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+---
+stage: Verify
+group: Runner
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
+---
+
+# Linux shared runners
+
+Linux shared runners on GitLab.com run in autoscale mode and are powered by Google Cloud Platform.
+
+Autoscaling means reduced queue times to spin up CI/CD jobs, and isolated VMs for each job, thus maximizing security. These shared runners are available for users and customers on GitLab.com.
+
+GitLab offers Ultimate tier capabilities and included CI/CD minutes per group per month for our [Open Source](https://about.gitlab.com/solutions/open-source/join/), [Education](https://about.gitlab.com/solutions/education/), and [Startups](https://about.gitlab.com/solutions/startups/) programs. For private projects, GitLab offers various [plans](https://about.gitlab.com/pricing/), starting with a Free tier.
+
+All your CI/CD jobs run on [n1-standard-1 instances](https://cloud.google.com/compute/docs/machine-types) with 3.75GB of RAM, CoreOS and the latest Docker Engine
+installed. Instances provide 1 vCPU and 25GB of HDD disk space. The default
+region of the VMs is US East1.
+Each instance is used only for one job, this ensures any sensitive data left on the system can't be accessed by other people their CI jobs.
+
+The `gitlab-shared-runners-manager-X.gitlab.com` fleet of runners are dedicated for GitLab projects as well as community forks of them. They use a slightly larger machine type (n1-standard-2) and have a bigger SSD disk size. They don't run untagged jobs and unlike the general fleet of shared runners, the instances are re-used up to 40 times.
+
+Jobs handled by the shared runners on GitLab.com (`shared-runners-manager-X.gitlab.com`),
+**time out after 3 hours**, regardless of the timeout configured in a
+project. Check the issues [4010](https://gitlab.com/gitlab-com/infrastructure/-/issues/4010) and [4070](https://gitlab.com/gitlab-com/infrastructure/-/issues/4070) for the reference.
+
+Below are the shared runners settings.
+
+| Setting                               | GitLab.com                                        | Default    |
+| -----------                           | -----------------                                 | ---------- |
+| Executor                              | `docker+machine`                                  | -          |
+| Default Docker image                  | `ruby:2.5`                                        | -          |
+| `privileged` (run [Docker in Docker](https://hub.docker.com/_/docker/)) | `true`          | `false`    |
+
+## Pre-clone script
+
+Linux shared runners on GitLab.com provide a way to run commands in a CI
+job before the runner attempts to run `git init` and `git fetch` to
+download a GitLab repository. The
+[`pre_clone_script`](https://docs.gitlab.com/runner/configuration/advanced-configuration.html#the-runners-section)
+can be used for:
+
+- Seeding the build directory with repository data
+- Sending a request to a server
+- Downloading assets from a CDN
+- Any other commands that must run before the `git init`
+
+To use this feature, define a [CI/CD variable](../../../ci/variables/index.md#custom-cicd-variables) called
+`CI_PRE_CLONE_SCRIPT` that contains a bash script.
+
+[This example](../../../development/pipelines.md#pre-clone-step)
+demonstrates how you might use a pre-clone step to seed the build
+directory.
+
+NOTE:
+The `CI_PRE_CLONE_SCRIPT` variable does not work on Windows runners.
+
+## `config.toml`
+
+The full contents of our `config.toml` are:
+
+NOTE:
+Settings that are not public are shown as `X`.
+
+**Google Cloud Platform**
+
+```toml
+concurrent = X
+check_interval = 1
+metrics_server = "X"
+sentry_dsn = "X"
+
+[[runners]]
+  name = "docker-auto-scale"
+  request_concurrency = X
+  url = "https://gitlab.com/"
+  token = "SHARED_RUNNER_TOKEN"
+  pre_clone_script = "eval \"$CI_PRE_CLONE_SCRIPT\""
+  executor = "docker+machine"
+  environment = [
+    "DOCKER_DRIVER=overlay2",
+    "DOCKER_TLS_CERTDIR="
+  ]
+  limit = X
+  [runners.docker]
+    image = "ruby:2.5"
+    privileged = true
+    volumes = [
+      "/certs/client",
+      "/dummy-sys-class-dmi-id:/sys/class/dmi/id:ro" # Make kaniko builds work on GCP.
+    ]
+  [runners.machine]
+    IdleCount = 50
+    IdleTime = 3600
+    MaxBuilds = 1 # For security reasons we delete the VM after job has finished so it's not reused.
+    MachineName = "srm-%s"
+    MachineDriver = "google"
+    MachineOptions = [
+      "google-project=PROJECT",
+      "google-disk-size=25",
+      "google-machine-type=n1-standard-1",
+      "google-username=core",
+      "google-tags=gitlab-com,srm",
+      "google-use-internal-ip",
+      "google-zone=us-east1-d",
+      "engine-opt=mtu=1460", # Set MTU for container interface, for more information check https://gitlab.com/gitlab-org/gitlab-runner/-/issues/3214#note_82892928
+      "google-machine-image=PROJECT/global/images/IMAGE",
+      "engine-opt=ipv6", # This will create IPv6 interfaces in the containers.
+      "engine-opt=fixed-cidr-v6=fc00::/7",
+      "google-operation-backoff-initial-interval=2" # Custom flag from forked docker-machine, for more information check https://github.com/docker/machine/pull/4600
+    ]
+    [[runners.machine.autoscaling]]
+      Periods = ["* * * * * sat,sun *"]
+      Timezone = "UTC"
+      IdleCount = 70
+      IdleTime = 3600
+    [[runners.machine.autoscaling]]
+      Periods = ["* 30-59 3 * * * *", "* 0-30 4 * * * *"]
+      Timezone = "UTC"
+      IdleCount = 700
+      IdleTime = 3600
+  [runners.cache]
+    Type = "gcs"
+    Shared = true
+    [runners.cache.gcs]
+      CredentialsFile = "/path/to/file"
+      BucketName = "bucket-name"
+```