1. Reading and Converting Permission Modes
Every file and directory on a Linux system carries a permission mode made of three permission classes — owner, group, and other — each expressed as a string of read (r), write (w),...
Read full chapter →The essential Linux File Permissions And Chmod Patterns cheat sheet: 6 concise chapters you can read in minutes, distilled from the full deck. When you're ready, drill the flashcards or test yourself under exam conditions.
Every file and directory on a Linux system carries a permission mode made of three permission classes — owner, group, and other — each expressed as a string of read (r), write (w),...
Read full chapter →The standard rwx bits cover most situations, but Linux also defines three additional flags that change the meaning of executable files and shared directories. The setuid bit, set w...
Read full chapter →Permissions only tell half the story; the other half is who owns a file. Ownership is changed with chown user:group path, optionally with -R to descend into subtrees, and with chgr...
Read full chapter →A handful of well-known system files have modes that look surprising on first contact, but each has a clear reason. SSH is the strictest case: the ~/.ssh directory must be 700 and...
Read full chapter →The classic user/group/other model is sufficient for many systems, but it cannot grant access to a fourth specific user without making the file world-readable. POSIX ACLs solve thi...
Read full chapter →When permissions behave unexpectedly, several layered tools help diagnose the cause. To find setuid binaries — both for auditing and for spotting potential privilege-escalation pat...
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