Is there any command that could set MIME type of a file? for example:

mime --set --MIME="image/pjpeg" filename.jpg  
  • It's quite old, but maybe it is still useful: rlog.rgtti.com/2010/11/22/… (sorry, no time to dig it out now...). Please add an answer yourself if it works!
    – Rmano
    Feb 17 '15 at 12:36
  • possible duplicate of How do I change the MIME type for a file? Feb 17 '15 at 12:47
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    @SylvainPineau The question you linked is similar but not a duplicate and There is no answer to my question in that link, nor any answer to the link question itself! Based on accepted answer in that link, problem of asker was not MIME type, but it was the file content itself. Feb 17 '15 at 13:16
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    @PHPLearner Look at help.ubuntu.com/community/AddingMimeTypes, especially the use of xml files and update-mime-database Feb 17 '15 at 13:23
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    @PHPLearner: I've removed my close vote Feb 17 '15 at 13:24

Question is already answered by @PHPLearner in a comment. However, here is a longer answer.

There is no particular command like mime as asked in the question, and no doubt one such command can be created. For adding a new MIME type, all it takes is editing the /etc/mime.types file.

Let's say you want to add MIME type with extension .btc, then

1. Check If MIME type already exists

Open a command line and enter the line below (replace btc with your extension)

grep 'btc' /etc/mime.types

Now, this command will output a line, If that MIME type is already added. It looks like this for particular MIME searches

$ grep 'cpp' /etc/mime.types
text/x-c++src                        c++ cpp cxx cc

$ grep 'py' /etc/mime.types
application/x-python-code                       pyc pyo
text/x-python                                   py 

$ grep 'btc' /etc/mime.types

If your extension does not output any lines (as for btc in this case), or if the lines outputed do not include your extension, you must create a new MIME type. Otherwise your extension already has a MIME type included in the file /etc/mime.types.

2.1 Creating the MIME type (IF needed)

If there was no output, or the output given did not include your extension, we must add a MIME type. For that type at command line

gksudo gedit /etc/mime.types

Modify the following text so that the word "extension" is replaced with your file extension (no period mark), add the line to the end of the mime.types file, and save. Here our extension is bitcoin and we write btc (NOT .btc) that will be seen as an extension for the bitcoin files.

text/extension                   extension

And copy the modified 'text/extension' part.

In our case it will look like

text/bitcoin-text                btc

Save the file and exit.

2.2 Adding MIME type using .xml file and update-mime-database

If editing /etc/mime.types file doesn't works for your extension, then you can try this workaround.

Create a new .xml file that describes your extension like this & Save it.

<?xml version="1.0" encoding="utf-8"?>
<mime-type xmlns="http://www.freedesktop.org/standards/shared-mime-info" type="text/bitcoin-text">
<glob pattern="*.btc"/>

Now add this file into /usr/share/mime/packages folder (ref).After you've added or modified whatever you need, run the command

sudo update-mime-database /usr/share/mime

3. Adding an Icon to MIME type

Now we need to associate an icon with the MIME type. Get an SVG icon and name it "text-extension.svg", or whatever your modified MIME type is named; this will be the icon to represent all instances of the MIME type on your system.

So, We rename the .svg file so that the it matches bitcoin-text.svg (or "insertYourMIMEtype.svg") so that the slashes are replaced with "-" and there are no capital letters.

Then simply run the following commands, with 'bitcoin-text' replaced with your MIME type.

 sudo cp bitcoin-text.svg /usr/share/icons/gnome/scalable/mimetypes
 sudo gtk-update-icon-cache /usr/share/icons/gnome/ -f

Relogin and all files ending in the MIME extension will display with that icon.

  • 5
    you actually need to add the xml file to /usr/share/mime/packages, if you add it to /usr/share/mime/application when you run update-mime-database it will be wiped out
    – Vlax
    Nov 5 '19 at 23:40
  • Thanks @Vlax for pointing it out. Apr 11 at 9:07
  • Thansk @vanadium for editing. Apr 11 at 9:08

To actually answer your question: MIME types aren't real. There isn't some piece of metadata in the file that says "this is a image/png". Instead, MIME types are guessed based on file extension and magic number. To serve a file as having a specific MIME type, you need to configure your web-server appropriately. See https://stackoverflow.com/questions/29017725/how-do-you-change-the-mime-type-of-a-file-from-the-terminal

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