Vero Monitor Service

This probe is on the development roadmap.

Description

The custom_check probe runs an approved executable and evaluates exit code, stdout content, or JSON output. This is the only probe that spawns a process — compiled separately with the vms_custom_check build tag.

Security requirements:

Executable must be an absolute path (no PATH lookup).
Probe refuses to run as root (uid 0) or Windows LocalSystem.
No shell — binary is invoked directly with argv.
Stdout capped at 1 MiB.

Config fields

Field	Type	Required	Default	Description
`type`	`string`	Yes	—	Must be `"custom_check"`
`executable`	`string`	Yes	—	Absolute path to the executable
`args`	`string[]`	No	—	Arguments to pass
`expectedExitCode`	`int`	No	`0`	Expected exit code. Mismatch → `down`
`expectedStdoutContains`	`string`	No	—	String that must appear in stdout
`parseJsonOutput`	`bool`	No	`false`	Parse stdout as JSON. Numeric/boolean fields become gauge metrics

Metrics

Metric	Type	Labels	Description
`vms.custom_check.status`	status	—	`up` or `down`
`vms.custom_check.value`	gauge	`key`	Per-field values when `parseJsonOutput = true`

Example config

{
  "type": "custom_check",
  "executable": "/opt/vms/checks/check-core.sh",
  "args": ["--quick"],
  "expectedExitCode": 0
}

Notes

Build tag vms_custom_check — not included in the default agent package.
JSON parse only supports top-level object with numeric/boolean fields.