Flowlin

A fast, private, keyboard-driven image browser for Linux.

Pick a folder in the tree, see its images as thumbnails, and step through them full size with the arrow keys (or W/A/S/D). Press R to see every image in a folder and all its subfolders in one grid. Flowlin stays smooth with tens of thousands of files and never touches the network.

Built with GTK 4 and libadwaita, written in Rust. Works on Wayland and X11.

https://github.com/user-attachments/assets/904e579f-aea3-4c84-ac4b-e7b98d1fa4d1

• Features
• Installation
• Getting started
• Using Flowlin
• Keyboard shortcuts
• Preferences
• Privacy
• Supported formats
• Troubleshooting
• Development
• License

Features

• Folder tree with favourites, Home, Pictures, the whole file system and mounted drives. Folders load lazily; folders without images are dimmed.
• Three layouts: grid, waterfall (masonry, keeps aspect ratios) and a sortable list with dimensions, size, date and type.
• Full-size viewer with fit / fill / 100 % / free zoom around the cursor, panning, high-quality downscaling, EXIF orientation, animated GIF / WebP / APNG, view-only rotation and a slideshow. Neighbouring images are decoded ahead of time, so stepping is instant.
• Recursive mode: all images below a folder in one grid, streamed in while the folder tree is walked.
• Keyboard first: W/A/S/D work like the arrow keys everywhere, Tab jumps between the folder tree and the thumbnails, Space opens and closes images.
• Videos (mp4, mkv, webm, mov, avi) with thumbnails and a player.
• Tabs, each with its own folder, history and recursive setting.
• File management: move to trash with undo, rename, copy / cut / paste (compatible with GNOME Files), drag and drop, new folder, open with another app, show in file manager, properties with an EXIF summary.
• Star ratings stored with the file (extended attributes, compatible with KDE), with filtering by rating.
• Live updates when files change on disk.
• Private by design: no network access, no thumbnail files on disk, no history of what you opened.

Installation

Flowlin has no prebuilt packages yet; build it from source. It takes a few minutes the first time.

1. Install the build dependencies

You need Rust 1.92 or newer, GTK 4.14+, libadwaita 1.5+ and GStreamer (for video).

Fedora

sudo dnf install rust cargo gcc gtk4-devel libadwaita-devel gdk-pixbuf2-devel \
  gstreamer1-devel gstreamer1-plugins-base-devel

Ubuntu 24.04+ / Debian 13+

sudo apt install build-essential pkg-config libgtk-4-dev libadwaita-1-dev \
  libgdk-pixbuf-2.0-dev libglib2.0-dev-bin \
  libgstreamer1.0-dev libgstreamer-plugins-base1.0-dev

The Rust compiler shipped by Debian and Ubuntu is too old. Install a current one with rustup:

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

Immutable systems (Fedora Silverblue / Kinoite, Bazzite, …): build inside a toolbox or distrobox container with the Fedora packages above. The resulting program runs directly on the host, since these systems already ship GTK 4 and libadwaita.

2. Build and install

git clone https://github.com/abuisman/flowlin.git
cd flowlin
cargo build --release
./build-aux/install.sh

install.sh installs into ~/.local (no root needed): the flowlin program, the app-menu entry, the icon and the settings schema. To install for all users instead:

sudo ./build-aux/install.sh /usr/local

After installing, Flowlin appears in your application menu. If ~/.local/bin is on your PATH, you can also start it from a terminal with flowlin.

To try it without installing anything:

cargo run --release -- ~/Pictures

Optional: more image formats

HEIF/HEIC, AVIF, JPEG XL and camera RAW previews are decoded by your system's image loaders. Install them if you want those formats:

# Fedora
sudo dnf install glycin-loaders libheif webp-pixbuf-loader
# Ubuntu / Debian
sudo apt install heif-gdk-pixbuf webp-pixbuf-loader

Video playback depends on the GStreamer plugins installed on your system (for example gstreamer1-plugins-good, -bad-free and -libav on Fedora, gstreamer1.0-plugins-good / -bad / -libav on Debian and Ubuntu).

Flatpak (experimental)

flatpak-builder --user --install build-dir build-aux/com.ronkatil.Flowlin.json
flatpak run com.ronkatil.Flowlin

The Flatpak has full access to your files (--filesystem=host). This is deliberate: Flowlin is a file browser, and the folder tree and recursive mode need to read folders directly. Portals only grant access to files you pick one by one.

Uninstalling

Remove the installed files (replace ~/.local with the prefix you used):

rm ~/.local/bin/flowlin \
   ~/.local/share/applications/com.ronkatil.Flowlin.desktop \
   ~/.local/share/metainfo/com.ronkatil.Flowlin.metainfo.xml \
   ~/.local/share/icons/hicolor/*x*/apps/com.ronkatil.Flowlin.png \
   ~/.local/share/icons/hicolor/symbolic/apps/com.ronkatil.Flowlin-symbolic.svg \
   ~/.local/share/glib-2.0/schemas/com.ronkatil.Flowlin.gschema.xml
glib-compile-schemas ~/.local/share/glib-2.0/schemas

To also reset your preferences: dconf reset -f /com/ronkatil/Flowlin/.

Getting started

Start Flowlin from the application menu, or from a terminal:

flowlin                      # opens your home folder
flowlin ~/Pictures/Holiday   # opens a folder
flowlin photo.jpg            # opens the folder and shows that image

You can also right-click a folder or image in your file manager and choose Open With → Flowlin. Opening something while Flowlin is already running adds a new tab to the existing window.

A typical session, keyboard only:

1. Use W/S (or ↑/↓) in the folder tree to walk through your folders. Each folder you land on is shown on the right.
2. Press Tab to jump into the thumbnails (Tab again jumps back).
3. Move with W/A/S/D or the arrow keys and press Space or Enter to view an image full size.
4. Step through images with A/D (or ←/→); W/S (↑/↓) move to the image one row above or below, exactly as in the grid.
5. Press Space, Enter or Esc to return to the thumbnails.

Press Ctrl+? at any time for the list of all shortcuts.

Using Flowlin

The window

• Header bar: sidebar toggle, favourite star, back / forward, the path of the current folder (click a part to go there; the last part lists sibling folders), the number of images, the include-subfolders toggle, layout buttons, open viewer, sort menu, main menu and "open in file manager".
• Tabs: Ctrl+T opens a tab, Ctrl+W closes it. Middle-click a folder in the tree to open it in a new tab.
• Sidebar: the folder tree. Right-click a folder for Open, Open with Subfolders, Open in New Tab, Add to Favourites, New Folder, Rename and Move to Trash. F9 hides or shows it.

Browsing folders

• Click a folder in the tree, or move to it with the keyboard.
• Space on a folder in the tree selects its first image, ready to open.
• Backspace / Alt+↑ goes to the parent folder; Alt+←/→ go back and forward.
• Ctrl+L lets you type or paste a path.
• Ctrl+D adds the current folder to your favourites at the top of the tree.
• Typing letters in the thumbnails jumps to the first file whose name starts with them (letters other than W, A, S, D and R).

Recursive mode (include subfolders)

Press R, click the search-folder button in the header, or right-click a folder and choose Open with Subfolders. The grid then shows every image in the folder and all folders below it. Each thumbnail shows which subfolder it comes from, and the sort menu gains a "Folder, Then Name" option. Very large trees are capped at 200 000 files (adjustable in Preferences).

Layouts, sorting and filtering

• Ctrl+1 / Ctrl+2 / Ctrl+3 switch between grid, waterfall and list.
• Ctrl+plus / Ctrl+minus or Ctrl+scroll change the thumbnail size.
• The sort menu sorts by name (natural order: img2 before img10), date modified, date created, size, type, dimensions or randomly, ascending or descending. In the list layout you can also click the column headers.
• Ctrl+F opens the filter bar. Type part of a file name, or a rating condition such as rating:>=3, rating:5 or rating:<2. You can combine both: beach rating:>=4.

The viewer

The viewer remembers "100 %", "fit" or "fill" when you choose them explicitly. The info bar at the bottom shows the file name, position, dimensions, file size and zoom level, and hides itself after two seconds.

Videos

Videos appear in the grid with a play badge and start playing muted when opened. A control bar provides play/pause, a seek bar and volume.

Videos can be hidden with Main menu → Show Videos.

Managing files

Select files with a click, Ctrl+click, Shift+click, or by dragging a rectangle over empty space (Ctrl+A selects all), then use the right-click menu or:

• Delete: move to trash. An "Undo" button appears for 10 seconds.
• Shift+Delete: delete permanently, after confirmation.
• F2: rename.
• Ctrl+C / Ctrl+X / Ctrl+V: copy, cut and paste, also to and from your file manager. Pasting shows an Undo button too.
• Drag and drop: drag thumbnails onto a folder in the tree or onto a tab to move them (hold Ctrl to copy). Files dropped in from other apps are copied into the current folder; a dropped folder is opened.
• Ctrl+Shift+N: new folder. Alt+Enter: properties, with dimensions, colour type and an EXIF summary (camera, lens, exposure, whether GPS data is present).

Ratings

Press 1–5 in the thumbnails to rate the selected images and 0 to clear the rating. In the viewer use 2–5, Shift+1 for one star and Shift+0 to clear (plain 1 and 0 are zoom keys there). Stars are shown on the thumbnails and in the list layout.

Ratings are stored in the file's user.baloo.rating extended attribute, the same place KDE uses, so they move with the file. File systems without extended attributes (for example FAT or exFAT USB sticks) cannot store ratings; Flowlin tells you when that happens.

Mouse gestures

Hold the right mouse button in the thumbnails, drag at least 40 pixels and release:

A short right-click without dragging opens the context menu as usual.

Keyboard shortcuts

Folders

Thumbnails

Files

Window

The viewer and video keys are listed in The viewer and Videos.

Preferences

Open them from the main menu or with Ctrl+,:

• Style: follow the system, or always light or dark.
• Show file names and Show folder under name in recursive mode.
• Single-key shortcuts: turn off to make every letter go to name search (type-ahead) instead of W/A/S/D/R and ratings.
• Show hidden files.
• Recursive mode stays on one file system: don't descend into other mounted drives.
• Recursive file limit (default 200 000).
• Slideshow interval (default 3 seconds).
• Thumbnail memory (default 256 MB): how much memory thumbnails may use.

Privacy

Flowlin is built to leave no trace of what you look at:

• It makes no network requests of any kind: no update checks, no telemetry.
• Thumbnails are kept in memory only. Nothing is written to ~/.cache/thumbnails or anywhere else, and they are gone when you quit.
• It does not remember the last folder, a browsing history or recently opened files, and it does not add files to the desktop's "recent files" list.
• The only things saved are your preferences (layout, sort order, thumbnail size, window size, the settings above) and the folders you explicitly add to favourites.

The trade-off is that thumbnails are generated again each time you start Flowlin. This is fast for common formats, because JPEG thumbnails are decoded at reduced size directly from the file.

Supported formats

Files without an extension are recognised by their content. Files whose extension doesn't match their content (a PNG named .jpg) are shown correctly. Damaged files show a placeholder instead of crashing the app.

Troubleshooting

Some formats show a placeholder icon. Run flowlin from a terminal; the first log line lists which optional loaders were found (for example heic=yes jxl=no). Install the missing loaders (see Optional: more image formats).

Videos don't play or show no thumbnail. Install the GStreamer plugins for the codec in question (often gstreamer1-libav / gstreamer1.0-libav).

"Could not move to trash". Some locations, such as /tmp and other system-internal mounts, have no trash. Use Shift+Delete to delete permanently.

More detail in the log. Start Flowlin with RUST_LOG=flowlin=debug flowlin. FLOWLIN_FRAME_LOG=1 additionally reports slow frames, which helps when reporting scrolling stutter.

Development

cargo test                                    # unit tests + GUI smoke test
cargo run --example gen_fixtures -- /tmp/fx   # test folder tree with every format
cargo run --release --bin flowlin-bench -- /path/to/folder [--recursive]
RUST_LOG=flowlin=debug cargo run -- /path

The GUI smoke test runs the real app under xvfb-run. It is skipped when xvfb-run isn't installed.

Before sending changes, please run cargo fmt and cargo clippy --all-targets -- -D warnings, as CI does.

Translations use gettext. build-aux/update-pot.sh regenerates po/flowlin.pot from the sources; add translations as po/<language>.po and list the language in po/LINGUAS.

Project layout:

License

Flowlin is free software, licensed under the GNU General Public License v3.0 or later.