Time Machine is one of the premiere features of Mac OS X 10.5 (Leopard). It allows anyone to back up their entire Mac easily and without muss or fuss – but what does it really back up? My analysis says ‘not quite everything.’

First let me say that what I am reporting on is a reflection of my experiences with Mac OS X 10.5.2 on a MacBook Pro. It is very possible that I missed some things or that my tests are not indicative of all Mac OS X 10.5.2 installations….

Here was the process that I went through to try to determine how my Time Machine backup differed from my Mac Book’s actual hard disk:

  1. Make a complete list of all files on my hard drive:
    cd /
    sudo find . * > /fileList_all_master.txt
  2. Make a complete list of all files on most recent Time Machine backup
    Pretty much like above except for a different directory
  3. Make a differences file for my file lists
    diff -y fileList_all_master.txt fileList_all_TM.txt > fileList_all_diffs.txt

I then opened fileList_all_diffs.txt with BBEdit and looked for mismatched lines. What fun!

Disk analysis
File/folder not present Comment
/private/var/run Folder present but empty.
/private/var/folders Folder present but empty.
/private/var/log Folder present but empty. This one surprised me. I wish it were backed up.
/Library/Logs Folder present but empty. This one surprised me. I wish it were backed up.
/Library/Caches Folder present but empty. Makes sense.
/private/var/spool Folder present but empty. Makes sense.
/private/var/run Folder present but empty.
/private/var/vm Folder present but empty. Makes sense.
/System/Library/Caches Folder present but empty. Makes sense.
/private/var/tmp Folder present but empty. Makes sense.
/fseventsd Not present. Makes sense to me.
/hotfiles.btree Not present. Makes sense to me.
/Spotlight-V100 Not present. Makes sense to me.
/.Trashes Not present. Makes sense to me.
/private/var/root/.Trash Not present. Makes sense to me.
/Desktop DB & /Desktop DF Not present. Makes sense to me.
/Users/Shared/SC Info/ Not present. No idea what it is.
Update: This may have to do with iTunes authorizations
/System/Library/Extensions/Caches/ Not present. Makes sense to me.
/private/var/db/dhcpclient/leases Not present. Makes sense to me.
/Library/Caches/ Not present. Makes sense to me.
/private/tmp Not present. Makes sense to me.
/private/var/db/dyld/ Not present.
/dev/ Not present.
/net/ Not present.

Home folder

Now I’ll take a closer look at my home folder on disk vs the Time Machine backup:

File/folder not present Comment
~/.Trash
~/Library/Application Support/MobileSync iPhone stuff
~/Library/Application Support/MobileSync/Backup More iPhone stuff, I think
~/Library/Application Support/SyncServices iSync stuff – including iPhone stuff I expect
~/Library/Caches Makes sense to me.
~/Library/iTunes/iPhone Software Updates Makes sense.
~/Library/iTunes/iPod Software Updates Makes sense.
~/Library/Logs This one surprised me. I wish it were backed up.
~/Library/Mirrors
~/Library/PubSub/Database
~/Library/PubSub/Feeds
~/Music/iTunes/Album Artwork/Local This one surprised me.
~/Pictures/iPhoto Library/iPod Photo Cache Makes sense.
~/Music/iTunes/iTunes Music Library.xml
~/Library/Mail/Envelope Index Makes sense.

It also appears that Time Machine does not back up mail in IMAP mailboxes. I’m not 100% sure of this, but it makes sense.

So, in summary, Time Machine seems to back up pretty much everything you could want preserved -except for log files (which I would prefer to keep). It does not back up data that is preserved elsewhere (IMAP mail) or can be regenerated without loss (Spotlight, caches).

Let me know if you find any mistakes or have any additions to my list.

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