OneDrive Will Not Sync One File: The Name Is Usually Why
Everything else syncs and this one does not. Nine times in ten it is the name or the path, and the failure is silent by design.
The symptom
Every other file in the folder syncs normally. One file stays put, shows no error, and never appears on your other devices.
Work down this list, not through it
Ordered by how often it turns out to be the cause. Run the check in the middle column before you change anything — each one takes under a minute, and it tells you whether that row is your problem or not.
| Cause | Confirm it’s this one | Fix |
|---|---|---|
| A restricted character in the name Most common | Look at the name for any of " * : < > ? / \ | and for a space at the very start or very end. | Rename the file, replacing the character with a hyphen. The file syncs within seconds of the rename. Microsoft lists " * : < > ? / \ | as unusable in a name, and states leading and trailing spaces are not allowed. |
| The full path is over 400 characters Very common in shared libraries | Copy the full path from the address bar and count the characters. Paste it into our checker if you would rather not count. | Shorten a folder name high in the tree rather than the file name - it fixes every file underneath at once. Microsoft: "The entire decoded file path, including the file name, can't contain more than 400 characters." |
| The file was created on a Mac Common in mixed teams | Ask where the file came from. If a colleague on macOS made it, check the name for a colon or a pipe. | Rename it. macOS will let you keep the name; the service will not. Microsoft notes the restricted characters "are supported on macOS", so a Mac creates the file happily and only the sync fails. |
| A reserved name Rare but absolute | Is the name, or the part before the extension, one of CON, PRN, AUX, NUL, COM0-COM9, LPT0-LPT9, .lock or desktop.ini? | Rename it to anything else. There is no setting that permits these. Microsoft lists these as names that cannot be used. Most are MS-DOS device names still reserved today. |
| The file is a temporary or lock file Often misread as a fault | Does the name end in .tmp, or start with ~$? | Nothing to fix - but if you were relying on sync to back up a .tmp working file, it is not being backed up. Microsoft states temporary TMP files will not be synced to OneDrive, and any file name starting with ~$ is excluded. |
| The file is over the size limit Rare | Check the file size. The documented maximum is 250 GB. | Split the file, or move it by another route. Microsoft documents a 250 GB maximum upload size for OneDrive and SharePoint. |
The reason this is frustrating rather than merely annoying is that nothing tells you anything.
There is no error dialog. No red mark on the file. The sync icon reports everything is up to date, because from the client's point of view everything is up to date — the file it cannot accept is simply not part of the set it is tracking.
So people reasonably conclude the software is broken, and start doing the things you do to broken software. Restart. Reinstall. Unlink the account and wait four hours for 200 GB to come back down. None of which touches the actual cause, which is sitting in the file name where anyone could read it.
Rename the folder, not the file
This is the single most useful thing on this page, and it is the opposite of what most people try.
When a path is too long, the instinct is to shorten the file name. You gain a dozen characters and fix that one file. The next file in the same folder is still over the line, so you shorten that one too, and gradually you accumulate a folder full of cryptic abbreviations.
Shorten a folder name near the top of the tree instead. Changing
2026 Client Projects and Proposals to 2026 Clients removes 26
characters from every path beneath it. Hundreds of files fixed with one edit, and everything
that was hovering just under 400 gets breathing room at the same time.
It takes ten seconds and it is structural rather than cosmetic.
The macOS asymmetry
Worth understanding properly, because it produces an argument in every mixed team.
Microsoft notes the restricted characters are supported on macOS. A designer on a Mac
names a file Brand: v2 <final>.ai and nothing objects. Finder shows it. It
opens. It sits in the shared folder looking entirely normal on their screen.
On Windows it never arrives, and the Windows user is told the file "was never shared". Both people are looking at accurate information about their own machine and drawing opposite conclusions.
If you work across both, this is worth saying out loud once to the whole team rather than rediscovering monthly.
Skipped is not the same as blocked
There is a distinction inside the rules that changes what you should do about it.
A file with an illegal character is rejected. A .tmp file is
skipped — Microsoft states temporary TMP files will not be synced.
Rejected is a problem to fix. Skipped is by design, and the danger is different: if an
application writes its working file as .tmp and you have been assuming cloud sync
covers it, that file has never once been backed up, and nothing has ever indicated that.
Files beginning ~$ are the same category. Those are Office lock files, and seeing
them usually means a document is open somewhere — occasionally on a machine in an office nobody
has visited since last year.
Names inherited from 1981
CON, PRN, AUX, NUL, COM1 through
COM9, LPT1 through LPT9.
These are MS-DOS device names. CON was the console, LPT1 was the
printer port. They have been reserved for four decades and remain so, which is why
CON.txt fails exactly as CON does — the extension is irrelevant.
Mostly harmless trivia, until a naming convention produces one by accident. Anyone with a
product line coded AUX, or a contact list with a surname of Aux, will
meet this eventually and have no idea why one row of an export refuses to save.
Check before you escalate
The order on this page is deliberate. The first two causes account for the overwhelming majority, cost nothing to check, and are fixed in seconds. Unlinking an account is at the bottom of the escalation list because it costs hours and fixes almost none of these.
If you would rather not count characters by hand, paste the name and path into our checker — it tests every rule above at once, in your browser, and tells you which one you have hit.
If it is still broken
- Check the file is not open in another application, including on a computer you have forgotten is switched on.
- Confirm you are not out of storage - a full account stops new uploads without a per-file error.
- Pause and resume sync from the OneDrive icon in the system tray or menu bar. This is the only "have you tried turning it off" step worth doing early.
- Copy the file out of the OneDrive folder, delete the original, and copy it back under a new name. This defeats any state attached to the old entry.
- If several files in one folder are affected rather than one, suspect the folder path rather than the files, and re-check the 400-character limit at the folder level.
- Only then consider unlinking and relinking the account, which re-downloads everything and is slow enough to be a last resort rather than a first one.
What we could not verify
- Whether the 400-character limit counts the tenant URL for SharePoint libraries or only the path below it.
- Whether OneDrive surfaces a per-file error anywhere in its interface when a name is rejected, or fails silently in all cases.
- Whether the restricted-character list differs between personal OneDrive and OneDrive for work or school.
- How long a rejected file remains in a pending state before the client stops retrying it.
Open questions rather than criticisms. Where the vendor does not publish an answer we say so instead of filling the gap with a plausible guess, because a confident wrong answer is worse here than no answer.
Questions people ask
Why is one file not syncing when everything else works?
Almost always the name or the path rather than the account. A restricted character, a reserved name, a ~$ prefix or a path over 400 characters will each stop a single file while everything around it syncs normally. Because the rejection is usually silent, the file simply never arrives.
Is the OneDrive path limit 260 or 400 characters?
Four hundred. Microsoft states the entire decoded file path including the file name cannot contain more than 400 characters. The 260 figure is the old Windows MAX_PATH, a separate operating system limit. Quoting the wrong one leads people to conclude they are safely under when they are not.
Which characters are not allowed in a OneDrive file name?
Why does the file sync on my Mac but not on Windows?
Because macOS permits characters the service refuses. Microsoft notes explicitly that the restricted characters are supported on macOS. So the file is created without complaint, looks fine locally, and fails when it meets OneDrive or a Windows client.
Should I unlink and relink my OneDrive account to fix this?
Not first. Relinking re-downloads your whole account, takes hours on a large one, and does nothing at all if the cause is a character in a file name. Check the name and the path length before you take an action measured in hours to solve a problem measured in seconds.
Where this information comes from
Product details change often. Each item below links to the primary source we checked, so you can confirm anything that matters to your decision.
Vendors change limits and interfaces without announcing it. If a step here no longer matches what you see, tell us and we will re-check it.