355

So I was going to back up my home folder by copying it to an external drive as follows:

sudo cp -r /home/my_home /media/backup/my_home

With the result that all folders on the external drives are now owned by root:root. How can I have cp keep the ownership and permissions from the original?

  • 23
    Yes, it would, be I'm glad he asked because google is still faster than 'man' :-). – Stijn Geukens Aug 4 '14 at 14:54
  • 3
    I'm glad he asked too – Ole Apr 7 '16 at 16:28
  • 5
    @StijnGeukens It's not even that google is faster, it's that even man to me is cryptic. In this case, man at -r says same as --preserve=mode,ownership,timestamps. How was I supposed to know that means keep the original permissions!? – Kolob Canyon Nov 15 '16 at 0:33
430
sudo cp -rp /home/my_home /media/backup/my_home

From cp manpage:

 -p     same as --preserve=mode,ownership,timestamps

 --preserve[=ATTR_LIST]
          preserve the specified attributes (default: mode,ownership,timestamps),
          if possible additional attributes: context, links, xattr, all
  • 114
    Much better to use cp -a. This also includes the -recursive flag, but it does more than that—it preserves everything about the file; SELinux attributes, links, xattr, everything. It's "archive mode." There are better tools for making a backup, but if you're using cp for a backup, don't use anything other than cp -a. – Wildcard Oct 14 '15 at 3:54
  • 22
    It works, but Patience is Good here. The command will only set everything right when it finishes: While it's still copying a directory, and you're running cp as root, the directory will be owned by root. It will only set it to the right permissions when it finishes with this directory. – Paul Nov 18 '15 at 17:01
  • 4
    cp -a doesn't work on some systems: e.g. OS X, where (in some versions at least) one needed to use cp -pR. On my current OS X system though (10.10.15), cp -a seems to be honored. – dubiousjim Sep 30 '17 at 16:30
  • If I use cp -a to copy a folder structure then use diff <(getfacl -R folder1) <(getfacl -R folder2) i sill seem to get different access control lists :( – philx_x May 29 at 18:20
93

You can also use rsync.

sudo rsync -a /home/my_home/ /media/backup/my_home/

From the rsync manpage:

 -a, --archive
              This  is  equivalent  to  -rlptgoD.  It  is a quick way of saying you want
              recursion and want to preserve almost everything (with -H being a  notable
              omission).    The   only  exception  to  the  above  equivalence  is  when
              --files-from is specified, in which case -r is not implied.

              Note that -a does not preserve hardlinks, because finding  multiply-linked
              files is expensive.  You must separately specify -H.

See this question for a comparison between cp and rsync: https://stackoverflow.com/q/6339287/406686

Note the trailing slashes (see manpage for details).

  • 3
    +1, cp -p is nice, but I like rsync's output so much more in general that I've aliased pcp to time rsync --progress -ah. Stands for "progress copy" in my mind. And both accept -r, so it works well for general terminal usage - but unfortunately, not in combination with sudo as shown in this question/answer. – Izkata Jul 20 '12 at 17:59
  • 14
    NB: rsync -a, does not preserve extended attributes (-X) and no ACLs (-A) - the short description says archive mode; equals -rlptgoD (no -H,-A,-X). E.g. SELinux contexts will not be preserverd without -X. For many use cases this is fine, but if you make a backup of your system partition, missing -X might break quite a lot. As far as I know, cp -a really preserves all file attributes. – Perseids Sep 23 '14 at 6:44
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    Just tested this, while sudo cp -a preserves ownership and groups, sudo rsync -a changes them into root. So, @Perseids is correct. – John Hamilton Mar 16 '18 at 11:59
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    @JohnHamilton Under Mint, this works perfectly... it only changes ownership and groups later on (I can't tell when). I've just copied my whole /home folder with rsync -aX /home /mnt/sdd/ and it worked like a charm. – Olivier Pons Oct 18 '18 at 7:04
53
cp -a

Where -a is short for --archive — basically it copies a directory exactly as it is; the files retain all their attributes, and symlinks are not dereferenced (-d).

From man cp:

   -a, --archive
          same as -dR --preserve=all
21

I use cp -pdRx which will -p preserve mode, ownership & timestamps, -d preserve links (so you get symlinks instead the file contents copied), -R do it recursively and -x stay on one file system (only really useful if you're copying / or something with an active mount point).

PS: -R instead of -r is just habit from using ls -lR.

  • 2
    cp -ax is a slightly shorter version of the same thing. This worked great - thank you! – EM0 Mar 25 '15 at 12:27
  • Actually there is a difference between -r and -R. Check the man page (even the particular part too long to be quoted here). – geckon Jul 8 '15 at 13:23
  • 2
    I don't think there is (although there may once have been and may still be on some versions of Unix). See man7.org/linux/man-pages/man1/cp.1.html It simply says -R, -r, --recursive copy directories recursively. – StarNamer Jul 8 '15 at 16:09
14

cp has an option to preserve file ownership. From the manual page of cp:

-p    Cause cp to preserve the following attributes of each source file in the copy: modification
      time, access time, file flags, file mode, user ID, and group ID, as allowed by permissions.
      Access Control Lists (ACLs) and Extended Attributes (EAs), including resource forks, will also
      be preserved.
11

You can do something like this:

tar cf - my_home | (cd /media/backup; sudo tar xf - )

tar keeps permissions, ownership and directory structure intact, but converts everything into a stream of bytes. You run a "subshell" (the parenthesized commands) that change directory, and then get tar to reverse the conversion. A steam of bytes becomes directories and files with correct ownership and permissions.

7

The answer is simple: cp has a -p option that preserves permissions (here's a fish).

But as Wojtek says in his comment, man cp (reading the fine manual) would be a good starting point (want to learn how to fish?).

1

you can use preserve=all, then your copy will keep all attributes like owner, group and timestamp of your files. So, do your backup safely with the following command.

cp -r --preserve=all /home/my_home /media/backup/my_home

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