Here’s a practical, step-by-step guide to migrate your files when switching to a new operating system. It covers planning, methods, and important things to check so you don’t lose data or time.

1. Plan before you touch anything

• Inventory what you need: documents, photos, videos, email, browser data, app settings, virtual machines, game saves, licenses/activation keys, and printer/scanner settings.
• Estimate total size to choose transfer method (external drive or cloud).
• Decide whether you’ll dual-boot, wipe the old system, or keep the old device as an archive.

2. Back up everything (mandatory)

• Make at least one full backup of your current system before migrating. Prefer 2 copies if possible (external drive + cloud).
• For Windows: use File History or make a system image.
• For macOS: use Time Machine.
• For Linux: use rsync or a disk image tool (dd, Clonezilla) for a full snapshot.

3. Choose a transfer method

• External drive (fast and simple): copy files to an external HDD/SSD or USB drive. Good for large amounts of data.
• Network transfer (fast on LAN): use SMB, AFP, SFTP, rsync, or built-in migration utilities across the local network.
• Cloud storage (Dropbox, Google Drive, OneDrive, iCloud): convenient and cross-platform, but can be slow and may cost for large storage.
• Direct cable (USB/Thunderbolt/ethernet): some OSs support direct transfers (Windows Easy Transfer alternatives, Migration Assistant for macOS).
• Disk cloning (if keeping same partition layout): clone the drive, then adjust partitioning/format as needed.

4. Use OS migration tools when available

• macOS Migration Assistant: migrates user accounts, files, apps, and settings from another Mac or Windows.
• Windows (fresh install): use OneDrive for files and Microsoft account sync for some settings; third-party tools exist for deeper migration.
• Linux: no single universal GUI migration tool—use rsync, tar, or crontab to copy home directories and configs.

5. Copy files and data (practical tips)

• Preserve timestamps and permissions: use tools that keep metadata (rsync -a on Linux/macOS, robocopy /COPYALL on Windows).
• For large photo/video libraries, copy the entire folder structure rather than exporting from each app.
• For email: export mailboxes (e.g., .pst for Outlook, Mailbox/mbox for many clients) or reconfigure accounts in the new OS and let mail sync if accounts are IMAP/Exchange.
• Browser data: sign in to browser (Chrome/Edge/Firefox) and enable sync; otherwise export bookmarks and passwords (use a password manager or browser export).
• Application settings: copy config files (~/Library on macOS, %APPDATA% on Windows, ~/.config on Linux) when possible. Not all app settings are cross-platform.

6. Handle licenses and activations

• Deactivate or sign out of software that limits activations (Adobe, Microsoft Office, some games) before wiping the old OS. Keep license keys and account info handy.

7. Deal with file system and permission differences

• Windows uses NTFS/ExFAT; macOS uses APFS/HFS+ or can read/write exFAT; Linux commonly uses ext4. Use exFAT for cross-platform read/write support on removable drives (beware performance/security).
• Long filenames, reserved characters, and case sensitivity differ—watch for filename clashes (e.g., ":" not allowed on Windows).
• If migrating to a case-sensitive filesystem, test apps (some macOS apps break on case-sensitive APFS).

8. Migrate hidden/advanced items if needed

• SSH keys (~/.ssh), GPG keys, cron jobs, VPN configs, Docker images/containers, virtual machines (export/import), and developer environments (node_modules can be reinstalled; note global packages).
• For databases, perform proper exports (mysqldump, pg_dump) and import into the new system.

9. Validate after transfer

• Check random samples of files open correctly (photos, documents, spreadsheets).
• Verify file counts and total size match (or understand why they differ).
• Test key apps, printers, scanners, and network shares.
• Keep the old system untouched until you confirm everything is migrated successfully.

10. Clean up and secure

• If you’re selling or disposing the old device, securely erase the drive (Windows: full disk wipe or factory reset; macOS: erase with Disk Utility; Linux: shred or secure-erase tools).
• Remove accounts and deauthorize services.
• Consider encrypting backups and enable full-disk encryption on your new OS (BitLocker, FileVault, LUKS).

Quick command examples

• rsync (Linux/macOS) preserving attributes: rsync -aHAX --progress /source/path/ /destination/path/
• robocopy (Windows) preserving metadata: robocopy "C:\Source" "D:\Destination" /MIR /COPYALL /R:2 /W:5
• Copy on macOS preserving resource forks: ditto /Source/ /Destination/

Common pitfalls

• Forgetting to export email or license keys.
• Using FAT32 for big files (max 4 GB). Use exFAT or NTFS/HFS+/APFS.
• Overlooking hidden files (dotfiles) that hold app settings.
• Assuming cloud sync moves everything (some local-only app data won’t sync).

Simple checklist (short)

• [ ] Full backup made (external + cloud if possible)
• [ ] Inventory created (files, apps, licenses)
• [ ] Transfer method chosen and tested with small set
• [ ] App licenses deactivated on old machine
• [ ] Files transferred with metadata preserved
• [ ] Key apps and files tested on new OS
• [ ] Old drive securely erased (if disposing)

If you tell me which OS you're moving from and to (Windows → macOS, macOS → Linux, Windows → Linux, etc.) and the approximate data size, I can give tailored commands and the fastest recommended method.