(Post edited to add more info.)

My Android phone contains, in the lowest user-accessible directories of both phone storage and SD card, several small files named xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx where x is a hex digit.

There are three of them in the phone storage /sdcard (all zero size), owned by root:sdcard_rw and mode 664. And there are six in the external SD card /mnt/extSdCard (some zero size, some 36 bytes long), owned by system:media_rw and mode 775. Dates range from 2013 to one week ago. All files are readable, and those who aren't empty contain only a string which is identical to the filename.

I was curious to know what is the purpose of these files and if they can be deleted safely.

Is it a coincidence that they have the same format as an UUID?

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    What size are those files? Were you able to look into one of them – and if so, are they readable (if unreadable, any readable parts at the start)? At least for the SD card I'd say they are safe to remove, but I'd better check first. – Izzy Jul 20 '15 at 16:24
  • Good questions. I've edited my original question to answer you. – dr01 Jul 21 '15 at 8:21
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    Thanks for the edit! Looks strange indeed. I'm pretty confident you can safely delete them at least from the SD card (for safety, you can create a temp folder and move them there; so if unexpected issues pop up after that, you can move them back). Not sure what you mean by "phone root dir": can you give a full path for that? Also, if possible, use a terminal app (or adb shell) to run ls -l on that location to verify their ownership, which might give us a better clue (for those not on SD card). – Izzy Jul 21 '15 at 10:52
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    Ah! I already suspected that. What you call "phone storage" is the internal SD card – "phone storage" is something different (/data and other things, the "phone root dir" would be /). OK, in that case it should be safe to remove all of them (and permissions do not tell us much here, as for SD cards, everything is owned by root:sdcard_rw resp. system:sdcard_rw with mode 755). Again, if you're afraid, you can first move them to a temp folder – and if "nothing strange" happens for a couple of days, delete that folder. – Izzy Jul 21 '15 at 12:30
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    I would not recommend deleting random files without trying to understand what they are or where they come from. – Lie Ryan Jul 21 '15 at 12:57

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