immutabilityflags

Immutability flags are metadata attributes attached to a resource that mark it as immutable, meaning it cannot be modified, deleted, or renamed through ordinary operations while the flag is set. They are used to protect data integrity, support compliance requirements, and prevent tampering.

In file systems, immutability flags are commonly implemented as inodes or metadata bits. On Linux file systems such as ext4, the immutable flag can be set with the chattr +i command and cleared with chattr -i; while set, most write, rename, or unlink operations are blocked except by privileged processes. There is also an append-only flag, chattr +a, which restricts modifications to append-only changes. On BSD-derived systems and macOS, the equivalent is the chflags tool with the uchg (user immutable) flag. These mechanisms are kernel-enforced and typically require elevated privileges to modify.

Outside traditional file systems, immutability flags appear in data stores and backup architectures to enforce write-once, read-many (WORM) behavior or time-based immutability policies. Some databases and object stores offer immutable or protected states for records or objects to meet legal or regulatory retention requirements. In versioning and content-addressable storage, immutability can be achieved by designating certain objects as unmodifiable after creation.

Limitations and risks include the fact that privileged users or kernel faults can override flags, and certain operations (snapshots, backups, or filesystem repairs) may bypass or diff er from active flags. Immutability flags are a layer of protection, not a complete security solution, and should be complemented with access controls and auditing. See also: file attributes, chattr, chflags, immutable storage, and WORM.