--- tags: - datacenter - l1 - flashcard-deck - firmware --- [Portal](../../../../library/portal/index.md) | **Level:** [L1: Foundations](../../../../library/portal/levels.md) | **Topics:** [Firmware / BIOS / UEFI](../../../../library/portal/topics.md) | **Domain:** Datacenter & Hardware id category difficulty tags question answer source_path firmware/19ad17a53dd3 firmware easy firmware, bios, uefi How do you check if a Linux system booted in UEFI or BIOS mode? Check for the EFI directory: [ -d /sys/firmware/efi ] && echo "UEFI" || echo "BIOS". If /sys/firmware/efi exists, the system booted in UEFI mode.\n\nUnder the hood: /sys/firmware/efi is created by the kernel's EFI stub at boot. Its absence means legacy BIOS or UEFI-CSM mode.\n\nGotcha: UEFI hardware booted in CSM (legacy) mode will NOT have /sys/firmware/efi even though the hardware supports UEFI. training/library/topics/firmware/primer.md firmware/a2b685e284fd firmware easy firmware, post, boot What is POST and what does it do? POST (Power-On Self-Test) is the firmware diagnostic sequence that runs before the OS loads. It initializes the CPU, tests memory, enumerates PCIe devices, initializes storage and network controllers, and hands off to the bootloader. training/library/topics/firmware/primer.md firmware/2e3abdd3685f firmware easy firmware, bmc, ipmi What is a BMC and what does it provide? A BMC (Baseboard Management Controller) is an independent processor on the server motherboard for out-of-band management. It provides remote console (KVM over IP), power control, hardware monitoring, firmware updates, and serial-over-LAN — all independent of the host OS. training/library/topics/firmware/primer.md firmware/1e30e7d720de firmware medium firmware, bios-vs-uefi, partitioning What are the key differences between legacy BIOS and UEFI? BIOS: 16-bit, MBR partitioning (max 2TB, 4 partitions), no secure boot, no networking. UEFI: 32/64-bit, GPT partitioning (no practical limit), Secure Boot, built-in shell and networking, NVRAM for boot variables, ESP (EFI System Partition) for bootloaders. training/library/topics/firmware/primer.md firmware/df337b7cd0c6 firmware medium firmware, ipmitool, sensors How do you read hardware sensors and check the System Event Log using ipmitool? Sensors: ipmitool sensor list (all sensors) or ipmitool sdr list (Sensor Data Repository). SEL: ipmitool sel elist (extended event log). Filter for boot issues: ipmitool sel list | grep -i "post\|boot\|memory\|cpu". training/library/topics/firmware/primer.md firmware/a3d00b681363 firmware medium firmware, fwupd, updates How do you check for and apply firmware updates on Linux? Use fwupd: fwupdmgr get-devices (list updateable devices), fwupdmgr get-updates (check for available updates), fwupdmgr update (apply updates). Most updates require a reboot. Dell systems can also use DSU (Dell System Update). training/library/topics/firmware/primer.md firmware/a6c6783063d4 firmware medium firmware, efibootmgr, boot-order How do you manage UEFI boot entries from Linux? Use efibootmgr: efibootmgr -v (list entries), efibootmgr -o 0001,0002,0003 (change boot order), efibootmgr -c -d /dev/sda -p 1 -L "Linux" -l '\EFI\ubuntu\grubx64.efi' (add entry). Boot variables are stored in NVRAM. training/library/topics/firmware/primer.md firmware/82dea816d9d8 firmware hard firmware, secure-boot, mokutil What is UEFI Secure Boot and how do you manage it from Linux? Secure Boot verifies that bootloaders and kernels are signed by trusted keys before executing them. Check status: mokutil --sb-state. List enrolled keys: mokutil --list-enrolled. Enroll a custom key (for custom kernels/modules): mokutil --import my-key.der. Unsigned or improperly signed code will not boot. training/library/topics/firmware/primer.md firmware/0abab7f06a8a firmware hard firmware, cmos, battery What are the symptoms of a dead CMOS battery and how does UEFI differ? Dead CMOS battery: clock resets every boot, BIOS settings revert to defaults, "CMOS checksum error" on POST. UEFI stores settings in NVRAM (flash), so it does not depend on the battery for settings — only for the real-time clock. training/library/topics/firmware/primer.md firmware/42f83ee6558b firmware hard firmware, fleet, management What is the recommended approach for fleet firmware updates in a datacenter? Stage firmware in a vendor repository (Dell Repository Manager, HPE SPP). Test on canary servers first. Schedule a maintenance window (most updates require reboot). Update all components: BIOS, BMC, NIC, RAID controller, and disk firmware. Verify post-update via SEL and diagnostics. training/library/topics/firmware/primer.md --- ## Wiki Navigation ### Related Content - [Case Study: BIOS Settings Reset After CMOS](../../../../library/case-studies/datacenter_ops/bios-settings-reset-after-cmos/README.md) (Case Study, L1) — Firmware / BIOS / UEFI - [Case Study: Firmware Update Boot Loop](../../../../library/case-studies/datacenter_ops/firmware-update-boot-loop/README.md) (Case Study, L2) — Firmware / BIOS / UEFI - [Case Study: HBA Firmware Mismatch](../../../../library/case-studies/datacenter_ops/hba-firmware-mismatch/README.md) (Case Study, L2) — Firmware / BIOS / UEFI - [Case Study: Node NotReady — NIC Firmware Bug, Fix Is Ansible Playbook](../../../../library/case-studies/cross-domain/node-notready-nic-firmware-ansible/README.md) (Case Study, L2) — Firmware / BIOS / UEFI - [Case Study: OS Install Fails RAID Controller](../../../../library/case-studies/datacenter_ops/os-install-fails-raid-controller/README.md) (Case Study, L2) — Firmware / BIOS / UEFI - [Case Study: PXE Boot Fails UEFI Mismatch](../../../../library/case-studies/datacenter_ops/pxe-boot-fails-uefi-mismatch/README.md) (Case Study, L1) — Firmware / BIOS / UEFI - [Datacenter & Server Hardware](../../../../library/topics/datacenter/index.md) (Topic Pack, L1) — Firmware / BIOS / UEFI - [Dell PowerEdge Servers](../../../../library/topics/dell-poweredge/index.md) (Topic Pack, L1) — Firmware / BIOS / UEFI - [Firmware](../../../../library/topics/firmware/index.md) (Topic Pack, L1) — Firmware / BIOS / UEFI - [Interview: Server Won't POST](../../../../library/interview-scenarios/11-server-wont-post.md) (Scenario, L2) — Firmware / BIOS / UEFI