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I run

ln /a/A /b/B

I would like to see at the folder a where the file A points to by ls.

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migrated from Jul 25 '09 at 22:53

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Hard links aren't pointers, symlinks are. They're multiple names for the same file (inode). After a link(2) system call, there's no sense in which one is the original and one is the link. This is why, as the answers point out, the only way to find all the links is find / -samefile /a/A. Because one directory entry for an inode doesn't "know about" other directory entries for the same inode. All they do is refcount the inode so it can be deleted when the last name for it is unlink(2)ed. (This is the "link count" in ls output). – Peter Cordes Apr 21 at 18:47
@PeterCordes: Is the refcount actually stored IN the hardlink entry? That's what your wording implies ("All they do is refcount the inode...") But that wouldn't make sense if the links don't know anything about each other, since when one updated, all the others would somehow have to be updated. Or is the refcount stored in the inode itself? (Forgive me if it's a dumb question, I consider myself a newbie and I'm still learning). – loneboat Jul 6 at 20:51
The refcount is stored in the inode, as you eventually figured out must be the case, from the other facts. :) Directory entries are named pointers to inodes. We call it "hard linking" when you have multiple names pointing to the same inode. – Peter Cordes Jul 6 at 20:58

9 Answers 9

up vote 79 down vote accepted

You can find inode number for your file with

ls -i


ls -l

shows references count (number of hardlinks to particular inode)

after you found inode number, you can search for all files with same inode:

find . -inum NUM

will show filenames for inode NUM in current dir (.)

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you could just run find . -samefile filename – BeowulfNode42 Nov 25 '13 at 0:02

There isn't really a well-defined answer to your question. Unlike symlinks, hardlinks are indistinguishable from the original file. Filenames in directories are just references to an inode (which contains the file contents and file attributes). Creating a hard link creates another reference to the same inode. These references are unidirectional (in typical filesystems, at least) -- the inode only keeps a reference count.

This means that the only way to find the other references to a given inode is to exhaustively search over the file system checking which files refer to the inode in question. You can use 'test A -ef B' from the shell to perform this check.

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That means that there is no such thing as a hard link to another file, as the original file is also a hard link; hard links point to a location on disk. – jtbandes Jul 26 '09 at 0:03
@jtbandes: Hard links point to an inode which points to the actual data. – dash17291 Jun 13 '13 at 19:34
ls -l

The first column will represent permissions. The second column will be the number of sub-items (for directories) or the number of paths to the same data (hard links, including the original file) to the file. Eg:

-rw-r--r--@    2    [username]    [group]    [timestamp]     HardLink
-rw-r--r--@    2    [username]    [group]    [timestamp]     Original
               ^ Number of hard links to the data
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Helpful in determining IF a given file has [other] hard links, but not WHERE they are. – mklement0 Feb 11 at 3:48

UNIX has hard links and symbolic links (made with "ln" and "ln -s" respectively). Symbolic links are simply a file that contains the real path to another file and can cross filesystems.

Hard links have been around since the earliest days of UNIX (that I can remember anyway, and that's going back quite a while). They are two directory entries that reference the exact same underlying data. The data in a file is specified by its inode. Each file on a file system points to an inode but there's no requirement that each file point to a unique inode - that's where hard links come from.

Since inodes are unique only for a given filesystem, there's a limitation that hard links must be on the same filesystem (unlike symbolic links). Note that, unlike symbolic links, there is no privileged file - they are all equal. The data area will only be released when all the files using that inode are deleted (and all processes close it as well, but that's a different issue).

You can use the "ls -i" command to get the inode of a particular file. You can then use the "find <filesystemroot> -inum <inode>" command to find all files on the filesystem with that given inode.

Here's a script which does exactly that. You invoke it with:

findhardlinks ~/jquery.js

and it will find all files on that filesystem which are hard links for that file:

pax@daemonspawn:~# ./findhardlinks /home/pax/jquery.js
Processing '/home/pax/jquery.js'
   '/home/pax/jquery.js' has inode 5211995 on mount point '/'

Here's the script.

if [[ $# -lt 1 ]] ; then
    echo "Usage: findhardlinks <fileOrDirToFindFor> ..."
    exit 1

while [[ $# -ge 1 ]] ; do
    echo "Processing '$1'"
    if [[ ! -r "$1" ]] ; then
        echo "   '$1' is not accessible"
        numlinks=$(ls -ld "$1" | awk '{print $2}')
        inode=$(ls -id "$1" | awk '{print $1}' | head -1l)
        device=$(df "$1" | tail -1l | awk '{print $6}')
        echo "   '$1' has inode ${inode} on mount point '${device}'"
        find ${device} -inum ${inode} 2>/dev/null | sed 's/^/        /'
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@pax: There seems to be a bug in the script. I start it by . ./findhardlinks.bash while being in OS X's Zsh. My current window in Screen closes. – Masi Jul 25 '09 at 16:31
@Masi The issue is your initial . (same as the source command). That causes the exit 1 command to exit your shell. Use chmod a+x findhardlinks.bash then execute it with ./findhardlinks.bash or use bash findhardlinks.bash – njsf Jul 25 '09 at 23:08
Please, see my reply to your answer at… – Masi Jul 26 '09 at 16:42
To do this programmatically, it's probably more resilient if you use this instead: INUM=$(stat -c %i $1). Also NUM_LINKS=$(stat -c %h $1). See man stat for more format variables you can use. – Joe Jan 3 '12 at 20:12
Best answer, by far. Kudos. – MariusMatutiae Jun 27 at 8:24

Based on the findhardlinks script (renamed it to hard-links), this is what I have refactored and made it work.


# ./hard-links /root

Item: /[10145] = /root/.profile
    -> /proc/907/sched
    -> /<some-where>/.profile

Item: /[10144] = /root/.tested
    -> /proc/907/limits
    -> /<some-where else>/.bashrc
    -> /root/.testlnk

Item: /[10144] = /root/.testlnk
    -> /proc/907/limits
    -> /<another-place else>/.bashrc
    -> /root/.tested


# cat ./hard-links
oIFS="${IFS}"; IFS=$'\n';
xFILES="`ls -al ${xPATH}|egrep "^-"|awk '{print $9}'`";
for xFILE in ${xFILES[@]}; do
  if [[ ! -r "${xITEM}" ]] ; then
    echo "Path: '${xITEM}' is not accessible! ";
    nLINKS=$(ls -ld "${xITEM}" | awk '{print $2}')
    if [ ${nLINKS} -gt 1 ]; then
      iNODE=$(ls -id "${xITEM}" | awk '{print $1}' | head -1l)
      xDEVICE=$(df "${xITEM}" | tail -1l | awk '{print $6}')
      echo -e "\nItem: ${xDEVICE}[$iNODE] = ${xITEM}";
      find ${xDEVICE} -inum ${iNODE} 2>/dev/null|egrep -v "${xITEM}"|sed 's/^/   -> /';
IFS="${oIFS}"; echo "";
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I posted comments on this script as a separate answer. – Daniel Andersson Jun 13 '12 at 7:40

This is somewhat of a comment to Torocoro-Macho's own answer and script, but it obviously won't fit in the comment box.

Rewrote your script with more straightforward ways to find the info, and thus a lot less process invocations.

xPATH=$(readlink -f -- "${1}")
for xFILE in "${xPATH}"/*; do
    [ -d "${xFILE}" ] && continue
    [ ! -r "${xFILE}" ] && printf '"%s" is not readable.\n' "${xFILE}" 1>&2 && continue
    nLINKS=$(stat -c%h "${xFILE}")
    if [ ${nLINKS} -gt 1 ]; then
        iNODE=$(stat -c%i "${xFILE}")
        xDEVICE=$(stat -c%m "${xFILE}")
        printf '\nItem: %s[%d] = %s\n' "${xDEVICE}" "${iNODE}" "${xFILE}";
        find "${xDEVICE}" -inum ${iNODE} -not -path "${xFILE}" -printf '     -> %p\n' 2>/dev/null

I tried to keep it as similar to yours as possible for easy comparison.

Comments on this script and yours

  • One should always avoid the $IFS magic if a glob suffices, since it is unnecessarily convoluted, and file names actually can contain newlines (but in practice mostly the first reason).

  • You should avoid manually parsing ls and such output as much as possible, since it will sooner or later bite you. For example: in your first awk line, you fail on all file names containing spaces.

  • printf will often save troubles in the end since it is so robust with the %s syntax. It also gives you full control over the output, and is consistent across all systems, unlike echo.

  • stat can save you a lot of logic in this case.

  • GNU find is powerful.

  • Your head and tail invocations could have been handled directly in awk with e.g. the exit command and/or selecting on the NR variable. This would save process invocations, which almost always betters performance severely in hard-working scripts.

  • Your egreps could just as well be just grep.

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xDEVICE=$(stat -c%m "${xFILE}") does not work on all systems (for example: stat (GNU coreutils) 6.12). If the script outputs "Item: ?" at the front of each line, then replace this offending line with a line more like the original script, but with xITEM renamed to xFILE: xDEVICE=$(df "${xFILE}" | tail -1l | awk '{print $6}') – kbulgrien Mar 28 '14 at 20:23
If you just want groups of hardlinks, rather than repeated with each member as the "master", use find ... -xdev -type f -links +1 -printf '%16i %p\n' | sort -n | uniq -w 16 --all-repeated=separate. This is MUCH faster, as it only traverses the fs once. For multiple FSes at once, you'd need to prefix the the inode numbers with a FS id. Maybe with find -exec stat... -printf ... – Peter Cordes Apr 21 at 19:14
turned that idea into an answer – Peter Cordes Apr 21 at 19:33

How about the following simpler one? (Latter might replace the long scripts above!)

If you have a specific file <THEFILENAME>and want to know all its hardlinks spread over the directory <TARGETDIR>, (which can even be the entire filesystem denoted by /)

find <TARGETDIR> -type f -samefile <THEFILENAME>

Extending the logic, if you want to know all the files in the <SOURCEDIR> having multiple hard-links spread over <TARGETDIR>:

find <SOURCEDIR> -type f -links +1 -printf "\n\n %n HardLinks of file : %H/%f \n" -exec find <TARGETDIR> -type f -samefile {} \;

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This is for me the best answer! but i would not use -type f because the file can be a directory too. – silvio Aug 30 '13 at 11:40
@silvio: You can only create hard links to files, not directories. – mklement0 Feb 11 at 3:45
@mklement0: You are right! – silvio Feb 11 at 10:38
The . and .. entries in directories are hardlinks. You can tell how many subdirs are in a directory from the link count of .. This is moot anyway, since find -samefile . still won't print any subdir/.. output. find (at least the GNU version) seems to be hardcoded to ignore .., even with -noleaf. – Peter Cordes Apr 21 at 18:53
also, that find-all-links idea is O(n^2), and runs find once for each member of a set of hardlinked files. find ... -printf '%16i %p\n' | sort -n | uniq -w 16 --all-repeated=separate would work, (16 isn't wide enough for a decimal representation of 2^63-1, so when your XFS filesystem is big enough to have inode numbers that high, watch out) – Peter Cordes Apr 21 at 19:06

A GUI solution gets really close to your question:

You cannot list the actual hardlinked files from "ls" because, as previous commentators have pointed out, the file "names" are mere aliases to the same data. However, there actually is a GUI tool that gets really close to what you want which is to display a path listing of file names that point to the same data (as hardlinks) under linux, it is called FSLint. The option you want is under "Name clashes" -> deselect "checkbox $PATH" in Search (XX) -> and select "Aliases" from drop-down box after "for..." towards the top-middle.

FSLint is very poorly documented but I found that making sure the limited directory tree under "Search path" with the checkbox selected for "Recurse?" and the aforementioned options, a listing of hardlinked data with paths and names that "point" to the same data are produced after the program searches.

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FSlint can be found at – mklement0 Feb 11 at 3:43

There are a lot of answers with scripts to find all hardlinks in a filesystem. Most of them do silly things like running find to scan the whole filesystem for -samefile for EACH multiply-linked file. This is crazy; all you need is to sort on inode number and print duplicates.

find directories.. -xdev ! -type d -links +1 -printf '%20D %20i %p\n' | sort -n | uniq -w 42 --all-repeated=separate (Thanks to @Tino for tweaking my original command to support a FS-id (%D), and to handle all non-directory file types, not just regular files. This will find your multiply-linked symlinks, pipes, etc.)

Using ! -type d -links +1 means that sort's input is only as big as the final output of uniq. Unless you run it on a subdirectory that only contains one of a set of hardlinks. Anyway, this will use a LOT less CPU time re-traversing the filesystem than any other posted solution.

sample output:

            2429             76732484 /home/peter/weird-filenames/test/.hiddendir/foo bar
            2429             76732484 /home/peter/weird-filenames/test.orig/.hiddendir/foo bar

            2430             17961006 /usr/bin/pkg-config.real
            2430             17961006 /usr/bin/x86_64-pc-linux-gnu-pkg-config

            2430             36646920 /usr/lib/i386-linux-gnu/dri/
            2430             36646920 /usr/lib/i386-linux-gnu/dri/
            2430             36646920 /usr/lib/i386-linux-gnu/dri/
            2430             36646920 /usr/lib/i386-linux-gnu/dri/
            2430             36646920 /usr/lib/i386-linux-gnu/dri/

TODO?: un-pad the output. uniq has very limited field-selection support, so I pad the find output and use fixed-width. 20chars is wide enough for the maximum possible inode or device number (2^64-1 = 18446744073709551615). XFS chooses inode numbers based on where on disk they're allocated, not contiguously from 0, so large XFS filesystems can have >32bit inode numbers even if they don't have billions of files. Other filesystems might have 20-digit inode numbers even if they aren't gigantic.

TODO: sort groups of duplicates by path. Having them sorted by mount point then inode number mixes things together, if you have a couple different subdirs that have lots of hardlinks. (i.e. groups of dup-groups go together, but the output mixes them up).

A final sort -k 3 would sort lines separately, not groups of lines as a single record. Preprocessing with something to transform a pair of newlines into a NUL byte, and using GNU sort --zero-terminated -k 3 might do the trick. tr only operates on single characters, not 2->1 or 1->2 patterns, though. perl would do it (or just parse and sort within perl or awk). sed might also work.

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%D is the filesystem identifier (it is unique for the current boot while no filesystems are umounted), so following is even more generic: find directories.. -xdev ! -type d -links +1 -printf '%20i %20D %p\n' | sort -n | uniq -w 42 --all-repeated=separate. This works as long no given directory contains another directory on the filesystem level, also it looks at everything which can be hardlinked (like devices or softlinks - yes, softlinks can have a link count greater than 1). Note that dev_t and ino_t is 64 bits long today. This likely will hold as long as we have 64 bit systems. – Tino Nov 9 at 14:34
@Tino: great point about using using ! -type d, instead of -type f. I even have some hardlinked symlinks on my filesystem from organizing some collections of files. Updated my answer with your improved version (but I put the fs-id first, so the sort order at least groups by filesystem.) – Peter Cordes Nov 9 at 18:45

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