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2026-11-12 16:13:03 Dave LeBlanc: Singularity updated on Thu Nov 12 16:12:23 2026
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+# Singularity
+
+---++ Intro
+
+Since there is a pressing need for the use of containers in a specific way, this document will begin limited to that specific context, and then branch from there.
+
+---++ Why Singularity and not Docker?
+
+Docker is a fine virtual abstraction system, however it requires administrator privileges to run. Further, once an image is running, Docker's default preference is to have input and output resources relevant to the container _within_ the container itself. Singularity overcomes these two issues by running images as the user envoking them, and then exposing the local filesystem on the host from within the running container. More detailed information can be found [[https://sylabs.io/guides/3.3/user-guide/quick_start.html#overview-of-the-singularity-interface][here]].
+
+---++ Build a container
+
+In this contextual need, we would like to be able to run Tensorflow. Singularity will allow us to obtain an existing container from a Singularity Container Library, a Singularity Hub, or a Docker Hub. In this particular case of Tensorflow, we'll download one of NVidia's premade Docker containers, which Singularity will convert into its own format.
+First, we need to obtain access to NVidia's library of Docker containers, located here:
+ [[https://ngc.nvidia.com/catalog/containers][Nvidia NGC]]
+
+This is initially done by requesting access through the [[https://ngc.nvidia.com/signup][Create Account]] link. Once an account is granted, the [[https://ngc.nvidia.com/setup/api-key][API key]] is needed.
+
+Once the API key is obtained, set it usable in the shell:
+
+<verbatim>
+ export SINGULARITY_DOCKER_USERNAME=$oauthtoken
+ export SINGULARITY_DOCKER_PASSWORD=<API key></verbatim>
+
+Now you may log into the Nvidia NGC and browse for containers. In this example, we'll download [[https://ngc.nvidia.com/catalog/containers/nvidia:tensorflow][Tensorflow]].
+There, it lists the container as:
+
+<verbatim>nvcr.io/nvidia/tensorflow:19.09-py3</verbatim>
+
+By default, singularity will write the entire container into your home directory and then the container will be specific to your account, hidden, and available only to you. To avoid that, we'll write it to a file instead, in Singularity Image Format (SIF).
+So, for singularity, we will *pull* the image as such:
+
+<verbatim>>singularity pull tf-19.09-py3.sif docker://nvcr.io/nvidia/tensorflow:19.09-py3</verbatim>
+
+Singularity will then download each blob-layer in the _tensorflow:19.09-py3_ tag, and cache it into your home directory.
+
+<verbatim>INFO: Converting OCI blobs to SIF format
+INFO: Starting build...
+Getting image source signatures
+Copying blob sha256:35c102085707f703de2d9eaad8752d6fe1b8f02b5d2149f1d8357c9cc7fb7d0a
+ 25.45 MiB / 25.45 MiB [====================================================] 1s
+Copying blob sha256:251f5509d51d9e4119d4ffb70d4820f8e2d7dc72ad15df3ebd7cd755539e40fd
+ 34.54 KiB / 34.54 KiB [====================================================] 0s
+Copying blob sha256:8e829fe70a46e3ac4334823560e98b257234c23629f19f05460e21a453091e6d
+ 848 B / 848 B [============================================================] 0s
+Copying blob sha256:6001e1789921cf851f6fb2e5fe05be70f482fe9c2286f66892fe5a3bc404569c
+ 162 B / 162 B [============================================================] 0s
+Copying blob sha256:109c7cec1178b6d77b59e8715fe1eae904b528bb9c4868519ff5435bae50c44c
+ 8.63 MiB / 8.63 MiB [======================================================] 0s
+<sniped for brevity>
+Copying blob sha256:df0616c98153f10db5b05626f314000ced06fb127a6cfaac37ff325d11488327
+ 452 B / 452 B [============================================================] 0s
+Copying blob sha256:7828d14d7927458867242e0274e706b1c902eb6b1207e5a28337a7fbc6400e17
+ 209.76 KiB / 209.76 KiB [==================================================] 0s
+Copying blob sha256:ae4e96299b2fca5dc08edbde4061cfdf25c313954a7d46a32dfc701af4e0edf6
+ 9.64 KiB / 9.64 KiB [======================================================] 0s
+Copying config sha256:ad94fc3cd170246d925f8c5aa8000b3e6cbe645d30ff185bf87b40cee8f41d32
+ 33.55 KiB / 33.55 KiB [====================================================] 0s
+Writing manifest to image destination
+Storing signatures
+INFO: Creating SIF file...
+INFO: Build complete: /home/leblancd/.singularity/cache/oci-tmp/52706b896af93123eb7f894f9671bbd31a1cabd15943aa3334eb7af3a710d262/tensorflow_19.09-py3.sif</verbatim>
+
+Now our container file is complete:
+
+<verbatim>-rwxrwxr-x 1 leblancd supergroup 3.3G Oct 4 18:39 tf-19.09-py3.sif</verbatim>
+
+---+++ Cache
+
+Before we move on, note that singularity also stored the SIF file in the user's cache, in the home directory (there is now a 3.3G file there, with overhead).
+You can view what is stored in the cache:
+
+<verbatim>>singularity cache list
+NAME DATE CREATED SIZE TYPE
+tensorflow_19.09-py3.s 2019-10-04 18:39:01 3.45 GB oci
+
+There 1 containers using: 3.45 GB, 68 oci blob file(s) using 3.70 GB of space.
+Total space used: 7.15 GB</verbatim>
+
+Clearing the cache is equally simple.
+
+<verbatim>
+>singularity cache clean -a</verbatim>
+
+Removes all images in the cache (with the -a parameter).
+
+By default, Singularity caches pulled files in your homedirectory with a structure as:
+
+<verbatim>
+$HOME/.singularity/cache/library
+$HOME/.singularity/cache/oci
+$HOME/.singularity/cache/oci-tmp</verbatim>
+
+One can change the default location of the cache by setting =SINGULARITY_CACHEDIR= to your desired location, for example (in bash shell):
+
+<verbatim>
+echo $SINGULARITY_CACHEDIR
+
+export $SINGULARITY_CACHEDIR=/tmp/leblancd_sing_cache
+
+echo $SINGULARITY_CACHEDIR
+/tmp/leblancd_sing_cache</verbatim>
+
+---+++ Build a container from scratch
+
+Now lets say we built this image but discovered it is lacking software that we need.
+We have a few options at this point, depending on how permanent we would like the software to be.
+One solution would be to build a new image from the image we pulled and built locally (above).
+
+Since creating an image from a definition requires root privelege, we cannot do this locally and need to
+employ the [[https://cloud.sylabs.io/builder][Remote Builder]] service.
+There, once we have an account created and retrieved an API code (good for 30 days), and saving it to =~/.singularity/sylabs-token=,
+we can proceed to build our new image with a definition file.
+
+Using our image from above, lets install 'astropy' into the image.
+We create a file definition, named =tensorflow-astropy.def=
+<verbatim>Bootstrap: docker
+From: nvcr.io/nvidia/tensorflow:19.09-py3
+
+%post
+ apt-get -y update
+ pip install astropy
+
+%environment
+ export LC_ALL=C
+ export PATH=/usr/local/bin:/usr/bin:/usr/sbin:$PATH</verbatim>
+
+Without going too deep into technical details, our definition begins with =Bootstrap=, which every definition file requires and describes the bootstrap agent; =docker= for Docker Hub images (whether from the Docker registry or other), and =library= for [[https://cloud.sylabs.io/library][Container Library]] images.%BR%
+=From:= describes where the Remote Builder will find the foundational image to build upon.%BR%
+Anything in the =%post%= section will be performed after the initial image has been pulled and built locally, namely =apt-get -y update= updates the installed software in the container, and =pip install astropy= will install the Python module "astropy" in the container.%BR%
+In the =%environment= we set the locale (LC_ALL=C), and the =$PATH= so that the system knows where =pip= is located.
+
+For mor information about building images from scratch and definition files, seek [[https://sylabs.io/guides/3.3/user-guide/definition_files.html][this documentation]].
+
+With our definition file, =tensorflow-astropy.def=, we can execute:
+<verbatim>singularity build --remote tf-astropy.sif tensorflow-astropy.def</verbatim>
+
+which will submit our definition file to the Remote Builder site and build our new image for us.
+
+---++ Interacting with the Image
+---+++ exec
+
+To run the container we just built, we need to decide how we would like to execute it.
+We can *exec* on the container, which will run a command inside the container:
+
+<verbatim>>singularity exec tf-19.09-py3.sif cat /etc/os-release
+ NAME="Ubuntu"
+ VERSION="18.04.3 LTS (Bionic Beaver)"
+ ID=ubuntu
+ ID_LIKE=debian
+ PRETTY_NAME="Ubuntu 18.04.3 LTS"
+ VERSION_ID="18.04"
+ HOME_URL="https://www.ubuntu.com/"
+ SUPPORT_URL="https://help.ubuntu.com/"
+ BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
+ PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
+ VERSION_CODENAME=bionic
+ UBUNTU_CODENAME=bionic</verbatim>
+
+This will execute any command from within the container, and then immediately exit.
+
+---+++ shell
+
+We can also obtain a *shell* within the container:
+
+<verbatim>>singularity shell tf-19.09-py3.sif
+ Singularity tf-19.09-py3.sif:/tmp> ls -al
+ total 3366992
+ drwxrwxrwt 10 root root 4096 Oct 4 18:45 .
+ drwxr-xr-x 1 leblancd supergroup 80 Oct 4 18:51 ..
+ -rwxrwxr-x 1 leblancd supergroup 3447758848 Oct 4 18:39 tf-19.09-py3.sif</verbatim>
+
+Notice that the current working directory is /tmp, which is not inside the container.
+When Singularity executes, it attempts to make available all your existing filespaces, such as your homedirectory, and any common directories existing on the physical host (such as /tmp). Only the files and directories inside the container are exposed over the filespace of the physical host. This makes it rather easy to write any output from the container to the local filesystem, or to an NFS mounted homedirectory.
+
+Now that we're interactively running the container, we can attempt to execute Tensorflow.
+
+<verbatim>Singularity tf-19.09-py3.sif:/tmp> python
+Python 3.6.8 (default, Aug 20 2019, 17:12:48)
+[GCC 8.3.0] on linux
+Type "help", "copyright", "credits" or "license" for more information.
+Could not open PYTHONSTARTUP
+FileNotFoundError: [Errno 2] No such file or directory: '/etc/pythonstart'
+>>> import tensorflow as tf
+2019-10-04 18:57:01.232584: I tensorflow/stream_executor/platform/default/dso_loader.cc:42] Successfully opened dynamic library libcudart.so.10.1
+>>> hello = tf.constant('Testing TF')
+>>> sess = tf.Session()
+2019-10-04 18:57:40.770169: I tensorflow/stream_executor/platform/default/dso_loader.cc:53] Could not dlopen library 'libcuda.so.1'; dlerror: libcuda.so.1: cannot open shared object file: No such file or directory; LD_LIBRARY_PATH: /usr/local/cuda/extras/CUPTI/lib64:/usr/local/cuda/compat/lib:/usr/local/nvidia/lib:/usr/local/nvidia/lib64:/.singularity.d/libs
+2019-10-04 18:57:40.770224: E tensorflow/stream_executor/cuda/cuda_driver.cc:318] failed call to cuInit: UNKNOWN ERROR (303)
+2019-10-04 18:57:40.773897: I tensorflow/stream_executor/cuda/cuda_diagnostics.cc:169] retrieving CUDA diagnostic information for host: ml-login3
+2019-10-04 18:57:40.773919: I tensorflow/stream_executor/cuda/cuda_diagnostics.cc:176] hostname: ml-login3
+2019-10-04 18:57:40.773959: I tensorflow/stream_executor/cuda/cuda_diagnostics.cc:200] libcuda reported version is: Not found: was unable to find libcuda.so DSO loaded into this program
+2019-10-04 18:57:40.774016: I tensorflow/stream_executor/cuda/cuda_diagnostics.cc:204] kernel reported version is: 435.21.0
+2019-10-04 18:57:40.789291: I tensorflow/core/platform/profile_utils/cpu_utils.cc:94] CPU Frequency: 2494100000 Hz
+2019-10-04 18:57:40.794142: I tensorflow/compiler/xla/service/service.cc:168] XLA service 0x4c48fa0 executing computations on platform Host. Devices:
+2019-10-04 18:57:40.794172: I tensorflow/compiler/xla/service/service.cc:175] StreamExecutor device (0): <undefined>, <undefined>
+>>></verbatim>
+
+Uh oh. The container couldn't locate the CUDA library necessary to execute the Tensorflow Python module in the container.
+
+---++++ nv
+
+This is because when the singularity shell was launched, it was not made aware of any NVidia software, and did not map any NVidia drivers/devices into the container. This is easily remedied with the _--nv_ parameter.
+
+<verbatim>>singularity shell --nv tf-19.09-py3.sif
+Singularity tf-19.09-py3.sif:/tmp> python
+Python 3.6.8 (default, Aug 20 2019, 17:12:48)
+[GCC 8.3.0] on linux
+Type "help", "copyright", "credits" or "license" for more information.
+>>> import tensorflow as tf
+2019-10-04 19:00:12.417390: I tensorflow/stream_executor/platform/default/dso_loader.cc:42] Successfully opened dynamic library libcudart.so.10.1
+>>> hello = tf.constant('Testing TensorF')
+>>> sess = tf.Session()
+2019-10-04 19:00:38.980743: I tensorflow/stream_executor/platform/default/dso_loader.cc:42] Successfully opened dynamic library libcuda.so.1
+2019-10-04 19:00:39.767134: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1640] Found device 0 with properties:
+name: TITAN RTX major: 7 minor: 5 memoryClockRate(GHz): 1.77
+pciBusID: 0000:84:00.0
+2019-10-04 19:00:39.767193: I tensorflow/stream_executor/platform/default/dso_loader.cc:42] Successfully opened dynamic library libcudart.so.10.1
+2019-10-04 19:00:39.825552: I tensorflow/stream_executor/platform/default/dso_loader.cc:42] Successfully opened dynamic library libcublas.so.10
+2019-10-04 19:00:39.854719: I tensorflow/stream_executor/platform/default/dso_loader.cc:42] Successfully opened dynamic library libcufft.so.10
+2019-10-04 19:00:39.868698: I tensorflow/stream_executor/platform/default/dso_loader.cc:42] Successfully opened dynamic library libcurand.so.10
+2019-10-04 19:00:39.929108: I tensorflow/stream_executor/platform/default/dso_loader.cc:42] Successfully opened dynamic library libcusolver.so.10
+2019-10-04 19:00:39.944015: I tensorflow/stream_executor/platform/default/dso_loader.cc:42] Successfully opened dynamic library libcusparse.so.10
+2019-10-04 19:00:40.054598: I tensorflow/stream_executor/platform/default/dso_loader.cc:42] Successfully opened dynamic library libcudnn.so.7
+2019-10-04 19:00:40.057032: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1763] Adding visible gpu devices: 0
+2019-10-04 19:00:40.072683: I tensorflow/core/platform/profile_utils/cpu_utils.cc:94] CPU Frequency: 2494100000 Hz
+2019-10-04 19:00:40.077704: I tensorflow/compiler/xla/service/service.cc:168] XLA service 0x50cd760 executing computations on platform Host. Devices:
+2019-10-04 19:00:40.077723: I tensorflow/compiler/xla/service/service.cc:175] StreamExecutor device (0): <undefined>, <undefined>
+2019-10-04 19:00:40.172994: I tensorflow/compiler/xla/service/service.cc:168] XLA service 0x50d0e80 executing computations on platform CUDA. Devices:
+2019-10-04 19:00:40.173041: I tensorflow/compiler/xla/service/service.cc:175] StreamExecutor device (0): TITAN RTX, Compute Capability 7.5
+2019-10-04 19:00:40.174405: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1640] Found device 0 with properties:
+ name: TITAN RTX major: 7 minor: 5 memoryClockRate(GHz): 1.77 pciBusID: 0000:84:00.0
+2019-10-04 19:00:40.174453: I tensorflow/stream_executor/platform/default/dso_loader.cc:42] Successfully opened dynamic library libcudart.so.10.1
+2019-10-04 19:00:40.174511: I tensorflow/stream_executor/platform/default/dso_loader.cc:42] Successfully opened dynamic library libcublas.so.10
+2019-10-04 19:00:40.174548: I tensorflow/stream_executor/platform/default/dso_loader.cc:42] Successfully opened dynamic library libcufft.so.10
+2019-10-04 19:00:40.174585: I tensorflow/stream_executor/platform/default/dso_loader.cc:42] Successfully opened dynamic library libcurand.so.10
+2019-10-04 19:00:40.174619: I tensorflow/stream_executor/platform/default/dso_loader.cc:42] Successfully opened dynamic library libcusolver.so.10
+2019-10-04 19:00:40.174680: I tensorflow/stream_executor/platform/default/dso_loader.cc:42] Successfully opened dynamic library libcusparse.so.10
+2019-10-04 19:00:40.174719: I tensorflow/stream_executor/platform/default/dso_loader.cc:42] Successfully opened dynamic library libcudnn.so.7
+2019-10-04 19:00:40.177149: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1763] Adding visible gpu devices: 0
+2019-10-04 19:00:40.180107: I tensorflow/stream_executor/platform/default/dso_loader.cc:42] Successfully opened dynamic library libcudart.so.10.1
+2019-10-04 19:00:42.739483: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1181] Device interconnect StreamExecutor with strength 1 edge matrix:
+2019-10-04 19:00:42.739536: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1187] 0
+2019-10-04 19:00:42.739545: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1200] 0: N
+2019-10-04 19:00:42.742016: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1326] Created TensorFlow device
+ (/job:localhost/replica:0/task:0/device:GPU:0 with 22756 MB memory) -> physical GPU
+ (device: 0, name: TITAN RTX, pci bus id: 0000:84:00.0, compute capability: 7.5)
+>>> a = tf.constant(10)
+>>> b = tf.constant(25)
+>>> sess.run(a+b)
+35</verbatim>
+
+---++ Container Reuse
+
+Now, we have built a container from NVidia, and demonstrated it as working, *can someone else use our container*?%BR%
+_Yes_, as long as you don't need to write anything into the container space, because the container will be mounted __read-only__ by default.
+This is likely expected behavior, as it seems undesirable to create a container that allows anyone to write files, creating unforeseen entropy into the otherwise pristine container.%BR%
+Regarding our example Tensorflow container above, it remains usable as __read-only__ since we are not modifying the binaries/scripts involved in running Tensorflow itself, and any data input or output can live safely and be accessed outside the container.%BR%
+Consider the following example:
+
+We have a very simple (example) Python script:%BR%
+
+<verbatim>
+>cat helloworld.py
+
+import tensorflow as tf
+hello = tf.constant('Hello, TF!')
+sess = tf.Session()
+print(sess.run(hello))</verbatim>
+
+That is in the current directory with our Tensorflow container:%BR%
+
+<verbatim>
+-rw-rw-r-- 1 leblancd supergroup 101 Oct 4 19:30 helloworld.py
+-rwxrwxr-x 1 leblancd supergroup 3.3G Oct 4 18:39 tf-19.09-py3.sif</verbatim>
+
+We can use our =helloworld.py= script like so:%BR%
+
+<verbatim>
+>singularity exec --nv ./tf-19.09-py3.sif python ./helloworld.py
+2019-10-09 17:34:30.078770: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1640] Found device 0 with properties:
+ name: TITAN RTX major: 7 minor: 5 memoryClockRate(GHz): 1.77 pciBusID: 0000:84:00.0
+...snip...
+2019-10-09 17:34:30.373594: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1763] Adding visible gpu devices: 0
+2019-10-09 17:34:30.388525: I tensorflow/core/platform/profile_utils/cpu_utils.cc:94] CPU Frequency: 2494100000 Hz
+2019-10-09 17:34:30.393509: I tensorflow/compiler/xla/service/service.cc:168] XLA service 0x56378c0 executing computations on platform Host. Devices:
+2019-10-09 17:34:30.393530: I tensorflow/compiler/xla/service/service.cc:175] StreamExecutor device (0): <undefined>, <undefined>
+2019-10-09 17:34:30.488286: I tensorflow/compiler/xla/service/service.cc:168] XLA service 0x5637f30 executing computations on platform CUDA. Devices:
+2019-10-09 17:34:30.488342: I tensorflow/compiler/xla/service/service.cc:175] StreamExecutor device (0): TITAN RTX, Compute Capability 7.5
+2019-10-09 17:34:30.489712: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1640] Found device 0 with properties:
+ name: TITAN RTX major: 7 minor: 5 memoryClockRate(GHz): 1.77 pciBusID: 0000:84:00.0
+...snip...
+2019-10-09 17:34:30.492309: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1763] Adding visible gpu devices: 0
+2019-10-09 17:34:30.495275: I tensorflow/stream_executor/platform/default/dso_loader.cc:42] Successfully opened dynamic library libcudart.so.10.1
+2019-10-09 17:34:33.013974: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1181] Device interconnect StreamExecutor with strength 1 edge matrix:
+2019-10-09 17:34:33.014043: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1187] 0
+2019-10-09 17:34:33.014054: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1200] 0: N
+2019-10-09 17:34:33.016631: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1326] Created TensorFlow device
+ (/job:localhost/replica:0/task:0/device:GPU:0 with 22756 MB memory) -> physical GPU
+ (device: 0, name: TITAN RTX, pci bus id: 0000:84:00.0, compute capability: 7.5)
+b'Hello, TF!'</verbatim>
+
+Likewise, redirecting output as:
+
+<verbatim>
+>singularity exec --nv ./tf-19.09-py3.sif python ./helloworld.py >> OUTPUT
+...snip...
+2019-10-09 17:59:52.089016: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1326]
+ Created TensorFlow device (/job:localhost/replica:0/task:0/device:GPU:0 with 22756 MB memory)
+ -> physical GPU (device: 0, name: TITAN RTX, pci bus id: 0000:84:00.0, compute capability: 7.5)
+></verbatim>
+
+Then our =OUTPUT= file will be:
+
+<verbatim>
+>ls -l
+total 3367004
+-rw-rw-r-- 1 leblancd supergroup 101 Oct 9 17:30 helloworld.py
+-rw-rw-r-- 1 leblancd supergroup 14 Oct 9 17:59 OUTPUT
+-rwxrwxr-x 1 leblancd supergroup 3447758848 Oct 9 17:09 tf-19.09-py3.sif*
+
+>cat OUTPUT
+b'Hello, TF!'</verbatim>
+
+---++ Instances
+
+So far, we have run our container with =shell= or =exec=, which runs the container in the foreground, meaning the running container terminates when we exit, either by quitting from the =shell= or by the end of execution from =exec=.%BR%
+We can, however, _detach_ a container and run it as a "service". In Singularity terms, this is called an *instance*.%BR%
+<verbatim>
+>singularity instance start --nv ./tf-19.09-py3.sif Tensorflow
+
+INFO: instance started successfully</verbatim>
+
+Now the instance is running, and we can launch however many as we like, though each instance needs a unique name.%BR%
+
+<verbatim>
+>singularity instance start --nv ./tf-19.09-py3.sif tensorflow
+INFO: instance started successfully
+>singularity instance start --nv ./tf-19.09-py3.sif tensorflow2
+INFO: instance started successfully</verbatim>
+
+To review what instances we have running:%BR%
+
+<verbatim>
+>singularity instance list
+INSTANCE NAME PID IMAGE
+Tensorflow 52226 /tmp/tf-19.09-py3.sif
+tensorflow 52358 /tmp/tf-19.09-py3.sif
+tensorflow2 52407 /tmp/tf-19.09-py3.sif</verbatim>
+
+__NOTE:__ we launched our instances with =--nv=, to expose the NVidia devices/drivers to the instances we launch (you cannot do this after the container instance is already running).
+
+Now, to access (or "attach") to the running instances, we can use =exec= or =shell= as before, but target the _instance_ like so:%BR%
+
+<verbatim>
+>singularity shell instance://tensorflow2
+Singularity tf-19.09-py3.sif:/tmp> nvidia-smi
+Wed Oct 9 18:24:58 2019
++-----------------------------------------------------------------------------+
+| NVIDIA-SMI 435.21 Driver Version: 435.21 CUDA Version: 10.1 |
+|-------------------------------+----------------------+----------------------+
+| GPU Name Persistence-M| Bus-Id Disp.A | Volatile Uncorr. ECC |
+| Fan Temp Perf Pwr:Usage/Cap| Memory-Usage | GPU-Util Compute M. |
+|===============================+======================+======================|
+| 0 TITAN RTX Off | 00000000:84:00.0 Off | N/A |
+| 21% 35C P0 N/A / N/A | 0MiB / 24220MiB | 0% Default |
++-------------------------------+----------------------+----------------------+
+
++-----------------------------------------------------------------------------+
+| Processes: GPU Memory |
+| GPU PID Type Process name Usage |
+|=============================================================================|
+| No running processes found |
++-----------------------------------------------------------------------------+</verbatim>
+
+Finally, to terminate our instances:%BR%
+
+<verbatim>
+>singularity instance stop Tensorflow
+Stopping Tensorflow instance of /tmp/tf-19.09-py3.sif (PID=52226)</verbatim>
+
+Or:
+
+<verbatim>
+>singularity instance stop -a
+Stopping tensorflow2 instance of /tmp/tf-19.09-py3.sif (PID=52407)
+Stopping tensorflow instance of /tmp/tf-19.09-py3.sif (PID=52762)</verbatim>
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9