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diff --git a/README.md b/README.md new file mode 100644 index 0000000..e9e6abb --- /dev/null +++ b/README.md @@ -0,0 +1,161 @@ +# prometheus-nano-exporter + +TODO: one-paragraph description. + +## Word of Warning + +There are no particularly compelling reasons to use this software over +the alternatives. On a Real Computer™, the standard [Prometheus node +exporter](https://github.com/prometheus/node_exporter) is perfectly +adequate, and has a much larger feature set, not to mention adoption +rate. On OpenWRT in particular, the standard community-supported +package repository already has a lightweight Lua rewrite as +[prometheus-node-exporter-lua](https://openwrt.org/packages/pkgdata/prometheus-node-exporter-lua), +which is even smaller in disk footprint, if you don't count the Lua +interpreter. + +The only reason why you would *need* this version is if you were +building for a particularly constrained system, and did not want to +include the Lua interpreter, or *any* foreign dependencies (other than +a C runtime library). + +Other than that, you might choose to use it for æsthetic reasons. + +## Installation + +TODO: instructions. + +The metrics collection is highly Linux-specific. You probably won't +have much luck on other operating systems. + +## Collectors + +For the most part, the produced metrics try to loosely (but not +slavishly) adhere to the format used by the standard Prometheus node +exporter (as of version v0.16). + +This is an overview of the available collectors. See the [Collector +Reference](#collector-reference) below for detailed documentation, +including generated metrics, labels and configuration options. + +| Name | Description | +| ---- | ----------- | +| [`cpu`](#cpu) | CPU usage from `/proc/stat` and CPU frequency scaling data from sysfs. | +| [`hwmon`](#hwmon) | Temperature, fan and voltage sensors from `/sys/class/hwmon`. | +| [`network`](#network) | Network device transmit/receive statistics from `/proc/net/dev`. | +| [`textfile`](#textfile) | Custom metrics from `.prom` text files dropped in a directory. | +| [`uname`](#uname) | Node information returned by the `uname` system call. | + +## Usage + +By default, all collectors are enabled. Use a command line argument of +the form `--{collector}-off` (e.g., `--cpu-off`) to selectively +disable specific collectors. Alternatively, if you explicitly enable +any collector with `--{collector}-on`, only such explicitly enabled +collectors are actually enabled. You probably don't want to mix both +`on` and `off` flags in the same invocation. + +The general command line arguments are documented below. Specific +collectors may also accept further arguments, which will always have +the prefix `--{collector}-`. They are documented in the [Collector +Reference](#collector-reference) section. + +| Flag | Description | +| ---- | ----------- | +| `--port=X` | Listen on port *X* instead of the default port (9100). | + +## Collector Reference + +### `cpu` + +Metrics and labels: + +* `node_cpu_seconds_total{cpu=N,mode=M}`: Number of CPU seconds spent + in various different modes, as reported in `/proc/stat`. *N* is the + CPU index, a number between 0 and one less than the number of + (logical) CPUs in the system. The mode *M* is one of `user`, `nice`, + `system`, `idle`, `iowait`, `irq`, `softirq` or `steal`. There will + be one row for each CPU and each mode in the scrape. +* `node_cpu_frequency_hertz{cpu=N}`: The current CPU clock frequency + in Hertz at the time of the scrape. This is the + `cpufreq/scaling_cur_freq` value under the CPU-specific sysfs + directory. + +### `hwmon` + +The `hwmon` collector pulls data from all the sysfs subdirectories +under `/sys/class/hwmon`. The supported entry types are temperature +(`temp*`), fan (`fan*` and voltage (`in*`) sensors. + +Metrics and dimensions: + +* `node_hwmon_temp_celsius`: Current temperature in degrees Celsius. +* `node_hwmon_fan_rpm`: Current fan speed in RPM. +* `node_hwmon_fan_min_rpm`: Threshold for minimum fan speed. +* `node_hwmon_fan_alarm`: Active fan alarm signal: `0`/`1`. +* `node_hwmon_in_volts`: Input voltage measurement. +* `node_hwmon_in_min_volts`: Lower threshold for a voltage alarm. +* `node_hwmon_in_max_volts`: Upper threshold for a voltage alarm. +* `node_hwmon_in_alarm`: Active voltage alarm signal: `0`/`1`. + +All the metrics have the same two labels: `chip` and `sensor`. The +`chip` label is derived from the sysfs directory path, while the +`sensor` label designates a specific sensor on the same (logical) +chip. + +The values are by default directly as reported in sysfs: there's no +built-in scaling. TODO: scaling options. + +### `network` + +Metrics and labels: + +* `node_network_receive_X{device=D}`: Metrics related to receiving + data on network interface *D*. +* `node_network_transmit_Y{device=D}`: Metrics related to sending data + on network interface *D*. + +The exact set of metrics (`X` and `Y` above) depends on the columns +included in your `/proc/net/dev` file. A normal set is: + +| Receive | Transmit | Metric | Description | +| ------- | -------- | ------ | ----------- | +| X | X | `bytes` | Byte counter | +| X | X | `packets` | Packet counter | +| X | X | `errs` | Errors while receiving/transmitting | +| X | X | `drop` | Dropped frame count | +| X | X | `fifo` | ? | +| X | | `frame` | ? | +| X | | `compressed` | ? | +| X | | `multicast` | Byte count | +| | X | `colls` | Collisions while transmitting | +| | X | `carrier` | ? | + +### `textfile` + +The `textfile` collector can be used to conveniently export custom +node-bound metrics. Metrics in any files ending in `.prom` in the +designated directory are included in the scrape. Generally you should +write to a file with a different suffix (say `.prom.tmp`) and then +atomically rename the file, to prevent the server for sending data +from incomplete metrics files. + +The implementation in this program copies the file contents directly +to the outgoing HTTP response. It is your responsibility to make sure +the files conform to the Prometheus exposition format. The only +modification done is to add a terminating newline to the file, is one +is not already present. + +### `uname` + +The `uname` collector exports data from the eponymous system call as +labels attached to the metric `node_uname_info`, which always has the +value 1. The attached labels are: + +* `machine` +* `nodename` +* `release` +* `sysname` +* `version` + +See your `uname(2)` man page for details of the values. |