Case sensitivity determines whether uppercase (FOO.txt) and lowercase (foo.txt) letters are handled as distinct (case-sensitive) or equivalent (case-insensitive) in a file name or directory.

• Case-sensitive: FOO.txt ≠ foo.txt ≠ Foo.txt
• Case-insensitive: FOO.txt = foo.txt = Foo.txt

Differences between Windows and Linux case sensitivity

When working with both Linux and Windows files and directories, you may need to adjust how case sensitivity is handled.

Standard behavior:

• Windows file system treats file and directory names as case-insensitive. FOO.txt and foo.txt will be treated as equivalent files.
• Linux file system treats file and directory names as case-sensitive. FOO.txt and foo.txt will be treated as distinct files.

The Windows file system supports setting case sensitivity with attribute flags per directory. While the standard behavior is to be case-insensitive, you can assign an attribute flag to make a directory case sensitive, so that it will recognize Linux files and folders that may differ only by case.

This may be especially true when mounting drives to the Windows Subsystem for Linux (WSL) file system. When working in the WSL file system, you are running Linux, thus files and directories are treated as case-sensitive by default.

Change the case sensitivity of files and directories

The following steps explain how to change a directory on the Windows file system so that it is case-sensitive and will recognize files and folders that differ only by case.

Inspect current case sensitivity

To check if a directory is case sensitive in the Windows filesystem, run the command:

fsutil.exe file queryCaseSensitiveInfo <path>

Replace<path> with your file path. For a directory in the Windows (NTFS) file system, the<path> will look like:C:\Users\user1\case-test or if you are already in theuser1 directory, you could just run:fsutil.exe file setCaseSensitiveInfo case-test

Modify case sensitivity

Support for per-directory case sensitivity began in Windows 10, build 17107. In Windows 10, build 17692, support was updated to include inspecting and modifying the case sensitivity flag for a directory from inside WSL. Case sensitivity is exposed using an extended attribute namedsystem.wsl_case_sensitive. The value of this attribute will be 0 for case insensitive directories, and 1 for case sensitive directories.

Changing the case-sensitivity of a directory requires that you runelevated permissions (run as Administrator). Changing the case-sensitivity flag also requires “Write attributes”, “Create files”, “Create folders” and “Delete subfolders and files” permissions on the directory.See the troubleshooting section for more about this.

To change a directory in the Windows file system so that it is case-sensitive (FOO ≠ foo), run PowerShell as Administrator and use the command:

fsutil.exe file setCaseSensitiveInfo <path> enable

To change a directory in the Windows file system back to the case-insensitive default (FOO = foo), run PowerShell as Administrator and use the command:

fsutil.exe file setCaseSensitiveInfo <path> disable

A directory must be empty in order to change the case sensitivity flag attribute on that directory. You cannot disable the case sensitivity flag on a directory containing folders/files whose names differ on only by case.

Case sensitivity inheritance

When creating new directories, those directories will inherit the case sensitivity from its parent directory.

Case sensitivity options for mounting a drive in WSL configuration file

Case sensitivity can be managed when mounting a drive on the Windows Subsystem for Linux using the WSL config file. Each Linux distribution that you have installed can have it's own WSL config file, called/etc/wsl.conf. For more information about how to mount a drive, seeGet started mounting a Linux disk in WSL 2.

To configure the case sensitivity option in thewsl.conf file when mounting a drive:

1. Open the Linux distribution you will be using (ie. Ubuntu).
2. Change directories up until you see theetc folder (this may require you tocd .. up from thehome directory).
3. List the files in theetc directory to see if awsl.conf file already exists (use thels command, orexplorer.exe . to view the directory with Windows File Explorer).
4. If thewsl.conf file does not already exist, you can create it using:sudo touch wsl.conf or by runningsudo nano /etc/wsl.conf, which will create the file upon saving from the Nano editor.
5. The following options are available for you to add into yourwsl.conf file:

Default setting:off for case sensitivity unavailable (all directories on mounted NTFS drives will be case insensitive).

[automount]options = case = off

Enabling case sensitivity per directory:dir

[automount]options = case = dir

Treat all directories on the (NTFS) drive as case sensitive:force

[automount]options = case = force

This option is only supported for mounting drives on Linux distributions running as WSL 1 and may require a registration key. To add a registration key, you can use this command from an elevated (admin) command prompt:reg.exe add HKLM\SYSTEM\CurrentControlSet\Services\lxss /v DrvFsAllowForceCaseSensitivity /t REG_DWORD /d 1.

You will need to restart WSL after making any changes to thewsl.conf file in order for those changes to take effect. You can restart WSL using the command:wsl --shutdown

Changing the case sensitivity on a drive mounted to a WSL distribution

NTFS-formatted drives mounted to a WSL distribution will be case-insensitive by default. To change the case sensitivity for a directory on a drive mounted to a WSL distribution (ie. Ubuntu), follow the same steps as listed above for the Windows file system. (EXT4 drives will be case-sensitive by default).

To enable case-sensitivity on a directory (FOO ≠ foo), use the command:

fsutil.exe file setCaseSensitiveInfo <path> enable

To disable case-sensitivity on a directory and return to the case-insensitive default (FOO = foo), use the command:

fsutil.exe file setCaseSensitiveInfo <path> disable

Configure case sensitivity with Git

The Git version control system also has a configuration setting that can be used to adjust case sensitivity for the files you are working with. If you are using Git, you may want to adjust thegit config core.ignorecase setting.

To set Git to be case-sensitive (FOO.txt ≠ foo.txt), enter:

git config core.ignorecase false

To set Git to be case-insensitive (FOO.txt = foo.txt), enter:

git config core.ignorecase true

Setting this option to false on a case-insensitive file system may lead to confusing errors, false conflicts, or duplicate files.

For more information, see theGit Config documentation.

Troubleshooting

My directory has files that are mixed case and require case sensitivity but Windows FS tools will not recognize these files

To use Windows file system tools to work on a Linux directory that contains mixed case files, you will need to create a brand new directory and set it to be case-sensitive, then copy the files into that directory (using git clone or untar). The files will remain mixed case. (Note that if you have already tried moving the files to a case-insensitive directory and there were conflicts, there were likely some files that were overwritten and will no longer be available.)

Error: The directory is not empty

You cannot change the case sensitivity setting on a directory that contains other files or directories. Try creating a new directory, changing the setting, then copying your mixed-case files into it.

Error: Access denied

Ensure that you have the “Write attributes”, “Create files”, “Create folders” and “Delete subfolders and files” permissions on the directory required for changing case-sensitivity. To check these settings, open the directory in Windows File Explorer (from command line, use the command:explorer.exe .). Right-click the directory and selectProperties to open the Document Properties window, then selectEdit to view or change permissions for the directory.

Error: A local NTFS volume is required for this operation

The case sensitivity attribute can only be set on directories within an NTFS-formatted file system. Directories in the WSL (Linux) file system are case sensitive by default (and cannot be set to be case insensitive using the fsutil.exe tool).

Additional resources

• DevBlog: Per-directory case sensitivity and WSL
• DevBlog: Improved per-directory case sensitivity support in WSL