# Environment Variables

Julia may be configured with a number of environment variables, either in the
usual way of the operating system, or in a portable way from within Julia.
Suppose you want to set the environment variable JULIA_EDITOR to
vim, then either 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 is
determined by evaluating ENV["JULIA_EDITOR"].

The environment variables that Julia uses generally start with JULIA. If
InteractiveUtils.versioninfo is called with verbose equal to true, then the
output will list defined environment variables relevant for Julia, including
those for which JULIA appears in the name.

# 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 points to the current Julia 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 @.,
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

A separated list of absolute paths that are to be appended to the variable
LOAD_PATH. (In Unix-like systems, the path separator is :; in
Windows systems, the path separator is ;.) The LOAD_PATH variable is where
Base.require and Base.load_in_path() look for code; it defaults to
the absolute path
$JULIA_HOME/../share/julia/stdlib/v$(VERSION.major).$(VERSION.minor) so that,
e.g., version 0.7 of Julia on a Linux system with a Julia executable at
/bin/julia will have a default LOAD_PATH of /share/julia/stdlib/v0.7.

# 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

$HOME/.julia/logs/repl_history.jl

# JULIA_PKGRESOLVE_ACCURACY

A positive Int that determines how much time the max-sum subroutine
MaxSum.maxsum() of the package dependency resolver
will devote to attempting satisfying constraints before giving up: this value is
by default 1, and larger values correspond to larger amounts of time.

Suppose the value of $JULIA_PKGRESOLVE_ACCURACY is n. Then

• the number of pre-decimation iterations is 20*n,
• the number of iterations between decimation steps is 10*n, and
• at decimation steps, at most one in every 20*n packages is decimated.

# 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.

# 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 Base.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 exceeds the number of available
physical CPU cores, then the number of threads is set to the number of cores. If
$JULIA_NUM_THREADS is not positive or is not set, or if the number of CPU
cores cannot be determined through system calls, then the number of threads is
set to 1.

# 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.

# JULIA_STACKFRAME_LINEINFO_COLOR

The formatting Base.stackframe_lineinfo_color() (default: bold, "\033[1m")
that line info should have during a stack trace at the terminal.

# JULIA_STACKFRAME_FUNCTION_COLOR

The formatting Base.stackframe_function_color() (default: bold, "\033[1m")
that function calls should have during a stack trace at the terminal.

# Debugging and profiling

# 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.

!!! note

These environment variables only have 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_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).

# JULIA_LLVM_ARGS

Arguments to be passed to the LLVM backend.

# JULIA_DEBUG_LOADING

If set, then Julia prints detailed information about the cache in the loading
process of Base.require.