I did search the forum and read the manual regarding the skull. It is memory-related. I checked the preference and compared it to the manual. Not much difference. DT is running on Mac OS Catalina with 16MB of RAM. The other thing I did not do is “run the script purge_non_existing_images.sh” Because I am hesitant to run the command in terminal.
I assume you mean 16GB of RAM?
Did you move that folder of images after you imported them to darktable? Are you sure darktable has full disk access in the System Preferences of macOS?
Sorry for the typing error. I didn’t move any folder. I was in the process of editing. Because there are a few hundred images that I usually close the program at night. I continue the progress the next day. Very strange that all folders have the same appearance.
I will check the system preference. Thanks.
I checked and changed the system preference. It will show some images if in full screen. Again all skulls if not in full screen.
The easiest way to resolve the issue is to run darktable-generate-cache from the terminal.
Not sure if it plays a role, but I see you have a lot of images per row (20). Is it possible that DT just has trouble generating the thumbnails at that size? Iow, do you get less skulls when you lower the number of thumbnails per row (I usually use 4 or 5, so I can see some detail in the images and read the overlays 
)
Hi there, what sort of command I need to type in the terminal. I am not familar with unix system. Thanks.
I just found out that the images that appeared on the second screen could not be opened in Darkroom. It said “the image is not available”.
I try to demonstrate all images in that folder. I don’t understand why it could show some images when it was in full screen.
It seems the stuff is on a mounted drive /Volumes/photos… maybe the mountpoint is no longer available. If there’re already generated thumbnails, you will see these instead of a skull.
Expected, the folder names are striked you have moved/deleted/renamed the folder or unmounted the drive where the RAW are. No surprise.
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This just means the database references are no longer valid…just remove all the skull using the script or if you are not comfortable select them and remove…now reimport… hopefully if you have edits on those files you have sidecar files…this should repopulate everything fine and your images will get new previews and be displayed…
@Pascal_Obry I’ve transferred all the images folder(in an ext drive already) to an SSD drive and re-imported them.
@priort It seems that DT is still reading from the old drive. As the old drive was reconnected, all photos back to normal. Is there a way it could make DT more portable, like working in another laptop or computer?
Use the “Sync local” feature: “Local copies” in the darktable usermanual
Did you remove the images from darktable that are on the ext drive? Is it possible that you have your images twice in darktable’s database: on the ext drive and on the SSD drive, and you are still trying to access the images through the ext drive?
If the images where imported twice using different directories they’re available in darktable twice. Darktable isnt able to guess, if this is an intended behaviour or not.
So it’s not a question of portability but of user workflow.
Simply select the affected images in collection ordered by folder and delete them if the images were moved and reimported.
To avoid this behaviour you also can use the „move“ function in darktable. Then the database keeps in sync with the location of the files
@MStraeten @Juha_Lintula I made a backup copy of the photo folder to an SSD. I wish to use SSD as the main drive. The skull images were noted when the ext drive is disconnected. I did re-import photos to SSD. However the ext drive has to be connected so as to view other collections. I have been using LR’s concept for years. Need to readjust the workflow. Thank you guys for valuable solutions.
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How much do you use the library…if you load DT with the command option :memory: it wont care and will just read your xmp files from whereever…so if you don’t use collections etc and just make edits…this is a good option not to have to try and keep a library db in sync…
I don’t use collections. I need the tagging which was widely used in LR. I also need two backup copies for my photos folder.
Is this command running from terminal? How to do it?
Are tags stored in xmp files that I don’t know
I’m on Windows so just add it to my shortcut command line…
https://www.darktable.org/usermanual/en/overview_chapter.html#darktable_commandline_parameters
–library
darktable keeps image information in an sqlite database for fast access. The default location of that database file is “$HOME/.config/darktable/library.db”. You may give an alternative location, e.g. if you want to do some experiments without compromising your original library.db. If the database file does not exist, darktable creates it for you. You may also give “:memory:” as a library file in which case the database is kept in system memory – all changes are discarded when darktable terminates.
Whenever darktable starts, it will lock the library to the current user. It does this by writing the current process identifier (PID) into a lock file “.lock” next to the library specified. If darktable finds an existing lock file for the library, it will terminate immediately.