vm$ dnf install httpd

vm$ vi /usr/bin/loop.sh
# -------------------- #
#!/usr/bin/bash

for i in {1..300}; do
        echo "httpd: loop $i"
        sleep 1
done

echo "httpd: ready"
systemd-notify --ready

echo "httpd: exit"
exit 1
# -------------------- #

vm$ chmod 777 /usr/bin/loop.sh

vm$ systemctl cat httpd.service
# /usr/lib/systemd/system/httpd.service

vm$ vi /usr/lib/systemd/system/httpd.service
[Unit]
Before=serial-getty@ttyS0.service
Wants=serial-getty@ttyS0.service

[Service]
Type=notify
ExecStart=/usr/bin/loop.sh
ExecStop=pkill loop.sh

vm$ systemctl daemon-reload

vm$ systemctl list-dependencies httpd.service --before
httpd.service
  ├─serial-getty@ttyS0.service
  └─shutdown.target
...

vm$ systemctl list-dependencies serial-getty@ttyS0.service --after
serial-getty@ttyS0.service
  ├─dev-ttyS0.device
  ├─httpd.service
...

vm$ systemctl enable httpd

vm$ reboot
# reboot hang for 5 minutes without login prompt
# because http.service stuck in loop.sh
#
# timeline:
#   http.service
#       => /usr/bin/loop.sh (5min)
#   serial-getty@ttyS0.service
#       => login prompt

                               GRUB version 2.12

 +----------------------------------------------------------------------------+
 |load_video                                                                  |
 |set gfxpayload=keep                                                         |
 |insmod gzio                                                                 |
 |linux ($root)/vmlinuz-6.19.10-300.fc44.x86_64 root=/dev/mapper/systemVG-LVR\|
 |oot ro  no_timer_check console=tty1 console=ttyS0,115200n8 systemd.unit=res\|
 |uce.target                                                                  |
 |initrd ($root)/initramfs-6.19.10-300.fc44.x86_64.img                        |
 +----------------------------------------------------------------------------+

      Minimum Emacs-like screen editing is supported. TAB lists
      completions. Press Ctrl-x or F10 to boot, Ctrl-c or F2 for
      a command-line or ESC to discard edits and return to the GRUB menu.

vm$ vi /etc/default/grub
# -------------------- #
GRUB_TERMINAL_INPUT="serial"
GRUB_TERMINAL_OUTPUT="serial"
GRUB_TIMEOUT_STYLE=menu
GRUB_TIMEOUT=10
GRUB_CMDLINE_LINUX_DEFAULT="no_timer_check console=tty1 console=ttyS0,115200n8"
# -------------------- #

vm$ grub2-mkconfig -o /boot/grub2/grub.cfg

                               GRUB version 2.12

 +----------------------------------------------------------------------------+
 |load_video                                                                  |
 |set gfxpayload=keep                                                         |
 |insmod gzio                                                                 |
 |linux ($root)/vmlinuz-6.19.10-300.fc44.x86_64 root=/dev/mapper/systemVG-LVR\|
 |oot ro  no_timer_check console=tty1 console=ttyS0,115200n8 systemd.journald\|
 |.forward_to_console=1                                                       |
 |initrd ($root)/initramfs-6.19.10-300.fc44.x86_64.img                        |
 +----------------------------------------------------------------------------+

      Minimum Emacs-like screen editing is supported. TAB lists
      completions. Press Ctrl-x or F10 to boot, Ctrl-c or F2 for
      a command-line or ESC to discard edits and return to the GRUB menu.

[   39.843013] loop.sh[1007]: httpd: loop 1
[   40.885196] loop.sh[1007]: httpd: loop 2
...
[   60.393537] loop.sh[1007]: httpd: loop 21
[   61.418861] loop.sh[1007]: httpd: loop 22
...

cont$ vi /ws/start_vm.sh
# -------------------- #
#!/usr/bin/bash

disk_a="Fedora-Server-Guest-Generic-44-1.7.x86_64.qcow2"
disk_b="disk_b.qcow2"
disk_c="disk_c.qcow2"

qemu-system-x86_64 -name vm \
    -m 4096 \
    -smp cpus=2 \
    -nographic \
    -drive file=$disk_a \
    -drive file=$disk_b \
    -drive file=$disk_c \
    -netdev user,id=net0 -device virtio-net-pci,netdev=net0 \
    -netdev bridge,br=br1,id=net1 -device virtio-net-pci,netdev=net1,mac=50:54:00:01:00:01 \
    -netdev bridge,br=br2,id=net2 -device virtio-net-pci,netdev=net2,mac=50:54:00:02:00:01 \
    -netdev bridge,br=br3,id=net3 -device virtio-net-pci,netdev=net3,mac=50:54:00:03:00:01 \
    -serial mon:stdio \
    -serial pty:/tmp/pty
# -------------------- #

                               GRUB version 2.12

 +----------------------------------------------------------------------------+
 |load_video                                                                  |
 |set gfxpayload=keep                                                         |
 |insmod gzio                                                                 |
 |linux ($root)/vmlinuz-6.19.10-300.fc44.x86_64 root=/dev/mapper/systemVG-LVR\|
 |oot ro  no_timer_check console=tty1 console=ttyS0,115200n8 console=ttyS1,11\|
 |5200n8 systemd.unit=rescue.target                                           |
 |initrd ($root)/initramfs-6.19.10-300.fc44.x86_64.img                        |
 +----------------------------------------------------------------------------+

      Minimum Emacs-like screen editing is supported. TAB lists
      completions. Press Ctrl-x or F10 to boot, Ctrl-c or F2 for
      a command-line or ESC to discard edits and return to the GRUB menu.

vm$ systemctl start serial-getty@ttyS0.service
vm$ systemctl start serial-getty@ttyS1.service

vm$

# switch to qemu control: ctrl-a c

(qemu) info chardev
serial1: filename=pty:/dev/pts/2
parallel0: filename=null
serial0: filename=mux
serial0-base: filename=stdio

cont$ screen /dev/pts/2 115200n8
# or: screen /tmp/pty 115200n8

# to exit screen: ctrl-a k

vm$ systemctl isolate default.target

vm$ watch systemctl list-jobs
Every 2.0s: systemctl list-jobs

JOB  UNIT             TYPE  STATE
830 httpd.service     start running
645 multi-user.target start waiting