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Linux Intermediate

What is ACL (Access Control List)?

An extension to standard Linux file permissions that allows setting fine-grained access rights for specific users and groups beyond owner/group/other.

Standard Unix permissions only allow three access levels: owner, group, and others. ACLs extend this by letting administrators grant permissions to any number of specific users or groups on a single file. For example, user alice can have read-write access while user bob gets read-only, without changing file ownership or group. Commands include getfacl (view ACLs), setfacl -m u:alice:rw file (set ACL), and setfacl -x u:alice file (remove ACL). Default ACLs on directories automatically apply to new files created within. ACLs require filesystem support (enabled in ext4, XFS by default).

Related Terms

SELinux
Security-Enhanced Linux — a mandatory access control system that confines programs to minimum required privileges beyond standard file permissions.
Daemon
A background process that runs continuously on a system, typically providing services like web serving or logging.
Firewalld
A dynamic firewall management tool for Linux that provides a D-Bus interface for managing firewall rules with zones.
Bash Script
A text file containing a series of shell commands that are executed sequentially by the Bash interpreter.
Systemctl
The primary command for managing systemd services, including starting, stopping, enabling, and checking service status.
SSH (Secure Shell)
A cryptographic network protocol for secure remote login and command execution over an unsecured network.
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