S.M.A.R.T. exporter for Prometheus

This is a Prometheus Exporter which exports S.M.A.R.T. metrics.

Core Features

• Secure: only the absolute necessary part of the code runs as root, in a separate process
• No guessing: re-uses the device database from the check_smart_attributes nagios check.

Architecture

We want to avoid having a service running as root exposed to the network. This is why the S.M.A.R.T. exporter is split in two parts:

1. a helper which runs as root (smart_exporter_helper)
2. the HTTP server which serves the data (prometheus_smart_exporter)

The helper runs as a service listening on UNIX socket (ideally managed by systemd, but can also be managed by the helper itself). When a client connects to the socket, the helper reads S.M.A.R.T. metrics and sends them to the client as serialised Python dict wrapped in a simple binary format.

The exporter listens on HTTP and when asked to export data, it connects to the UNIX socket and receives the current S.M.A.R.T. metrics. All interpretation, filtering and Prometheus-specific formatting of the data is done in the exporter and as unprivilegued user.

Socket Protocol

The binary protocol is dead-simple:

Byte range	Type	Usage
0	unsigned	Protocol Version. Must be 1.
1-8	unsigned	Length of the data in bytes
9..end	UTF-8 encoded text	repr() of python dict containing the S.M.A.R.T. data.

Security

Since part of this code runs as root, this deserves its own section. The helper is the only process which is supposed to run as root. Do not run the exporter itself as root.

The helper is less than 300 lines of nearly dependency-free (the exception are the systemd helpers for socket activation and journalling) python, making it easy to audit. It does not accept input from its clients (in fact, it immediately closes the receiving direction of the socket once it is accepted).

Installation

Install via PyPI:

pip3 install prometheus_smart_exporter

Installation via PyPI does not install any system-wide configuration. You need to do that yourself.

Configuration

Services and Sockets

It is recommended to use systemd to manage the UNIX socket for the helper. It allows you fine control over the user, group and mode of the socket, thus allowing to expose the socket only to the exporter process. In addition, at allows for seamless restarts of the helper service.

Example service files for use with systemd are included in the git repository.

S.M.A.R.T. device database

This exporter uses a device database in the same format as the famous nagios check_smart_attributes does. If you already use or have used the check_smart_attributes, you can simply continue using your device database. Otherwise, you will find a device database in the linked github repository.

The only information used from the device DB is the information whether a RAW_VALUE or a VALUE should be exported. At some point, it may be configurable to only export metrics for values which have thresholds and/or perfs set.

Attribute Mapping

An additional JSON file specifies how S.M.A.R.T. attributes are mapped to Prometheus metric names. It defines rules which, based on the S.M.A.R.T. attribute ID and name, decide the type and name of the Prometheus metric.

The basic format is the following:

{
  "generic": [
    < rules ... >
  ]
}

Each rule looks like this:

{
  "id": < integer >,
  "match": < regular expression as string >,
  "name": < string >,
  "type": < "counter" or "gauge" >
}

"id"

is mandatory and the S.M.A.R.T. attribute ID for which this rule is used

"match"

is an optional regular expression. Only if the name of the attribute matches the regular expression, the rule is applied.

"name"

the name of the Prometheus metric to use. All metric names are automatically prefixed with smart_; the prefix must not be included in the "name" attribute.

"type"

the type of the Prometheus metric to use (generally "gauge" or "counter").

A default attribute mapping is included in the package itself. Pull requests for additional rules are welcome.

Helper

The helper is configured using command line arguments only.

usage: smart_exporter_helper [-h] [--socket-path SOCKET_PATH]
                             [--smartctl-arg SMARTCTL_ARG] [--timeout TIMEOUT]
                             [-v]

optional arguments:
  -h, --help            show this help message and exit
  --socket-path SOCKET_PATH
                        Path at which the unix socket will be created.
                        Required if the process is not started via systemd
                        socket activation.
  --smartctl-arg SMARTCTL_ARG
                        Pass an additional argument to the smartctl command.
                        Can be specified multiple times.
  --timeout TIMEOUT     Time in seconds to wait between connections. Defaults
                        to infinity.
  -v

--timeout

specifies the time for which the service stays alive after finishing the last request. This can be used to help conserve memory at the cost of measurement latency and CPU/disk-IO.

--socket-path

If systemd socket activation is not used, this argument must be given to specify at which location the socket shall be created. If a socket is already present at that location, it is unlinked at startup and replaced with a fresh socket. In general, it is recommended to use systemd with socket activation instead.

--smartctl-arg

By default, the service uses the smartctl -iA command to get S.M.A.R.T. data for a specific device. Additional arguments can be provided to the command to customize the behavior of smartctl. For example, --smartctl-arg=--nocheck=standby can be used to ensure that drives that are in standby mode are not woken up.

HTTP Exporter

The HTTP exporter is configured using the aforementioned JSON files and command line arguments.

usage: prometheus_smart_exporter [-h] [--device-db DEVICE_DB]
                                 [--attr-mapping ATTR_MAPPING] [-v]
                                 [--journal] [-p PORT] [-a ADDR]
                                 socket

positional arguments:
  socket                Path to UNIX socket where the helper listens

optional arguments:
  -h, --help            show this help message and exit
  --device-db DEVICE_DB
                        Device database in JSON format (default:
                        /usr/share/ch-monitoring-smart-data/devices.json)
  --attr-mapping ATTR_MAPPING
                        Attribute mapping in JSON format (default: <...>)
  -v                    Increase verbosity (up to -vvv)
  --journal             Log to systemd journal
  -p PORT, --listen-port PORT
                        Port number to bind to (default: 9257)
  -a ADDR, --listen-address ADDR
                        Address to bind to (default: 127.0.0.1)

--device-db

path to the S.M.A.R.T. device database (see above)

--attr-mapping

path to the attribute map attr-mapping (see above). By default, the attribute map delivered with the package is used.

--journal

enable logging to the systemd journal. By default, logs go to standard output.

--listen-port

configure the TCP port to bind to

--listen-address

configure the TCP address to bind to

socket

path to the UNIX socket where the helper listens