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

[Ralf Mardorf]

On Sat, 3 Feb 2018 11:55:47 +0100, Ralf Mardorf wrote:
>On Sat, 3 Feb 2018 11:51:18 +0100, Ralf Mardorf wrote:
>>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.  
>
>Within the same directory, which actually seems to be your question:
>
>[rocketmouse at archlinux ~]$ cd /tmp/dir_3/
>[rocketmouse at archlinux dir_3]$ ls -hAl
>total 0
>-rw-r--r-- 1 rocketmouse rocketmouse 0 Feb  3 11:46 test
>[rocketmouse at archlinux dir_3]$ mv
>-i /tmp/dir_3/test /tmp/dir_3/test_new [rocketmouse at archlinux dir_3]$
>ls -hAl total 0
>-rw-r--r-- 1 rocketmouse rocketmouse 0 Feb  3 11:46 test_new
>[rocketmouse at archlinux dir_3]$
>
>IOW it does "rename", since the operation is atomic.

PPS: IOW I was mistaken, you seemingly ask, if the operation is atomic.
Yes, "mv" within the same partition/directory does "rename", it does not
copy and remove (delete).

However, I might be mistaken, so use google, or much better run strace.

[rocketmouse at archlinux ~]$ cd /tmp/dir_3/
[rocketmouse at archlinux dir_3]$ ls -hAl
total 0
-rw-r--r-- 1 rocketmouse rocketmouse 0 Feb  3 11:46 test_new
[rocketmouse at archlinux dir_3]$ strace mv -i test_new test_new_2
[snip]
rename("test_new", "test_new_2")        = 0
[snip]
+++ exited with 0 +++
[rocketmouse at archlinux dir_3]$ ls -hAl
total 0
-rw-r--r-- 1 rocketmouse rocketmouse 0 Feb  3 11:46 test_new_2
[rocketmouse at archlinux dir_3]$