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.

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 @. 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.

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 :.

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. This allows easy appending, prepending, etc. of the depot path value in shell scripts regardless of whether JULIA_DEPOT_PATH is already set or not. For example, to prepend the directory /foo/bar to DEPOT_PATH just do

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

If the JULIA_DEPOT_PATH environment variable is already set, its old value will be prepended with /foo/bar. On the other hand, if JULIA_DEPOT_PATH is not set, then it will be set to /foo/bar: which will have the effect of prepending /foo/bar to the default depot path. 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. If you want the default depot path, either unset the environment variable or if it must have a value, set it to the string :.

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_PKG_SERVER

Used by Pkg.jl, for downloading packages and updating the registry. By default, Pkg uses https://pkg.julialang.org to fetch Julia packages. You can use this environment variable to select a different server. 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=""

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.

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.

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.

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_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. Generally, these 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.

Debugging and profiling

JULIA_DEBUG

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

JULIA_GC_ALLOC_POOL, JULIA_GC_ALLOC_OTHER, JULIA_GC_ALLOC_PRINT

If set, these environment variables take strings that optionally start with the character 'r', followed by a string interpolation of a colon-separated list of three signed 64-bit integers (int64_t). This triple of integers a:b:c represents the arithmetic sequence a, a + b, a + 2*b, ... c.

• If it's the nth time that jl_gc_pool_alloc() has been called, and n belongs to the arithmetic sequence represented by $JULIA_GC_ALLOC_POOL, then garbage collection is forced.
• If it's the nth time that maybe_collect() has been called, and n belongs to the arithmetic sequence represented by $JULIA_GC_ALLOC_OTHER, then garbage collection is forced.
• If it's the nth time that jl_gc_collect() has been called, and n belongs to the arithmetic sequence represented by $JULIA_GC_ALLOC_PRINT, then counts for the number of calls to jl_gc_pool_alloc() and maybe_collect() are printed.

If the value of the environment variable begins with the character 'r', then the interval between garbage collection events is randomized.

JULIA_GC_NO_GENERATIONAL

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

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.

ENABLE_JITPROFILING

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

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.