I need to edit the boot parameters of the Debian installer to add
priority=critical to the arguments. (this is for preseeding). What should I do to apply these parameters to the installer?
It depends on which architecture (i386, amd64, etc.), which media (CD/DVD/BD, USB-HDD, netboot, etc.), which release (jessie, wheezy, etc.), or which firmware (BIOS, UEFI, etc.) you want to boot to run Debian Installer.
For Debian jessie ISO images for Intel PC BIOS based architecture, you will use isolinux boot loader. You can find menu entry
/isolinux/adtxt.cfg which you should choose for preseeding installation:
label auto menu label ^Automated install kernel /install.amd/vmlinuz append auto=true priority=critical vga=788 initrd=/install.amd/initrd.gz --- quiet
You can also configure default entry to boot and time out value in
# D-I config version 2.0 # search path for the c32 support libraries (libcom32, libutil etc.) path include menu.cfg default vesamenu.c32 prompt 0 timeout 0
For example it will start preseeding installation automatically after 10 sec delay on boot by the following configuration.
default auto prompt 1 timeout 100 # in units of 0.1 sec
Take care not to accidentally start the installer on existing installed systems. It would wipe everything on them automatically!