Linux File Permissions

Status: draft · Confidence: low (0.43) · Basis: verified_sources

Quality notes: generic_source_homepage, no_verified_sources, partial_source_verification

## TL;DR

Linux file permissions use a 3-tier model: Owner, Group, Others — each with Read (r=4), Write (w=2), Execute (x=1) permissions. Permission bits: `rwxr-xr--` means owner can read/write/execute, group can read/execute, others can read. `chmod 755 file` sets these numerically.

## Core Explanation

Octal notation: `chmod 755` = rwxr-xr-x. Special bits: setuid (4000, run as file owner), setgid (2000, run as group), sticky bit (1000, only owner can delete — used on /tmp). `chown user:group file` changes ownership. Default permissions: umask (subtracted from 666 for files, 777 for dirs). ACL (setfacl/getfacl) provides per-user permissions beyond owner/group/other.

## Further Reading

- [Linux Documentation Project — File Permissions](undefined)

## Related Articles

- [File Systems: FAT, NTFS, ext4, ZFS — Design, Performance, and Reliability](../file-systems-fat-ntfs-ext4-zfs-design-performance-and-reliability.md)
- [Linux Kernel Modules](../linux-kernel-modules.md)
- [Linux Kernel: Process Scheduling, Memory Management, and System Calls](../linux-kernel-process-scheduling-memory-management-and-system-calls.md)