In this lesson, you will learn how to preserve complex Access Control Lists (ACLs) during system backups and migrations to ensure your security posture remains intact.
The Challenge of Metadata Preservation
When you perform a standard file copy using commands like cp or move data between filesystems, the operating system often focuses only on the file contents and traditional UGO (User, Group, Other) bits. Because ACLs exist as "extended attributes" stored in the filesystem metadata, a naive backup process will often strip these permissions away, leaving your files accessible to the wrong users once restored.
Reliable Preservation Techniques
To migrate or back up data while keeping ACLs, you must use tools that explicitly support extended attributes.
1. Using rsync
The rsync utility is the industry standard for this task. By default, it ignores ACLs, but the -A (or --acls) flag forces the tool to preserve them.
# Sync files from source to destination while keeping ACLs
rsync -avA /source/directory/ /backup/directory/
2. Using getfacl and setfacl for exports
If you need to archive permissions separately (for example, to version control your security policy or apply it to a fresh filesystem), you can export the ACL configuration into a flat text file:
# Save all ACLs in a directory to a file
getfacl -R /path/to/data > permissions_backup.acl
# Restore the ACLs later using setfacl
setfacl --restore=permissions_backup.acl
Why This Matters
If you migrate a shared project folder from an old server to a new one and forget to preserve these attributes, you effectively "reset" the security of the files to the basic UGO defaults. This can lead to sensitive data being exposed to users who were previously restricted by an ACL, or conversely, it can lock out authorized collaborators who relied on named user entries to access the directory. Always verify that your backup workflow includes the -A flag or a similar metadata-preservation mechanism before performing major filesystem maintenance.
Key Takeaway: Standard copy commands ignore extended attributes; always use tools like rsync -A or getfacl/setfacl to ensure your defined ACLs survive the migration process.