How do I debug "Error: spawn ENOENT" on node.js?

node.js debugging error-handling child-process spawn

557,553

Solution 1

How to research the spawn call raising the error:

Use NODE_DEBUG=child_process, Credits to @karl-richter. Simple, quick, October 2019
Use a wrapper to decorate child_process.spawn, Credits to @jiaji-zhou. Simple, quick, January 2015
Long procedure, credits to @laconbass. Complex, time-cost, December 2014

Known, usual causes

Environment issues
- The command executable does not exist within the system (dependency not being installed). see prominc's answer
- The command executable does not exist within a directory of those specified by PATH environment variable.
- The executable binary was compiled with uncompatible libraries. see danilo-ramirez answer
Windows-only bugs/quirks
- '.cmd' extension / shell: true. see li-zheng answer
- Administrator permisions. see steve's answer
Wrong spawn('command', ['--argument', 'list'], { cwd, env, ...opts }) usage
- Specified working directory (opts.cwd) does not exist · see leeroy-brun's answer
- Argument list within command String ~~spawn('command --wrong --argument list')~~
- Env vars within command string ~~spawn('ENV_VAR=WRONG command')~~
- Argument list Array specified as String ~~spawn('cmd', '--argument list')~~
- Unset PATH env variable ~~spawn('cmd', [], { env: { variable } }~~ => spawn('cmd', [], { env: { ...process.env, variable } }

There are 2 posible origins for ENOENT:

Code you are writing

Code you depend on

When origin is code you depend on, usual cause is an Environment Issue (or windows quirk)

Solution 2

NOTE: This error is almost always caused because the command does not exist, because the working directory does not exist, or from a windows-only bug.

I found a particular easy way to get the idea of the root cause of:

Error: spawn ENOENT

The problem of this error is, there is really little information in the error message to tell you where the call site is, i.e. which executable/command is not found, especially when you have a large code base where there are a lot of spawn calls. On the other hand, if we know the exact command that cause the error then we can follow @laconbass' answer to fix the problem.

I found a very easy way to spot which command cause the problem rather than adding event listeners everywhere in your code as suggested in @laconbass' answer. The key idea is to wrap the original spawn call with a wrapper which prints the arguments send to the spawn call.

Here is the wrapper function, put it at the top of the index.js or whatever your server's starting script.

(function() {
    var childProcess = require("child_process");
    var oldSpawn = childProcess.spawn;
    function mySpawn() {
        console.log('spawn called');
        console.log(arguments);
        var result = oldSpawn.apply(this, arguments);
        return result;
    }
    childProcess.spawn = mySpawn;
})();

Then the next time you run your application, before the uncaught exception's message you will see something like that:

spawn called
{ '0': 'hg',
  '1': [],
  '2':
   { cwd: '/* omitted */',
     env: { IP: '0.0.0.0' },
     args: [] } }

In this way you can easily know which command actually is executed and then you can find out why nodejs cannot find the executable to fix the problem.

Solution 3

Step 1: Ensure `spawn` is called the right way

First, review the docs for child_process.spawn( command, args, options ):

Launches a new process with the given command, with command line arguments in args. If omitted, args defaults to an empty Array.

The third argument is used to specify additional options, which defaults to:

{ cwd: undefined, env: process.env }

Use env to specify environment variables that will be visible to the new process, the default is process.env.

Ensure you are not putting any command line arguments in command and the whole spawn call is valid. Proceed to next step.

Step 2: Identify the Event Emitter that emits the error event

Search on your source code for each call to spawn, or child_process.spawn, i.e.

spawn('some-command', [ '--help' ]);

and attach there an event listener for the 'error' event, so you get noticed the exact Event Emitter that is throwing it as 'Unhandled'. After debugging, that handler can be removed.

spawn('some-command', [ '--help' ])
  .on('error', function( err ){ throw err })
;

Execute and you should get the file path and line number where your 'error' listener was registered. Something like:

/file/that/registers/the/error/listener.js:29
      throw err;
            ^
Error: spawn ENOENT
    at errnoException (child_process.js:1000:11)
    at Process.ChildProcess._handle.onexit (child_process.js:791:34)

If the first two lines are still

events.js:72
        throw er; // Unhandled 'error' event

do this step again until they are not. You must identify the listener that emits the error before going on next step.

Step 3: Ensure the environment variable `$PATH` is set

There are two possible scenarios:

You rely on the default spawn behaviour, so child process environment will be the same as process.env.
You are explicity passing an env object to spawn on the options argument.

In both scenarios, you must inspect the PATH key on the environment object that the spawned child process will use.

Example for scenario 1

// inspect the PATH key on process.env
console.log( process.env.PATH );
spawn('some-command', ['--help']);

Example for scenario 2

var env = getEnvKeyValuePairsSomeHow();
// inspect the PATH key on the env object
console.log( env.PATH );
spawn('some-command', ['--help'], { env: env });

The absence of PATH (i.e., it's undefined) will cause spawn to emit the ENOENT error, as it will not be possible to locate any command unless it's an absolute path to the executable file.

When PATH is correctly set, proceed to next step. It should be a directory, or a list of directories. Last case is the usual.

Step 4: Ensure `command` exists on a directory of those defined in `PATH`

Spawn may emit the ENOENT error if the filename command (i.e, 'some-command') does not exist in at least one of the directories defined on PATH.

Locate the exact place of command. On most linux distributions, this can be done from a terminal with the which command. It will tell you the absolute path to the executable file (like above), or tell if it's not found.

Example usage of which and its output when a command is found

> which some-command
some-command is /usr/bin/some-command

Example usage of which and its output when a command is not found

> which some-command
bash: type: some-command: not found

miss-installed programs are the most common cause for a not found command. Refer to each command documentation if needed and install it.

When command is a simple script file ensure it's accessible from a directory on the PATH. If it's not, either move it to one or make a link to it.

Once you determine PATH is correctly set and command is accessible from it, you should be able to spawn your child process without spawn ENOENT being thrown.

Solution 4

As @DanielImfeld pointed it, ENOENT will be thrown if you specify "cwd" in the options, but the given directory does not exist.

Solution 5

in windows, simply adding shell: true option solved my problem:

incorrect:

const { spawn } = require('child_process');
const child = spawn('dir');

correct:

const { spawn } = require('child_process');
const child = spawn('dir', [], {shell: true});

View more solutions

557,553

Author by

laconbass

I love rhythm. The rhythm in music, at the flow of source code lines, at life... I love following that rhythm, break it down, faster, slowler, STOP. And start again... #SOreadytohelp

Updated on July 08, 2022

Comments

laconbass almost 2 years
When I get the following error:
```
events.js:72
        throw er; // Unhandled 'error' event
              ^
Error: spawn ENOENT
    at errnoException (child_process.js:1000:11)
    at Process.ChildProcess._handle.onexit (child_process.js:791:34)
```
What procedure can I follow to fix it?

Author note: Lots of issues with this error encouraged me to post this question for future references.

Related questions:
Adam Monsen about 9 years

Here's another idea: just change spawn() to exec() and try again. exec() will tell you what command it tried to run.
fredrikekelund about 9 years

The problem for me was indeed that PATH was undefined. Do you know what causes this? I asked a question about it as well stackoverflow.com/questions/29652582/…
laconbass about 9 years

I remember a time it was undefined because the way I was spawning the node proccess.
Dan Nissenbaum almost 9 years

Important: Make sure to place the code above as close to the start of the main JS file as possible. If you load other modules first, they can stash away the 'spawn' function and the override here will never be called.
CodeManiak almost 9 years

This has been very helpful to my debugging of Spawn ENOENT. I've referenced it multiple times. Thanks!
Alexander Mills over 8 years

if it's an ENOENT error, why would the command not be recognized on the OS? it seems reasonable that the command is recognized but something is wrong with reading the file itself...
laconbass over 8 years

@AlexMills Usually the situation you describe is reported as EACCES
Daniel Imfeld over 8 years

I've also found that ENOENT will be thrown if you specify cwd in the options, but the given directory does not exist.
GreenAsJade over 8 years

@DanielImfeld TOTAL SAVIOUR. You should write an answer that says this.
cdaringe about 8 years

I have a linux box and an osx box, both node versions reporting using v4.2.4. On the OSX machine if a try/catch wrap a call to spawn('bogus-binary', ...), it lands in the catch statement. in the linux box, it shows up in the event emitter. this is wild.
laconbass about 8 years

@cdaringe please post a new question with the code and let's see what the problem may be
Nilzor about 8 years

And what's the solution?
Nilzor about 8 years

Using node-cross-spawn worked for me. See answer below: stackoverflow.com/a/35561971/507339
laconbass about 8 years

Thinking on refactoring my answer to provide a "general guide", and leaving details to each cause of the problem (miss dependencies, incorrect calls, wrong environment,...).
anty over 7 years

When you are using spawn('some-command', ['--help'], { env: env }); as exemplified by Step 3 in this answer and are passing a custom environment, be sure to specify the PATH, for instance: { env: { PATH: process.env.PATH } }. The env option will not inherit variables from your current env by default.
reduckted over 7 years

Spent ages trying to find what was wrong and this ended up being the problem. I gave up on spawn and just used exec instead.
Bogdan Trusca over 7 years

worked except it is a drop-in, no need for child_process. Exactly the same way as node's spawn or spawnSync, so it's a drop in replacement. var spawn = require('cross-spawn'); // Spawn NPM asynchronously var child = spawn('npm', ['list', '-g', '-depth', '0'], { stdio: 'inherit' });
Emile Bergeron over 7 years

This is a duplicate of chayasan's answer
newguy over 7 years

I have no luck using the script. It doesn't work at all.
Felix Eve about 7 years

So how would you use this method in a grunt file? I'm not sure where to put this.
Yann Duran about 7 years

This worked perfectly for me. I just put this at the top of my gulpfile.js file, and bingo bango bongo, spawn logging!
Somename about 7 years

Does windows need ImageMagick installed as well? Im testing on windows and getting error
Deilan almost 7 years

Where to do these modifications?
laconbass almost 7 years

Don't quote the arguments inside the array
Joel B almost 7 years

@laconbass This is an obviously trivial example to convey the concept and so the quotes could be removed. However, there are cases where you absolutely need to quote the arguments (for example if you need to pass an argument that has a path with a space in it: "C:\Program Files\..."). I posted it here because, even though it may not have been the cause of your specific error case, it will hopefully help someone else experiencing this cryptic error because of Node's handling of quotes on Windows like I was encountering.
laconbass almost 7 years

node.js already makes some Black Magic and silently quotes arguments "properly". Your example should work without the undocumented option you mention, by unquoting argument inside the array.
Mitro over 6 years

so is there a way to execute in a specific directory the command?
Alexander Mills over 6 years

everyone who likes this answer, may also be interested in this native alternative: gist.github.com/ORESoftware/7bf225f0045b4649de6848f1ea5def4c
Tom over 5 years

I was running the command as root/ with sudo so the PATH environment variable was not the same. Step 3 was the step that pointed this out to me. Thanks!
Ted Nyberg over 5 years

Key part is adding shell: true
A Gupta over 5 years

This is called as monkey patching ! :)
Troncoso over 5 years

Just to add my own experience, I was running a java process from node. This error happened to me because of quotes around the command, rather than the argument. Test with spaces in the command path and it still works without quotes
demisx over 5 years

Hmm... Didn't work for me. Placed it at the top of gulpfile.js
Museful over 5 years

In Windows (7) it seems you also need to include the drive letter in the cwd path: 'c:/...' and not just '/...'
Nickofthyme over 5 years

I was able to solve my issue by passing shell: true to the spawn options.
laconbass over 5 years

While this may be a solution for win specific fixes, I don't see how it helps to debug the real cause of the ENOENT
Darius about 5 years

Replace console.log(arguments) with console.log(JSON.stringify(arguments, null, 4)) in case of nested (non-circular) objects that you want to print
givanse about 5 years

Downvoted because if what you want to have is a shell then you should use child_process.exec or pass shell: true to spawn.
Alexander Mills about 5 years

@givanse not necessarily true - you may want to run zsh or bash or fsh depending on what shell you want to use, and the behavior is also different
Matt Molnar about 5 years

Also, if your Node process is running inside a container like Docker, make sure the command you're trying to run has been added to the Dockerfile
Mathieu CAROFF almost 5 years

I have no idea why, but the spawn call would work in the node repl without the .cmd, but fail in a typescript jest test. -- This error can be quite hard to figure out, this answers deserves more upvotes.
Nick about 4 years

Wow such a simple solution and it worked for me! Everyone should try this first to see if it solves the issue.
laconbass almost 4 years

Again, related do filesystem path some way. The extension probably can't reach a path without admin permissions
laconbass almost 4 years

do you know the minimum node --version to be able to use this technique?
Kalle Richter almost 4 years

@laconbass No. I think that's a good SO question which will be anwered within hours.
laconbass almost 4 years

Just got curious. It's way better and cleaner than answer I've checked as accepted
MrYellow almost 4 years

Another issue is that shell MUST be a simple file path with no arguments. To setup a shell like Docker or similar where args need to be passed it must be wrapped in a proxy bash script.
laconbass almost 4 years

@MrYellow see stackoverflow.com/a/62551786/1894803
MrYellow almost 4 years

@laconbass Yeah that overloading of spawn works, although the call in my case was buried within a module, made sense to use a bash script (which cleanly accepted -c command only) to call the actual shell with arguments (innershell --foo $1 "$2") rather than monkey patching it deeply within the JS.
laconbass almost 4 years

@MrYellow NODE_DEBUG=child_process may also help avoiding the monkey-patching solution => stackoverflow.com/a/58474965/1894803
bFunc over 3 years

Thanks! This fixed my issue, no need to define cmd or path
Marcello de Sales over 3 years

I was executing execa with "ab" command, but "Apache Bench" was not installed in the container... So, the first "Environment Issues" case...
laconbass over 3 years

The .cmd extension thing is already covered by existing answers
Gal Bracha over 3 years

Running yarn (To install) fixed it
laconbass almost 3 years

Your issue seems more related to npm itself rather than to node's child_process.spawn(). And seems like a windows quirk
John Vandivier almost 3 years

miss-installed programs or non-interoperable installations (even when both may follow the documentation). Example: I installed python via amazon-linux-extras on Amazon Linux 2 but it installed to the entity python3.8 where PythonShell library for Node expected to invoke python3. I aliased the first to the second and continued failure. Now, change the installation to directly yum install python3 and remove the alias - no issue anymore.
John Vandivier almost 3 years

the command does not exist agree, or sometimes even when it does exist but only as an alias
laconbass over 2 years

Thanks for the tip
Paul over 2 years

Simply run brew install imagemagick
AmiNadimi about 2 years

The first two lines of this answer fixed my problem!
Topher Fangio about 2 years

Adding { shell: true } works on MacOS as well.