s8tuner hosted here is a free tuner on Windows. But with Wine it can run on Linux, too.
On Linux Mint, install Wine and Winetricks from Software Manager. Download s8tuner_e307.zip and extract it to ~/apps. Then run:
cd ~/apps/s8tuner_e307
winetricks mfc42
wine s8tuner.exe
After the application start, I blew the 4th hole on the blues harmonica, it showed C5 and 0525.7 Hz, which is exactly the same with the frequency of C5 (523.251 Hz) in Piano key frequencies.
You can play the C4 in section Pitch standards and Standard pitch of Pitch to test the software's capability.
There is another application FMIT which can be installed via Software Manager. Or download installer in its release page (for both Linux and Windows). But it can't give right results in the 440 Hz test above. And its interface is hard to understand compared with s8tuner.