$ v4l
v4l2-compliance  v4l2-dbg         v4l-conf         v4l-info
v4l2-ctl         v4l2-sysfs-path  v4lctl

$ v4l-conf
v4l-conf: using X11 display :1
dga: version 2.0
WARNING: No DGA direct video mode for this display.
mode: 1366x768, depth=24, bpp=32, bpl=5464, base=unknown
/dev/video0 [v4l2]: no overlay support

$ v4lctl -c  --device=/dev/video0 V4L2_CID_EXPOSURE 5
v4l2: open --device=/dev/video0: No such file or directory
vid-open: failed: libv4l
no grabber device available