Chrome "unknown error: Chrome failed to start: crashed" in CI

Chrome launched under WebDriver but the process crashed before it was ready. In CI the fix is almost always startup flags: --no-sandbox for root containers, --headless=new since there is no display, and --disable-dev-shm-usage for a small /dev/shm.

What this error means

Selenium fails with "unknown error: Chrome failed to start: crashed. (chrome not reachable)" or "DevToolsActivePort file doesn't exist" when launching Chrome in a container.

Chrome

selenium.common.exceptions.WebDriverException: Message: unknown error: Chrome failed to start:
crashed.
  (chrome not reachable)
  (The process started from chrome location /usr/bin/google-chrome is no longer running,
   so ChromeDriver is assuming that Chrome has crashed.)

Common causes

The sandbox cannot run as root

The container runs as root, so Chrome's sandbox fails and the process dies without --no-sandbox.

No display or too little shared memory

Without headless mode there is no display to attach to, and a tiny /dev/shm makes Chrome crash unless --disable-dev-shm-usage is set.

How to fix it

Add the standard CI Chrome flags

Pass the flags that make Chrome run headless in a root container with limited shared memory.

Python

from selenium.webdriver.chrome.options import Options
opts = Options()
opts.add_argument('--headless=new')
opts.add_argument('--no-sandbox')
opts.add_argument('--disable-dev-shm-usage')
driver = webdriver.Chrome(options=opts)

Install the browser libraries too

A crash can also come from missing OS libraries; install them so the process stays up.

Terminal

sudo apt-get update
sudo apt-get install -y libnss3 libgbm1 libasound2

How to prevent it

Always run headless in CI with --headless=new.
Pass --no-sandbox for root containers and --disable-dev-shm-usage for small /dev/shm.
Install Chrome's OS libraries so the process does not crash at startup.