Foundations - BMC
A BMC (Baseboard Management Controller) is a small embedded computer on the server motherboard. It runs independently of the host CPU and OS, so it can still work when the server is down, hung, or otherwise inaccessible.
What it can do
Section titled “What it can do”Through the BMC, you can usually:
- Power the server on, off, or cycle it
- Read hardware sensors such as temperature, fan speed, and voltage
- Access a serial console when SSH is unavailable
- Read hardware inventory
- View the system event log for hardware-level failures and events
- Provision a server before the OS is installed
Vendor names
Section titled “Vendor names”| Vendor | BMC Name |
|---|---|
| Dell | iDRAC |
| HPE | iLO |
| Lenovo | XCC |
| Supermicro | BMC / IPMI |
Standby power
Section titled “Standby power”The BMC runs on standby power. A server that is “powered off” can still have a working BMC unless it is fully unplugged.
Out-of-band vs. in-band management
Section titled “Out-of-band vs. in-band management”| In-band | Out-of-band | |
|---|---|---|
| Path | Through the host OS, over the production network | Through the BMC, over the management network |
| Requires OS | Yes | No |
| Common tools | SSH and agents | ipmitool and Redfish API |
| Use cases | Standard operations like log collection and software updates | Recovery, provisioning, and hardware operations |
Why this matters
Section titled “Why this matters”At scale, the BMC is the control plane for hardware operations. If a host is hung, powered off, or missing an OS, the BMC is often the only reliable way to recover or inspect it.