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During bootup, when the GRUB2 menu shows up, press the e key for edit. Add the following parameter at the end of the linux16 line on x86-64 BIOS-based systems, or the linuxefi line on UEFI systems: systemd.debug-shell The systemd will configure the debug shell on TTY9. Press Ctrl+Alt+F9 to connect to the debug shell (no credential needed).
rootパスワード不明時に便利
