I connected my phone using USB in Mass storage mode(MSC) to a HUMAX TV receiver, and after I disconnect the phone, when I opened the sd card in a files explorer app, all of the files and folders were named "FSCKxxxx.REN" except 8 folders and 3 filesScreenshot of the sd card in windows files explorer

also the folders that are named "FSCKxxxx.REN" contain files named "FSCKxxxx.REN", and it looks like that the original size of the files didn't change.

What is the cause of this problem, and how to fix it, is it even fixable without root? I searched for before I ask, but I couldn't fix the problem, maybe because I don't have root.

  • The prefix FSCK sounds like pointing to File System ChecK (the corresponding command is also named fsck). As fsck usually runs on boot or if invoked manually, my guess is it wasn't triggered by your Android device but by the TV box ("new disk drive detected") – and this had obviously issues reading those files. If it is the external SD card, you could connect it to your PC to check if it's not broken – before trouble increases. – Izzy Aug 13 '18 at 5:03
  • I connected the phone to the TV receiver in Mass storage mode(MSC) previously, and this problem didn't occur. – Azzam Alsharafi Aug 13 '18 at 6:58
  • Maybe "previously" the card was OK, but "now" is having issues? That's why I suggested to check it whether it has bad sectors or the like. – Izzy Aug 13 '18 at 7:01
  • I did what you have said and connected the SD card to my PC, when I connected it, a pop-up message appeared in the PC, it was something like this: "Fix problems" , I clicked "fix", and then after little time it said that the SD card was successfully "fixed", I opened it in files explorer, but nothing happened, the "FSCKxxxx.RET" files and folders still there. – Azzam Alsharafi Aug 13 '18 at 7:05
  • 1
    I discovered something new, it looks like that the data isn't lost, and as you said the files are just "renamed", I tried to use "file" command in bash, and it sill can know which file is video or image or XML file, even if I try to open a file that is a "ISO Media, MP4 Base Media v1 [IS0 14496-12:2003]" in a video player it will open correctly, I think your suspicion is right. – Azzam Alsharafi Aug 13 '18 at 8:46

Summing up from the comments:

The most likely cause is your SD card being in the process of "breaking down": When you connected it to your receiver, it detected problems and ran fsck (the File System ChecK utility) to repair it – which found issues with some files and directories, couldn't figure their names, and thus "saved" what it found using those "cryptic names" (the FSCK prefix seems to confirm this, though normally such "recovered blocks" are moved into a LOST+FOUND folder).

After having connected the card to your PC using a card reader, the PC again found the card faulty and had to repair things. Of course it couldn't restore the FSCK* files and directories to their original name, as that name was lost. As you correctly discovered, using the file command you can determine the file type, rename the files manually, and many, most or (if you're very lucky) even all or them might be intact.

So here's what you should do:

  1. Back up the entire contents of the card
  2. Get yourself a new card ASAP
    (until you did, repeat the previous step regularly; it might very soon start losing data)
  3. Copy the backup to the new card, and use that

And next to that, go the described way to identify the FSCK* files, which you then can rename to "useful names" and also copy back to the new card.

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