How to use rsync with external microsd in Termux on Android 12?

[tigran123]

Hello,

I have used rsync in Termux to synchronise a copy of my library for ages and up until Android 12 everything worked fine (i.e. on Android 5, 6, 8 and 10). But now I got this new Note10+ phone with Android 12 and run into a serious problem.

If I store books in /storage/XXXX-YYYY/Android/data/com.termux/Books then rsync works perfectly (in both directions, i.e. from Linux to Termux or from Termux to Linux), but none of the applications (i.e. Koreader, Ebookdroid, etc) can read the books, so this option is useless. If, however, I store the books in /storage/XXXX-YYYY/Android/media/Books then all programs can see it, but doing rsync (again, in either direction) fails with this strange error:

sending incremental file list
md5sums.txt
rsync: [receiver] rename "/data/data/com.termux/files/home/sd/Books/.md5sums.txt.iy7eyw" -> "md5sums.txt": Operation not permitted (1)

and the thing is -- I can manually rename files in the same directory!

$ touch md5sums.txt
$ ls -l md5sums.txt 
-rwxrwx--- 1 root everybody 0 Dec 19 19:46 md5sums.txt
$ mv md5sums.txt new
$ ls -l new
-rwxrwx--- 1 root everybody 0 Dec 19 19:46 new

so the rsync command is doing something other than what mv does (I suppose I could ltrace both to find out). Any ideas how to make rsync work in Termux in Android 12?

The microsd is formatted as exFAT (using Linux mkfs.exfat). The rsync options I use are --delete --size-only -rvW i.e. the same as if it was FAT32 filesystem (as exFAT is the same wrt permissions, I think).

[tigran123]

Oh, I found a workaround -- --inplace option of rsync! If I pass it (in either direction) then rsync does not create temporary files in the destination and everything works perfectly on Android 12!

Of course I understand the dangers of --inplace, but I think if one is careful, i.e. always checks that everything is completed correctly, then no corrupted "half-copied" files should ensue.