Ubuntu – How to make Thunar regenerate thumbnails

This shell script will regenerate your thumbnails of sizes 128px and 360px so you'll see at least something in viewer.

sqlite3 ~/.local/share/shotwell/data/photo.db \
  "select id||' '||filename from PhotoTable order by timestamp desc" | 
  while read id filename; do
    for size in 128 360; do
      tf=$(printf ~/.cache/shotwell/thumbs/thumbs${size}/thumb%016x.jpg $id);
      test -e "$tf" ||  {
        echo -n "Generating thumb for $filename ($tf)";
        convert "$filename" -auto-orient -thumbnail ${size}x${size} $tf
        echo
      }
    done
  done

Nautilus's thumbnailing routines actually come from the libgnome-desktop library, so it is possible to run the same thumbnailers outside of the file manager.

The API is a little complex, but the following Python script should help:

#!/usr/bin/python
import os
import sys

from gi.repository import Gio, GnomeDesktop

def make_thumbnail(factory, filename):
    mtime = os.path.getmtime(filename)
    # Use Gio to determine the URI and mime type
    f = Gio.file_new_for_path(filename)
    uri = f.get_uri()
    info = f.query_info(
        'standard::content-type', Gio.FileQueryInfoFlags.NONE, None)
    mime_type = info.get_content_type()

    if factory.lookup(uri, mtime) is not None:
        print "FRESH       %s" % uri
        return False

    if not factory.can_thumbnail(uri, mime_type, mtime):
        print "UNSUPPORTED %s" % uri
        return False

    thumbnail = factory.generate_thumbnail(uri, mime_type)
    if thumbnail is None:
        print "ERROR       %s" % uri
        return False

    print "OK          %s" % uri
    factory.save_thumbnail(thumbnail, uri, mtime)
    return True

def thumbnail_folder(factory, folder):
    for dirpath, dirnames, filenames in os.walk(folder):
        for filename in filenames:
            make_thumbnail(factory, os.path.join(dirpath, filename))

def main(argv):
    factory = GnomeDesktop.DesktopThumbnailFactory()
    for filename in argv[1:]:
        if os.path.isdir(filename):
            thumbnail_folder(factory, filename)
        else:
            make_thumbnail(factory, filename)

if __name__ == '__main__':
    sys.exit(main(sys.argv))

Save this to a file and mark it executable. You may also need to install the gir1.2-gnomedesktop-3.0 package if it is not already installed.

After that, simply invoke the script with the files or folders you want to thumbnail as arguments. Thumbnails will be saved to ~/.thumbnails where applications like Nautilus expect to find them.