Ambiguous result from sha256sum checking of Xubuntu 16.04 LTS ISO file

Where did you download the file to ?
Is your pwd in the same folder as the file you downloaded?

Hello Andrew,
I downloaded the file to an external HDD.
I had planned to burn the ISO file to a DVD to have a Live session and to start from to instal 16.04 to the hard disk.

If by pwd you intend hash, yes, ISO file and a txt I created to write the hashes in are in the same folder.

|
|_ FOLDER
          |_Download from France mirror (ISO file, hashes.txt)
          |
          |_Download from German mirror (ISO file, hashes.txt)

But...
After your answer I tried and cut both hashes.txt to a pen drive in order to put some distance (!) between hashe.txt and ISO file and I unplugged the pen. (Feeling silly)
Then I performed a new sha256sum but the result was as follows:

xubuntu@xubuntu:/media/xubuntu/476 GiB Volume/Xubuntu-16-04-LTS/Xubuntu-16-04-LTS-from-France-mirror$ sha256sum -c --strict xubuntu-16.04-desktop-i386.iso
sha256sum: 101 restricted/binary-i386/Release: No such file or directory
     101 restricted/binary-i386/Release: FAILED open or read
sha256sum: 1605 restricted/binary-i386/Packages.gz: No such file or directory
    1605 restricted/binary-i386/Packages.gz: FAILED open or read
sha256sum: 3694 restricted/binary-i386/Packages: No such file or directory
    3694 restricted/binary-i386/Packages: FAILED open or read
sha256sum: 99 universe/binary-i386/Release: No such file or directory
      99 universe/binary-i386/Release: FAILED open or read
sha256sum: 40 universe/binary-i386/Packages.gz: No such file or directory
      40 universe/binary-i386/Packages.gz: FAILED open or read
sha256sum: 0 universe/binary-i386/Packages: No such file or directory
       0 universe/binary-i386/Packages: FAILED open or read
sha256sum: 101 multiverse/binary-i386/Release: No such file or directory
     101 multiverse/binary-i386/Release: FAILED open or read
sha256sum: 40 multiverse/binary-i386/Packages.gz: No such file or directory
      40 multiverse/binary-i386/Packages.gz: FAILED open or read
sha256sum: 0 multiverse/binary-i386/Packages: No such file or directory
       0 multiverse/binary-i386/Packages: FAILED open or read
sha256sum: 95 main/binary-i386/Release: No such file or directory
      95 main/binary-i386/Release: FAILED open or read
sha256sum: 6931 main/binary-i386/Packages.gz: No such file or directory
    6931 main/binary-i386/Packages.gz: FAILED open or read
sha256sum: 18161 main/binary-i386/Packages: No such file or directory
   18161 main/binary-i386/Packages: FAILED open or read
sha256sum: WARNING: 4504774 lines are improperly formatted
sha256sum: WARNING: 12 listed files could not be read

Quite the same, to me...
Thanks
Regards, Alberto

Hello Andrew,
I re-installed Xubuntu 14.04 LTS, updated and tried to perform a new sha256sum to the ISO file. Hashes are in my unplugged pen drive. The result does not change...

Hello Andrew, hello Techies,
eventually I found a way to check the integrity of the ISO file.
It seems obvious in retrospect...
I burnt it to a DVD, then I booted the machine from it in order to start a Live session.
At the very beginning of the start procedure I pressed F1 and selected "Check disc for defects" in the external menu.
This took some minutes and the result was that no errors had been found.

I didn't find any explanation about the errors I got running: sha256sum [file] -c --strict
and about why the hashes actually match. It's probably matter for developers.
But I feel happy I found a way to keep on with my installation.

To me there are two possible explanations:

1. sha256sum -c --strict [ISO] is NOT a proper procedure, as the result is full of errors,

2. my sha256sum command is corrupted and doesn't work properly. So I can't check the ISO.

What do you think?

md5sum filename.iso

Copy the generated hash and paste it into a websearch. If you get hits then you are good.

Hello Andrew!
Well, I downloaded the hashes from the same Xubuntu site I downloaded the ISO.
The hashes match, of course.
Nevertheless if I add -c --strict options I get similar result I get adding the same options to sha256sum.

I didn't use md5sum so far because "man md5sum" says:

[...]BUGS
 The MD5 algorithm should not be used any more for security related purposes. Instead, better use an SHA-2 algorithm, implemented in the programs sha224sum(1), sha256sum(1), sha384sum(1), sha512sum(1) [...]

That's why I preferred using sha256sum.
And what I'd like to understand from some of you Techie is if preferring sha256sum and adding the above mentioned options is correct or not. If it's not I go back to simple md5sum command.
I feel concerned because my installation seems to have some weird problems, according to questions 293996 and especially 294103.

Many thaks for your attention.

cd ~/Downloads
wget http://releases.ubuntu.com/xenial/MD5SUMS
md5sum -c MD5SUMS | grep OK

Easy peasy. No output equals bad file.

I need you to be a bit more vorbose :-)
Can you please explain step by step what I'm suggested to do?
Thanks by a newbie

I assumed the ISO is in your downloads folder.
Run each line one at a time, in a terminal.

I did it.
The result is:

alberto@jalopy:~/Downloads$ md5sum -c MD5SUMS | grep OK
md5sum: ubuntu-16.04-desktop-amd64.iso: No such file or directory
md5sum: ubuntu-16.04-desktop-i386.iso: No such file or directory
md5sum: ubuntu-16.04-server-amd64.img: No such file or directory
md5sum: ubuntu-16.04-server-amd64.iso: No such file or directory
md5sum: ubuntu-16.04-server-i386.img: No such file or directory
md5sum: ubuntu-16.04-server-i386.iso: No such file or directory
md5sum: WARNING: 6 listed files could not be read

Ehm, so?

Well, I run Xubuntu, not Ubuntu...

Then the file is not in the folder. Move the file to the Downloads folder and rerun

The file is in the folder, actually.
But I downloaded Ubuntu hashes, when my ISO is Xubuntu.
I followed the procedure you told me but for Xubuntu and the result (for xubuntu-16.04-desktop-i386.iso) is:
ok.

And I'm glad, even because I learned something new. Command line use is intriguing...

So: do you think --strict option is not proper, just a weird idea of a newbie? Do you think I can avoid adding it?
Thanks

Or:

do you think it has sense running:

md5sum --strict MD5SUMS | grep OK

?

Hello Manfred,
I agree, there's been some misunderstanding.
What I wanted to know is whether the command I typed is wrong or right.
Now I know I wrote a wrong command, I made a syntax error... This is exactly what I wanted to know.
I'm going to study the "Verify Iso How to" link, at first sight it looks interesting.

Your answer solved my problem!
Many many thanks

P.S. Thanks to Andrew, too...

Thanks Manfred Hampl, that solved my question.