lsb_release -a; # tested with
Description: Debian GNU/Linux 12 (bookworm)

#  previously this was tested with
cat /etc/os-release |grep PRETTY
PRETTY_NAME="Debian GNU/Linux 11 (bullseye)"


duplicate files are a waste of disk space.

every system experiences catastrophic failures, slow downs and crashes of programs, when RAM or disk space runs out 😀

BUT: under no circumstances shall a program be designed, to allow accidents that delete ALL files 😀 (without saveguards like: “you will delete all fiels under this folder?” “are you sure?” “are you really sure?”

sometimes files are stored in a certain folder for a reason.

there are programs, that allow

  1. finding duplicate files
  2. then deleting one copy
  3. then setting a link to the still existing copy

= disk space is saved, and all files are still accessible via their folders

precautions: be careful!

developers make mistakes, users make mistakes, computers make mistakes.

things can go wrong fast, so it’s always good to:

  1. backup (and detach from any computer to not allow ransomeware access and store it double-triple-metall-shielded to avoid any dataloss due to electro-magnetism)
  2. backup (and detach from any computer to not allow ransomeware access and store it double-triple-metall-shielded to avoid any dataloss due to electro-magnetism)
  3. backup (and detach from any computer to not allow ransomeware access and store it double-triple-metall-shielded to avoid any dataloss due to electro-magnetism)

done that? scroll to continue X-D

GNU Linux (Debian) – how to – find the largest 30 duplicate files wasting disk space – multi line sorting madness (mlsm) – how to output x blocks of text separated by delimiter – build (Bill Poser’s and BSDs) msort from src

how to find largest files?

very minimalistic pure bash (busybox approved) way:

vim /scripts/

if [ -z "$1" ]
	# list 30 biggest files or directories (qnap-busybox tested)
	du -a / | sort -n -r | head -n 30;
	du -a $1 | sort -n -r | head -n 30;

# run it
chmod +x /scripts/*.sh
/scripts/ /home/user
# another variant
# du -sx /* | sort -rh | head -30;



hardlink is a tool which replaces copies of a file with hardlinks, therefore it can be usefull for saving diskspace.


# start a test dry-run on the current directory
hardlink -v --dry-run .

it also per default searches in all subdirectories of the current directory:

# do it for real
hardlink -v .

how much diskspace could be saved?

So how much can efficiently be salvaged if all duplicate data would be replaced with links (pointers) to the real data on disk?

# dryrun = test run (no modification to files)
# how much hardlinking duplicate files could save disk space?
# depending on amount of files and CPU power this will run for a while
time hardlink -v --dry-run /home/user
Mode: dry-run
Method: sha256
Files: 634617
Linked: 54028 files
Compared: 0 xattrs
Compared: 5217072 files
Saved: 107.06 GiB <- nice
Duration: 1577.789062 seconds

how to find largest duplicate files?

no idea yet.

if a package manager with access to packages is possible (for Debian users it usually is):

su - root
apt update
apt install rmlint
# there is also a (python based) gui for it
# BUT 1) it's not ment to be run as root (LOADS OF WARNINGS!)
# 2) as non-root it kind of "nothing found" malfunctioned
# apt install rmlint-gui
Ctrl+D # become non-root

# test it out
mkdir temp
cd temp
touch 1 2 3
time dd if=/dev/zero bs=64M count=16 iflag=fullblock
cp -rv
time rmlint .

# Empty file(s):
    rm '/home/user/temp/1'
    rm '/home/user/temp/2'
    rm '/home/user/temp/3'

# Duplicate(s):
    ls '/home/user/temp/'
    rm '/home/user/temp/'

==> Note: Please use the saved script below for removal, not the above output.
==> In total 7 files, whereof 1 are duplicates in 1 groups.
==> This equals 1.00 GB of duplicates which could be removed.
==> 3 other suspicious item(s) found, which may vary in size.
==> Scanning took in total 2.729s.

Wrote a json file to: /home/user/temp/rmlint.json
Wrote a sh file to: /home/user/temp/

real	0m2.742s

# manpage:
# online documentation
# for thrills run it on user's home dir
# (no modifications just reporting, "dryrun" mode so some users says)
time rmlint ~

# sample output:
==> Note: Please use the saved script below for removal, not the above output.
==> In total 505311 files, whereof 158835 are duplicates in 78903 groups.
==> This equals 137.71 GB of duplicates which could be removed.
==> 3603 other suspicious item(s) found, which may vary in size.
==> Scanning took in total 12m 30.727s.

Wrote a sh file to: /home/user/
Wrote a json file to: /home/user/rmlint.json

# it ran for 	12m30.936s (i5 + ssd) on, rmlint reports runtime by default so no need to append time
du -hs .
760GBytes of data

So in one’s case 18.11% of disk space saving would be possible 😀

It is interesting to note that “hardlinks” reports 14.08% of disk space save-able.

Where the difference comes from? One does not know (yet).

Thanks all involved!




WARNING: jdupes IS NOT a drop-in compatible replacement for fdupes!

identify and delete or link duplicate files


jdupes -m .
Scanning: 7 files, 1 items (in 1 specified)
6 duplicate files (in 1 sets), occupying 6 MB

     -L --linkhard
              replace all duplicate files with hardlinks to the first file in each set of duplicates


identifies duplicate files within given directorie (fdupes.manpage.txt)

su - root;
apt update;
apt install fdupes;
-H --hardlinks
normally, when two or more files point to  the  same  disk  area
they are treated as non-duplicates; this option will change this behavior


fdupes -r -m .
8 duplicate files (in 1 sets), occupying 8.4 megabytes



su - root;
apt update;
apt install rdfind;
# dry run (no file is removed)
rdfind -dryrun true ./search/in/this/folder

rdfind -deleteduplicates true ./search/in/this/folder





su - root;
apt-get update;
apt-get install duff; # install duff

duff examples:

Normal mode

Shows normal output, with a header before each cluster of duplicate files, in this case using

  • recursive search (-r) in .folder /comics
duff -r comics
2 files in cluster 1 (43935 bytes, digest ea1a856854c166ebfc95ff96735ae3d03dd551a2)
3 files in cluster 2 (32846 bytes, digest 00c819053a711a2f216a94f2a11a202e5bc604aa)
2 files in cluster 3 (26596 bytes, digest b26a8fd15102adbb697cfc6d92ae57893afe1393)
2 files in cluster 4 (30332 bytes, digest 11ff80677c85005a5ff3e12199c010bfe3dc2608)

The header can be customized (with the -f flag) for example outputing only the number of files that follow:

duff -r -f '%n' comics

Excess mode

Duff can report all but one file from each cluster of duplicates (with the -e flag).

This can be used in combination with for examplerm to remove duplicates, but should only be done if you don’t care which duplicates are removed.

duff -re comics



czkawka it is the rust rewritten successor to fslint (fslint is no longer in the default Debian repo, for whatever reason)

what is neat about czkawka:

  • it searches a directory for duplicate files and lists the biggest files first
  • be-aware:
    • the terminal version is sufficient (imho)
      • Debian 11 (yet): was unable to install the gui
      • plz prepare for a lengthy install that involves downloading a lot of software and compiling it


# as default user
curl --proto '=https' --tlsv1.2 -sSf | sh

# check rust is installed
rustc --version
rustc 1.64.0 (a55dd71d5 2022-09-19)

cargo install czkawka_cli

# run it
czkawka_cli dup --directories /where/to/search/for/duplicates | less

# if the gui was required
# become root
su - root
apt update
apt install software-properties-common ffmpeg
apt install libgdk-pixbuf-2.0-dev libghc-pango-dev libgraphene-1.0-dev librust-pango-sys-dev libglib2.0-dev cairo-dev libcairo2-dev librust-pango-sys-dev

# Ctrl+D (logoff root)
cargo install cairo-dev

# can try to install gui, but won't work
cargo install czkawka_gui

help & more examples:

czkawka_cli --help
czkawka 6.0.0

    czkawka_cli  [SCFLAGS] [SCOPTIONS]

  -h, --help     Print help
  -V, --version  Print version

  dup            Finds duplicate files
  empty-folders  Finds empty folders
  big            Finds big files
  empty-files    Finds empty files
  temp           Finds temporary files
  image          Finds similar images
  music          Finds same music by tags
  symlinks       Finds invalid symlinks
  broken         Finds broken files
  video          Finds similar video files
  ext            Finds files with invalid extensions
  tester         Small utility to test supported speed of 
  help           Print this message or the help of the given subcommand(s)

    try "czkawka_cli  -h" to get more info about a specific tool

    czkawka dup -d /home/rafal -e /home/rafal/Obrazy  -m 25 -x 7z rar IMAGE -s hash -f results.txt -D aeo
    czkawka empty-folders -d /home/rafal/rr /home/gateway -f results.txt
    czkawka big -d /home/rafal/ /home/piszczal -e /home/rafal/Roman -n 25 -x VIDEO -f results.txt
    czkawka empty-files -d /home/rafal /home/szczekacz -e /home/rafal/Pulpit -R -f results.txt
    czkawka temp -d /home/rafal/ -E */.git */tmp* *Pulpit -f results.txt -D
    czkawka image -d /home/rafal -e /home/rafal/Pulpit -f results.txt
    czkawka music -d /home/rafal -e /home/rafal/Pulpit -z "artist,year, ARTISTALBUM, ALBUM___tiTlE"  -f results.txt
    czkawka symlinks -d /home/kicikici/ /home/szczek -e /home/kicikici/jestempsem -x jpg -f results.txt
    czkawka broken -d /home/mikrut/ -e /home/mikrut/trakt -f results.txt
    czkawka extnp -d /home/mikrut/ -e /home/mikrut/trakt -f results.txt

recovery of deleted files?

if the original data is deleted, the softlink becomes “invalid” (does not point to anything anymore) and the data is gone (under ext3 undelete can be done wth ease, recovery data from ext4 is much harder and often only the data can be (completely or partially) be recovered but NOT the filename, which can leave the user with a massive mess of data to be (manually?) sorted.

Uusually there should be backups of data on other disks, so it would actually be cool to tell extundelete or photorec: “check it out, the filenames might be lost, but the data is still (at least partially) there. please look at this backup disk and try to compare if an (partly) identical file is in the backup, and reconstruct (undelete) the file under ./where/the/accident/happened accordingly

GNU Linux – recover deleted files NTFS – undelete ext3 vs ext4 – rescue accidentally deleted data files – overwritten partition table – foremost – gpart

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