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_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.

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.

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.

• 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.