Quickly read what the kernel received at boot and diagnose boot issues. 16.11.2025 | reading time: 3 min The kernel command line reveals the exact parameters the kernel received at boot; check it to diagnose root selection, init choices or security toggles and to confirm what the bootloader actually passed. Quick hands-on check Tell the system what it already knows: read the live kernel command line with a single command and compare it to bootloader settings by running: ```bash cat /proc/cmdline ``` Typical output on a test machine looks like: ```text BOOT_IMAGE=/vmlinuz-5.15.0 root=/dev/mapper/vg-root ro quiet splash init=/lib/systemd/systemd ``` Use that line as the authoritative source for what the running kernel received. Diagnose common problems If root is wrong, swap device names, or the wrong init is used, the system may drop to emergency mode; inspect `/proc/cmdline` first, then check the bootloader config file for mismatches, because the kernel uses these parameters very early and they control mounting and init behavior. Useful kernel parameters Look for parameters that matter most: the root= device, ro or rw, init=, crashkernel=, console=, and security or mitigation flags like selinux= or mitigations=; short flags such as quiet and splash just change verbosity, while a wrong root= will prevent boot entirely. Where bootloaders come in The kernel line is built by the bootloader at boot time, so to change it persistently edit GRUB or systemd-boot configuration or use EFI tools for boot entries; after editing regenerate configs or update the NVRAM entry so the kernel receives the new string on next boot. Live validation tips Compare `/proc/cmdline` with grub config files under `/boot` or `/etc/default/grub`, and inspect UEFI entries with `efibootmgr`; when debugging initramfs issues, enable verbose console output via console= and remove quiet to capture more messages in the early boot log. Final thought The kernel command line is small, visible and powerful; reading it is the fastest way to verify what the kernel was told at boot and to focus further troubleshooting steps, so make it the first stop in every boot investigation. Join Bits & Bytes Academy First class LINUX exam preparation. boot-process utilities troubleshooting
