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Frequently asked questions

conda-store fails to build Conda environment and worker is spontaneously killed (9 SIGKILL)​

The following error most likely indicates that you have not allocated enough memory to conda-store-workers for solving and building the given environment. Solve this by increasing the memory allocated to the container.

Process 'ForkPoolWorker-31' pid:90 exited with 'signal 9 (SIGKILL)'

Task handler raised error: WorkerLostError('Worker exited prematurely: signal 9 (SIGKILL) Job: 348.')

Traceback (most recent call last):
File "/opt/conda/envs/conda-store-server/lib/python3.9/site-packages/billiard/pool.py", line 1265, in mark_as_worker_lost

    raise WorkerLostError(

billiard.exceptions.WorkerLostError: Worker exited prematurely: signal 9 (SIGKILL) Job: 348.

Why are environment builds stuck in building state?​

Recently conda-store added a feature to cleanup builds which are stuck in the BUILDING state and are not currently running on the workers. This feature only works for certain brokers e.g. redis. Database celery brokers are not supported.

This issue occurs when the worker spontaneously dies. This can happen for several reasons:

  • worker is killed due to consuming too much memory (conda solver/builds can consume a lot of memory)
  • worker was killed for other reasons e.g. forced restart
  • bugs in conda-store

Build path length​

Conda packages are guaranteed to be relocatable as long as the environment prefix length is <= 255 characters. In conda-store, the said prefix is specified in Build.build_path. When building an environment, you might see an error like this:

build_path too long: must be <= 255 characters

If so, try configuring the conda-store CondaStore.store_directory to be as close to the filesystem root as possible. Additionally, 255 characters is also a common limit for individual files on many filesystems. When creating environments, try using shorter namespace and environment names since they affect both the build_path length and the filename length.

Build key versions​

The part of the build path that identifies a particular environment build is the build key. Originally, conda-store used the following format, known as version 1:

c7afdeffbe2bda7d16ca69beecc8bebeb29280a95d4f3ed92849e4047710923b-20231105-035410-510258-12345678-this-is-a-long-environment-name
^ (1)                                                            ^ (2)                  ^ (3)    ^ (4)

It consists of:

  1. a SHA-256 hash of the environment specification (CondaSpecification, which represents a user-provided environment, is converted to a dict and passed to datastructure_hash, which recursively sorts it and calculates the SHA-256 hash)
  2. a human-readable timestamp (year, month, day, -, hour, minute, second, -, microsecond)
  3. the id of a build
  4. the environment name.

To help mitigate build path length issues, a shorter build key format was introduced, known as version 2:

c7afdeff-1699156450-12345678-this-is-a-long-environment-name
^ (1)    ^ (2)      ^ (3)    ^ (4)

It consists of:

  1. a truncated SHA-256 hash of the environment specification (CondaSpecification, which represents a user-provided environment, is converted to a dict and passed to datastructure_hash, which recursively sorts it and calculates the SHA-256 hash)
  2. a Unix timestamp
  3. the id of a build
  4. the environment name.

The version 2 format is now the default. Environments created using the version 1 format will continue to be accessible in the UI, but new builds will use the version 2 format. No changes are needed for existing deployments of conda-store.

There is no real reason to use the version 1 format anymore, but it can be explicitly set via the config:

c.CondaStore.build_key_version = 1

The version 2 format can also be explicitly set if needed (this is the same as the default):

c.CondaStore.build_key_version = 2

Long paths on Windows​

conda-store supports Windows in standalone mode. However, when creating environments with certain packages, you may see errors like:

ERROR:root:[WinError 206] The filename or extension is too long: 'C:\\...'

This error is due to the fact that Windows has a limitation that file paths cannot be more than 260 characters.

See conda-store issue #588 for more details.

Solution 1: Extended-length path prefix (\\?\)​

If you don't have administrator privileges, try using the following config option:

c.CondaStore.win_extended_length_prefix = True

This adds the extended-length path prefix (\\?\) to conda-store build_path and environment_path methods, which should allow for a maximum total path length of 32,767 characters when building packages.

See this Microsoft support article for more details on the extended-length path prefix.

Solution 2: LongPathsEnabled​

If you have administrator privileges, set the registry key Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\FileSystem\LongPathsEnabled (Type: REG_DWORD) to 1, which removes this MAX_PATH limitation.

See this Microsoft support article for more details on how to set this registry key.

Solution 3: store_directory​

If it is not possible to set the registry key, for instance, because you do not have access to administrator privileges, you should configure the conda-store CondaStore.store_directory to be as close to the filesystem root as possible, so that the total length of the paths of package files is minimized.

Solution 4: build_key_version​

Use the short build key version as explained above:

c.CondaStore.build_key_version = 2

What are the resource requirements for conda-store-server​

conda-store-server is a web server and should not require any specific resources. 1 GB of RAM and 1 CPU should be plenty.

conda-store-worker does the actual builds of the conda environments. Solving for conda environments can take a lot of memory in some circumstances. Make sure to allocate at least 4 GB of RAM to the worker along with at least one CPU.