How can I "relink" a lot of broken symlinks?

Question

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?

Answer 1

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 "$1")" "$1"' sh {} \;

It would be better to make these symbolic links relative. Assuming ln is from GNU coreutils 8.22, just pass the -r option to ln in addition to the other options and it will convert the target to a relative path. For older systems or for bulk rewriting of valid links, there's a convenient little utility called symlinks (originally by Mark Lord, 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.

Answer 2

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 {} \;

Hope this help somebody

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

Answer 3

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

Answer 4

One of the otherwise great answers states:

There is no command to retarget a symbolic link, all you can do is remove it and create another one.

The rename command's -s option will "rename a symbolic link target, not the symbolic links itself". It will also operate on multiple symbolic links at once. This seems to be the behavior the OP requested.

The rename command is part of the util-linux package and is available from https://www.kernel.org/pub/linux/utils/util-linux/. It has been available since at least June 2011.

OP said:

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

The rename command can do that and it can do it for multiple files (symbolic links) at once. Unfortunately, the OP uses a, b, c, d, e as example filenames. Those names don't seem realistic, so I won't use them in my answer. (If the OP is working with multiple subdirectories the solution may be more complex than what I'm presenting, but I still think rename is a very convenient tool for this general requirement, and it can be combined with other tools such as find ... -execdir ....)

I did just use rename to fix multiple broken symbolic links as shown below. This is the "before" listing from ls:

second.files -> first.files.tar.zst
second.files.sig -> first.files.tar.zst.sig

The targets first.files.tar.zst* do not exist. This is analogous to the OP's situation.

I used this command to fix all the broken symbolic links:

rename -s 'first' 'second' second.files*

The two single-quoted arguments apply to the target. The last argument, second.files* selects the links upon which to operate. Those symbolic links are not renamed. Due to the use of the -s option, the search/replace operation is performed on the targets.

Here is the "after" listing from ls after running the above rename command

second.files -> second.files.tar.zst
second.files.sig -> second.files.tar.zst.sig

The links have been "relinked" and they work correctly now.

Here is an example of using it to relink any symbolic links that has the pattern "somelinks*" in its name where we want to change the target location from /home to /mnt/home.

rename -s '/home' '/mnt/home' somelinks*

The man page suggests that the single quotes are mandatory. In this case, multiple broken links matching the pattern somelinks* were fixed, which means they were retargeted to point to the correct location. The symbolic links name itself was not changed, but the file it pointed to was changed.

It would be better to use relative symbolic links.

I'm sure the person who wrote the above statement had good justification. However, we actually prefer absolute symbolic links in our environment (where we utilize network shares). If the directories on the clients and fileserver are laid out consistently, absolute symbolic links will work across file systems and even over network shares. Within our team, they provide for a very consistent and robust navigation solution. We can all share consistent file paths with each other. Haven't had problems with this approach over the last 8 or so years. But if your situation is different, by all means consider relative symlinks as Gilles suggested.

Answer 5

I wrote a fix_broken_symlinks bash script tool:

I'm hoping it will become a companion tool to the popular symlinks, which does some other useful things.

Here is my tool:

# find all broken symlinks
fix_broken_symlinks path/to/dir
dry-run fix them
fix_broken_symlinks path/to/dir find_regex replacement_str
actually fix them (passing -f to force it)
fix_broken_symlinks path/to/dir find_regex replacement_str -f

I put a lot of effort into getting really pretty and aligned output.

Example run:

/home/gabriel/GS/dev/RESEARCH$ fix_broken_symlinks . '/home/gabriel/GS/dev' '/home/gabriel/GS/dev/RESEARCH' -f
4 broken symlinks found!

'--force' is on! Writing new relative symlinks!

1/4:    BROKEN: './lldb/Link to Debuggers_General' -> '/home/gabriel/GS/dev/Debuggers_General'
        FIXED : './lldb/Link to Debuggers_General' -> '/home/gabriel/GS/dev/RESEARCH/Debuggers_General'
        FINAL : './lldb/Link to Debuggers_General' -> '../Debuggers_General'
2/4:    BROKEN: './Link to notes - Gabriel.odt' -> '/home/gabriel/GS/dev/notes - Gabriel.odt'
        FIXED : './Link to notes - Gabriel.odt' -> '/home/gabriel/GS/dev/RESEARCH/notes - Gabriel.odt'
        FINAL : './Link to notes - Gabriel.odt' -> 'notes - Gabriel.odt'
3/4:    BROKEN: './books/Link to 104The Pragmatic Programmer, From Journeyman To Master - Andrew Hunt, David Thomas - Addison Wesley - 1999.pdf-1.desktop' -> '/home/gabriel/GS/dev/Design_Docs/104The Pragmatic Programmer, From Journeyman To Master - Andrew Hunt, David Thomas - Addison Wesley - 1999.pdf-1.desktop'
        FIXED : './books/Link to 104The Pragmatic Programmer, From Journeyman To Master - Andrew Hunt, David Thomas - Addison Wesley - 1999.pdf-1.desktop' -> '/home/gabriel/GS/dev/RESEARCH/Design_Docs/104The Pragmatic Programmer, From Journeyman To Master - Andrew Hunt, David Thomas - Addison Wesley - 1999.pdf-1.desktop'
        FINAL : './books/Link to 104The Pragmatic Programmer, From Journeyman To Master - Andrew Hunt, David Thomas - Addison Wesley - 1999.pdf-1.desktop' -> '../Design_Docs/104The Pragmatic Programmer, From Journeyman To Master - Andrew Hunt, David Thomas - Addison Wesley - 1999.pdf-1.desktop'
4/4:    BROKEN: './books/TDD--James Grenning Test-Driven Dev for Embedded C/pragprog.com/Link to TDD_code' -> '/home/gabriel/GS/dev/books/TDD_code'
        FIXED : './books/TDD--James Grenning Test-Driven Dev for Embedded C/pragprog.com/Link to TDD_code' -> '/home/gabriel/GS/dev/RESEARCH/books/TDD_code'
        FINAL : './books/TDD--James Grenning Test-Driven Dev for Embedded C/pragprog.com/Link to TDD_code' -> '../../TDD_code'



'--force' is on! New relative symlinks written!

Run 'fix_broken_symlinks` "."' one more time to check if any symlinks are
still broken.
real    0m0.157s
user    0m0.101s
sys 0m0.086s

Details

I just wrote a tool I used to fix nearly 100 broken symlinks. It's called fix_broken_symlinks.sh, and it's part of my eRCaGuy_dotfiles repo.

Here's how to get it:

# download it and make it executable
wget https://raw.githubusercontent.com/ElectricRCAircraftGuy/eRCaGuy_dotfiles/master/useful_scripts/fix_broken_symlinks.sh
chmod +x fix_broken_symlinks
help menu, with tons of info., & examples
./fix_broken_symlinks -h

General usage & examples:

# General usage
fix_broken_symlinks path/to/dir find_regex replacement_str
(Dry run) fix all broken symlinks in the current dir (.) by replacing their
target paths with John's home dir instead of Gabriel's.
fix_broken_symlinks . '/home/gabriel/some/dir' 'home/john/some/dir'
Pass -f to force it to actually apply the changes
fix_broken_symlinks . '/home/gabriel/some/dir' 'home/john/some/dir' -f

From the help menu:

'fix_broken_symlinks' version 0.1.0
USAGE
    fix_broken_symlinks [options] <dir> [<find_regex> <replacement_string>]
DESCRIPTION
Find all broken symlinks in directory 'dir', then extract the target paths they point to, search
those paths for 'find_regex', and replace those findings with 'replacement_string'. Finally,
recreate the symlinks as relative symlinks with those replacements to the target paths in
place.

If the 'find_regex' and 'replacement_string' are not provided, it will simply find and print out
the broken symlinks as they currently are.

All runs are dry-runs unless you use '--force'.


OPTIONS
    -h, -?, --help
        Print help menu
    -v, --version
        Print version information.
    --run_tests
        Run unit tests.
    -d, --debug
        Turn on debug prints.
    -f, --force
        Actually do the symlink replacements. Without this option, all runs are dry runs.
EXAMPLE USAGES:
fix_broken_symlinks -h
    Print help menu.
fix_broken_symlinks --help
    Print help menu.
fix_broken_symlinks .
    Recursively find all broken symlinks in the current directory (.).
fix_broken_symlinks . '/home/gabriel/some/dir' 'home/john/some/dir'
    (Dry run) fix all broken symlinks in the current dir (.) by replacing their target paths
    with John's home dir instead of Gabriel's.
fix_broken_symlinks . '/home/gabriel/some/dir' 'home/john/some/dir' -f
    (Real run) fix all broken symlinks in the current dir (.) by replacing their target paths
    with John's home dir instead of Gabriel's. **Relative** symlinks will be created in the end.

Other tools I use are:

1. Manually fix one-off broken symlinks with the following cmds:

   Note: -n is required if the symlink you're about to replace is to a directory. See the discussion beginning with my comment here for details: How can I "relink" a lot of broken symlinks?

   # NB: **All** of these options are important, and what I want. See 'man ln' 
   # for what each does.
   ln -svnri target_path symlink_path
   

2. Convert all symlinks from absolute to relative with:

   symlinks -rsvt .  # dry run
   symlinks -rsvc .  # the real replacement
   

   Install symlinks in Ubuntu with:

   sudo add-apt-repository universe
   sudo apt update
   sudo apt install symlinks
   

   See: https://www.makeuseof.com/how-to-find-and-fix-broken-symlinks-in-linux/

For more of my notes

See:

1. fix_broken_symlinks -h
2. My notes in this document here: eRCaGuy_dotfiles/git & Linux cmds, help, tips & tricks - Gabriel.txt. Search it for = Symlink Utilities: =.