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

Question

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.

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Answer 1

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:

1. You rely on the default spawn behaviour, so child process environment will be the same as process.env.
2. 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.

Answer 2

I ran into the same problem, but I found a simple way to fix it. It appears to be spawn() errors if the program has been added to the PATH by the user (e.g. normal system commands work).

To fix this, you can use the which module (npm install --save which):

// Require which and child_process
const which = require('which');
const spawn = require('child_process').spawn;
// Find npm in PATH
const npm = which.sync('npm');
// Execute
const noErrorSpawn = spawn(npm, ['install']);

Answer 3

If you're on Windows Node.js does some funny business when handling quotes that may result in you issuing a command that you know works from the console, but does not when run in Node. For example the following should work:

spawn('ping', ['"8.8.8.8"'], {});

but fails. There's a fantastically undocumented option windowsVerbatimArguments for handling quotes/similar that seems to do the trick, just be sure to add the following to your opts object:

const opts = {
    windowsVerbatimArguments: true
};

and your command should be back in business.

 spawn('ping', ['"8.8.8.8"'], { windowsVerbatimArguments: true });

Answer 4

Add C:\Windows\System32\ to the path environment variable.

Steps

1. Go to my computer and properties

2. Click on Advanced settings

3. Then on Environment variables

4. Select Path and then click on edit

5. Paste the following if not already present: C:\Windows\System32\

6. Close the command prompt

7. Run the command that you wanted to run

Answer 5

solution in my case

var spawn = require('child_process').spawn;

const isWindows = /^win/.test(process.platform); 

spawn(isWindows ? 'twitter-proxy.cmd' : 'twitter-proxy');
spawn(isWindows ? 'http-server.cmd' : 'http-server');

Answer 6

Ensure module to be executed is installed or full path to command if it's not a node module