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Smallstep Agent for Linux

The Smallstep Agent for Linux is a background component of the Smallstep Desktop App. Choose one or the other depending on your deployment needs.

Background

While macOS and Windows can manage certificates and authentication settings via Mobile Device Management (MDM), Linux does not include automated remote management facilities. The Smallstep Agent brings vital certificate management features to your Linux users and endpoints. It can be installed independently on any Linux device running systemd.

In this document, we will install, configure, and start the Smallstep Agent on a Linux device running systemd. We also show how to use the agent’s built-in PKCS#11 (smart card) service. With the PKCS#11 service, you can access Smallstep certificates and keys from applications that support PKCS#11.

System Requirements

  • Supported operating systems:
    • Enterprise Linux (RHEL, CentOS Stream, Rocky Linux, Alma Linux, etc)
    • Ubuntu (Current Stable and LTS)
    • Debian (Current Releases)
    • Fedora (Current Releases)
  • We support amd64 and arm64 architectures
  • The following package dependencies will be installed:
    • polkitd, to assign service manager privileges to the agent
    • p11-kit and tpm-tss2, for TPM 2.0 integration
  • The following directories are used by default:
    • runtime state in /run/step-agent
    • configuration in /etc/step-agent
    • certificates in/var/lib/step-agent and in your configured locations
  • The agent will connect to the following Smallstep hosts:
    • Your CA: <your-team>.ca.smallstep.com and subdomains
    • Agent API: control.infra.smallstep.com
    • Smallstep API: gateway.smallstep.com
    • TPM Attestation CA: att.smallstep.com

Quick Install

On a system with bash and curl, run the following as root:

curl -sL https://packages.smallstep.com/scripts/smallstep-agent-install.sh | bash

Manual Install

Fedora

  1. In the Terminal, add our package repository to your system:

    cat << EOF | sudo tee /etc/yum.repos.d/smallstep.repo
[smallstep]
name=Smallstep
baseurl=https://packages.smallstep.com/stable/fedora/
enabled=1
repo_gpgcheck=0
gpgcheck=1
gpgkey=https://packages.smallstep.com/keys/smallstep-0x889B19391F774443.gpg
EOF

  2. Install the Smallstep agent:

    sudo dnf makecache && sudo dnf install -y step-agent-plugin

  3. Check that it was installed correctly:

    step-agent-plugin version

    Output:

    🚀 step-agent-plugin/0.38.0 (linux/amd64)
   Release Date: 2024-10-10T14:55:48Z

Enterprise Linux (RHEL, CentOS Stream, Rocky Linux, Alma Linux, etc)

  1. In the Terminal, add our package repository to your system:

    cat << EOF | sudo tee /etc/yum.repos.d/smallstep.repo
[smallstep]
name=Smallstep
baseurl=https://packages.smallstep.com/stable/el/
enabled=1
repo_gpgcheck=0
gpgcheck=1
gpgkey=https://packages.smallstep.com/keys/smallstep-0x889B19391F774443.gpg
EOF

  2. Install the Smallstep agent:

    sudo dnf makecache && sudo dnf install -y step-agent-plugin

  3. Check that it was installed correctly:

    step-agent-plugin version

    Output:

    🚀 step-agent-plugin/0.38.0 (linux/amd64)
   Release Date: 2024-10-10T14:55:48Z

Debian

  1. In the Terminal, install dependencies:

    sudo apt-get update && sudo apt-get install -y --no-install-recommends curl gpg ca-certificates

  2. Add our package repository to your system:

    sudo curl -fsSL https://packages.smallstep.com/keys/apt/repo-signing-key.gpg -o /etc/apt/trusted.gpg.d/smallstep.asc && \
    echo 'deb [signed-by=/etc/apt/trusted.gpg.d/smallstep.asc] https://pkgs.infra.smallstep.com/stable/debian debs main' \
    | sudo tee /etc/apt/sources.list.d/smallstep.list

  3. Install the Smallstep agent:

    sudo apt-get update && sudo apt-get -y install step-agent-plugin

  4. Check that it was installed correctly:

    step-agent-plugin version

    Output:

    🚀 step-agent-plugin/0.38.0 (linux/amd64)
   Release Date: 2024-10-10T14:55:48Z

Ubuntu

  1. In the Terminal, install dependencies:

    DEBIAN_FRONTEND=noninteractive
sudo apt-get update && sudo apt-get install -y --no-install-recommends curl gpg ca-certificates

  2. Add our package repository to your system:

    sudo curl -fsSL https://packages.smallstep.com/keys/apt/repo-signing-key.gpg -o /etc/apt/trusted.gpg.d/smallstep.asc && \
    echo 'deb [signed-by=/etc/apt/trusted.gpg.d/smallstep.asc] https://packages.smallstep.com/stable/debian debs main' \
    | sudo tee /etc/apt/sources.list.d/smallstep.list

  3. Install the Smallstep agent

    sudo apt-get update && sudo apt-get -y install step-agent-plugin openssl-tpm2-engine

  4. Check that it was installed correctly

    step-agent-plugin version

    Output:

    🚀 step-agent-plugin/0.38.0 (linux/amd64)
   Release Date: 2024-10-10T14:55:48Z

Configure the agent

To configure the agent and register your Linux device with Smallstep, run:

step-agent-plugin register

Alternatively, you can configure the agent manually. Simply update /etc/step-agent/agent.yaml config file, with your Smallstep team ID and Smallstep Agent CA fingerprint.

team: "yourteamname"
fingerprint: "40523785c1d1d11EXAMPLE017b660d52a5fa5f2cb94cf0e1a9e9209dbea0826"
  • Your team ID (team slug). This is the value after /app/ in your Smallstep dashboard URL.
  • Your agent CA fingerprint. Find this value in your dashboard:
    • In the Smallstep dashboard, select Authorities
    • Select the Smallstep Agents authority
    • Use the sha256 Root fingerprint displayed on this page

Start the Smallstep agent

Finally, enable and start the agent:

sudo systemctl daemon-reload
sudo systemctl enable --now step-agent

If you get any errors, check the agent’s status:

sudo systemctl status step-agent.service

PKCS#11 Support

The Smallstep agent provides a PKCS#11 server that can be used for a variety of integration use cases, such as NetworkManager and wpa_supplicant connections or web browser certificates. The PKCS#11 server is exposed as a UNIX socket at $XDG_RUNTIME_DIR/step-agent/step-agent-pkcs11.sock.

Example usage: Google Chrome

For this example, we’re using Ubuntu 24.04. The location of p11-kit-client.so may vary.

Let’s make client certificates and keys from the agent available to Google Chrome via PKCS#11 tokens. We will use modutil and an NSS database. Google Chrome defaults to storing an NSS database in ~/.pki/nssdb, so we can leverage that.

To use Smallstep certificates in Chrome, run:

modutil -dbdir ~/.pki/nssdb -add step-agent \
        -libfile /usr/lib/x86_64-linux-gnu/pkcs11/p11-kit-client.so
export P11_KIT_SERVER_ADDRESS=unix:path=$XDG_RUNTIME_DIR/step-agent/step-agent-pkcs11.sock

Next, start Chrome from the command line.

In Chrome, you should now have access to certificates managed by Smallstep.

For regular usage, add P11_KIT_SERVER_ADDRESS to your environment more permanently. For example, you might add P11_KIT_SERVER_ADDRESS=unix:path=$XDG_RUNTIME_DIR/step-agent/step-agent-pkcs11.sock to your global /etc/environment file.

Troubleshooting

The agent produces a log file or journal entries in systemd, depending on how it is installed and run.

You can use tools like pkcs11-tool for troubleshooting PKCS#11 support:

pkcs11-tool --module /usr/lib/x86_64-linux-gnu/pkcs11/p11-kit-client.so \
         --list-slots

See the p11-kit documentation for more details.