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Old 10-29-2005, 02:36 PM   #1
mimithebrain
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using tar


I want to backup my root folder, using tar, how do I create a backup of the root folder, and keep the user ownership, file attributes and so on?

Then, how do I extract it properly so the owners and attributes are the same as before? how can I keep the symlinks?

thanks
 
Old 10-29-2005, 03:27 PM   #2
trickykid
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man tar gives you all available options but file permissions should be preserved by default... but the -p option is for preserve.

tar -cpvf root/ root.tar
 
Old 10-29-2005, 05:10 PM   #3
ahedler
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I'm pretty sure that the -f option requires the filename right after the option, so it should read:

tar -cpvf root.tar /root

This should create the root.tar file in the current directory and include the contents of /root and any subdirectories.

-Alan
 
Old 10-29-2005, 05:15 PM   #4
ahedler
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Oops, forgot the extract part.

tar -xvf root.tar

should untar all the files and subdirectories to your current directory, so be aware of where you are when you untar the file. Any symbolic links should be created as they were saved, but could point to non-existant locations if the tar file is extracted on a different box or in a different location. It depends partly on whether the links used absolute paths or relative paths, and whether they were pointing to something that was also in the tar file.
 
Old 10-29-2005, 05:32 PM   #5
trickykid
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Quote:
Originally posted by ahedler
I'm pretty sure that the -f option requires the filename right after the option, so it should read:

tar -cpvf root.tar /root

This should create the root.tar file in the current directory and include the contents of /root and any subdirectories.

-Alan
Whoops, yeah, wasn't thinking but the name of the file does come before the directory or files your tar'ing up. Good eye..
 
Old 10-29-2005, 07:56 PM   #6
mimithebrain
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ah thanks
perfect!

Is there a way to make the symlinks relative instead of absolute?
 
Old 11-02-2005, 10:33 PM   #7
ahedler
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Yeah, but it can be a bit confusing. The basic syntax is just like a copy command, that is:

ln -s <target> <link>

So, for instance, if I want a link called media in my homedir that points at /download/media, it will be like this:

ln -s /download/media ~alan/media

This will create a link to an absolute path, /download/media.

But if I want to make a link to my brother's media stuff in his homedir that is parallel to mine (that is, mine may be /home/alan and his is /home/marty), then I can make it relative like this:

ln -s ../marty/media ~alan/media

Bear in mind that this relative path must be with respect to MY HOMEDIR, that is, with respect to where the link is created, rather than where I am when I create the link.

In other words, I can be at /root (or anywhere at all) and issue that 'ln -s' command just above, and it will point to the right place, ~marty/media, because it is how to get there from *where the link gets put*.

So if I were to tar up only my homedir, but not my brother's, when I untar it somewhere else, that link will be pointing to a non-existant directory, but if I tar the /home directory, it will still find my brother's media directory, no matter where it gets untarred.

Some people get confused because they specify the target relative to where they are when they issue the link command, which works OK if you are in the directory where the link will be created, but doesn't work if you are in a directory above or below, or elsewhere.

The easy way is to be in the directory where the link will be and specify the link relative to where you are.

The less-intuitive way is to specify the target relative to where the link will be. This actually would allow you to create a link that points at a non-existant directory when you create the tar file, but will point at a real directory when it gets untarred in its intended destination. Obscure, even weird, but doable.

-Alan
 
Old 11-02-2005, 11:06 PM   #8
jschiwal
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You may want to use the -l (local) option, so that you don't back up files from your cdrom. If you have several partitions mounted, such as separate /home and /usr partitions, then doing this you will need to include each one separately.

There is a fairly lengthy manual, that you can produce from the source package/tarball. It isn't included in the "make" default target, but if you use "make pdf" or "make dvi" or "make ps", you will produce the manual.

Also, consider how you will select the files to be backed up in the future. You may want to use the file command to produce a list of files changed after the last date. Another thing to consider is using kar or kdar to produce the backups instead. Tar was written with tape backups in mind, while dar was written to make cdrom and dvd backups easier.
 
Old 11-03-2005, 01:52 AM   #9
happy78
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Quote:
Originally posted by trickykid
man tar gives you all available options but file permissions should be preserved by default... but the -p option is for preserve.

tar -cpvf root/ root.tar
But it doesn't preserve the ownership.
I had a bunch of files owned by user A
user B tar A's files. When B untar it, file permissions are preserved, but the owner now is B, instead of A.

Is there any way to preserve ownership?
 
Old 11-03-2005, 01:13 PM   #10
mimithebrain
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I think it does preserve it, from what I just read and the subscequant experiment... however, if you change system altogether, and the user ID are different, I experienced that the username gets mixed...
 
Old 11-03-2005, 03:00 PM   #11
ahedler
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The -p option should preserve the permissions, and I believe, ownership. When extracting, you also need to use the -p. If the ID doesn't exist on the box when extracting, it will probably show the UID of the previous owner.

(I tried to look up this info in man pages, but they are incomplete and say to read the info pages, but I have to go back and relearn how to use info - not at all intuitive!)

-Alan
 
  


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