None of the command line volume controls for vlc work in Linux.

A workaround is to play an audio file in vlc using the full vlc GUI and adjust the volume in the Audio menu. Then play the same audio file from the command line with vlc or cvlc: vlc "remembers" the volume set previously.

vlc /usr/share/sounds/Fresh_and_Clean/stereo/desktop-login.ogg > /dev/null &

(Note: the master control in the system GUI must not conflict with the vlc GUI control.)