Debug step by step systemd boot process

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Environment

SUSE Linux Enterprise Server 12 Service Pack 3 (SLES 12 SP3)

SUSE Linux Enterprise Server 12 Service Pack 4 (SLES 12 SP4)

SUSE Linux Enterprise Server 15 Service Pack 1 (SLES 15 SP1)

Situation

Unpredicted changes or failing commands during boot process hidden by bootsplash or excessive logging.

Resolution

During boot when seeing grub boot menu press "e" for edit, then scroll down until you see your boot entry:

---snip---

    echo "Loading Linux...

    linux

---snap---

On the line with "linux" remove following entries if present:

splash=silent quiet showopts

then add following entries to get step by step booting including a early access shell on console 9:

 plymouth.enable=0 systemd.confirm_spawn=true systemd.debug-shell=1 systemd.log_level=debug systemd.unit=multi-user.target console=tty1

plymouth.enable=0 will disable plymouth bootsplash

systemd.confirm_spawn=true asks for confirmation when spawning processes

systemd.debug-shell=1 enables a root shell on console 9 (reachable via F9)

systemd.log_level=debug enables debug logging

systemd.unit=multi-user.target avoids switch to console 7 for output and input stays at console 1

console=tty1 avoids switch of input/ouput to console 9 where bash will get attached

With CTRL+x or F10 start "one time" booting with the given changes.

For testing purposes yo ucan also add those options to GRUB_CMDLINE_LINUX_DEFAULT:

/etc/default/grub

Depending on the keyboard layout accept each step with "z" (or "y") until "vconsol-setup" is confirmed, then with "y".

If issue has been found/fixed pressing "c" will continue without asking anymore

Cause

Disclaimer

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