Linux Permissions Unleashed: A Deep Dive into Access Control Lists (ACLs)

"How do you grant write access to a file to just one specific user who isn't the owner and isn't in the owning group? How do you allow two different groups read access, but only one of them write access? How do you ensure files created in a shared directory automatically get specific permissions for a certain team?"

"Trying to juggle group memberships for these cases quickly becomes a nightmare. This is where Access Control Lists (ACLs) come in. They provide a more flexible, fine-grained permission mechanism that extends the traditional ugo/rwx model."

"We have already discussed in the previous two articles about file and folder permissions along with special permissions that are supported in linux. The permissions are effective for many scenarios. But what happens when you need more granularity?"

Standard Linux file and folder permissions and special bits (setuid, setgid, sticky) handle many common access needs but lack fine-grained flexibility for certain scenarios. Examples include granting write access to a single non-owner user, giving read access to two different groups while allowing write to only one, and ensuring newly created files in shared directories inherit specific team permissions. Managing these cases through group membership alone becomes complex and error-prone. Access Control Lists (ACLs) provide a more flexible, fine-grained permission mechanism that extends the traditional ugo/rwx model, allowing per-user and per-group permissions beyond the single owner and group.

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