Filesystem Features

Extended Attributes

Filesystems support extended attributes (xattr). Extended attributes associate metadata not interpreted directly by the filesystem with files.

There are four flags that can be set on files/directories to modify the extended attributes:

• i: Immutable, cannot be modified/deleted/renamed and no hardlink.
• a: Append-only. Can only be opened for writing and appending.
• d: no dump. Files with this flag will be ignored when dump program is run.
• A: access time (atime) of the file will not be updated.

Only the superuser can modify these flags.

We can use lsattr to list and chattr to modify file/directory xattr.

There are four namespaces:

• user
• trusted
• security - used by SELinux.
• system - Used to access Access Control Lists (ACLs)

Quota

Linux allows to control filesystem usage for users/groups.

sudo apt install quota

quotacheck
quotaon
quotaoff
edquota
quota

Quota operations require the existence of the files aquota.user and aquota.group in the root directory of the filesystem using quotas.