Htydjtk

I copied thousands of files into an exFAT MicroSD card.

The number of files and bytes is identical, but how do I know whether the data is corrupt or not?


[Edit 1:]
← Before clicking this triangle that points down, please explain the downvote.

[Edit 2:]
It would be good if the JackPal Android Terminal also supports the command, but if you have a solution, pleasa answer nevertheless.

Unmount, eject, and remount the device. Then use

diff -r source destination

In case you used rsync to do the copy, rsync -c might be very convenient, and it is nearly as good as diff. It doesn't do a bit-for-bit comparison though; it uses an MD5 checksum.

Using MD5 sums is a good way, but the canonical way to use it is:

1. 
   

   cd to the directory of the source files and issue:

   
   
   

   md5sum * >/path/to/the/checksumfile.md5
   
   

   
   

If you have directories with many levels, you can use shopt -s globstar and replace * by **/*.

Notice that the file specs in the MD5 file are exactly as provided in the command line (relative paths unless your pattern starts with a /).

2. 
   

   cd to the directory of the copied files and issue:

   
   
   

   md5sum -c /path/to/the/checksumfile.md5
   
   

   
   

With -c, md5sum reads the file specs in the provided MD5 file, compute the MD5 of these files, and compares them to the values from the MD5 file (which is why the file specs are usually better left relative, so you can re-use the MD5 file on files in various directories).

Using MD5 sum this ways immediately tells you about MD5 differences, and also about missing files.

It is possible to generate hashsums for individual files and output them into one text file, of which the MD5 hash can be generated.
I use MD5 due to it's higher speeds. MD5 might not be the newest algorithm, but it is certainly good enough to verify offline data integrity.

Run these commands on both source and destination:

md5sum /path/to/folder/* | tee -a hash.files.txt |cut -f 1 -d " " >>hash.list.txt #extracts hashsum string only for the output, because I noticed that Android Terminal formats the output differently.

md5sum hash.list.txt

…or with a single command:

md5sum /path/to/folder/* | tee -a hash.files.txt | cut -f 1 -d " " | tee -a hash.list.txt | md5sum

The name of the hashsum list files (hash.list.txt and hash.files.txt in my example) can be anything you specify. Generating two files to be able to identify damaged files (the first file contains the file names as well, the second file is for comparison).