In Linux systems, you can use the following commands to start Jenkins:

If Jenkins is installed as a WAR file, you can use:
```bash
java -jar jenkins.war
```

If Jenkins is installed via a system service, such as using apt on Ubuntu, you can use:
```bash
sudo systemctl start jenkins
```

Additionally, if Jenkins is running in a Docker container, you can use the following command to start a Jenkins container:
```bash
docker run -p 8080:8080 -p 50000:50000 jenkins/jenkins:lts
```

What command can be used to start Jenkins?