Operating Systems
The three families
Windows uses NTFS and often UEFI/GPT; macOS uses APFS; Linux typically uses ext4 or xfs. Account types differ in name but not spirit: Administrator, root, and sudoers have full control, while standard users do not. Linux is case-sensitive; Windows is not. Hidden files are dot-prefixed on Linux and macOS, and attribute-based on Windows.
Processes and permissions
Task Manager, Activity Monitor, top, and ps show processes; services (Windows Services, systemd, launchd) run in the background. Linux permissions use rwx for owner, group, and other; Windows uses NTFS ACLs. A 'permission denied' error usually means wrong ownership or a missing write bit, not a corrupted file.
Command line basics
cd, ls or dir, cp or copy, mv or move, rm or del, cat or type, grep or findstr, chmod, and sudo. A file extension does not guarantee content, so verify the actual file type.
Traps
- Assuming admin rights are free; UAC prompts are a security control.
- Deleting permanently when recovery may be needed instead of using trash or recycle bin.
- Confusing a service with a process.
- Forgetting 32-bit versus 64-bit compatibility.
- Editing system files without a backup.
Worked example
A Linux user cannot save to /var/www. Run ls -l and see the directory owned by root with 755 permissions. Rather than chmod 777 (a classic wrong answer), add the user to the appropriate group or correct ownership, then re-test the save.