How to Increase Boot Log Verbosity to Debug Linux Boot Problems

Updated: 28 September 2026 · Applies to: systemd 252 to 259 and dracut on AlmaLinux and Rocky Linux 9 and 10 and RHEL 9 and 10; Ubuntu 24.04 and 26.04 and Debian 13

When a server hangs or fails during boot, the normal boot screen shows little. A few kernel parameters make the kernel, the initramfs and systemd print much more detail, so you can see where it stops. Add them for one boot from the GRUB menu while troubleshooting, and remove them afterwards: debug output slows the boot down.

Parameters that add detail

• Remove rhgb quiet (AlmaLinux, Rocky Linux, RHEL) or quiet splash (Ubuntu): shows normal boot messages instead of a splash screen.
• systemd.log_level=debug systemd.log_target=console: systemd prints every step to the screen.
• loglevel=7: the kernel prints all messages, including debug level.
• rd.debug: detailed output from the dracut initramfs (AlmaLinux, Rocky Linux, RHEL), useful when the root disk is not found.
• systemd.debug-shell=1: opens a root shell on terminal 9 (Ctrl+Alt+F9) early in the boot, to investigate a hang. Use only while debugging; it gives root access without a password to anyone at the console.

Add them for one boot

1. In the GRUB menu, select the entry and press e.
2. On the line starting with linux, remove rhgb quiet and add the parameters you need, for example systemd.log_level=debug systemd.log_target=console.
3. Press Ctrl+X to boot.

More detail on editing the boot entry: how to change GRUB kernel parameters before booting.

Read the messages after the boot

journalctl -b -o short-monotonic      # this boot, with seconds since start
journalctl -b -1 -p warning           # warnings and errors of the previous boot
systemd-analyze blame                 # which services took longest
systemd-analyze critical-chain        # the chain that delayed the boot

Keep the setting for several boots

If the problem only appears sometimes, add the parameters permanently while you investigate (AlmaLinux, Rocky Linux, RHEL):

grubby --update-kernel=DEFAULT --remove-args="rhgb quiet" --args="systemd.log_level=debug"

Undo it afterwards with --remove-args="systemd.log_level=debug" --args="rhgb quiet". On Ubuntu and Debian, edit GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub and run update-grub.

A serial console

On servers with a serial console (for example over IPMI Serial-over-LAN), add console=tty0 console=ttyS0,115200 so the messages appear there too.

Official documentation: systemd kernel command line and dracut.cmdline.