This question already has an answer here:
Can I set "live" as the default option so that I don't have to type it each time I boot the PC?
Can the config file below be changed somehow to achieve it? Currently it looks so. I've never changed it before.
$ cat syslinux/txt.cfg default live label live menu label ^Start Kubuntu kernel /casper/vmlinuz append noprompt cdrom-detect/try-usb=true persistent file=/cdrom/preseed/kubuntu.seed boot=casper maybe-ubiquity initrd=/casper/initrd.lz quiet splash --- label check menu label ^Check disc for defects kernel /casper/vmlinuz append noprompt boot=casper integrity-check initrd=/casper/initrd.lz quiet splash --- label memtest menu label Test ^memory kernel /install/mt86plus label hd menu label ^Boot from first hard disk localboot 0x80
It's Ubuntu 16
Please, mark this question as duplicate of How to boot from ubuntu live usb with 'try ubuntu' directly?
The answer that worked for me was https://askubuntu.com/a/865314/572615