Although JetPack was intended for Ubuntu 14.04 some people here have made minor changes and got it to work on 16.04…one of those people may be able to help on that.
Meanwhile, if you just want to flash on command line, you can do this on any 64-bit Linux PC without requiring Ubuntu at all. If you later get JetPack working you can then use this for package installs without a flash.
Go to the L4T R24.2.1 release page:
Download the driver and sample rootfs packages.
tar xjfv Tegra210_Linux_R24.2.1_aarch64.tbz2
sudo tar xjfp /whereever/samplerootfs/is/Tegra_Linux_Sample-Root-Filesystem_R24.2.1_aarch64.tbz2
# Place JTX1 in recovery mode with micro-B USB cable.
# Verify it is found on the host:
lsusb -d 0955:7721
# Verify you have approximately 25GB or more space available as ext4:
df -H -T .
# Actual flash with sudo.
sudo ./flash.sh -S 14580MiB jetson-tx1 mmcblk0p1