permission denied in jenkins pipeline running bash script

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05-10-2024

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"Permission Denied" in Jenkins Pipelines: Demystifying Bash Script Execution Errors

Scenario: You've meticulously crafted your Jenkins pipeline, incorporating a powerful Bash script to automate crucial tasks. However, when the pipeline executes, a dreaded error message pops up: "Permission denied." Frustration sets in – your script works flawlessly on the command line, but fails miserably within the pipeline.

Problem: This "Permission denied" error often arises when the Jenkins user lacks the necessary permissions to access files, directories, or execute commands within the context of your Bash script.

Understanding the Root Cause:

Imagine Jenkins as a dedicated worker, diligently carrying out your pipeline instructions. This worker, however, doesn't have the same access privileges as you when you're logged in as a regular user. Your Bash script might attempt to modify files, create directories, or run commands that require elevated privileges.

Replicating the Issue:

pipeline {
  agent any
  stages {
    stage('Bash Execution') {
      steps {
        sh '''
          echo "Trying to write to a file..."
          echo "This is some text" > /path/to/file.txt
        '''
      }
    }
  }
}

This simple pipeline attempts to write text to a file located at /path/to/file.txt. If Jenkins doesn't have write access to this location, the script will fail with the "Permission denied" error.

Solutions to the "Permission Denied" Dilemma:

1. Granting Permissions:

   • File/Directory Permissions: Use chmod to adjust permissions for the specific files or directories accessed by your script. For instance: chmod 777 /path/to/file.txt gives full permissions to the file.

2. Running with Elevated Privileges (With Caution):

   • Jenkins Credentials: Securely store your credentials (username and password) for a user with elevated privileges within Jenkins. Use the withCredentials block to access these credentials and execute commands as the privileged user.

   pipeline {
     agent any
     stages {
       stage('Bash Execution') {
         steps {
           withCredentials([usernamePassword(credentialsId: 'admin-credentials', usernameVariable: 'ADMIN_USER', passwordVariable: 'ADMIN_PASS')]) {
             sh "sudo -u ${ADMIN_USER} -p ${ADMIN_PASS} sh -c 'echo 'This is some text' > /path/to/file.txt'"
           }
         }
       }
     }
   }
   

3. Leveraging Jenkins' Built-in Features:

   • Workspace Access: Utilize Jenkins' workspace functionality to ensure your scripts operate within a dedicated location with the appropriate permissions.

   pipeline {
     agent any
     stages {
       stage('Bash Execution') {
         steps {
           sh '''
             echo "This is some text" > file.txt 
           '''
         }
       }
     }
   }
   

4. Minimizing Privilege Escalation:

   • Principle of Least Privilege: Design your scripts to require the minimal permissions necessary. If only reading access is needed, avoid granting write permissions. This enhances security and reduces potential vulnerabilities.

Important Considerations:

• Security Best Practices: Running scripts with elevated privileges carries inherent risks. Consider using specific Jenkins plugins like the Credentials Binding plugin to manage credentials securely.
• Context Matters: Always ensure your script's permissions are evaluated within the context of its execution environment, which might be different from your local development environment.

By understanding the reasons behind "Permission denied" errors in Jenkins pipelines and implementing the appropriate solutions, you can efficiently overcome these obstacles and execute your scripts with confidence.