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

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轻奢々
轻奢々 2020-11-22 03:00

When I get the following error:

events.js:72
        throw er; // Unhandled \'error\' event
              ^
Error: spawn ENOENT
    at errnoException (chil         


        
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  • 2020-11-22 03:39

    I was getting this error when trying to debug a node.js program from within VS Code editor on a Debian Linux system. I noticed the same thing worked OK on Windows. The solutions previously given here weren't much help because I hadn't written any "spawn" commands. The offending code was presumably written by Microsoft and hidden under the hood of the VS Code program.

    Next I noticed that node.js is called node on Windows but on Debian (and presumably on Debian-based systems such as Ubuntu) it's called nodejs. So I created an alias - from a root terminal, I ran

    ln -s /usr/bin/nodejs /usr/local/bin/node

    and this solved the problem. The same or a similar procedure will presumably work in other cases where your node.js is called nodejs but you're running a program which expects it to be called node, or vice-versa.

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  • 2020-11-22 03:42

    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.

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  • 2020-11-22 03:43

    Although it may be an environment path or another issue for some people, I had just installed the Latex Workshop extension for Visual Studio Code on Windows 10 and saw this error when attempting to build/preview the PDF. Running VS Code as Administrator solved the problem for me.

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  • 2020-11-22 03:45

    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.

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  • 2020-11-22 03:45

    Windows solution: Replace spawn with node-cross-spawn. For instance like this at the beginning of your app.js:

    (function() {
        var childProcess = require("child_process");
        childProcess.spawn = require('cross-spawn');
    })(); 
    
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  • 2020-11-22 03:45

    I got the same error for windows 8.The issue is because of an environment variable of your system path is missing . Add "C:\Windows\System32\" value to your system PATH variable.

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