Start with the failure type. If SeleniumBase UC Mode starts on a GUI-less Linux host but the site shows a CAPTCHA, block page, or HTTP 429, you have a site-side challenge. If a WebDriver command returns “connection refused,” you likely have a local display or driver-startup problem. For UC Mode on a server without a desktop, the first configuration to test is SeleniumBase’s SB() context manager with Xvfb—not headless mode:
from seleniumbase import SB
with SB(uc=True, xvfb=True) as sb:
sb.uc_open_with_reconnect("https://example.com", reconnect_time=4)SeleniumBase documentation warns that UC Mode is detectable in headless mode. A project maintainer’s February 17, 2026 answer to a Linux connection-refused report also says that Driver() lacks the special Xvfb code needed on GUI-less Linux and recommends SB() instead.
First identify what “detected” means
Do not change several launch flags before recording the exact symptom. “Detection failure” commonly refers to four different problems:
- Challenge after navigation: the browser opens, then the site displays a CAPTCHA, challenge page, block page, or 429 response.
- Connection refused: UC Mode launches or appears to launch, but the first WebDriver command cannot connect locally.
- GUI helper failure: PyAutoGUI or a CAPTCHA helper needs a display that a headless server does not provide.
- Driver or browser startup failure: Chrome never starts, exits immediately, or SeleniumBase cannot create a session.
Save the Linux distribution, container image, SeleniumBase and Python versions, browser name and version, UC setting, headless/headed/Xvfb settings, the first failing command, and the complete exception or HTTP response. This separates a local launch fault from a site rejecting an otherwise working browser.
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Use SB() with Xvfb for UC Mode on GUI-less Linux
A server can run a normal, headed browser inside a virtual X display. Xvfb supplies that display without a physical monitor. SeleniumBase exposes it with xvfb=True in Python or --xvfb in command-line runs.
Python context-manager example
from seleniumbase import SB
with SB(uc=True, xvfb=True) as sb:
sb.uc_open_with_reconnect("https://example.com", reconnect_time=4)
print(sb.get_title())Use the current option names accepted by your installed SeleniumBase version. The project’s Linux examples use the SB context-manager form for UC Mode. Do not combine UC Mode with headless mode when your goal is to avoid the documented headless detectability warning.
Why Driver() can fail here
In Discussion #4245, maintainer mdmintz wrote on February 17, 2026: “The Driver() format doesn’t have the special Xvfb virtual display code that’s needed when running on a GUI-less Linux machine.” The next sentence recommends using SB() for UC Mode on such a machine. This addresses the reported connection-refused case; it is not a promise that every website will accept the resulting browser.
Command-line form
pytest test_file.py --uc --xvfbKeep the rest of the launch configuration unchanged while testing. SeleniumBase’s current command-line help is the authority for flags in your installed release; copied options from old issues may no longer match.
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Headless versus Xvfb
| Choice | What it provides | When to test it | Important limitation |
|---|---|---|---|
| Headless | No graphical display | Workloads that do not need GUI interaction and where the target permits headless browsers | SeleniumBase warns that UC Mode can be detected in headless mode; PyAutoGUI does not work headlessly |
| Xvfb | A virtual display for a regular browser | GUI-less Linux, UC Mode, PyAutoGUI, or GUI-based CAPTCHA helpers | It changes display availability, not the target site’s rules |
A headed setting alone does not prove that a display exists. Confirm that Xvfb is actually active and that the browser is attached to it. SeleniumBase’s SB manager includes special virtual-display support for GUI actions.
Check Chrome and Chromium in Docker
Container images frequently include Chromium even when examples assume Google Chrome. In a February 2024 Docker discussion, the maintainer said Chrome and Chromium differed in that UC Mode context: the modified driver did not fully mask traces with Chromium, while the maintainer reported that it did with Chrome. Treat this as a controlled diagnostic lead, not a universal rule for every browser version or site.
- Record the browser binary and version inside the container.
- Run the same SeleniumBase version, UC setting, display mode, URL, and network conditions with Chrome.
- Repeat with Chromium while changing nothing else.
- Compare whether the browser starts, which request receives a challenge, and whether the response is a CAPTCHA, 429, or block page.
The original Docker reporter said the suggested settings did not visibly resolve the issue. A browser can operate normally while a target still rejects its traffic, so do not describe Chrome, Xvfb, or one UC option as a guaranteed bypass.
Use UC navigation and reconnect helpers at the right points
UC Mode provides navigation and interaction methods that temporarily disconnect and reconnect the driver around actions a site may inspect. Use the documented helpers where the flow calls for them:
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uc_open_with_reconnect(url, reconnect_time=...)for navigation that needs a reconnect delay.uc_click(selector)for clicks that benefit from the same pattern.uc_gui_click_captcha()and related helpers for supported GUI-based interactions.
These methods are not universal CAPTCHA solvers. GUI helpers require a suitable display, so use Xvfb rather than headless mode on a server. Record the challenge provider, URL stage, response code, and whether the same URL works manually under the same network conditions before attributing the result to a SeleniumBase flag.
Separate driver installation from site detection
SeleniumBase normally downloads drivers as needed into its seleniumbase/drivers directory. A separate driver on PATH is generally unnecessary for SeleniumBase tests. The project documents sbase get chromedriver for manual retrieval and explains that PATH-based installation is mainly relevant when another workflow, such as Selenium Grid, specifically requires it.
Minimal non-UC test
from seleniumbase import SB
with SB(xvfb=True) as sb:
sb.open("https://example.com")
print(sb.get_title())If this basic launch fails, fix the browser, driver, permissions, shared libraries, or display before investigating anti-bot behavior. If it succeeds but UC navigation receives a challenge, the local driver layer is probably not the primary fault.
A repeatable Linux troubleshooting workflow
- Capture the baseline. Save versions, browser binary, container details, display settings, command, exception, URL, and response.
- Prove a display. On GUI-less Linux, run
SB(uc=True, xvfb=True); do not infer display support fromheaded=Truealone. - Test without UC. A normal
SB(xvfb=True)launch distinguishes startup problems from site-side detection. - Hold variables constant. Compare Chrome and Chromium, or headless and Xvfb, one change at a time.
- Use reconnect helpers. Apply
uc_open_with_reconnect()oruc_click()only at the navigation or action that needs it. - Classify the response. A local refusal, browser crash, CAPTCHA, 429, and blank page require different fixes.
- Retest current versions. Browser releases and site checks change; historical Chrome 121/122 advice from the 2024 discussion is not current version guidance.
Common symptoms, causes, and fixes
| Symptom | Likely area | Next action |
|---|---|---|
| Connection refused on first UC command | Display/session startup on GUI-less Linux | Switch from Driver() to SB(uc=True, xvfb=True); verify the browser starts |
| PyAutoGUI or GUI CAPTCHA helper fails | No usable display or headless mode | Run with Xvfb and a regular browser |
| CAPTCHA, block page, or 429 after successful launch | Site-side policy or traffic reputation | Log the stage and response; test network and browser variables separately; do not assume a UC flag guarantees access |
| Works on Windows but not Linux | Display, browser packaging, permissions, or versions | Compare Chrome/Chromium, Xvfb/headless, and exact versions |
| Driver cannot be found | Installation or custom workflow | Let SeleniumBase manage its driver, or use the documented sbase get chromedriver command when manual installation is required |
Performance, reliability, and cost considerations
Xvfb adds a virtual display process and can consume more memory than a headless browser, but it enables GUI-dependent actions and follows SeleniumBase’s documented UC guidance for GUI-less Linux. Container browser choice also affects image size, startup time, and compatibility. Measure your own workload after the configuration is stable; the cited project discussions do not establish a universal detection rate or performance benchmark.
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For reliable diagnosis, pin or record browser and SeleniumBase versions, keep a minimal test URL, capture logs, and avoid changing browser, display, proxy, and navigation behavior in one experiment. A successful local session only proves that the session works; it does not prove that a particular site will allow automation.
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What to conclude from a failed test
On GUI-less Linux, test SB() plus Xvfb first for UC Mode. Then verify Chrome versus Chromium and separate local startup errors from site-side challenges. SeleniumBase’s documentation and maintainer guidance support that order, but no setting guarantees acceptance by a changing target site.
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Frequently Asked Questions
Does Xvfb make SeleniumBase undetectable?
No. Xvfb supplies a virtual display and enables GUI actions; it does not guarantee that a website will accept automated traffic.
Should I install ChromeDriver globally?
Usually not for SeleniumBase tests. SeleniumBase manages drivers in its own directory; use a manual command or PATH installation only when your workflow specifically requires it.
Why can a script pass locally but fail in Docker?
Docker may use Chromium, a different display mode, browser build, network identity, or missing GUI libraries. Compare those variables one at a time.
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