Backing up your data is the most important thing you can do with your computer--even more important than tweeting or posting on Facebook. If you don't back up your Mac regularly, you may lose those photos that you want to share; you may find that your latest holiday videos are missing; and your music library may go poof!
Time Machine is a great tool for ensuring that your data is safe, and it's pretty easy to set up and use. But for some users, the basic Time Machine interface isn't enough. As with most of OS X's functions, there is a command-line tool that lets you do many things with Time Machine. Here's how you can use the tmutil command to control and tweak Time Machine from Apple's command-line tool, Terminal.
Most people won't need to use this command for their backups because the Time Machine interface will suffice. Who will need it? People who want to manage remote Macs or who want to run scripts containing commands for Time Machine.
The basics of the tmutil command can be found by typing man tmutil in Terminal. (You'll find the Terminal app in your /Applications/Utilities folder.) The man page tells you what you can do with this command.
For example, to turn Time Machine on or off, you can run these commands:
sudo tmutil enable
sudo tmutil disable
The sudo command is required for many of the commands you issue with tmutil because you need administrative privileges; you'll have to enter your password after running the above commands.
If you want to run a Time Machine backup right away, on a Mac that either has Time Machine disabled, or, say, just before updating to a new version of OS X, you can run this command:
This is the same as choosing Back Up Now from the Time Machine menu in the menu bar at the top of your screen.
And if you ever want to stop a backup, just run this:
Save disk space on your laptop
Since your laptop isn't always connected to its backup disk, Time Machine retains "local snapshots," or files that it will copy to your backup disk the next time it is available. However, these local snapshots take up space, and you may want to turn this feature off if you don't have much room on your hard disk. You can do so with the following command:
sudo tmutil disablelocal
Running this command will also delete any local snapshots. You can turn local snapshots back on by running:
sudo tmutil enablelocal
Exclude files and folders
You can exclude certain files and folders from your Time Machine backups from the Time Machine pane in System Preferences. Naturally, you can also do this from the command line, too. Run this command:
sudo tmutil addexclusion
The part stands for the path to a file or folder. For example, if I want to exclude my Downloads folder from Time Machine backups, I would run the following:
sudo tmutil addexclusion ~/Downloads
The tmutil addexclusion command has an interesting property: it's sticky. When you use this command, the item you exclude remains in the Time Machine exclusion list even if you move it, which is not the case when you exclude items from the Time Machine preference pane. If you use the above command with the -p flag, then it will not be sticky, and will be the same as an exclusion you add from the Time Machine preference pane.
Manage remote backups
If you're managing a remote Mac, such as a server, you may want to change Time Machine settings for that computer. You can start by finding where Time Machine backups are stored. Run this command:
You'll see something like this in Terminal:
Name : TM Backup
Kind : Local
Mount Point : /Volumes/TM Backup
ID : B9DAT9A6-0C37-4C39-A2AE-10A3403C97F9
To change the destination, you can use two commands. First, remove the current destination like this:
In place of , type in the text string returned by the destinationinfo command. Then run this command to set up a new destination disk:
tmutil setdestination volume_name
Replace volume_name with the name of the disk or volume you want to use. You can add multiple destinations as well, since Time Machine can rotate its backups on several disks or volumes. See man tmutil for more on setting up multiple backup destinations. (You can now do this without the command line too, see "How to create redundant Time Machine backups.")
Get Time Machine stats
Time Machine saves a lot of backups: one per hour for the past 24 hours; one a day for the past week; and one a week before that. You can get a list of all the backups on your Time Machine disk with this command:
This will show the full path of each backup.
If you're curious about how much has changed in your Time Machine backups, there's a command that will let you find out how much of each backup is new. Run this command to see the delta between each of the Time Machine backups on your backup disk or volume:
tmutil calculatedrift backup_folder
Replace backup_folder with the path of the folder containing your backups. This is not the Backups.backupdb folder at the top level of your Time Machine volume, but rather the next folder down; this is generally labeled with your Mac's name.
For example, when I ran this command on my backups, I saw data like this:
Note that this command takes a long time to run, as your Mac has to calculate a lot of information.
The tmutil command offers many other options, such as the ability to inherit destinations, perform detailed comparisons of backups, restore items and much more. See man tmutil to find out all that you can do.
If you love delving into the nitty-gritty, and especially if you manage remote Macs, you'll find this to be a very useful tool.