Does mv on a FAT filesystem actually rename or does it copy and delete?

[Ralf Mardorf]

On Sat, 3 Feb 2018 09:50:31 +0000, Chris Green wrote:
>I want to rename some picture files on a mounted digital camera
>filesystem.  It is a VFAT filesystem.
>
>If I rename one of the files using 'mv <xxxx.yyy>' will the file
>*actually* be renamed by changing the directory entry only or will
>mv copy the file to one with the new name and then delete the old one? 

"mv" is atomic, you could verify, if I'm mistaken by using strace. "mv"
sometimes is used to workaround the non-atomic operation "ln".

However, I suspect you aren't asking if "mv" works atomic.
"mv <xxxx.yyy>" isn't a complete command. Take a look at the manpage:

http://manpages.ubuntu.com/manpages/xenial/man1/mv.1.html

"SYNOPSIS

       mv [OPTION]... [-T] SOURCE DEST
       mv [OPTION]... SOURCE... DIRECTORY
       mv [OPTION]... -t DIRECTORY SOURCE..."

So using your syntax it means

mv </path/from/xxxx.yyy> </path/to/pppp.qqq>

[rocketmouse at archlinux ~]$ cd /tmp/
[rocketmouse at archlinux tmp]$ mkdir dir_1 dir_2
[rocketmouse at archlinux tmp]$ ls -hAl dir_1 dir_2
dir_1:
total 0

dir_2:
total 0
[rocketmouse at archlinux tmp]$ touch dir_1/test
[rocketmouse at archlinux tmp]$ ls -hAl dir_1 dir_2
dir_1:
total 0
-rw-r--r-- 1 rocketmouse rocketmouse 0 Feb  3 11:46 test

dir_2:
total 0
[rocketmouse at archlinux tmp]$ mv -i dir_1/test dir_2/ 
[rocketmouse at archlinux tmp]$ ls -hAl dir_1 dir_2
dir_1:
total 0

dir_2:
total 0
-rw-r--r-- 1 rocketmouse rocketmouse 0 Feb  3 11:46 test
[rocketmouse at archlinux tmp]$ mv -i dir_2 dir_3
[rocketmouse at archlinux tmp]$ ls -hAl dir_1 dir_2 dir_3
ls: cannot access 'dir_2': No such file or directory
dir_1:
total 0

dir_3:
total 0
-rw-r--r-- 1 rocketmouse rocketmouse 0 Feb  3 11:46 test
[rocketmouse at archlinux tmp]$

To some extent "-i" ensures that you don't overwrite something by
accident.