Getting started

A first session: install BackDown, open it, index two drives, see what's duplicated, and ask whether one of them is safe to wipe. Everything can be done in the app's window or in a terminal; this page shows both. The examples use an old drive mounted at /media/old-drive and an archive drive at /media/archive. Use your own paths; on Windows, drive letters such as E:\.

BackDown only reads the drives you index. The one file it writes is its index, in your own data folder (where the index lives).

Install#

Download what suits your computer from the download page, and SHA256SUMS.txt from the same release. Checking the file against it tells you it arrived whole and is the one in that release. From v1.0.0-beta.4, each release also has SHA256SUMS.txt.sig, a signature of SHA256SUMS.txt made with BackDown's release key: checking it tells you the sums are the ones we published. BackDown's builds aren't signed with an Apple or Microsoft certificate yet.

# Linux
sha256sum -c --ignore-missing SHA256SUMS.txt
# macOS
shasum -a 256 -c --ignore-missing SHA256SUMS.txt

# Windows: compare this with the file's line in SHA256SUMS.txt
Get-FileHash .\BackDown-*.msi

The installers add BackDown to your applications menu, Launchpad or Start menu. The plain archives hold the backdown program, a README.txt and the third-party licences; backdown desktop install adds one of them to your applications afterwards. Either way, it's one program: the app and the backdown command are the same thing.

Linux#

The .deb installs the program as /usr/bin/backdown, the menu entry and icons, and a background service for each user that nobody's turned on:

sudo apt install ./backdown-io_*_amd64.deb

The package is called backdown-io because Debian and Ubuntu already have an unrelated duplicate remover called backdown. If a terminal ever suggests sudo apt install backdown, that's the other program. Both install /usr/bin/backdown, so ours replaces it, along with the backdown package of BackDown beta.1 and earlier.

Nothing starts by itself: open BackDown from your applications menu. The package manager keeps it up to date (download the new .deb); backdown update says so rather than changing a packaged file.

The AppImage needs no installing. Make it executable and run it: with no arguments it opens BackDown's window, and with arguments it's the backdown command.

chmod +x BackDown-*-x86_64.AppImage
./BackDown-*-x86_64.AppImage                       # the app
./BackDown-*-x86_64.AppImage index /media/old-drive  # the command
./BackDown-*-x86_64.AppImage desktop install       # add it to the applications menu

An AppImage can't replace itself: to update, download the new one.

The plain archive is one static program. Unpack it and put it on your PATH (without sudo, ~/.local/bin works as well, if it's on your PATH):

mkdir backdown && tar xzf backdown-*-linux-*.tar.gz -C backdown
sudo mv backdown/backdown /usr/local/bin/
backdown --version
backdown desktop install    # optional: the applications menu

macOS#

Open the .dmg and drag BackDown onto Applications (or unzip the .zip and move BackDown.app there). BackDown isn't notarised by Apple yet, so the first time macOS may say it can't check it:

1. In Applications, right-click (or Control-click) BackDown and choose Open, then Open again.
2. On macOS 15 and later, if there's no Open button: System Settings > Privacy & Security, then Open Anyway beside BackDown's name.

After that it opens like any other app. The backdown command is inside it; to use it in a terminal, link it onto your PATH:

sudo ln -s /Applications/BackDown.app/Contents/MacOS/backdown /usr/local/bin/backdown

With the plain archive instead, remove the quarantine flag once (or allow it in System Settings > Privacy & Security after the first try):

mkdir backdown && tar xzf backdown-*-macos-universal.tar.gz -C backdown
xattr -d com.apple.quarantine backdown/backdown
sudo mv backdown/backdown /usr/local/bin/
backdown desktop install    # optional: ~/Applications/BackDown.app

Windows#

The .msi installs BackDown for you alone, without administrator rights: into %LOCALAPPDATA%\Programs\BackDown, with a Start menu entry, and on your PATH for terminals opened afterwards. The setup .zip does the same without Windows Installer: unzip it and double-click Install BackDown.cmd; it opens BackDown when it's done. Either one is removed in Settings > Apps.

Because the files aren't code-signed yet, SmartScreen may ask the first time: More info, then Run anyway.

With the plain .zip, unzip it and run backdown.exe from a terminal (PowerShell or Command Prompt) in that folder, or add the folder to your PATH; backdown desktop install adds a Start menu entry.

Open BackDown#

Open BackDown from your applications menu, Launchpad or Start menu, or in a terminal:

backdown app

It starts BackDown's background service if it isn't running (the one you installed, or else one of its own), and opens in a window of its own. The window is Chrome, Chromium, Edge or Brave, whichever you have, running as an app with a profile of its own; without any of them, BackDown opens in a tab of your usual web browser. Opening it again brings the open window forward instead of starting anything twice.

The first time, Activity welcomes you with the drives connected to this computer. Choose Index this on each drive you want to know about, or type a folder under "Or a folder" and press Index it. BackDown only reads them. Each drive appears on the left when its scan is done, and hashing follows by itself. Then:

• Duplicates shows what's stored twice, the groups that free the most first: open one to see where each copy is, or group by Folders to see which folders hold copies of each other. The filter bar narrows it by type, size, date and hidden files, and the copies you tick go to Free up;
• What's here shows what things are: mail stores, phone backups, photo libraries and more;
• a drive's Report button gives the whole picture.

On Linux and macOS, a drive that isn't mounted can be mounted from Activity, read-only (mounting drives).

The background service keeps running after you close the window, rescanning drives when they're due or plugged back in. To have it start whenever you log in, backdown service install (keep it running).

The same in a terminal#

Index two drives#

backdown index /media/old-drive /media/archive

/media/old-drive: 44 files, 182 MB (new 44, changed 0, gone 0) · scan 1
  full walk in under a second: Linux keeps no change log for drives; not an NTFS drive
/media/archive: 39 files, 222 MB (new 39, changed 0, gone 0) · scan 2
  full walk in under a second: Linux keeps no change log for drives; not an NTFS drive

Each path you index becomes a root: a drive, or a top-level folder, that BackDown keeps track of. Indexing records every file's path, size and modification time. It doesn't read the files' contents yet, so it's quick. The numbers here come from a small demo; a real drive has hundreds of thousands of files. The second line says how the drive was scanned, and why: on Windows and macOS a rescan can often read the drive's own change log instead of every folder (fast rescans).

Every run is a scan. Run the same command again later and BackDown records what's new, changed or gone, keeps what it already knows about unchanged files, and keeps the earlier versions for the time slider.

On Windows:

backdown index E:\ F:\Archive

See what's duplicated#

backdown dupes

dupes first hashes whatever could be a duplicate, then lists groups of identical files, the ones that waste the most space first. A file whose size no other file shares is never read; the rest are sampled, and only files whose samples match are read in full (how hashing works).

219 MB reclaimable in 32 groups of duplicates (files ≥ 1M)

120 MB  3 × 60 MB  sha256 f5511040fea1…
    /media/archive/Backups/laptop-2019/VM/win10-copy.vdi
    /media/archive/Backups/laptop-2019/VM/win10.vdi
    /media/old-drive/VM/win10.vdi
5 MB  2 × 5 MB  sha256 cccfc2d24435…
    /media/archive/Media/Photos/2014/IMG_2014003.jpg
    /media/old-drive/Photos/2014/IMG_2014003.jpg

--min-size 100M leaves out smaller files; --limit 50 lists more groups. Hardlinks count once, so the reclaimable figure is real.

Is the old drive safe to wipe?#

backdown check /media/old-drive

/media/old-drive
  44 files, 182 MB
  verified       162 MB in 37 files (identical copy elsewhere)
  unique          20 MB in 7 files (no copy anywhere else)

COPY FIRST: 20 MB in 7 files exists nowhere else.
       19 MB         5 files  Photos
      767 KB         1 files  Documents
        14 B         1 files  .
  (--list shows every file)

A drive is safe to wipe when every file on it has a SHA-256-identical copy somewhere outside it. Here 7 files don't, so the verdict is "copy first", with the folders they're in. --list names them. Once they're copied and the archive is indexed again, the same command says:

SAFE TO WIPE: every file has a SHA-256-identical copy outside /media/old-drive.

check exits with 0 when the drive is safe to wipe and 2 when it isn't, so scripts can use it. What "safe to wipe" means has the details, and Free up a drive goes on from here.

Browse it#

backdown serve

BackDown browser for /home/you/.local/share/backdown/index.db at
  http://127.0.0.1:8787/?t=4f0c…
(only this link, only on this computer; Ctrl-C to stop)

serve opens the same browser as the app, in your web browser, without the background service: every indexed drive, every folder as it was at any scan, every version and copy of a file, and read-only viewers for photos, PDFs, documents, databases, code and more. It listens on this computer only (unless you ask for more), and the link carries a private token that changes each time. It can't change anything (copying, freeing up, rescues and rescans need the service), and says which command to run instead. Browse without restoring shows what it can do.

Keep it running#

The background service (the daemon) rescans each drive daily and whenever one is plugged back in, hashes after every scan, reads each drive's health, and keeps the browser available.

backdown service install
backdown open

service install runs it as you, with no extra rights: a systemd user service on Linux, a LaunchAgent on macOS, and a scheduled task that starts it when you log on on Windows. If you installed the .deb, its service is already there: systemctl --user enable --now backdown turns it on. backdown open opens the browser in your usual web browser, and backdown app in its own window. The daemon explains what it does.

Produce a report#

The whole picture as one document: every drive with its verdict, what's on it, how much of it exists elsewhere, and the biggest duplicates.

backdown report > report.md
backdown report --html -o report.html

The browser's "What's here" view has the same report, as a page or a Markdown download. The report reads the index as it is, so run backdown dupes or backdown hash first to count every duplicate.

Where next#

• Concepts: drives, scans, hashes and what "safe to wipe" means.
• Free up a drive: delete only what has a verified copy.
• File your old drives into one archive: a plan, then verified copies.
• Settings, updates and licences: the Settings view, updates, and what's free.
• CLI reference: every command and option.