How can I change the HDMI resolution of my running Raspbian (Jessie) system without rebooting my Raspberry Pi 3?
You can sort of. But it is not working really well. At least in the command line you can turn off the HDMI port and get it back on with a different resolution. So you are good for Raspbian Lite.
Here is what you have to do:
tvservice --off ; turn off tv service tvservice -e "DMT 68 DVI" ; set it on (you will see a black screen) sudo chvt 2 ; change to different virtual terminal sudo chvt 1 ; change back to the previous virtual terminal fbset -g 1920 1200 1920 1200 32 ; adjust the size of the framebuffer
(Adapt the values as needed.)
This also works for OpenGL applications but it does not with a desktop environment. There is something different missing after powering on the HDMI port to get xserver back instead of
I think Unix StackExchange is a better place to ask about that.
You cant. You have to set it in the /boot/config.txt which is used for the boot config. Once you change the default there - it will use the resolution you specified on boot. Each time you change it will require a reboot.
You can use the "tvservice" command for this. For example
tvservice --explicit="DMT 35 HDMI"
This powers on
HDMI explicitly with "DMT mode 35" which is 60 HZ at 1280x1024 pixels.
There is also
tvservice --off if you've want to turn the output off completely.
For more information try both
tvservice --help and looking here for a tabular listing of modes.