MinMon - an opinionated minimal monitoring and alarming tool (for Linux)
This tool is just a single binary and a config file. No database, no GUI, no graphs. Just monitoring and alarms. I wrote this because the existing alternatives I could find were too heavy, mainly focused on nice GUIs with graphs (not on alarming), too complex to setup, or targeted at cloud/multi-instance setups.
Checks
Implemented are these checks:
See Roadmap for further ideas.
Actions
Report
The absence of alarms can mean two things: everything is okay or the monitoring/alarming failed altogether. That's why MinMon can trigger regular report events to let you know that it's up and running.
Design decisions
- No complex scripting language.
- No fancy config directory structure - just a single TOML file.
- No users, groups or roles.
- No cryptic abbreviations. The few extra letters in the config file won't hurt anyone.
- There are no predefined threshold names like "Warning" or "Critical". You might might want more than just two, or only one. So that's up to you to define in the config.
- The same check plugin can be used multiple times. You might want different levels to trigger different actions for different filesystems at different intervals.
- Alarms are timed in "cycles" (i.e. multiples of the
intervalof the check) instead of seconds. It's not very user-friendly but helps to keep the internal processing and the code simple and efficient. - Alarms stand for themselves - they are not related. This means that depending on your configuration, two (or more) events may be triggered at the same time for the same check. There are cases where this could be undesirable.
- Simple, clean, bloat-free code with good test coverage.
- Depending on your configuration, there may be similar or identical blocks in the config file. This is a consequence of the flexibility and simpleness of the config file format.
- All times and dates are UTC. No fiddling with local times and time zones.
- No internal state is stored between restarts.
- As of now it's only for Linux but it should be easy to adapt to other *NIXes or maybe even Windows.
- Some of the things mentioned above may change in the future (see Roadmap).
Config file
The config file uses the TOML format and has the following sections:
Architecture
System overview
graph TD
A(Config file) --> B(Main loop)
B -->|interval| C(Check 1)
B -.-> D(Check 2..n)
C -->|data| E(Alarm 1)
C -.-> F(Alarm 2..m)
E -->|cycles, repeat_cycles| G(Action)
E -->|recover_cycles| H(Recover action)
E -->|error_repeat_cycles| I(Error action)
style C fill:green;
style D fill:green;
style E fill:red;
style F fill:red;
style G fill:blue;
style H fill:blue;
style I fill:blue;
Alarm state machine
Each alarm has 3 possible states. "Good", "Bad" and "Error".
It takes cycles consecutive bad data points to trigger the transition from "Good" to "Bad" and recover_cycles good ones to go back. These transitions trigger the action and recover_action actions. During the "Bad" state, action will be triggered again every repeat_cycles cycles (if repeat_cycles is not 0).
The "Error" state is a bit special as it only "shadows" the other states. An error means that there is no data available at all, e.g. the filesystem usage for /home could not be determined. Since this should rarely ever happen, the transition to the error state always triggers the error_action on the first cycle. If there is valid data on the next cycle, the state machine continues as if the error state did not exist.
stateDiagram-v2
direction LR
[*] --> Good
Good --> Good
Good --> Bad: action/cycles
Good --> Error: error_action
Bad --> Good: recover_action/recover_cycles
Bad --> Bad: repeat_action/repeat_cycles
Bad --> Error: error_action
Error --> Good
Error --> Bad
Error --> Error: error_repeat_action/error_repeat_cycles
Example
Check the mountpoint at /home every minute. If the usage level exceeds 70% for 3 consecutive cycles (i.e. 3 minutes), the "Warning" alarm triggers the "Webhook 1" action. The action repeats every 100 cycles until the "Warning" alarm recovers. This happens after 5 consecutive cycles below 70% which also triggers the "Webhook 1" action. If there is an error while checking the filesystem usage, the "Log error" action is triggered. This is repeated every 200 cycles.
Config
[[checks]]
interval = 60
name = "Filesystem usage"
type = "FilesystemUsage"
mountpoints = ["/home"]
[[checks.alarms]]
name = "Warning"
level = 70
cycles = 3
repeat_cycles = 100
action = "Webhook 1"
recover_cycles = 5
recover_action = "Webhook 1"
error_repeat_cycles = 200
error_action = "Log error"
[[actions]]
name = "Webhook 1"
type = "Webhook"
url = "https://example.com/hook1"
body = """{"text": "{{alarm_name}}: {{check_name}} on mountpoint '{{check_id}}' reached {{level}}%."}"""
headers = {"Content-Type" = "application/json"}
[[actions]]
name = "Log error"
type = "Log"
level = "Error"
template = """{{check_name}} check didn't have valid data for alarm '{{alarm_name}}' and id '{{alarm_id}}'."""
The webhook text will be rendered into something like "Warning: Filesystem usage on mountpoint '/home' reached 70%."
Diagram
graph TD
A(example.toml) --> B(Main loop)
B -->|every 60 seconds| C(FilesystemUsage 1: '/srv')
C -->|level '/srv': 60%| D(LevelAlarm 1: 70%)
D -->|cycles: 3, repeat_cycles: 100| E(Action: Webhook 1)
D -->|recover_cycles: 5| F(Recover action: Webhook 1)
D -->|error_repeat_cycles: 200| G(Error action: Log error)
style C fill:green;
style D fill:red;
style E fill:blue;
style F fill:blue;
style G fill:blue;
Some (more exotic) ideas
Just to give some ideas of what's possible:
- Run it locally on your workstation and let it send you notifications to your desktop environment using the Process action and
notify-sendwhen the filesystem fills up. - Use the report in combination with the Webhook action and telepush and let it send you "I'm still alive, since {{minmon_uptime}} seconds!" once a week to your Telegram messenger for the peace of mind.
Placeholders
To improve the reusability of the actions, it's possible to define custom placeholders for the report, events, checks, alarms and actions. When an action is triggered, the placeholders (generic and custom) are merged into the final placeholder map. Inside the action (depending on the type of the action) the placeholders can be used in one or more config fields using the {{placeholder_name}} syntax. There are also some generic placeholders that are always available and some that are specific to the check that triggered the action. Placeholders that don't have a value available when the action is triggered will be replaced by an empty string.
Installation
Docker image
To pull the docker image use
docker pull ghcr.io/flo-at/minmon:latest
or the example docker-compose.yml file.
In both cases, read-only mount your config file to /etc/minmon.toml.
Build and install using cargo
Make sure cargo and OpenSSL are correctly installed on your local machine.
You can either install MinMon from crates.io using
cargo install --all-features minmon
Or if you already checked out the repository, you can build and install your local copy like this:
cargo install --all-features --path .
Copy the systemd.minmon.service file to /etc/systemd/system/minmon.service and place your config file at path /etc/minmon.toml. You can enable and start the service with systemctl daemon-reload && systemctl enable --now minmon.service.
If you don't want to include the systemd integration, leave out the --all-features option.
Install for the AUR (Arch Linux)
Use your package manager of choice to install the minmon package from the AUR.
Place your config file at path /etc/minmon.toml. You can enable and start the service with systemctl daemon-reload && systemctl enable --now minmon.service.\
systemd integration (optional)
- Logging to journal.
- Notify systemd about start-up completion (
Type=notify). - Periodically reset systemd watchdog (
WatchdogSec=x).
lm_sensors integration (optional)
Build with --features sensors to enable support for lm_sensors.
For the docker image, optionally mount your lm_sensors config file(s) to /etc/sensors.d/.
Note: libsensors is not cooperative and might theoretically block the event loop.
Roadmap
Check ideas
- Filesystem inode usage
- Folder size
- S.M.A.R.T.
- Load
- Ping
- HTTP response, keyword, ..
- HTTPS certificate expiration date
- Docker/Podman container status
General ideas
- Store data/status in time-based database (e.g. rrdtool) and visualize on web interface or ncurses UI. This should be optional and separated from the existing code.
Contributions
Contributions are very welcome! Right now MinMon is pretty basic but it's also super easy to extend. Even if it's just a typo in the documentation, I'll be happy to merge your PR. If you're looking for a new check or action type, just open a new issue (if it doesn't exist yet) and tag it with the "enhancement" label.
If you have an idea for a new check or action please use use the discussions page instead of opening a new issue.
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