Because everyone needs a good preseed

cmd

wget -nc http://ftp.debian.org/debian/dists/jessie/main/installer-amd64/current/images/netboot/debian-installer/amd64/linux
wget -nc http://ftp.debian.org/debian/dists/jessie/main/installer-amd64/current/images/netboot/debian-installer/amd64/initrd.gz
cp -nv ~/.ssh/id_rsa.pub .
qemu-system-x86_64 -machine accel=kvm -kernel linux -initrd initrd.gz -m 1G -smp 2 -append "blacklist=vga16fb fb=false video=false vga=normal auto=true url=http://10.0.2.10:8080/debian-preseed.txt hostname=otto domain=" -net user,guestfwd=:10.0.2.10:8080-cmd:"/bin/busybox httpd -i" -hda /dev/shm/deb.img -net nic -display none

deb-testing-cmd

wget -nc https://d-i.debian.org/daily-images/amd64/daily/netboot/debian-installer/amd64/linux
wget -nc https://d-i.debian.org/daily-images/amd64/daily/netboot/debian-installer/amd64/initrd.gz
cp -nv ~/.ssh/id_rsa.pub .
time qemu-system-x86_64 -machine accel=kvm -kernel linux -initrd initrd.gz -m 1G -smp 2 -append "blacklist=mac80211 fb=false video=false vga=normal auto=true url=http://10.0.2.10:8080/debian-preseed.txt hostname=otto domain=" -net user,guestfwd=:10.0.2.10:8080-cmd:"/bin/busybox httpd -i" -hda /dev/shm/deb.img -net nic -display curses

debian-preseed.txt

# Derived from  https://www.debian.org/releases/stable/example-preseed.txt
d-i debian-installer/locale string en_US
d-i keyboard-configuration/xkb-keymap select us
d-i netcfg/choose_interface select auto
d-i netcfg/get_hostname string unassigned-hostname
d-i netcfg/get_domain string unassigned-domain
d-i netcfg/hostname string hostname
d-i netcfg/wireless_wep string
d-i mirror/country string manual
d-i mirror/http/hostname string http.us.debian.org
d-i mirror/http/directory string /debian
d-i mirror/http/proxy string http://172.19.1.1:3142
d-i passwd/root-login boolean true
d-i passwd/root-password-crypted password !00000000000000000000000000000000
d-i passwd/make-user false
d-i clock-setup/utc boolean true
d-i time/zone string US/Eastern
d-i clock-setup/ntp boolean true
d-i partman-auto/method string regular
d-i partman-lvm/device_remove_lvm boolean true

d-i partman-md/device_remove_md boolean true
d-i partman-lvm/confirm boolean true
d-i partman-lvm/confirm_nooverwrite boolean true
d-i partman-auto/expert_recipe string                         \
      root ::                                            \
              40 300  100000000 btrfs                                 \
                      $primary{ }                             \
                      $bootable{ }                            \
                      method{ format } format{ }              \
                      use_filesystem{ } filesystem{ btrfs }    \
                      mountpoint{ / }                     \
              .                                            \
d-i partman-partitioning/confirm_write_new_label boolean true
d-i partman/choose_partition select finish
d-i partman-basicfilesystems/no_swap boolean false
d-i partman/confirm boolean true
d-i partman/confirm_nooverwrite boolean true
d-i partman-md/confirm boolean true
d-i partman-partitioning/confirm_write_new_label boolean true
d-i partman/choose_partition select finish
d-i partman/confirm boolean true
d-i partman/confirm_nooverwrite boolean true
tasksel tasksel/first multiselect
d-i pkgsel/include string wget openssh-server vim build-essential git net-tools curl strace htop lsof rsync wget
d-i preseed/late_command string \
in-target sh -c "mkdir -m 700 /root/.ssh ; wget --no-proxy -O /root/.ssh/authorized_keys 10.0.2.10:8080/id_rsa.pub ; wget --no-proxy -O /etc/sysctl.d/local.conf 10.0.2.10:8080/local.conf; chmod 600 /root/.ssh/authorized_keys; echo GRUB_TERMINAL=console >>/etc/default/grub; update-grub"
popularity-contest popularity-contest/participate boolean false
d-i grub-installer/only_debian boolean true
d-i grub-installer/with_other_os boolean true
d-i grub-installer/bootdev  string default
d-i finish-install/reboot_in_progress note
d-i debian-installer/exit/poweroff boolean true

debian-run

qemu-system-x86_64 -machine accel=kvm -m 1G -smp 2 -hda /dev/shm/deb.img -net user,hostfwd=::2200-:22 -display none -net nic -monitor stdio

gistfile1.txt

time qemu-system-x86_64 -machine accel=kvm -m 4G -smp 2 -kernel ubuntu/linux -initrd ubuntu/initrd.gz -net nic -net user,tftp=. -hda /dev/shm/preseed-min.img -append "blacklist=vga16fb fb=false video=false vga=normal auto=true priority=high  locale=en_US.UTF-8 kdb-chooser/method=us netcfg/choose_interface=auto hostname=otto domain= url=tftp://10.0.2.2/preseed.cfg" -curses

local.conf

net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1
net.ipv6.conf.ens3.disable_ipv6 = 1

preseed-lvm.cfg

d-i debian-installer/locale string en_US
d-i console-setup/ask_detect boolean false
d-i keyboard-configuration/layoutcode string us
d-i netcfg/choose_interface select auto
d-i netcfg/get_hostname string otto
d-i netcfg/get_domain string example.pvt
d-i netcfg/wireless_wep string
d-i mirror/country string manual
d-i mirror/http/hostname string archive.ubuntu.com
d-i mirror/http/directory string /ubuntu
d-i mirror/http/proxy string http://10.0.2.2:3142/
d-i clock-setup/utc boolean true
d-i time/zone string US/Eastern
d-i clock-setup/ntp boolean true

d-i partman-auto/disk string /dev/sda
d-i partman-auto/method string lvm
d-i partman-lvm/device_remove_lvm boolean true
d-i partman-lvm/device_remove_lvm_span boolean true
d-i partman-auto/purge_lvm_from_device  boolean true
d-i partman-auto-lvm/new_vg_name string system
d-i partman-lvm/confirm_nooverwrite boolean true
d-i partman-auto/purge_lvm_from_device boolean true
d-i partman-auto-lvm/guided_size    string  max
d-i partman-lvm/confirm boolean true
d-i partman/confirm_write_new_label boolean true
d-i partman-auto/expert_recipe string                         \
      boot-root ::                                            \
              40 300 300 ext4                                 \
                      $primary{ }                             \
                      $bootable{ }                            \
                      method{ format } format{ }              \
                      use_filesystem{ } filesystem{ ext4 }    \
                      mountpoint{ /boot }                     \
              .                                               \
              2000 10000 10000 ext4                      \
                      $lvmok{ }                               \
                      method{ format } format{ }              \
                      use_filesystem{ } filesystem{ ext4 }    \
                      mountpoint{ / }                         \
              .\
	      2000 10000 100000000 ext4                      \
                      $lvmok{ }                               \
                      method{ format } format{ }              \
                      use_filesystem{ } filesystem{ ext4 }    \
                      mountpoint{ /srv }                         \
              .                                               \
d-i partman-lvm/confirm boolean true
d-i partman/confirm_write_new_label boolean true
d-i partman/confirm_nooverwrite boolean true
d-i partman/choose_partition select Finish partitioning and write changes to disk
d-i partman/confirm boolean true
d-i partman-basicfilesystems/no_swap boolean false
d-i passwd/root-login boolean true
d-i passwd/make-user boolean false
d-i passwd/root-password password r00tme
d-i passwd/root-password-again password r00tme
d-i user-setup/allow-password-weak boolean true
d-i grub-installer/only_debian boolean true
d-i grub-installer/with_other_os boolean true
d-i pkgsel/update-policy select none
tasksel tasksel/first multiselect openssh-server
d-i preseed/late_command string \
in-target sed -i 's/PermitRootLogin .*/PermitRootLogin yes/' /etc/ssh/sshd_config ; \
in-target sh -c "echo GRUB_TERMINAL=console | tee -a /etc/default/grub" ; \
in-target sh -c "grub-install /dev/sda && grub-mkconfig >/boot/grub/grub.cfg"
d-i finish-install/reboot_in_progress note

preseed.cfg

d-i debian-installer/locale string en_US
d-i console-setup/ask_detect boolean false
d-i keyboard-configuration/layoutcode string us
d-i netcfg/choose_interface select auto
d-i netcfg/get_hostname string ubuntu
d-i netcfg/get_domain string example.com
d-i netcfg/wireless_wep string
d-i mirror/country string manual
d-i mirror/http/hostname string archive.ubuntu.com
d-i mirror/http/directory string /ubuntu
d-i mirror/http/proxy string http://172.19.1.1:3142/
d-i clock-setup/utc boolean true
d-i time/zone string US/Eastern
d-i clock-setup/ntp boolean true
d-i partman-auto/method string regular
d-i partman-auto/choose_recipe select atomic
d-i partman-partitioning/confirm_write_new_label boolean true
d-i partman/confirm_nooverwrite boolean true
d-i partman/choose_partition select Finish partitioning and write changes to disk
d-i partman/confirm boolean true
d-i passwd/root-login boolean true
d-i passwd/make-user boolean false
d-i passwd/root-password password r00tme
d-i passwd/root-password-again password r00tme
d-i user-setup/allow-password-weak boolean true
d-i grub-installer/only_debian boolean true
d-i grub-installer/with_other_os boolean true
d-i pkgsel/update-policy select none
tasksel tasksel/first multiselect openssh-server
d-i preseed/late_command string \
in-target sed -i 's/PermitRootLogin .*/PermitRootLogin yes/' /etc/ssh/sshd_config
d-i finish-install/reboot_in_progress note
d-i debian-installer/exit/poweroff boolean true

qconf

# qemu config file

[drive]
  media = "disk"
  index = "0"
  file = "news.img"

[chardev "compat_monitor1"]
	backend = "stdio"

[net]
  type = "user"
  hostfwd = "::2200-:22"

[net]
  type = "nic"

[mon "compat_monitor2"]
  mode = "readline"
  chardev = "compat_monitor1"
  pretty = "off"

[machine]
  accel = "kvm"

[memory]
  size = "1G"

[smp-opts]
  cpus = "2"

qemu-run.sh

qemu-system-x86_64 -machine accel=kvm -m 4G -smp 2 -redir :8024::22 -hda /mnt/out/preseed.img -curses

You can also check /var/log/installer/syslog for debugging purposes after install has completed.

Thank you so much, I have been trying to login as root all day after a preseeded install, your preseed finally helped me figure it out!