Amarok (Linux music player) does not have a native support to submit played songs to Libre.fm. It was possible with the script Amarok2LibreFM for Amarok and the service lastfmsubmitd. But I discovered (March 2018) that it stopped submitting songs. So I modified both of them:

• lastfmsubmitd: This modified version only submit songs to Libre.fm, but works again (based on pylast library for submitting song).
• Amarok2LibreFM: Submit the correct song length, and handle a bug that was present in Amarok 2.5 and 2.6.

I suggest the following installation procedure:

• Download my copy of lastfmsubmitd in a directory in your home.
• Create a file ~/.lastfmsubmitd/conf with the your name and password like that:

[account]
user = my_account_name_in_lowercase
password = my_password

• Download my copy of Amarok2LibreFM in this directory: “/home/MY_USER_NAME/.kde/share/apps/amarok/scripts“. So you will have a directory “Amarok2LibreFM” under the directory “script“.
• Modify the file “Amarok2LibreFM/main.js” so the variable “SUBMIT_CMD” points to your installation of lastfmsubmitd.
• Find a way to start automatically lastfmsubmitd when you open your session. You can for example do that graphically using the KDE settings, or manually by creating a link “/home/MY_USER/.config/autostart-scripts/lastfmsubmitd” that will point on the lastfmsubmitd script.
  
• Just for this time, manually start lastfmsubmitd.
• Restart Amarok and play a song.