackups | /usr/bin/grep "$COMPUTER_NAME" | /usr/bin/wc -l)
OLDEST_BACKUP=$(/usr/bin/tmutil listbackups | /usr/bin/grep "$COMPUTER_NAME" | /usr/bin/head -n1)
LATEST_BACKUP=$(/usr/bin/tmutil latestbackup)
echo Latest backup: $LATEST_BACKUP
if [[ -n "$LATEST_BACKUP" && "$LATEST_BACKUP" != "$OLDEST_BACKUP" ]]
then
    echo "$NBACKUPS backups. Delete oldest: ${OLDEST_BACKUP##*/} [y/N]? \c"
    read answer
    case $answer in
   y*)
  echo Running: /usr/bin/sudo /usr/bin/tmutil delete "$OLDEST_BACKUP"
  /usr/bin/sudo time /usr/bin/tmutil delete "$OLDEST_BACKUP"
    echo "Do you wish to reclaim the free space now? [y/N]? \c"
    read answer
    case $answer in
    y*)
     mkdir -p /Volumes/TM
     mount_afp 'afp://user:pass@afp_server_address/share_name' /Volumes/TM
     hdiutil compact "/Volumes/TM/$(scutil --get ComputerName).sparsebundle"
     umount /Volumes/TM/
    ;;
    *)
 echo No change
    ;;
        esac
   ;;
   *)
  echo No change
   ;;
    esac
else
    echo "No backup available for deletion"
fi

In the script above, don't forget to change the afp URL (afp://user:pass@afp_server_address/share_name) to your own.