- Error number
- 5120
- Severity
- 16 (user-correctable error)
- State
- 101
- Product
- Microsoft SQL Server Database Engine
- Versions
- All supported SQL Server versions (2016 to 2025), Azure SQL Managed Instance
- Category
- Database State & Recovery
- Last reviewed
- 23 October 2026
On this page
What it means
Error 5120 means SQL Server tried to open an existing database file (to attach it, bring a database online or start it) and Windows refused; the operating system error number in the message says why.
SQL Server opens database files itself, on the server, as the SQL Server service account (for an attach, sometimes while impersonating your Windows login). When Windows returns an error, SQL Server reports 5120 with the path and the operating system error, and the statement that needed the file fails: an attach is followed by 1802, a SET ONLINE by 5181 and 5069. At service startup the same failure leaves the database unusable, and every later attempt to use it fails with error 945.
Read the number after Operating system error: 2 means the file is not at that path, 5 means access is denied (the most common case after copying files from another server or a user folder), and 32 means another process has the file open. If the folder itself does not exist, SQL Server reports 5133 instead.
Common causes
- The path is wrong or the file was moved, renamed or deleted (OS error 2). Remember the path is on the server, not on your workstation.
- The SQL Server service account (or your impersonated login) has no permission on the file, for example .mdf files copied from another server, downloaded, or kept in a user profile folder (OS error 5).
- A file that was detached keeps restrictive permissions, so reattaching it from a network share fails (OS error 5, documented by Microsoft).
- The file is open in another process: another instance still has it attached, or a backup or antivirus tool holds it (OS error 32).
- The file is marked read-only or is on read-only or compressed media.
Diagnose it
Read-only These queries only read metadata and dynamic management views. They do not change data, permissions or configuration, so they are safe to run first.
Which account opens the files?
SELECT servicename, service_account
FROM sys.dm_server_services;The account of the SQL Server service. It needs read and write permission on the file and its folder; compare with the permissions on the instance default data folder.
Where are the files the database expects?
SELECT DB_NAME(database_id) AS database_name, type_desc, physical_name, state_desc
FROM sys.master_files
WHERE database_id = DB_ID(N'AppDb');For an existing database, the exact paths SQL Server opens. Compare them with where the files really are on the server.
Read every 5120 in the error log
EXEC sp_readerrorlog 0, 1, N'Unable to open the physical file';Each failed open with its path and operating system error, including failures at service startup that no client saw.
How to fix it
Each fix is labelled with what it changes. Try read-only checks and the least invasive fix first, and test changes outside production.
Correct the path
Client or network sideFor OS error 2, check on the server that the file exists at exactly the path in the message, and fix typos or the drive letter. For an existing database whose files were moved, point the catalogue at the new path with ALTER DATABASE ... MODIFY FILE and then SET ONLINE (see error 945).
Give the service account access to the file
Changes permissionsFor OS error 5, grant the SQL Server service account Full control on the .mdf, .ndf and .ldf files and their folder, or move the files into the instance data folder, which already has the right permissions. Remove the read-only attribute if it is set.
Caution: Grant access to the service account only. Opening database files to Everyone or Users exposes all the data in them.
Release the file from the other process
Client or network sideFor OS error 32, find what has the file open: another SQL Server instance (detach it there first), a copy still running, or an antivirus or backup agent. Exclude database files from antivirus scanning.
Retry the attach
Changes database stateOnce the files are in place and accessible, attach them again, listing the data file and the log file.
CREATE DATABASE AppDb
ON (FILENAME = N'D:\SqlData\AppDb.mdf'),
(FILENAME = N'D:\SqlData\AppDb_log.ldf')
FOR ATTACH;Examples
Attaching a file that is not in the folder
-- C:\Users\Public exists, but AppDbArchive.mdf is not in it
CREATE DATABASE AppDbArchive
ON (FILENAME = N'C:\Users\Public\AppDbArchive.mdf')
FOR ATTACH;Msg 5120, Level 16, State 101, Line 2 Unable to open the physical file "C:\Users\Public\AppDbArchive.mdf". Operating system error 2: "2(The system cannot find the file specified.)". Msg 1802, Level 16, State 7, Line 2 CREATE DATABASE failed. Some file names listed could not be created. Check related errors.
Reproduced on SQL Server 2025 (17.0.1145.4), 23 October 2026.
How to prevent it
Keep database files in folders created for SQL Server (the instance default data and log folders, or folders given the same permissions), never in user profiles or download folders. When moving databases between servers, prefer BACKUP and RESTORE over copying files: a restore creates files with the right owner and permissions.
Change the service account only through SQL Server Configuration Manager, which updates file permissions, and alert on databases that are not ONLINE after a restart.
Common questions
Why do I get access denied when I can open the file myself?
SQL Server opens the file as its service account (or, for some attach operations, by impersonating your login), on the server. Your own access in Explorer does not count; give the service account permission on the file and folder.
Can I attach a .mdf file without its .ldf file?
Only if the database was shut down cleanly; then CREATE DATABASE ... FOR ATTACH_REBUILD_LOG can create a new log. If the database was not shut down cleanly, the missing log means lost transactions, so restore from backup instead.
What is the difference between 5120 and 5133?
Error 5120 is raised when an existing file cannot be opened. Error 5133 is raised when the folder in the path cannot be looked up, for example because it does not exist.
Learn more on CodeWithSQL
Official documentation
Last technically reviewed 23 October 2026; examples and diagnostics run on SQL Server 2025 (17.0.1145.4). Message text checked against the engine's sys.messages catalogue.