How to set file permissions in WSL (Windows Subsystem for Linux)

What is WSL?

Windows Subsystem for Linux (WSL) lets you run a Linux environment directly on Windows — including tools like grep, sed, awk, and SSH. This guide uses Ubuntu 18 on Windows 10.

The Problem

If you run chmod inside WSL to set permissions on a file (e.g., a .pem key), the change doesn’t stick. Windows and Linux handle permissions differently, so WSL ignores chmod by default unless you configure it to respect Linux metadata.

For SSH keys (.pem, .cer), you typically need permissions set to 600 (rw-------). Without the fix below, you’ll see “permissions are too open” errors.

Fix: Enable metadata in WSL

Step 1: Create or edit /etc/wsl.conf

sudo nano /etc/wsl.conf

Add the following:

[automount]
enabled  = true
root     = /mnt/
options  = "metadata,umask=22,fmask=11"

Save with Ctrl + X, then Y, then Enter.

Step 2: Shut down WSL

Open a regular Windows Command Prompt (not WSL) and run:

wsl --shutdown

Step 3: Apply permissions

Re-open Windows Terminal, switch to Ubuntu, then set your permissions:

chmod 600 mykey.pem

Step 4: Verify

ls -l mykey.pem

You should see:

-rw------- 1 user group ... mykey.pem

Reference links

1. Setup WSL on Windows
2. Reset WSL distro password
3. Get Windows Terminal
4. Understanding Linux file permissions
5. chmod in WSL doesn’t work — Stack Overflow