54

I have a directory tree which has a bunch of symbolic links to files under /home... however, I have moved /home to /mnt/home and need a way to "relink" all of the symlinks. Does such functionality exist or do I need to write a script to do so?

As an example, I have something like the following:

[root@trees ~]# ls -l /mnt/home/someone/something
total 4264
lrwxrwxrwx 1 jnet www-data      55 2011-08-07 13:50 a -> /home/someone/someotherthing/a
lrwxrwxrwx 1 jnet www-data      55 2011-08-07 13:50 b -> /home/someone/someotherthing/b
lrwxrwxrwx 1 jnet www-data      55 2011-08-07 13:50 c -> /home/someone/someotherthing/c
lrwxrwxrwx 1 jnet www-data      55 2011-08-07 13:50 d -> /home/someone/someotherthing/d
lrwxrwxrwx 1 jnet www-data      55 2011-08-07 13:50 e -> /home/someone/someotherthing/e

/mnt/home/someone/something/subdir:
total 4264
lrwxrwxrwx 1 jnet www-data      55 2011-08-07 13:50 a -> /home/someone/someotherthing/subdir/a
lrwxrwxrwx 1 jnet www-data      55 2011-08-07 13:50 b -> /home/someone/someotherthing/subdir/b
lrwxrwxrwx 1 jnet www-data      55 2011-08-07 13:50 c -> /home/someone/someotherthing/subdir/c
lrwxrwxrwx 1 jnet www-data      55 2011-08-07 13:50 d -> /home/someone/someotherthing/subdir/d
lrwxrwxrwx 1 jnet www-data      55 2011-08-07 13:50 e -> /home/someone/someotherthing/subdir/e

I want a command which will find all the symlinks and relink to the same places but underneath /mnt/home instead of /home

Does such a command exist?

55

There is no command to retarget a symbolic link, all you can do is remove it and create another one. Assuming you have GNU utilities (e.g. under non-embedded Linux or Cygwin), you can use the -lname primary of find to match symbolic links by their target, and readlink to read the contents of the link. Untested:

find /mnt/home/someone/something -lname '/home/someone/*' \
     -exec sh -c 'ln -snf "/mnt$(readlink "$0")" "$0"' {} \;

It would be better to make these symbolic links relative. There's a convenient little utility called symlinks (originally by Mark Lords, now maintained by J. Brandt Buckley), present in many Linux distributions. Before the move, or after you've restored valid links as above, run symlinks -c /mnt/home/someone/something to convert all absolute symlinks under the specified directory to relative symlinks unless they cross a filesystem boundary.

  • No offense, this is a great one-liner, but Bash's string substitution could probably do some magic w.r.t. the path change and would be easier. – 0xC0000022L Feb 8 '12 at 20:30
  • @STATUS_ACCESS_DENIED How so? The only string operation is to prepend /mnt to a path; you need no fancier string operation than concatenation. – Gilles 'SO- stop being evil' Feb 8 '12 at 20:41
  • @Gilles: sorry, I was thinking more about your remark with the relative paths. For an exact "translation" of your example you are of course right. – 0xC0000022L Feb 8 '12 at 20:55
13

I know this is not exactly what the author is requesting but it seems they already have their answer so I'm adding this for others like me who stumble upon the question.

The following should help if a more flexible solution is required such as having a bunch of broken symbolic links which can be fixed by replacing part of the symbolic link's targets.

eg. After a change of username, to replace the old username with the new username in the target of many links, after the move had already been done. Create a script called replace-simlinks shown below:

#!/bin/bash
link=$1
# grab the target of the old link
target=$(readlink -- "$1")

# replace the first occurrence of oldusername with newusername in the target string
target=${target/oldusername/newusername}

# Test the link creation
echo ln -s -- "$target" "$link"

# If the above echo shows the correct commands are being issued, then uncomment the following lines and run the command again
#rm "$link"
#ln -s "$target" "$link"

and call it with the following command:

find /home/newusername/ -lname '/home/oldusername/*' -exec ~/bin/replace-simlinks {} \;

Thanks Gilles for the kickstart on this script and the tip about using the symlinks script to make the links relative.

  • 1
    I find this solution better because it uses a string replace, which helps in cases where you have to change the name of a folder in the middle of the path. The solution is also quite easy to modify to perform more complex transformations if required. – Gallaecio Nov 29 '14 at 22:56
  • I'd recommend quoting the arguments to the string substitution, as that must be done to use slashes, e.g. for the path in the OP's question. target=${target/"/home"/"/mnt/home"} Very helpful, though. Thanks. – Walter Nissen Nov 29 '18 at 18:08
4

Create /home as a symlink to /mnt/home, and all the existing symlinks will be valid again.

  • 2
    Bind-mounting often tends to be less fragile than symlinks in scenarios where programs are aware of symlinks and act differently depending on the fact ... – 0xC0000022L Feb 8 '12 at 20:27

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