• Run scripts as a privileged user
• Run scripts as an unprivileged user
• Selecting your shell
• Security
• Terminating and killing processes

The Shell executor

The Shell executor is a simple executor that you use to execute builds locally on the machine where GitLab Runner is installed. It supports all systems on which the Runner can be installed. That means that it’s possible to use scripts generated for Bash, PowerShell Core, Windows PowerShell, and Windows Batch (deprecated).

Run scripts as a privileged user

The scripts can be run as unprivileged user if the --user is added to the gitlab-runner run command. This feature is only supported by Bash.

The source project is checked out to: <working-directory>/builds/<short-token>/<concurrent-id>/<namespace>/<project-name>.

The caches for project are stored in <working-directory>/cache/<namespace>/<project-name>.

Where:

• <working-directory> is the value of --working-directory as passed to the gitlab-runner run command or the current directory where the Runner is running
• <short-token> is a shortened version of the Runner’s token (first 8 letters)
• <concurrent-id> is a unique number, identifying the local job ID on the particular Runner in context of the project (accessible via the CI_CONCURRENT_PROJECT_ID pre-defined variable)
• <namespace> is the namespace where the project is stored on GitLab
• <project-name> is the name of the project as it is stored on GitLab

To overwrite the <working-directory>/builds and <working-directory/cache specify the builds_dir and cache_dir options under the [[runners]] section in config.toml.

Run scripts as an unprivileged user

If GitLab Runner is installed on Linux from the official .deb or .rpm packages, the installer will try to use the gitlab_ci_multi_runner user if found. If it is not found, it will create a gitlab-runner user and use this instead.

All shell builds will be then executed as either the gitlab-runner or gitlab_ci_multi_runner user.

In some testing scenarios, your builds may need to access some privileged resources, like Docker Engine or VirtualBox. In that case you need to add the gitlab-runner user to the respective group:

usermod -aG docker gitlab-runner
usermod -aG vboxusers gitlab-runner

Selecting your shell

GitLab Runner supports certain shells. To select a shell, specify it in your config.toml file. For example:

...
[[runners]]
  name = "shell executor runner"
  executor = "shell"
  shell = "powershell"
...

Security

Generally it’s unsafe to run jobs with shell executors. The jobs are run with the user’s permissions (gitlab-runner) and can “steal” code from other projects that are run on this server. Depending on your configuration, the job could execute arbitrary commands on the server as a highly privileged user. Use it only for running builds from users you trust on a server you trust and own.

Terminating and killing processes

The shell executor starts the script for each job in a new process. On UNIX systems, it sets the main process as a process group.

GitLab Runner terminates processes when:

• A job times out.
• A job is canceled.

On UNIX system gitlab-runner sends SIGTERM to the process and its child processes, and after 10 minutes sends SIGKILL. This allows for graceful termination for the process. Windows doesn’t have a SIGTERM equivalent, so the kill signal is sent twice. The second is sent after 10 minutes.