Environment Variables

Julia can be configured with a number of environment variables, set either in the usual way for each operating system, or in a portable way from within Julia. Supposing that you want to set the environment variable JULIA_EDITOR to vim, you can type ENV["JULIA_EDITOR"] = "vim" (for instance, in the REPL) to make this change on a case by case basis, or add the same to the user configuration file ~/.julia/config/startup.jl in the user's home directory to have a permanent effect. The current value of the same environment variable can be determined by evaluating ENV["JULIA_EDITOR"].

The environment variables that Julia uses generally start with JULIA. If InteractiveUtils.versioninfo is called with the keyword verbose=true, then the output will list any defined environment variables relevant for Julia, including those which include JULIA in their names.

Note

It is recommended to avoid changing environment variables during runtime, such as within a ~/.julia/config/startup.jl.

One reason is that some julia language variables, such as JULIA_NUM_THREADS and JULIA_PROJECT, need to be set before Julia starts.

Similarly, __init__() functions of user modules in the sysimage (via PackageCompiler) are run before startup.jl, so setting environment variables in a startup.jl may be too late for user code.

Further, changing environment variables during runtime can introduce data races into otherwise benign code.

In Bash, environment variables can either be set manually by running, e.g., export JULIA_NUM_THREADS=4 before starting Julia, or by adding the same command to ~/.bashrc or ~/.bash_profile to set the variable each time Bash is started.

File locations

JULIA_BINDIR

The absolute path of the directory containing the Julia executable, which sets the global variable Sys.BINDIR. If $JULIA_BINDIR is not set, then Julia determines the value Sys.BINDIR at run-time.

The executable itself is one of

$JULIA_BINDIR/julia
$JULIA_BINDIR/julia-debug

by default.

The global variable Base.DATAROOTDIR determines a relative path from Sys.BINDIR to the data directory associated with Julia. Then the path

$JULIA_BINDIR/$DATAROOTDIR/julia/base

determines the directory in which Julia initially searches for source files (via Base.find_source_file()).

Likewise, the global variable Base.SYSCONFDIR determines a relative path to the configuration file directory. Then Julia searches for a startup.jl file at

$JULIA_BINDIR/$SYSCONFDIR/julia/startup.jl
$JULIA_BINDIR/../etc/julia/startup.jl

by default (via Base.load_julia_startup()).

For example, a Linux installation with a Julia executable located at /bin/julia, a DATAROOTDIR of ../share, and a SYSCONFDIR of ../etc will have JULIA_BINDIR set to /bin, a source-file search path of

/share/julia/base

and a global configuration search path of

/etc/julia/startup.jl

JULIA_PROJECT

A directory path that indicates which project should be the initial active project. Setting this environment variable has the same effect as specifying the --project start-up option, but --project has higher precedence. If the variable is set to @. (note the trailing dot) then Julia tries to find a project directory that contains Project.toml or JuliaProject.toml file from the current directory and its parents. See also the chapter on Code Loading.

Note

JULIA_PROJECT must be defined before starting julia; defining it in startup.jl is too late in the startup process.

JULIA_LOAD_PATH

The JULIA_LOAD_PATH environment variable is used to populate the global Julia LOAD_PATH variable, which determines which packages can be loaded via import and using (see Code Loading).

Unlike the shell PATH variable, empty entries in JULIA_LOAD_PATH are expanded to the default value of LOAD_PATH, ["@", "@v#.#", "@stdlib"] when populating LOAD_PATH. This allows easy appending, prepending, etc. of the load path value in shell scripts regardless of whether JULIA_LOAD_PATH is already set or not. For example, to prepend the directory /foo/bar to LOAD_PATH just do

export JULIA_LOAD_PATH="/foo/bar:$JULIA_LOAD_PATH"

If the JULIA_LOAD_PATH environment variable is already set, its old value will be prepended with /foo/bar. On the other hand, if JULIA_LOAD_PATH is not set, then it will be set to /foo/bar: which will expand to a LOAD_PATH value of ["/foo/bar", "@", "@v#.#", "@stdlib"]. If JULIA_LOAD_PATH is set to the empty string, it expands to an empty LOAD_PATH array. In other words, the empty string is interpreted as a zero-element array, not a one-element array of the empty string. This behavior was chosen so that it would be possible to set an empty load path via the environment variable. If you want the default load path, either unset the environment variable or if it must have a value, set it to the string :.

Note

On Windows, path elements are separated by the ; character, as is the case with most path lists on Windows. Replace : with ; in the above paragraph.

JULIA_DEPOT_PATH

The JULIA_DEPOT_PATH environment variable is used to populate the global Julia DEPOT_PATH variable, which controls where the package manager, as well as Julia's code loading mechanisms, look for package registries, installed packages, named environments, repo clones, cached compiled package images, configuration files, and the default location of the REPL's history file.

Unlike the shell PATH variable but similar to JULIA_LOAD_PATH, empty entries in JULIA_DEPOT_PATH are expanded to the default value of DEPOT_PATH, excluding the user depot. This allows easy overriding of the user depot, while still retaining access to resources that are bundled with Julia, like cache files, artifacts, etc. For example, to switch the user depot to /foo/bar just do

export JULIA_DEPOT_PATH="/foo/bar:"

All package operations, like cloning registrise or installing packages, will now write to /foo/bar, but since the empty entry is expanded to the default system depot, any bundled resources will still be available. If you really only want to use the depot at /foo/bar, and not load any bundled resources, simply set the environment variable to /foo/bar without the trailing colon.

There are two exceptions to the above rule. First, if JULIA_DEPOT_PATH is set to the empty string, it expands to an empty DEPOT_PATH array. In other words, the empty string is interpreted as a zero-element array, not a one-element array of the empty string. This behavior was chosen so that it would be possible to set an empty depot path via the environment variable.

Second, if no user depot is specified in JULIA_DEPOT_PATH, then the empty entry is expanded to the default depot including the user depot. This makes it possible to use the default depot, as if the environment variable was unset, by setting it to the string :.

Note

On Windows, path elements are separated by the ; character, as is the case with most path lists on Windows. Replace : with ; in the above paragraph.

Note

JULIA_DEPOT_PATH must be defined before starting julia; defining it in startup.jl is too late in the startup process; at that point you can instead directly modify the DEPOT_PATH array, which is populated from the environment variable.

JULIA_HISTORY

The absolute path REPL.find_hist_file() of the REPL's history file. If $JULIA_HISTORY is not set, then REPL.find_hist_file() defaults to

$(DEPOT_PATH[1])/logs/repl_history.jl

JULIA_MAX_NUM_PRECOMPILE_FILES

Sets the maximum number of different instances of a single package that are to be stored in the precompile cache (default = 10).

JULIA_VERBOSE_LINKING

If set to true, linker commands will be displayed during precompilation.

Pkg.jl

JULIA_CI

If set to true, this indicates to the package server that any package operations are part of a continuous integration (CI) system for the purposes of gathering package usage statistics.

JULIA_NUM_PRECOMPILE_TASKS

The number of parallel tasks to use when precompiling packages. See Pkg.precompile.

JULIA_PKG_DEVDIR

The default directory used by Pkg.develop for downloading packages.

JULIA_PKG_IGNORE_HASHES

If set to 1, this will ignore incorrect hashes in artifacts. This should be used carefully, as it disables verification of downloads, but can resolve issues when moving files across different types of file systems. See Pkg.jl issue #2317 for more details.

Julia 1.6

This is only supported in Julia 1.6 and above.

JULIA_PKG_OFFLINE

If set to true, this will enable offline mode: see Pkg.offline.

Julia 1.5

Pkg's offline mode requires Julia 1.5 or later.

JULIA_PKG_PRECOMPILE_AUTO

If set to 0, this will disable automatic precompilation by package actions which change the manifest. See Pkg.precompile.

JULIA_PKG_SERVER

Specifies the URL of the package registry to use. By default, Pkg uses https://pkg.julialang.org to fetch Julia packages. In addition, you can disable the use of the PkgServer protocol, and instead access the packages directly from their hosts (GitHub, GitLab, etc.) by setting: export JULIA_PKG_SERVER=""

JULIA_PKG_SERVER_REGISTRY_PREFERENCE

Specifies the preferred registry flavor. Currently supported values are conservative (the default), which will only publish resources that have been processed by the storage server (and thereby have a higher probability of being available from the PkgServers), whereas eager will publish registries whose resources have not necessarily been processed by the storage servers. Users behind restrictive firewalls that do not allow downloading from arbitrary servers should not use the eager flavor.

Julia 1.7

This only affects Julia 1.7 and above.

JULIA_PKG_UNPACK_REGISTRY

If set to true, this will unpack the registry instead of storing it as a compressed tarball.

Julia 1.7

This only affects Julia 1.7 and above. Earlier versions will always unpack the registry.

JULIA_PKG_USE_CLI_GIT

If set to true, Pkg operations which use the git protocol will use an external git executable instead of the default libgit2 library.

Julia 1.7

Use of the git executable is only supported on Julia 1.7 and above.

JULIA_PKGRESOLVE_ACCURACY

The accuracy of the package resolver. This should be a positive integer, the default is 1.

JULIA_PKG_PRESERVE_TIERED_INSTALLED

Change the default package installation strategy to Pkg.PRESERVE_TIERED_INSTALLED to let the package manager try to install versions of packages while keeping as many versions of packages already installed as possible.

Julia 1.9

This only affects Julia 1.9 and above.

Network transport

JULIA_NO_VERIFY_HOSTS

JULIA_SSL_NO_VERIFY_HOSTS

JULIA_SSH_NO_VERIFY_HOSTS

JULIA_ALWAYS_VERIFY_HOSTS

Specify hosts whose identity should or should not be verified for specific transport layers. See NetworkOptions.verify_host

JULIA_SSL_CA_ROOTS_PATH

Specify the file or directory containing the certificate authority roots. See NetworkOptions.ca_roots

External applications

JULIA_SHELL

The absolute path of the shell with which Julia should execute external commands (via Base.repl_cmd()). Defaults to the environment variable $SHELL, and falls back to /bin/sh if $SHELL is unset.

Note

On Windows, this environment variable is ignored, and external commands are executed directly.

JULIA_EDITOR

The editor returned by InteractiveUtils.editor() and used in, e.g., InteractiveUtils.edit, referring to the command of the preferred editor, for instance vim.

$JULIA_EDITOR takes precedence over $VISUAL, which in turn takes precedence over $EDITOR. If none of these environment variables is set, then the editor is taken to be open on Windows and OS X, or /etc/alternatives/editor if it exists, or emacs otherwise.

To use Visual Studio Code on Windows, set $JULIA_EDITOR to code.cmd.

Parallelization

JULIA_CPU_THREADS

Overrides the global variable Base.Sys.CPU_THREADS, the number of logical CPU cores available.

JULIA_WORKER_TIMEOUT

A Float64 that sets the value of Distributed.worker_timeout() (default: 60.0). This function gives the number of seconds a worker process will wait for a master process to establish a connection before dying.

JULIA_NUM_THREADS

An unsigned 64-bit integer (uint64_t) that sets the maximum number of threads available to Julia. If $JULIA_NUM_THREADS is not positive or is not set, or if the number of CPU threads cannot be determined through system calls, then the number of threads is set to 1.

If $JULIA_NUM_THREADS is set to auto, then the number of threads will be set to the number of CPU threads.

Note

JULIA_NUM_THREADS must be defined before starting julia; defining it in startup.jl is too late in the startup process.

Julia 1.5

In Julia 1.5 and above the number of threads can also be specified on startup using the -t/--threads command line argument.

Julia 1.7

The auto value for $JULIA_NUM_THREADS requires Julia 1.7 or above.

JULIA_THREAD_SLEEP_THRESHOLD

If set to a string that starts with the case-insensitive substring "infinite", then spinning threads never sleep. Otherwise, $JULIA_THREAD_SLEEP_THRESHOLD is interpreted as an unsigned 64-bit integer (uint64_t) and gives, in nanoseconds, the amount of time after which spinning threads should sleep.

JULIA_NUM_GC_THREADS

Sets the number of threads used by Garbage Collection. If unspecified is set to the number of worker threads.

Julia 1.10

The environment variable was added in 1.10

JULIA_IMAGE_THREADS

An unsigned 32-bit integer that sets the number of threads used by image compilation in this Julia process. The value of this variable may be ignored if the module is a small module. If left unspecified, the smaller of the value of JULIA_CPU_THREADS or half the number of logical CPU cores is used in its place.

JULIA_IMAGE_TIMINGS

A boolean value that determines if detailed timing information is printed during during image compilation. Defaults to 0.

JULIA_EXCLUSIVE

If set to anything besides 0, then Julia's thread policy is consistent with running on a dedicated machine: the master thread is on proc 0, and threads are affinitized. Otherwise, Julia lets the operating system handle thread policy.

REPL formatting

Environment variables that determine how REPL output should be formatted at the terminal. The JULIA_*_COLOR variables should be set to ANSI terminal escape sequences. Julia provides a high-level interface with much of the same functionality; see the section on The Julia REPL.

JULIA_ERROR_COLOR

The formatting Base.error_color() (default: light red, "\033[91m") that errors should have at the terminal.

JULIA_WARN_COLOR

The formatting Base.warn_color() (default: yellow, "\033[93m") that warnings should have at the terminal.

JULIA_INFO_COLOR

The formatting Base.info_color() (default: cyan, "\033[36m") that info should have at the terminal.

JULIA_INPUT_COLOR

The formatting Base.input_color() (default: normal, "\033[0m") that input should have at the terminal.

JULIA_ANSWER_COLOR

The formatting Base.answer_color() (default: normal, "\033[0m") that output should have at the terminal.

NO_COLOR

When this variable is present and not an empty string (regardless of its value) then colored text will be disabled on the REPL. Can be overridden with the flag --color=yes or with the environment variable FORCE_COLOR. This environment variable is commonly recognized by command-line applications.

FORCE_COLOR

When this variable is present and not an empty string (regardless of its value) then colored text will be enabled on the REPL. Can be overridden with the flag --color=no. This environment variable is commonly recognized by command-line applications.

System and Package Image Building

JULIA_CPU_TARGET

Modify the target machine architecture for (pre)compiling system and package images. JULIA_CPU_TARGET only affects machine code image generation being output to a disk cache. Unlike the --cpu-target, or -C, command line option, it does not influence just-in-time (JIT) code generation within a Julia session where machine code is only stored in memory.

Valid values for JULIA_CPU_TARGET can be obtained by executing julia -C help.

Setting JULIA_CPU_TARGET is important for heterogeneous compute systems where processors of distinct types or features may be present. This is commonly encountered in high performance computing (HPC) clusters since the component nodes may be using distinct processors.

The CPU target string is a list of strings separated by ; each string starts with a CPU or architecture name and followed by an optional list of features separated by ,. A generic or empty CPU name means the basic required feature set of the target ISA which is at least the architecture the C/C++ runtime is compiled with. Each string is interpreted by LLVM.

A few special features are supported:

  1. clone_all

    This forces the target to have all functions in sysimg cloned. When used in negative form (i.e. -clone_all), this disables full clone that's enabled by default for certain targets.

  2. base([0-9]*)

    This specifies the (0-based) base target index. The base target is the target that the current target is based on, i.e. the functions that are not being cloned will use the version in the base target. This option causes the base target to be fully cloned (as if clone_all is specified for it) if it is not the default target (0). The index can only be smaller than the current index.

  3. opt_size

    Optimize for size with minimum performance impact. Clang/GCC's -Os.

  4. min_size

    Optimize only for size. Clang's -Oz.

Debugging and profiling

JULIA_DEBUG

Enable debug logging for a file or module, see Logging for more information.

JULIA_PROFILE_PEEK_HEAP_SNAPSHOT

Enable collecting of a heap snapshot during execution via the profiling peek mechanism. See Triggered During Execution.

JULIA_TIMING_SUBSYSTEMS

Allows you to enable or disable zones for a specific Julia run. For instance, setting the variable to +GC,-INFERENCE will enable the GC zones and disable the INFERENCE zones. See Dynamically Enabling and Disabling Zones.

JULIA_GC_NO_GENERATIONAL

If set to anything besides 0, then the Julia garbage collector never performs "quick sweeps" of memory.

Note

This environment variable only has an effect if Julia was compiled with garbage-collection debugging (that is, if WITH_GC_DEBUG_ENV is set to 1 in the build configuration).

JULIA_GC_WAIT_FOR_DEBUGGER

If set to anything besides 0, then the Julia garbage collector will wait for a debugger to attach instead of aborting whenever there's a critical error.

Note

This environment variable only has an effect if Julia was compiled with garbage-collection debugging (that is, if WITH_GC_DEBUG_ENV is set to 1 in the build configuration).

ENABLE_JITPROFILING

If set to anything besides 0, then the compiler will create and register an event listener for just-in-time (JIT) profiling.

Note

This environment variable only has an effect if Julia was compiled with JIT profiling support, using either

  • Intel's VTune™ Amplifier (USE_INTEL_JITEVENTS set to 1 in the build configuration), or
  • OProfile (USE_OPROFILE_JITEVENTS set to 1 in the build configuration).
  • Perf (USE_PERF_JITEVENTS set to 1 in the build configuration). This integration is enabled by default.

ENABLE_GDBLISTENER

If set to anything besides 0 enables GDB registration of Julia code on release builds. On debug builds of Julia this is always enabled. Recommended to use with -g 2.

JULIA_LLVM_ARGS

Arguments to be passed to the LLVM backend.

JULIA_FALLBACK_REPL

Forces the fallback repl instead of REPL.jl.