Green Metrics Tool
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Flows on the host

A flow with container: null (or an empty container: key) in a usage_scenario.yml → runs its commands directly on the host system instead of inside a container.

name: Host Execution
author: Jane Doe
description: Runs flow commands directly on the host instead of inside a container

flow:
  - name: Host Echo
    container: null
    commands:
      - type: console
        command: echo "hello from the host"
        note: Running echo on the host

  - name: Compile on host
    container: null
    commands:
      - type: console
        command: make -j4
        shell: bash

If you only want to measure a single command on the host you do not need a usage_scenario.yml at all. See Shell mode →.

Commands in host flows are not sandboxed. They run directly on the measurement machine with the permissions of the user that runs GMT. GMT adds a warning to every run that contains host flows, because the measurement data is not directly comparable to fully containerized runs.

Rules

  • Host flows only support commands of type console.
  • The user that runs the measurement needs the measurement.orchestrators.host capability. Otherwise the run aborts with a PermissionError right after the usage scenario is parsed. On a fresh installation only the DEFAULT user (id 1) has this capability. See User Management →.
  • Without shell the command is split like a command line and executed directly without a shell.
  • With shell the command is executed in that shell with the strict shell options →. You can change them with shell-options.
  • Notes and logs of host flows are shown under the name [HOST].
  • services is optional. If the usage_scenario.yml has no services, GMT disables all metric providers that need containers (the ones ending in _container, for example cpu_utilization_cgroup_container) and adds a warning for each of them.

Host flows and container flows can be mixed in the same scenario.

Shell options on the host

On the host you can also use shells that do not follow the POSIX -c convention. The strict shell options → then depend on the shell.

  • powershell and pwsh have no such switches. GMT prepends $ErrorActionPreference = 'Stop' and Set-StrictMode -Version Latest as statements to the command instead. There is no equivalent for pipefail. If you set shell-options for PowerShell, a string is prepended as one statement and a list as one statement per entry.
  • cmd has no way to express these options. GMT sets none and aborts the run if you configure non-empty shell-options.
  • Every other shell is treated as a POSIX shell and gets -o errexit -o nounset -o pipefail like inside a container.
Shell mode (shell.py)
Comparing measurements