I want to backup my home directory to an external drive nightly using a cron job to execute rsync. I am unsure of the exact behavior of rsync's symbolic link flags.

  1. rsync's -a flag includes the -l flag (i.e. "copy symlinks as symlinks"). Does this just mean it will copy the link or that it will follow the link and copy everything in the link-to directory? I want to avoid that because I have links to directories full of media files that would involve copying hundreds of gigabytes I don't need to back up.
  2. Fearing (but not certain) that rsync -a would copy all those media files I instead added the --no-links flag. This does not seem to be behavior I want. It just ignores copying any link which is problematic because I do have links I want copied (e.g. links to common header files from different project directories).
  3. Assuming #1 above (without the --no-links flag) is what I really want and it just copies the link without copying the linked-to files, will the links break when they are backed up? For example I may rsync source directory /home/me/projects/misc to /media/extdrive/backup/home/me/projects/misc. In this case I assume rsync is not smart enough nor does it try to correct the contents of symlinks for the relative directory changes. Is this correct? This is okay, it doesn't matter if the links are broken in the backup directories so long as they would be fixed and working if such time comes when they need to be restored.
  • 2
    The -L flag is probably what you want. From the rsync man page on Centos Linux: "-L, --copy-links transform symlink into referent file/dir." I recommend testing this with some sample directories and links to make sure you don't overwrite any data that you don't intend to. Edited to included warning about possible data loss. ;) – Mick T Oct 23 '15 at 19:22
up vote 65 down vote accepted
  1. "Copy symlinks as symlinks" means exactly what it says: If rsync sees a symlink in the source directory, it will create an identical symlink in the destination. Nothing more.

    (A few lines down in the manual page, a different option, --copy-links, describes the opposite behavior (always copying the data) which you described as undesirable.)

    See also the section "Symbolic links":

    If --links is specified, then symlinks are recreated with the same target on the destination.

  2. It's not the behavior you want because you're misinterpreting what --links does and therefore asking for the wrong behavior (see answer #1).

  3. By default, it copies the destination exactly.

    That is, if the link pointed to an absolute path (e.g. /home/me/projects), it'll continue pointing to the same path; it won't break, it'll just continue pointing to a file in your home directory rather than the one in your backup.

    Meanwhile, if the link pointed to a relative path (e.g. ../../projects), it'll also continue pointing to the same path, but since it's relative to the symlink's location, the symlink in your backup will also be pointing to a file in your backup.

    Unfortunately there doesn't seem to be any option to translate absolute symlinks for their new base (only an option to break them entirely). To avoid problems, you should change existing symlinks to relative ones (which is a good idea generally, for links inside $HOME).

  • ummm so what's the difference between --copy-links and --links? – Alexander Mills 14 hours ago

There are several very good pages which describe rsync in great detail.

http://www.jveweb.net/en/archives/2010/11/synchronizing-folders-with-rsync.html

http://www.mikerubel.org/computers/rsync_snapshots/index.html

I would also recommend utilities such as backintime or rsnapshot.

  • 21
    Please include some relevant snippets into you currently link-only answer. – Cristian Ciupitu Sep 25 '15 at 19:08

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