getfacl

getfacl is a command-line utility used to retrieve extended file attributes (ACLs) from files and directories on Unix-like systems. It is essential for auditing and managing access controls that go beyond traditional Unix file permissions.

Overview

• Purpose: Retrieves and displays the ACL information attached to files or directories, allowing administrators to review detailed access permissions.

• Usage Context: Commonly used on filesystems that support extended attributes (such as ext4, XFS, or Btrfs) to inspect the ACLs applied to files, ensuring proper security configurations.

Basic Syntax

getfattr [OPTIONS] FILE...

• FILE...: One or more files or directories to query.

• OPTIONS: Command-line flags to control the output.

Common Options

• -d or --dump: Dump all extended attributes in a human-readable format.

  getfattr -d filename.txt

• -n <name>: Retrieve the value of a specific attribute.

  getfattr -n user.comment filename.txt

• -m <regexp>: Only display attributes that match the specified regular expression.

  getfattr -m "user.*" filename.txt

• -R or --recursive: Recursively retrieve attributes from directories and subdirectories.

  getfattr -R -d /path/to/directory

• -q or --quiet: Suppress warnings for files without extended attributes.

  getfattr -q filename.txt

Example Usage

1. Dump All ACLs for a File:

   getfattr -d document.txt

   This command displays all extended attributes (including ACLs) for document.txt.

2. Retrieve a Specific Attribute:

   getfattr -n user.comment document.txt

   This retrieves the user.comment attribute from document.txt.

3. Recursively Retrieve ACLs for a Directory:

   getfattr -R -d /shared/documents

   This command dumps extended attributes for all files and subdirectories within /shared/documents.

Best Practices

• Auditing and Reporting: Incorporate getfattr in scripts to periodically audit ACL settings on sensitive files or directories.

• Combine with setfacl: Use getfattr to verify that changes made with setfacl have been correctly applied.

• Backup ACL Settings: Save the output of getfattr before making significant changes to ensure that you can restore previous ACL configurations if needed.

Conclusion

getfattr is an essential tool for retrieving extended file attributes, particularly ACLs, on Unix-like systems. It enables administrators to inspect and audit file permissions, ensuring that security policies are correctly implemented and maintained across the system.