15. Depots
The packages installed for a particular environment, defined in the files Project.toml and Manifest.toml within the directory structure, are not actually installed within that directory but into a "depot". The location of the depots are set by the variable DEPOT_PATH.
For details on the default depot locations and how they vary by installation method, see the DEPOT_PATH documentation.
Packages which are installed by a user go into the first depot and the Julia standard library is in the last depot.
You should not need to manage the user depot directly. Pkg will automatically clean up the depots when packages are removed after a delay. However you may want to manually remove old .julia/compiled/ subdirectories if you have any that reside for older Julia versions that you no longer use (hence have not been run to tidy themselves up).
Configuring the depot path with JULIA_DEPOT_PATH
The depot path can be configured using the JULIA_DEPOT_PATH environment variable, which is used to populate the global Julia DEPOT_PATH variable at startup. For complete details on the behavior of this environment variable, see the environment variables documentation.
Unlike the shell PATH variable, empty entries in JULIA_DEPOT_PATH have special behavior for easy overriding of the user depot while retaining access to system resources. For example, to switch the user depot to /custom/depot while still accessing bundled resources, use a trailing path separator:
export JULIA_DEPOT_PATH="/custom/depot:"The trailing path separator (: on Unix, ; on Windows) is crucial for including the default system depots, which contain the standard library and other bundled resources. Without it, Julia will only use the specified depot and will have to precompile standard library packages, which can be time-consuming and inefficient.
Shared depots for distributed computing
When using Julia in distributed computing environments, such as high-performance computing (HPC) clusters, it's recommended to use a shared depot via JULIA_DEPOT_PATH. This allows multiple Julia processes to share precompiled packages and reduces redundant compilation.
Since Julia v1.10, multiple processes using the same depot coordinate via pidfile locks to ensure only one process precompiles a package while others wait. However, due to the caching of native code in pkgimages since v1.9, you may need to set the JULIA_CPU_TARGET environment variable appropriately to ensure cache compatibility across different worker nodes with varying CPU capabilities.
For more details, see the FAQ section on distributed computing and the environment variables documentation.