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# Machine-check exception

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This article aims to help users implement services to actively monitor, log, and report hardware errors. A machine check exception (MCE) is an error generated by the CPU when the CPU detects that a hardware error or failure has occurred.

Machine check exceptions (MCEs) can occur for a variety of reasons ranging from undesired or out-of-spec voltages from the power supply, from cosmic radiation flipping bits in memory DIMMs or the CPU, or from other miscellaneous faults, including faulty software triggering hardware errors.

## Installation

Install the rasdaemonAUR package. rasdaemon written by Mauro Carvalho Chehab is one of the tools to gather MCE information.

Previously, the task was performed by the `mcelog` package. However, it has been deprecated, and Arch kernels are not even compiled with the necessary configuration option CONFIG_X86_MCELOG_LEGACY (FS#55657) now.

## Configuration

There are two systemd services that need to be started and enabled. `ras-mc-ctl.service` registers DIMM labels (from `/etc/ras/dimm_labels.d/`) with EDAC drivers. On consumer-grade motherboards it usually logs a `No dimm labels for <motherboard model>` error and does nothing. `rasdaemon.service` runs as a daemon and logs RAS events to systemd journal.

See ras-mc-ctl(8) and rasdaemon(1) for more information.

## Usage

You can use `ras-mc-ctl --error-count` and `ras-mc-ctl --summary` to quickly glance at the recorded errors. Errors are logged to the journal as well as the sqlite database at `/var/lib/rasdaemon/ras-mc_event.db`. The schema of the sqlite database is changing often; after deleting the sqlite database file, restarting the rasdaemon service will create a fresh sqlite database file with the correct schema.

## See also

- Wikipedia:Machine_Check_Exception
- Wikipedia:Machine_check_architecture
- Rasdaemon initial announcement
- Monitoring ECC memory on Linux with rasdaemon

### Hardware documentation

- AMD64 Architecture Programmer's Manual, Volume 2: System Programming
- BIOS and Kernel Developer's Guide for AMD Athlon™ 64 and AMD Opteron™ Processors

Categories:

- CPU
- Kernel

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