What is Time Machine

Time Machine is a backup package, that was first introduced in Mac OS X 10.5 (Leopard).  While the backup software is included, it relies on a secondary hard drive to act as the repository for the backup.  The backup drive and the backed up drives have to be Mac OS Extended Journaled (HFS+) format.

How does Time Machine work?

Time Machine works, by making an Master Snapshot of the computer, and then periodically recording any differences/deltas between the last snapshot, and the current state of the hard drive.

Time Machine supports the following backup devices:

• An external disk (USB or FireWire)
• A secondary partition  (Personally not recommended!)
• A secondary internal disk
• A Time Capsule
• An external disk (USB or FireWire) attached to another Mac running Leopard or Snow Leopard on the same local network
• An available Mac OS X Server version 10.5 or 10.6 volume
• Airport Extreme w/Connected external Media

How this differs from Retrospect, or other packages, is as follows:

• Time Machine backups are incremental backups, not differential.
  • Technically Time Machine uses “Incremental Forever” backups. After a first backup, only the changes since the last backup are stored.  Each time a file is modified, it will be stored on the Time Machine drive, when Time Machine runs.  For smaller files, this has a minimal impact, but if the file is a large file (eg. Movie, MP3, etc), the impact will be much larger due to storing all the variant versions of the file.   While this simplifies the backup and restoration process, it can greatly increase the storage space that you need.
  • Retrospect performs an first full backup, and then stores the differentials.  Retrospect will compare the new version of the file versus the old version, and store only the changed portion of the file.  While a differential backup greatly reduces the space requirements, the restoration process becomes much more complex.  To restore a differential backup, the software would have to restore the original file, and then re-apply each change, repeating as necessary.  If any of the differential backups become damaged, then the file can not be completed restored.
  • So the incremental Time Machine backups do consume more space, but they are potentially more reliable by design.  As a bonus, since the backups are incremental, the user does not even need to use Time Machine to restore the backup, the user can find the copy they wish to restore, and manually drag it to the new place.
• Time Machine offsets the Incremental backup space requirements, by making all the unchanged files, a hard link to a previous snapshot of the directory or file.  This allows Time Machine to not duplicate any  files, or directories, that have not changed.  The only files that are stored in a backup, are the ones that have been changed since the last backup.
• To some extent Time Machine relies on Spotlight.  Spotlight and Time Machine both rely on the same basic File Change tracking mechanism (fsevents). See http://arstechnica.com/apple/reviews/2007/10/mac-os-x-10-5.ars/7

Practical Time Machine Requirements

• Mac OS X 10.5 or Higher (10.6 or 10.7 recommended!)
• A Hard drive to store the Time Machine Backups on
  • Internal (eg Mac Pro) Hard Drive is ideal (But not another partition on the boot disk)
  • External Hard Drive (eg. Firewire 800, or eSata) is ideal
  • External Hard Drive (eg. Firewire 400) is Excellent / Good
  • External Hard Drive (eg. USB 2) is Good
  • External Hard Drive (eg. USB 1) is not worth it.
  • An Network File Share (eg. Hosted via a 10.5 or 10.6 system, or Time Capsule / Airport Extreme), will work, but expect USB 2 or less performance.  Do not consider using this if you are using 802.11 A/B/G, this is only reasonable if you have a 802.11 N network.  Wired Ethernet should be at least 100 Mbit, or 1 Gb.
• The amount of Drive Space for the Hard Drive is seriously based on your current Hard Drive size, but consider at least 3 times your current total hard drive space.  The absolute minimum, I recommend, is 1 TB of  disk space.  Hard Drive storage is becoming less expensive every day, and you can get 2 TB of storage for under $150 USD.

Turning On or Off Time Machine

1. Log on to your computer with an account that has administrative privileges.
2. Open System Preferences by clicking on the icon in the dock.
3. Choose the “Time Machine” control panel from under the “System” category.
4. Is there a hard drive listed in the Time Machine panel, if not Choose Select Disk, and set it to the drive you wish to use.

• To turn off, move the On/Off Slider to the “Off” setting.
• To Turn on, move the On/Off Slider to the “On” setting.

Don’t forget to Click the lock in the lower-left corner of the window to prevent further changes to Time Machine settings.

Turning On or Off via Command line

You can control Time Machine’s status by using defaults write, to change it’s On or Off status in the System Preferences panel.

To turn On Time Machine, use :     defaults write /Library/Preferences/com.apple.timemachine AutoBackup -boolean true

To turn Off Time Machine, use :     defaults write /Library/Preferences/com.apple.timemachine AutoBackup -boolean false

Force a Back up to Start Immediately

• /System/Library/CoreServices/backupd.bundle/Contents/Resources/backupd-helper -auto

What is being Backed up

Time Machine, by default, backups up every local drive on your machine.  It won’t backup network mounted drives, but any local drive that is not excluded is by default added into the backup.  Apple has a standard list of exclusions, but since Apple has not officially documented these exclusions they may change unpredictably in the future.  But for now, the following directories, are automatically excluded:

• /.Spotlight-V100
• /private/var/db/Spotlight
• /private/var/db/Spotlight-V100
• /.Trashes
• /.fseventsd
• /.hotfiles.btree
• /Backups.backupdb
• /Desktop DB
• /Desktop DF
• /Previous Systems
• /Users/Shared/SC Info
• /Users/Guest
• /dev,  /home,  /net
• /Volumes
• /Network
• /automount
• /.vol
• /tmp
• /cores
• /private/tmp
• /private/Network
• /private/tftpboot
• /private/var/automount
• /private/var/folders
• /private/var/run
• /private/var/tmp
• /private/var/vm
• /private/var/db/dhcpclient
• /private/var/db/fseventsd
• /Library/Caches
• /Library/Logs
• /System/Library/Caches
• /System/Library/Extensions/Caches
• /private/var/log
• /private/var/spool/cups
• /private/var/spool/fax
• /private/var/spool/uucp
• ~/Library/Application Support/SyncServices/data.version
• ~/Library/Caches
• ~/Library/Logs
• ~/Library/Mail/Envelope Index
• ~/Library/Mail/AvailableFeeds
• ~/Library/Mirrors
• ~/Library/PubSub/Database
• ~/Library/PubSub/Downloads
• ~/Library/PubSub/Feeds
• ~/Library/Safari/Icons.db
• ~/Library/Safari/WebpageIcons.db
• ~/Library/Safari/HistoryIndex.sk

The exclusions below are based on our work place settings, and are designed for maximizing the amount of available backup disk space.

• We do not backup the ~/Music, and ~/Movies folder, since that is the users responsibility since these systems are intended for work use only.
• The Thunderbird exclusion is due to the monolithic nature of the database, it could rapidly consume your Time Machine free disk space…
• Excluding Podcasts, and Music Downloads is reasonable, since the contents can be re-downloaded when the system is restored.

Exclusions are dangerous.

Remember, any exclusions mean the potential for data loss… Because of this, I urge people to consider what they are excluding….  And be sensible about their acceptable risk levels.

The very basic exclusions that I use at home, are the following:

• ~/Music/iTunes/”iTunes Music”/Podcasts
• ~/Music/iTunes/”iTunes Music”/Downloads
• ~/DropBox
• /”System Folder (from old Mac)”
• /”Applications (Mac OS 9)”
• /”Applications (from old Mac)”
• Please note:  File Vault v1 users need to make sure that their user folder is excluded, when using Time Machine.  If they do not, they will be backing up their user folder twice.  Once from the virtual home directory, and once from the Sparse Bundle image file, when logged out.  Normally this is automatically added, but if you clear your exclusions, you may have removed this exclusion.

Download the basic shell script here: TimeMachine-exclusions-v1_3-Basic (345 downloads)  Please note, these script will erase all your old exclusions, and replace them with the default set from the script.

In addition to the basic exclusions, I have an “aggressive exceptions” list, which includes the following:

• /Developer
• /System
• /Library/Audio
• /Library/Printers
• ~/Music
• ~/Movies
• /Applications
• /Applications (from old Mac)
• /Users/Shared/Infected

The ~/Music directory normally has your iTunes data, if you do exclude that directory, please make sure to backup your iTunes files manually.

Download the Shell script, here:  TimeMachine-exclusions-v1_3-Aggressive (311 downloads)  The aggressive script will append these entries to your existing exclusions.

The downside to excluding the System files

Why should or shouldn’t you exclude the system files?  Well, the advantage is that you’ll save a tremendous amount of space on your Time Machine drive, but the disadvantage is that if you want to do a full system restore, you’ll need to re-install from a DVD (or other media), and then choose to restore from a Time Machine backup when offered.

Excluding the system files does not prevent your preferences from being backed up, so you should not have to reconfigure your applications, but you would need to run Software update to make sure that the latest patches were re-applied.

Removing backups

You can remove files from backups by viewing the enclosing folder in the Finder, then enter Time Machine. Find the file or folder, right/control-click and choose either delete that specific backup, or delete all backups (versions) of the file.

1. connect your time machine backup drive
2. click on the time machine logo in the menu bar
3. select “Enter Time Machine”
4. navigate to and select those files/folders in the Time Machine window
5. click on the gear menu icon
6. select “Delete all backups of” ….  Time Machine will prompt for your password and delete all of the backups of the file/folder. You can then exclude these files/folders from future backups. To do so:
   1. go to the Time Machine preference pane in the System Preferences
   2. click “Options…”
   3. add the file/folder you wish to exclude from future backups

Suggested best practices

• Where possible, use a local hard drive for your Time Machine Backup.  While Time Capsules, & other network based drives can be used, the speed difference, and reliability differences are impressive.  Network backups can be used, but your life will be much more comfortable if you use local storage instead.
• Upgrade to Snow Leopard (10.6.1) if possible.  It fixes two significant bugs, and is much faster and more reliable than Leopard (10.5.8).
• Have as few exclusions as possible, to help reduce the chances of data loss.

Time Machine and FileVault v1

Time Machine can backup File Vault, but there are many considerations to keep in mind, if you intend to use Time Machine & File Vault.

• A File Vault v1 Disk Image made  in 10.4 or lower, can not be backed up incrementally.  Each time you backup, a new copy of the entire file vault archive will be copied to the Time Machine Disk.  This means that a you will rapidly consume disk space, and possibly fill up your Time Machine drive.
  • To solve this issue, turn off File Vault v1, allow your File Vault to decrypt, and then when running under 10.5 or higher, re-enable File Vault.  This will recreate your File Vault achieve, using a SparseDiskBundle.  Sparse Disk Bundles, can be incrementally backed up.
  • Please keep in mind, that 10.7 (Lion) appears to have a whole disk encryption system, which could replace File Vault.
• Time Machine backups up File Vault, but it requires the user to be logged out (at the login window).  So your backups will not occur in on a hourly schedule, it requires the user to logout, and not shut down the system. Most users do not leave there systems logged out for any significant length of time. This requires the user to be accept downtime, while the system backups up.
• File Vault v1 users have to manually restore file through the file system. The “Galaxy” user interface is not available.

Potential Issues with Time Machine

• Annoyance factor.
  • With Leopard (10.5) Time Machine will ask to use every disk that you attach to the system.
  • With Snow Leopard (10.6) Time Machine will ask only once, when you attach the Disk.  Your choice will be saved, so that if you disconnect and reconnect the drive, you will not be asked again.  You can use the Time Machine Preference Panel, to choose the drive, if you ever decide to use it for Time Machine.
  • A work around is to open a terminal window, and type “defaults write com.apple.TimeMachine DoNotOfferNewDisksForBackup -bool YES” to turn this prompt off.
• If the Free Space Allocation table is damaged, Time Machine can become “stuck” at the Preparing phase and never finish preparing.  Eventually the system will eventually lock up (system is still responsive, but drive related function may not occur in a timely manner. (eg can’t log out, reboot, restart, or start an application).
• This MacOSXHints article walks through the setup of a non-support disk with Time Machine.
• Will time machine backup the system if you are not logged in?  Yes and No.  The only time that Time Machine will back up the system when you are logged out, is that you are using File Vault.  Otherwise, no Time Machine will not backup your system without a user being logged in, unless you hack the system. This setting should allow the backup:

• sudo defaults write /Library/Preferences/SystemConfiguration/autodiskmount AutomountDisksWithoutUserLogin -bool true
  (See MacOSXHints for more details.)

• Time Machine is very boolean in it’s operation.  It either was successful or failed.  So if there is a single file that it can’t backup, it aborts it’s current backup, and shuts down until the next backup cycle.  Non-optimal.  Other backup software will log an error on a particular file, but continue with the current backup cycle, until done.  Time Machine does not have any built-in mechanism to verify a set of backups as being valid. That’s one issue with Time Machine, being consumer orientated instead of enterprise…Performing a Disk Repair in Disk Utility doesn’t validate the Time Machine backup data, but will verify the structure and integrity of the backup disk. (Of course, Disk Warrior verifies / repairs in a complementary manner).The only way that I see that you could verify the data in the backup is to do a full restore.
  • Update 7/23/2010 - Time Machine does have a limited verification method, if you are using a Time Capsule.  Option-Click on the Time Machine Menu Extra, and you will see (starting with 10.64) a option called Verify Backups.  This Apple Technote(HT4076) discusses the process, and it is simply running a Disk Utility / Verify Disk on the Time Capsule disk image.  This does not necessarily verify the data was accurately backed up, but verifies the integrity of the Disk Image.

Please note, you can open the Console logs, and filter against BACKUPD to see what happens during a backup, and see if any error conditions occurred.

Time Machine Logging

Time Machine logs information to two different places.  First, check the Console Logs, specifically “All Messages” for any items marked from com.apple.backupd (Backup Daemon).  The other log file is stored in the actual Time Machine backup directory, for example,Backups.backupdb/nerv/Latest or Backups.backupdb/nerv/2009-12-13-034918. If you use the backup logfile, the file name is .Backup.log, which is a hidden file, and you will need to have authorization to open the file.  It’s much more detailed than the console log.

Time Machine Error Messages

Here’s what some common messages mean:

• Event store UUIDs don’t match naming(Hard drive name)
  • TM can’t be sure the OSX internal log of file changes that it normally uses is correct. This is normal on your first backup. Otherwise, it’s usually caused by an improper shutdown, a full restore, certain hardware repairs, removal of certain exclusions, a large volume of changes (including an OSX update), or many days without a successful backup. It may cause a lengthy backup, so if you see it frequently, without a good reason, you need to figure out why.
• Event store UUIDs don’t match naming (Hard drive/partition name)
  • TM isn’t sure that everything on it is what TM expects. This may be because the drive was disconnected improperly, or it doesn’t appear to be the drive TM expects. This is normal for the first backup to an empty disk/partition, but if you see this without a good reason, investigate.
• . . . node requires deep traversal
  • Instead of the log of file changes TM normally uses, it must examine every file and folder on the named drive/partition and compare it to your backups to be sure what’s changed and needs to be backed-up. Obviously, this is a lengthy procedure. You may not see any more messages for quite a while. This may be especially lengthy if you’re doing wireless backups. Note that while this is in progress, you’ll see “Preparing”.
• Backup content size: xxx MB/GB excluded items size: yyy MB/GB for volume zzz
  • These sizes are rough estimates (and sometimes quite far off).
• . . . xxx MB/GB requested (including padding), yyy MB/GB available
  • The amount requested is more, usually about 20% more, than the total of the Backup content sizes listed, as TM needs extra free workspace on the TM drive/partition.
• No pre-backup thinning needed. - TM has room for the new backup.
• Starting pre-backup thinning usually followed by:
  • No expired backups exist – deleting oldest backups to make room and a list of deleted backups – These are weekly backups that TM must delete to make room for the new backup.
  • No post-backup thinning needed. There are no expired backups.
  • Starting post-backup thinning, followed by a list of deleted backups – These backups are either hourly backups over 24 hours old, or daily backups over a month old.

• Backup failed with error: 11
  • I haven’t seen Error 11’s in a while, so this may have been resolved in a 10.5.x update, or Snow Leopard.
  • This appears to be a error when building the current backup, or a failure in clean up of a prior backup, so it is a fairly generic error.
  • Before formatting or performing exotic repairs, try changing your USB or Firewire cable.  It could be a marginal or defective cable.
  • The solution appears to be to delete the *date*.inProgress file.  See this blog entry for locally attached drives.
  • For network based Time Machine backups, please take a look at this MacOSXHints entry.
• Indexing a file failed. Returned -12 for *filename*
  • Try rebuilding your spotlight cache for the drive that *filename* is located on.
• Waiting for index to be ready (100), Waiting for index to be ready (101), Indexer unavailable (200)
  • Use Disk Utility and/or Disk Warrior to examine the hard drive, and ensure everything is fine with the underlying structure.
  • There maybe a communications issue with the external drive, this has been seen if the bandwidth to the drive goes too low (network), or if there is an USB/Firewire issue on the bus.
  • Check the Available Disk space & if quotas are enabled.  I have had at least one report, that indicate that some network volumes may have issues if Quota’s are enabled.  Some NAS units will report the available disk space, ignoring the fact that the quota may prevent you from using the entirety of the available disk space.  This results in Time Machine running out of disk space, even though the Finder is reporting there is plenty of space available.  This conflict can result in corrupted SpareDiskBundles, and other issues.
• You do not have appropriate access privileges to save file “.” in folder
  • A temporary file was not cleaned up properly during a backup, and is preventing Time Machine from continuing.
  • At the prompt, type the following exactly as shown in the example, substituting the name of your TM drive exactly, including any spaces, between the quotes; and the string of numbers & letters from the message where the series of x’s are (keep the dot):
    

            sudo chmod 644 /volumes/"TM drive name"/.xxxxxxxxxxxx

    example: sudo chmod 644 /volumes/"TM Backups"/.0a1b2c3d4e5f

    Press Return. You’ll get some warnings and a request for your Administrator’s password. Type it in (it won’t be displayed) and press Return again.

    Then try a Back Up Now from the TM icon in your Menubar, or by right-clicking the TM icon in your dock.

• The Backup Volume is Read Only.
  • Run Disk Utility or Disk Warrior on the Time Machine Volume.
  • If this is an Airport disk, then ensure that the Airport Utility has the drive marked as Read/Write, not as a Read Only Volume.
• With Snow Leopard, there have been some reports of Time Machine being stuck in a cycle where it only backs up 93 bytes…  This maybe triggered by doing a live verification of the disk (not a disk permissions repair) in disk utility.  The suspicion is that a process is being temporarily turned off, but may not be restarting after the verification (fsevents?).  A reboot of the system seems to solve this problem.

Time Machine Workarounds

• Removing Obsolete disks from Time Machine – How can you remove the contents of a disk that is no longer connected to your system from your Time Machine Backup?  The solution is to navigate in the Time Machine interface not to the disk itself, but to the backup entry for that disk on the Time Machine disk itself. Specifically, in Time Machine’s Finder view, select the Time Machine disk, then enter the Backups.backupdb folder, and drill down to find the last entry for the obsolete disk. Then tell Time Machine to delete all backups of that entry. The original disk need not be connected!   If you think about this, it’s an unexpected behavior since it’s outside the standard paradigm of pointing to the “real file” you want to remove the backups of.
• Checking the Time Machine backup via Disk Utility can be a troublesome issue.  Especially with Large volumes, the tests may not finish.  This hint on Mac OS X hints, discuss using a large fsck_hfs cache to speed the process up.  Summary, sudo fsck_hfs -f -c 2200m /dev/disk2
• Changing the backup Interval, an hour might be too often for your taste.  Maybe you prefer setting Time Machine to backup once every day?
  • TimeMachine Scheduler allows you to set the interval via the application… see http://www.klieme.com/TimeMachineScheduler.html
  • Every Hour - sudo defaults write /System/Library/LaunchDaemons/com.apple.backupd-auto StartInterval -int 3600
  • Every 2 hours - sudo defaults write /System/Library/LaunchDaemons/com.apple.backupd-auto StartInterval -int 7200
  • Every 4 hours - sudo defaults write /System/Library/LaunchDaemons/com.apple.backupd-auto StartInterval -int 14400
  • Every 6 hours - sudo defaults write /System/Library/LaunchDaemons/com.apple.backupd-auto StartInterval -int 21600
  • Every 12 hours - sudo defaults write /System/Library/LaunchDaemons/com.apple.backupd-auto StartInterval -int 43200
  • Once a day - sudo defaults write /System/Library/LaunchDaemons/com.apple.backupd-auto StartInterval -int 86400
• Compressing Sparse Image files.  This will, as explained in the man page, reclaims completely unused band files only.  Use the following Command line:
  • hdiutil compact image.sparsebundle

• Normally Time Machine is not location sensitive, for example, if you wish to use a specific backup drive at work, and a different one at home, you need to use the Time Machine Control Panel to switch between drives.  This blog entry explains how to switch between drives automatically using shell scripts, and Marco Polo.
• Normally to remove a file or folder from Time Machine, you would open Time Machine, highlight the file or folder, and then choose Remove from Backup in the options pull down.But to do this with an invisible directory in the Finder by using Go -> Go to Folder… (command-shift-G) and enter the path. Once it’s showing, Enter Time Machine and follow the steps here.Note: you can delete the folder you’re looking at (instead of a file/folder within it) by right/control-clicking in the Finder window in Time Machine and selecting the Delete All… option with its name there.
• One Method to use an encrypted disk image to back up with Time Machine, without using File Vault.  It’s an video….
• One of the features we were most looking forward to was the ability to set Time Machine to use a NAS volume. defaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes 1 and you should be able to select NAS volumes in the Time Machine preferences. Of course, you should only re-enable carefully since Apple has their reasons for restricting Time Machine volumes to the Airport line of products.  See the Potential issues for details.
• Disabling the Time Machine Background (Starfield) - MacPilot has a setting for this, as well as Secrets, and TinkerTool.
• Changing the Backup Progress Window Location – in the com.apple.finder.plist preference file, you will find the x, y coordinates for that window in the “BackupProgressWindowLocation“.  Please note, the key is listed as a STRING, not an Integer…
• Verification of an Backup. In the end, a Time Machine backup is a collection of folders for each backup date. Each of those folders holds all files that existed on that date. So, you can compare the names and contents of all those files with those on your Mac.Of course, many files will change by simply using your Mac. So the results take some common sense to interpret. The best option is to close all running applications, run Time Machine, and then compare right away.  After you have connected your backup disk, use the following in Terminal to find the differences. For the cd command below you might want to use Tab command line completion and not just by pasting the first line:cd /Volumes/Backup*/Backups.backupdb/*/Latest/*/ echo “Current folder on backup disk: $(pwd -P)” sudo diff -qr . / 2>&1 | tee $HOME/timemachine-diff.logThis will compare the current folder (being the latest backup) with the root of your Mac. It shows the results on the screen, but also captures these in the file timemachine-diff.log in your home folder.  The above will run a VERY long time (hours, maybe even days), so for testing you can first limit to a specific folder. Like for your desktop:

  cd /Volumes/Backup*/Backups.backupdb/*/Latest/*/$HOME/Desktop echo “Current folder on backup disk: $(pwd -P)” sudo diff -qr . $HOME/Desktop 2>&1 | tee $HOME/timemachine-diff.log

  If there’s no output, then there are no differences. For testing just rename a file on your desktop, which should give you both “Only in .” for the original name (which is only on your backup) and “Only in /Users/username/Desktop” for the new name (which is not in the backup).

Using CRON to automate Time Machine Backups

• Using Cron to turn Time Machine off and on at specific times during the day

Time Machine Aware Software

• Finder
• Apple Mail
• Address Book
• BackupLoupe – Will show how much was backed up per backup & historical information on the backup..
• iLife 2008 (iPhoto 2008, Garage Band 2008, iMovie 2008, iWeb 2008)
• Grand Perspective
• MacPilot (For setting hidden options)
• iTimeMachine
• TinkerTool (For setting hidden options)
• Plus Many More

Time Machine Resources

• Ars Technica – Leopard review - http://arstechnica.com/apple/reviews/2007/10/mac-os-x-10-5.ars/14
• Ars Technica – Deborking Mac w/TM - http://arstechnica.com/apple/news/2009/01/time-machine-lessons-deborking-your-mac.ars

Time Machine Diagnostic Software

• Grand Perspective
• Time Machine Buddy
• Time Machine Reporter (My own package)
• Time Machine Editor
• TM Error Logger
• TimeCopy Differences script Perl (287 downloads) , Time Machine Differences script originally found here.  I Mirrored it, incase it is taken down….
• Time Dog
• Back in Time
• Time Tracker - TimeTracker is a quick-and-dirty application that displays the contents of your Time Machine backups, and shows what’s changed since the previous backup.   From Charlesoft..
• Time Tamer - Don’t want Time Machine to fill up your whole Drobo? This application for OS X based upon an Automator action provides a simple way when you’re setting up Time Machine to force it to only use up 2x the size of your internal hard drive for backup on your external hard drive. Please note, as with all DroboApps, this is unsupported by either Apple or Data Robotics so please use at your own risk.