[BACKGROUND]
I'm trying to implement a super simple kdump service(s) for Archlinux.
The idea is super simple, just use the default linux kernel installed as
kernel/initramfs for the kexec environment.
So there is a kexec.service to setup the environment, with extra systemd
options to disable th kexec.service itself, and start the kdump.service:
```
[Unit]
Description=Setup kexec environment
After=local-fs.target
[Service]
Type=oneshot
RemainAfterExit=true
ExecStart=/usr/bin/kexec -p /boot/vmlinuz-linux
--initrd=/boot/initramfs-linux.img --append="root=/dev/os/root rw
console=ttyS0 nr_cpus=1 reset_devices systemd.mask=kexec.service
systemd.unit=kdump.service"
ExecStop=/usr/bin/kexec -p -u
[Install]
WantedBy=multi-user.target
```
So that after a crash we can boot into the same kernel/initramfs combo
and do whatever to collect the vmcore.
The kdump.service will just call makedumpfile and exit (hopefully also
reboot the system):
```
[Unit]
Description=Save the kernel crash dump after a crash
After=multi-user.target
[Service]
Type=idle
ExecStart=/bin/sh -c 'mkdir -p /var/crash/ && /usr/bin/makedumpfile -z
-d 31 /proc/vmcore "/var/crash/crashdump-$$(date +%%F-%%T)"'
ExecStartPost=reboot
UMask=0077
StandardInput=tty-force
StandardOutput=inherit
StandardError=inherit
```
[PROBLEM]
The vmcore collection happens well, but reboot failed:
```
Failed to connect to system scope bus via local transport: No such file
or directory
```
Then the system hang and I have to force reboot the VM instead.
So any idea what's the proper way to reboot the system inside a service
triggered by `systemd.unit=` boot option?
Thanks,
Qu
