File and directory permissions

Not running Starting usually ~20 s

Step 6 of 6 · summary · 2 min

Summary

A file's permissions are three rwx triples: for the owner, for the group, and for others.
A process gets one triple, in order: owner, group, others; triples do not add up.
On a directory r opens the list of names, x lets you pass to files by name, and w creates and deletes names.
The report at the start of the lesson was yours, and your cat got the empty owner triple ---; www-data read it through the others triple r--.

Articles

Basic file commands — Navigation and files — ls, cd, cp, mv, rm, cat, less, head, tail, terminal copy-paste.
ls — list directory contents — The ls command lists files and directories with permissions, owner, size and modification time, hidden ones too.
stat — file metadata — Full file information — size, permissions, owner, timestamps (atime/mtime/ctime), inode.
Paths — basename, dirname, realpath — Splitting a path into a name and a directory, getting an absolute path; a script's own directory.
File permissions — The Unix permission model — read/write/execute, owner/group/other, special bits.
namei — permissions at every step of a path — The namei command walks a path part by part and shows the type, mode and owner of each directory down to the file.
Users and groups — Linux accounts and groups; usermod -G without -a replaces all of a user's supplementary groups instead of adding one.
Extended permissions (ACL) — Flexible rights beyond rwx — getfacl/setfacl, per-user and per-group grants.
Processes — Viewing processes, signals and priorities; finding the processes that hog CPU or memory.
sudo — running commands as another user — Grants temporary root rights via sudoers; edit the file only through visudo, or a mistake locks everyone out of sudo.

Ubuntu 24.04