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Frequently asked answers to common questions and issues regarding JEB 3 and JEB 4. The last section is for questions regarding JEB 2, and is kept for reference only. All users are encouraged to migrate to the latest version of JEB.


Where is the end-user license agreement?#

The up-to-date end-user license agreement for JEB can be found here.

Can I generate license keys for additional machines?#

Yes, as long as the additional machines are operated by the licensee, they may install JEB on them. Contact licensing to request the ability to generate additional keys. We handle those requests promptly.

Can I revoke license keys?#

Yes, JEB license keys can be deprecated. Contact licensing to request key revocation. We handle those requests promptly.

I need to reinstall JEB on a different machine. Should I generate a new license key?#


Keys are specific to a user account. If you need to (re)install a non-floating build or the Controller for a floating build on a new system, make sure to generate a key on that system.

If you are planning to copy configuration files over, remove the .LicenseKey entry of jeb-client.cfg and generate a new key upon first run.

How do I check my license type, license identifier, or license key?#

From the command-line: execute JEB with the -c --license switches, eg:

$ jeb_wincon.bat -c --license

From the UI client: open the menu entry Help, About.

How do floating licenses work?#

Floating licenses work on a per-seat basis, as opposed to other license types that work on a per-user basis. Example:

  • A floating build valid for 3 seats allow any 3 users within your organization concurrently.
  • A non-floating build valid for 3 users allow 3 fixed, determined users to use JEB. No other user can use it.

Therefore, floating builds provide great flexibility for organizations where many users are planning to use JEB irregularly and/or at different times (e.g., teams split across various regions).

Please refer to this Manual entry to learn about setting up floating Controller and Clients.

What happens when my license subscription expires?#

JEB works on subscription. Past the expiration date, your software will continue to work and allow you to open and work on existing JDB2 projects, but you will not be able to create new projects.

Do subscriptions renew automatically?#

No. We do not perform auto-payments or auto-renewals. Please email sales when you need to renew a subscription.

Do you offer subscriptions valid for more than one year?#

Yes, we do offer custom subscriptions for up to 3 years. Email us at sales for details.

Do you offer perpetual licenses?#

No, we do not offer perpetual licenses at this point. However, we recommend you email sales and let us know your specific needs: we always strive to accommodate customers' needs.

Do you provide professional support?#

We do offer an additional support plan for JEB Pro and JEB Pro Floating licenses. Refer to the Buy page for details.

Do you offer large volume subscriptions?#

Yes, we do have plans for large enterprise and government. Those plans include the possibility to generate large amount of license keys. Reach out to sales for additional details.

We developed internal tools built around JEB. Can other users in my organization use them without breaking the EULA?#

Yes. As long as your JEB subscription is valid, users in your organization may access and use data produced by JEB.


Which version of Java shall I use to run JEB UI client?#

We recommend users to run the JEB client with a JDK 11 or above.

With Java 9 and above, the native launcher (jeb.exe on Windows, jeb on Linux, on macOS) may not run smoothly. If that happens, you can bypass the native launcher by using the -j flag with your start-up script. Example, on Linux: -j.

If you have installed multiple versions of Java, make sure to set the JAVA_HOME environment variable to the JDK of your choice.

The JEB client can always be started directly by executing jebc.jar on the command line: java -jar bin/app/jebc.jar

Which version of Java shall I use to run non-UI clients?#

The back-end components of JEB, jeb.jar, works with with any version of Java 8.191 or above.

Which build of the JDK should I use?#

Oracle builds or OpenJDK builds are preferred.

It seems some UI problems with GTK/Linux were caused by custom builds, such as JetBrains's JDK. Other problems, including slowdowns and crashes during intensive processing, were reported by users using AdoptOpenJDK. For this reason, we strongly recommend to use Oracle/OpenJDK.

I am encountering strange problems on Windows, what can I do?#

The native launcher (jeb.exe) is called by jeb_wincon.bat by default on Windows. It does not play well with third-party JDKs, such as AdoptOpenJDK. To avoid problems, use -j to avoid using the native launcher: jeb_wincon.bat -j. Alternatively, you may use an Oracle JDK.

JEB complains that it "requires a Java runtime environment", although I have one installed.#

Your java binary should be accessible from the PATH environment variable. It is also recommended to set a JAVA_HOME environment variable pointing to your Java installation folder (bin/).

Make sure to install a 64-bit Java environment

A common source of problems are 64-bit systems having a 32-bit JRE accessible from the PATH or JAVA_HOME. You may have different versions of Java installed, but always make sure that paths refer to one that matches your system specifications.

How can I increase the maximum amount of memory usable by JEB?#

Create or edit the jvmopt.txt file at the root of your JEB folder. To increase the maximum amount of memory usable by JEB, adjust the -Xmx value.

Example: -Xmx8G: allow JEB to use up to 8 Gb of memory.

The settings in jvmopt.txt must be on a single line. After modifying this file, restart JEB with your usual start-up script. On start-up, a message in the logger output will reflect the updated capability:


Do not edit the configuration files buried in bin/app/... or bin/ folders. The memory settings in those files are automatically pulled from jvmopt.txt.


On which platforms can I run JEB?#

The UI desktop client runs on Windows (x64), Linux (x64, arm64), and macOS (x64, arm64).

The JEB back-end components, which can be used separately to build other clients or analysis pipelines, run on all systems for which a JDK 8 (or above) is available.

What do I need to run JEB?#

The only external dependency is Java: JDK 11 (or above) recommended; JDK 8 is also accepted but its support will be deprecated in 2022.

How can I run multiple instances of JEB?#

Multiple instances of JEB can run natively without configuration changes.

How can I redirect JEB logs to files on disk?#

Command-line runners, such as the floating license Controller or a script runner, can easily write log output to files. (Note that other clients, such as the UI desktop client, can do that via scripting - refer to GlobalLog.)

Use the --logfile=... flag. Consult the Usage info for additional details on that switch ("--help")

Example: Start a JEB Controller on Windows and log all INFO-level (or above) output to "controller.log.N" files (max. 5 rotating files, max. 2 Mb of log per file):

jeb_wincon.bat -c --controller --logfiles=controller.log,INFO,5,2

Does JEB run natively on Apple Silicon? Is Rosetta 2 needed to run JEB on Apple Silicon machines?#

JEB (>=4.0-beta.4) can run natively on arm64-powered macOS systems. The Rosetta conversion system is not needed.

JEB clients can no longer connect to a JEB floating controller using SSL. It used to be the case. What happened?#


This problem only manifests itself 1) with JEB <= 4.2 and 2) for which the controller uses a JDK >= April 2021 and 3) for which the controller is set up to use SSL/HTTPS (the .ControllerProtocol has the value 1) to communicate with floating clients.

On April 20 2021, Oracle shipped JDKs deprecating the TLS v1/v1.1 protocols (e.g. JDK 8u291 onward, JDK 11.0.11 onward, etc.), which JEB floating clients <=4.2 require when connecting to a JEB controller.

With default Java settings, the floating controller will simply reject such clients. You have 3 options:

  • The solution is to upgrade JEB to 4.2.1/4.3 or above (recommended).
  • A workaround is to tweak the Java settings on the controller: edit your file (located in your JDK folder). You will see that "TLSv1" is located in the jdk.tls.disabledAlgorithms entry. Remove it from this entry and add it to the jdk.tls.legacyAlgorithms one. This will allow your JEB controller to accept incoming client requests.
  • Another workaround is to use a slightly older Java build on the controller, for which TLSv1 is not deprecated.


JEB messages and strings are in my current (non-English) locale. How do I switch to English?#

By default, JEB does its best to display messages in the current user's language settings. You may change the locale to English (or another one of the 10 supported languages) via the Edit, Language menu. See the Settings for details.

I am trying to debug an Android application, but my device cannot be found.#

JEB relies on the Android Debug Bridge (adb) to debug Android applications. Make sure to:

  • install the Android SDK (or at least have a stand-alone, working adb binary accessible from your PATH - some Linux distributions ship adb and other SDK platform tools in separate, leaner packages)
  • have the SDK path referenced in one of the following environment variables: ANDROID_SDK_ROOT (preferred) or ANDROID_HOME (legacy).

To troubleshoot your system, you may enable Developer Mode in your JEB options and examine the logger output. You will see lines like the following indicating how and where JEB is attempting to find adb:

[adb] ANDROID_HOME: Environment variable added to list of candidate Android SDK locations
[adb] ANDROID_SDK_ROOT: Environment variable NOT found
[adb] PATH: added to list of searched folders: (redacted)
[adb] Searching for 'adb.exe' in folders, by order: (redacted)
[adb] Found and using: C:\Users\nicol\AppData\Local\Android\sdk\platform-tools\adb.exe

Inside "Find text" widgets or filter fields, why are my regular expressions invalid or not working?#

JEB uses Java-style regular expressions, not PCRE, Boost, or other type of regex. Although the differences are minimal and subtle, complex regular expressions need to be carefully crafted and abide by the Java Pattern standard (refer to the "Comparison to Perl 5" section specifically).

I am using Ubuntu 16.04 LTS; the GUI behaves strangely and JEB closes unexpectedly.#

If you are using Ubuntu 16 with a recent version of JEB, the following error message may be reported in the console:

WARNING: GTK+ version too old (micro mismatch)
WARNING: SWT requires GTK 3.20.0
WARNING: Detected: 3.18.9

When trying to use menus and widgets, unexpected errors will likely happen, including program termination.

The reason is JEB 3.20+ UI framework (SWT) does not work properly with GTK 3.18-, used by Ubuntu 16: recent SWT builds require GTK 3.20+. In order to upgrade GTK without upgrading your entire distro to Ubuntu 18 or Ubuntu 20, you may use the following commands:

sudo add-apt-repository ppa:gnome3-team/gnome3-staging
sudo add-apt-repository ppa:gnome3-team/gnome3
sudo apt update
sudo apt upgrade

On Linux, I am seeing GTK error messages in the console.#

Most of those messages are harmless. If you are suspecting issues, please email support.

However, you may see the following message: "HoverWidget can not be loaded due to xxxxxxx because there is no underlying browser available. Please ensure that WebKit with its GTK 3.x bindings is installed (WebKit2 API level is preferred). Additionally, please note that GTK4 does not currently have Browser support. Is libwebkitgtk-1.0-0 package installed?". It indicates that some pop-up overlays will not work until you install libwebkit2gtk:

# find what version is available on your distro
apt-cache search libwebkit2gtk
# install the package (e.g. here, version 4.0.37)
sudo apt install libwebkit2gtk-4.0.37

I am using an old version of Ubuntu (18, 16), and JEB crashes or behaves strangely.#

A workaround is to start JEB with that environment variable set to avoid strange problems: GTK_DEBUG=no-pixel-cache

The easiest way to set this up once and for all is to export GTK_DEBUG=no-pixel-cache and then run


I work in a limited-connectivity environment, how can I update the software manually?#

The procedure i:

  • Check your registered email address for a JEB update email ("JEB xxx is available...")
  • Download the software archive
  • Copy the archive to the root of your JEB folder and rename the file to
  • Create a text file named update.pwd
  • Store the email-provided password inside this file
  • Start JEB as normal; the update will be installed automatically

I access Internet via a proxy. Can I still use JEB?#

Proxy settings can be stored at those two locations:

  • The UI client's settings, stored in jeb-client.cfg. If you are using the UI desktop client, they can be modified via the Options panel.
  • In headless mode, set the proxy settings in jeb-engines.cfg instead.

In each aforementioned configuration file, the network proxy data is stored as a key-value pair having the following format: .NetworkProxy = type|hostname|port|<username>|<password>|<whitelist>

  • Allowed types: http, socks.
  • 'username'/'password' can be left blank if your proxy does not require authentication
  • 'whitelist' is an optional, comma-separated list of wildcard hostnames/IPs to which JEB should always attempt to direct-connect (no proxy)

A few examples of valid proxy strings:

- http||8080
- http||8080||
- http||8080|||
- http||8080|||*
- socks||8088|user|pass|*


Do not forget the leading dot in .NetworkProxy!

How do I update from JEB n to JEB n+1?#

At the time of writing, you must install JEB n+1 (e.g. JEB 4) in a separate location. The auto-updater will only notify you that a JEB n+1 build is available for you to install. Check your email to download and install that new version.

Can I update from the command-line?#

Yes, you can run:

$ <jeb_startup_script> -c --check-update

After the update is downloaded, execute JEB normally.

JEB just auto-updated and I am now experiencing strange runtime issues. What can I do?#

If the issues you are experiencing are showing up after a software update, at seemingly random times during program execution, and involve error messages like "Error invoking method" or "Failed to launch JVM", it is likely that your last JEB update did not fully complete.

Try to execute your start-up script (eg, on Windows, jeb_wincon.bat) instead of any native launcher you may have been previously using (such as an OS desktop task bar shortcut).

If the issue is recurring, please email Support.


Can I execute a JEB Python script from the command line?#

Yes. Here's how to use the built-in script runner. You will need a Pro license.

  • Make sure your JEB scripts/ folder contains the jython-xxx.jar.
  • Execute your JEB startup script with --srv2 and --script parameters, as well as optional script arguments after --

Example on Windows:

$ jeb_wincon.bat -c --srv2 -- foo bar

Use -c --help to learn about other options.


Command-line arguments (in the example above: foo, bar) can be retrieved via IClientContext.


Alternate ways exist to run scripts or plugins in headless contexts. Read through this guide and associated sample code if you want to know more about writing your own front-end clients.

Can I write back-end extensions (plugins, contributions, etc.) in Python?#

Not at the moment. Back-end extensions should be written in Java (or any other language compiling to Java classfile, e.g. Kotlin).


Is there a public bug/feature tracker?#

Not at the moment. We are pretty responsive when it comes to answering users' queries though. Here's how to reach out:

  • Join us on Slack and ask your question or make suggestions on #general
  • For private inquiries, email us at Support
  • You may also message us on the JEB Google Groups (although we don't use it much these days as it was superseded by the Slack channel)
  • And of course, you can also reach out to us on Tweeter @jebdec