FSlint

The GUI-based FSlint [3] tool, which is based on the findbl command-line tool (in the fslint package) belongs in the same category as symlinks. If you call findbl without any other parameters (or -d), it searches the current directory for broken links and prints the matches one by one.

Listing 9 shows the result of the call, which is practically identical to those from Listing 2 and Listing 8. The behavior of findbl becomes clear after a closer look: It is simply a shell script that relies on find for searching.

01 $ /usr/share/fslint/fslint/findbl .
02 project/version2/data/dataset3 -> project/version1/data/dataset3

rmlint and chase

I combined the rmlint [4] and chase [5] tools as a final option. (Shredder, rmlint's graphical front end, looked really great on the rmlint website, but I could not reproduce it on Debian GNU/Linux 11.)

Similar to FSlint, rmlint aims to find and clean up inconsistencies in entries in the filesystem, including detecting broken links. You can see the call to do this in line 1 of Listing 10.

01 $ rmlint -T bl -o pretty:stdout .
02 $ chase old
03 /project/version1

The -T switch lets you select what rmlint will look for; bl is the abbreviation for "broken links." The -o option determines the output format, and the pretty:stdout value gives you a prettified display. Figure 2 shows a sample call in which rmlint detects two broken links (and that's how it's supposed to be).

Figure 2: The rmlint search results for the example.

The chase tool also performs an exciting task: It tracks down the file to which a symbolic link actually points. It returns 1 in case of an error if the reference target does not exist. Line 2 in Listing 10 shows the call to the old reference from our example, and the result is the filename.

Avoiding Mistakes

How do you prevent the occurrence of broken links in the first place? Basically, the only advice here is to be more careful because (apart from the filesystem) there is no place where all the links are stored. I'm not aware of a service that checks in the background to make sure that links remain intact and warns you before you break a link.

It makes sense to check, with any of the tools discussed in this article, to see if symbolic links for a file exist before proceeding to delete the file. If you only have access to find and readlink, follow the steps shown in Listing 11. The call lists both components – the link and the link target – side by side. To do this, find uses the -exec option to echo the name and then display the link destination determined via readlink.

$ find . -type l -exec echo -n {} "-> " ';' -exec readlink {} ';'
./project/version2/data/dataset3 -> project/version1/data/dataset3
./project/old -> project/version1
./project/current -> project/version2

Keep in mind that symbolic links can cross filesystem boundaries. Your only option is to check everything that is mounted in the filesystem.