launches all currently configured parallel subkernels.


launches n local subkernels on the current computer.


launches the kernel specified by ker.


launches the kernels keri.

Details and Options

  • LaunchKernels[] uses $DefaultKernels to determine the list of kernels to launch.
  • Additional configurations for kernels on remote machines can be made available with the Wolfram Lightweight Grid and the Cluster Integration Package.


open allclose all

Basic Examples  (1)

Launch the default kernels:

Close all running kernels and start two new ones:

Scope  (11)

Kernel Specifications  (4)

Launch the default kernels as described in $DefaultKernels:

Launch two more local kernels, in addition to those already running:

Launch kernels on a remote machine:

Use RemoteKernelObject to specify additional details of the desired kernels:

Local Kernels  (3)

Use a specific local kernel, given by its absolute path:

Alternatively, give the path and kernel count in the first argument as a URL:

For local kernels, the default number of parallel kernels is equal to $ProcessorCount, license permitting:

SSH Kernels  (3)

Give the path to the remote kernel as an option of RemoteKernelObject:

Alternatively, specify the path and kernel count as part of the ssh URL:

Specify the remote operating system to automatically choose a suitable kernel command:

When using a URL short form, the number of parallel kernels can be specified with "?n":

WSTPServer Kernels  (1)

Connect to a WSTPServer and request a number of parallel kernels:

Generalizations & Extensions  (1)

Close all kernels:

Launch copies of the previously running kernels:

Applications  (1)

Measure the speedup of the same calculation with different numbers of kernels used:

Properties & Relations  (1)

Distributed definitions and shared variables apply to running kernels and new ones:

Packages read with ParallelNeeds also apply to running and new kernels:

Close all running kernels and launch new ones:

The new kernels inherit previously distributed definitions and shared variables:

The new kernels also inherit packages read previously:

Possible Issues  (4)

If any kernels are already running, LaunchKernels[] does not launch the default kernels:

Close all running kernels, then launch the default set of kernels:

Kernels may be automatically launched when first needed:

Manually close the kernels:

Now, no kernels are launched automatically:

If no kernels are available, most parallel calculations are done sequentially:

No kernels are launched by default on a single-core computer:

Specify the number of desired kernels to launch them anyway:

Neat Examples  (1)

Specify a kernel on a remote machine:

Ask it for the number of processor cores:

Update the kernel specification with the kernel number returned:

Launch the parallel kernels:

Wolfram Research (2008), LaunchKernels, Wolfram Language function,


Wolfram Research (2008), LaunchKernels, Wolfram Language function,


@misc{reference.wolfram_2021_launchkernels, author="Wolfram Research", title="{LaunchKernels}", year="2008", howpublished="\url{}", note=[Accessed: 21-September-2021 ]}


@online{reference.wolfram_2021_launchkernels, organization={Wolfram Research}, title={LaunchKernels}, year={2008}, url={}, note=[Accessed: 21-September-2021 ]}


Wolfram Language. 2008. "LaunchKernels." Wolfram Language & System Documentation Center. Wolfram Research.


Wolfram Language. (2008). LaunchKernels. Wolfram Language & System Documentation Center. Retrieved from