Hidden Files and File Extensions in Ubuntu

A filename contains more information than the words you first notice. Its ending can suggest the file type, while a dot at the beginning can keep it out of the normal Files view.

Those two dots mean different things.

Read the extension at the end

A file extension is the ending after the final dot in many filenames.

• notes.txt is normally plain text.
• index.html contains HTML markup.
• styles.css contains CSS rules.
• app.js contains JavaScript.
• types.ts contains TypeScript.
• archive.zip is a compressed archive.
• installer.deb is a Debian package file used by Ubuntu and related systems.

The extension is a useful clue, not proof that the contents are safe or correctly formatted. Renaming photo.jpg to photo.txt changes the name; it does not convert the picture into text.

Applications often use the extension to decide how to open a file. Keep it when renaming unless you deliberately understand the format change.

A leading dot makes a hidden name

Linux desktop tools normally hide names that begin with a dot.

notes.txt is visible in an ordinary folder view.

.notes.txt is a different filename, and Files normally hides it.

Press Ctrl + H in Files to toggle Show Hidden Files. Hidden items appear, often with a lighter visual treatment. Press the shortcut again to return to the usual view.

Why Ubuntu has hidden folders

Applications keep many per-user settings inside hidden locations.

• .config commonly stores application configuration.
• .local commonly stores per-user data and files.
• .bashrc is a shell configuration file that later terminal lessons may discuss.

You do not need to remove these items to keep Home tidy. Hiding reduces visual clutter while leaving applications access to their settings.

Practice with a harmless file

Inside the File practice folder from the previous lesson, create or choose a disposable text file named visible.txt.

Rename it to .visible.txt. It should disappear from the ordinary view.

Press Ctrl + H, find the file, and rename it back to visible.txt. Toggle hidden files off again.

If the file does not disappear, check that the dot is the very first character and that Show Hidden Files is currently off.

Ubuntu filenames are case-sensitive

Notes.txt and notes.txt can be two different files on a typical Ubuntu filesystem.

This can surprise someone coming from a system that treats the names as equal. Pay attention to uppercase and lowercase letters when linking web files too: Styles.css and styles.css may not refer to the same file.

Case behavior can differ on a USB formatted for another operating system. Use the behavior of the actual destination instead of assuming every drive follows the same rules.

Names with several dots

Only the final ending normally acts as the extension. In lesson.notes.txt, the common extension is .txt; the earlier dot is part of the descriptive name.

A name beginning with a dot can still have an extension. .settings.json is hidden because it starts with a dot and suggests JSON content because it ends in .json.

Common mistakes

Thinking Ctrl + H deleted files. It only toggles whether hidden items are displayed.

Removing an extension while renaming. Rename the file again and restore the correct ending.

Adding a dot at the end instead of the beginning. Hidden names start with ., as in .notes.txt.

Editing .bashrc from an unrelated guide. It changes shell behavior and belongs in later terminal material. Leave it unchanged until the purpose and recovery steps are clear.

Assuming capitalization never matters. Copy the exact name when a web page or application refers to a file.

What to learn next

Continue to Use USB Drives and External Storage in Ubuntu to see how Files represents storage outside Home.