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On this page we provide help for a number of common problems encountered with the OT. If you have any further questions or discover a new bug, please contact us via the ALMA Helpdesk. Please note that the following advice assumes that the user is running an up-to-date version of the OT.

Which version of Java should I install?

Users should install the official release of Java 8 from Oracle, available at Only the Java Runtime Environment, or JRE for short, needs to be downloaded. The JDK is only for developers and is a bigger installation. The OT will not work with Java versions earlier than 8 and a 64-bit version is required.

Oracle has recently moved to a six-monthly release cycle and the highest version of Java currently available is 11. However, Java 8 remains the default version when downloading and users are not being automatically offered updates to Java versions 9 and higher. In fact, updates to Java 8 continue to be issued and this is expected to last until at least December 2020. Java 8 is a so-called Long Term Support (TLS) release.

Testing has indicated that the the OT is unlikely to run on Java versions 9 and higher. It is certain that the OT will not run on Java 11.

How do I install Java on a Mac?

On a Mac, the JRE download will consist of a .dmg file that should be opened as usual. This will do most of the installation for you, but it will not set the path to the Java installation, which must therefore be done manually. On a Mac, the java executables should reside in '/Library/Internet Plug-Ins/JavaAppletPlugin.plugin/Contents/Home/bin/' and this directory should be added to your path. As the name of that directory implies, all browsers running on a Mac should automatically pick up the necessary plugin.

Important: Mac OS versions before 10.7.3 (Lion) can only install Java 6 or earlier - the OS should therefore be upgraded if at all possible.

How do I install Java on Linux?

On a Linux system, the user will be able to choose where the JRE is installed. Afterwards, the installation's 'bin/' directory should be added to the user's PATH. In addition, the internet plugin must be installed manually. This is done by, in your browser's plugins directory, creating a symbolic link to the file '' which can be found inside the JRE directory tree (probably in 'lib/amd64/'). In the case of Firefox, the 'plugins' directory is probably '$HOME/.mozilla/plugins'. Finally, you should also check to see that your browser is configured to use the correct version of Java Web Start. This can be important as some versions of Linux come pre-installed with 'Open JDK' versions of Java (e.g. 'Iced Tea') which we do not recommend. For Firefox, which version is being used can be set in the Applications tab of the Preferences menu - it should point to the 'javaws' executable in the JRE's 'bin/' directory.

What version of Java am I running?

If the above instructions for installation have been followed, the version being used by the OT can be shown via the command line i.e.
>java -version
java version "1.8.0_201"
Java(TM) SE Runtime Environment (build 1.8.0_201-b09)
Java HotSpot(TM) 64-Bit Server VM (build 25.201-b09, mixed mode)

As the Web Start version of the OT explicitly uses the internet, a more reliable test of which Java version is being used is done using a browser. Oracle host a web page which will inform you of the version.

Finally, the version can be viewed using the Java Console. On a Mac this is available via the System Preferences menu, but for all installations is available as an executable ('ControlPanel') in the 'bin/' directory of the Java installation. If this directory has been added to your path, just typing this at the command line should work.

The command-line Java version is different to the browser version!

It can happen that the Java version reported using 'java -version' and by the browser are different. This should only happen on a Mac as this allows both a JRE and a JDK to be installed. The JDK also contains a JRE and it is probably this one that is being used for the command line, whilst the stand-alone JRE is used by the browser. As only the browser JRE is automatically updated, the version numbers can get out of sync. In principle, having different versions of a JRE installed is not a problem, so long as both are kept up to date. However, it is not necessary to install a JDK in order to run the OT.

Should I install the Web Start or the tarball version of the OT?

In general, we recommend that you install the Web Start version as this will automatically check for any updates each time it is started, and automatically download and install these if available. However, as stated above, there was a bug in Java 9 Web Start and this has been removed completely from Java 11. If it does not prove possible to use Web Start, the tarball should be installed instead and should work correctly with all Oracle Java versions 8 and above. It will also check for updates to the OT, but these must be installed manually.

Nothing happens when I start the Web Start OT on my Mac!

What is happening here is probably due to a Mac feature called 'Gatekeeper'. Introduced in Mountain Lion, this defaults to only allowing applications to run that have either been downloaded from the App Store or have an Apple Developer ID. As the OT does not have one of the latter, a Mac will force the user to manually open the application. This is done by opening the downloaded .jnlp file via the Download window, opening it with the Finder and right-clicking to access the 'Open With' option. Alternatively, Gatekeeper can be turned off via the 'Security & Privacy' System Preferences menu item: select 'Anywhere'.

Do I always have to start the OT from the Science Portal?

No, this is not necessary. It should normally be the case that installing the Web Start OT will cause a shortcut to be created on the user's Desktop. Starting the OT can henceforth be most easily accomplished by double-clicking on this.

My Java installation is not updating automatically

This probably means that you are running on a 32-bit Linux operating system. For some reason, automatic updates for Linux are only enabled on 64-bit installations. In fact, the update tab in the Control Panel is completely absent. Upgrading Java on a 32-bit Linux system therefore requires that the JRE be downloaded and installed manually each time an update is released.

What do I do if the OT fails to start?

Sometimes, the Web Start version of the OT will fail to start for no apparent reason whatsoever. Actually, simply trying again will often fix the problem. If this doesn't work, it may be necessary to delete the existing installation and re-install from scratch.

Problems can also arise with the user's preferences which are stored in the $HOME/.almaot directory. It can happen that after an apparent normal startup the OT GUI will never appear and deleting the .almaot directory is the usual solution here.

It seems that trying to run the OT on a 32-bit Java installation will fail without any warning whatsoever. The OT now requires a 64-bit installation of Java.

Finally, it seems that problems with graphics drivers can also lead to the OT failing to start - the "Java..." splashscreen will appear and then vanish. This problem has so far only been reported by Windows 7 users, but we cannot rule out that other operating systems are also affected. The solution appears to be to update the graphic drivers and may also require that Java be reinstalled.

The OT freezes when I try and input text

It seems that operation of the OT can be affected if other Java applications are run at the same time. To date we only know of problems with the time-management software "RescueTime", but there may be others.

I'm running the OT on a 32-bit machine

If you have no choice but to run the OT in a 32-bit environment, you will need to use the tarball version of the OT. After installing this as normal, open the '' file in a text editor and replace '-Xmx3072m' with '-Xmx1024m'. The OT should now run correctly, but it may not be possible to validate and submit complicated proposals that use many Science Goals and/or which make use of the OT's clustering algorithm (sources separated by >10 degrees).

How do I delete the Web Start version of the OT?

This is done via the Cache Viewer in the Control Panel. The most convenient way to bring this up is via the command line i.e.
>javaws -viewer

The OT GUI is taking forever to start!

What may have happened here is that the GUI that requests the user's password has got lost under other windows.