nodejs/node · error · Exception

Environment variable "%s" required to be set to valid path

Error message

Environment variable "%s" required to be set to valid path

What it means

After parsing the 'set' output into an env dict, _ExtractImportantEnvironment requires SYSTEMROOT, TEMP, and TMP to be present. These are needed to spawn compile/link processes correctly. If any is missing (the setup script's environment did not define them), gyp raises rather than emit a broken environment block.

Source

Thrown at tools/gyp/pylib/gyp/msvs_emulation.py:1133

    # This occasionally happens and leads to misleading SYSTEMROOT error messages
    # if not caught here.
    if output_of_set.count("=") == 0:
        raise Exception("Invalid output_of_set. Value is:\n%s" % output_of_set)
    for line in output_of_set.splitlines():
        for envvar in envvars_to_save:
            if re.match(envvar + "=", line.lower()):
                var, setting = line.split("=", 1)
                if envvar == "path":
                    # Our own rules (for running gyp-win-tool) and other actions in
                    # Chromium rely on python being in the path. Add the path to this
                    # python here so that if it's not in the path when ninja is run
                    # later, python will still be found.
                    setting = os.path.dirname(sys.executable) + os.pathsep + setting
                env[var.upper()] = setting
                break
    for required in ("SYSTEMROOT", "TEMP", "TMP"):
        if required not in env:
            raise Exception(
                'Environment variable "%s" required to be set to valid path' % required
            )
    return env


def _FormatAsEnvironmentBlock(envvar_dict):
    """Format as an 'environment block' directly suitable for CreateProcess.
    Briefly this is a list of key=value\0, terminated by an additional \0. See
    CreateProcess documentation for more details."""
    block = ""
    nul = "\0"
    for key, value in envvar_dict.items():
        block += key + "=" + value + nul
    block += nul
    return block


def _ExtractCLPath(output_of_where):

View on GitHub (pinned to 1b2de5e052)

Solutions

In the shell where gyp runs, confirm the missing variable is set: echo %SYSTEMROOT% / %TEMP% / %TMP%.
Set any missing variable (e.g. set SYSTEMROOT=C:\Windows) before invoking gyp/ninja.
If using a container, bake these variables into the image.
Verify the VS setup script isn't clearing them.

Example fix

// before: shell lacks SYSTEMROOT
// after
C:\> set SYSTEMROOT=C:\Windows
C:\> set TEMP=C:\Users\me\AppData\Local\Temp
C:\> set TMP=C:\Users\me\AppData\Local\Temp
C:\> gyp --depth=. my.gyp

Defensive patterns

Strategy: validation

Validate before calling

import os
for required in ('SYSTEMROOT', 'TEMP', 'TMP'):
    if not os.environ.get(required):
        raise EnvironmentError(f'{required} must be set before running gyp/ninja on Windows')

Type guard

def windows_env_complete() -> bool:
    import os
    return all(os.environ.get(v) for v in ('SYSTEMROOT', 'TEMP', 'TMP'))

Prevention

In CI containers, explicitly set SYSTEMROOT, TEMP, TMP.
Verify the VS developer command prompt sets all three before invoking gyp.
Log the parsed env block once during setup to catch regressions.

When it happens

Trigger: The parsed environment block lacks one of SYSTEMROOT, TEMP, or TMP — typically because the 'set' output did not contain a matching line (case-insensitive regex match on 'var=').

Common situations: A stripped-down or containerized Windows environment where these variables are not set; a CI image that cleared TEMP/TMP; a VS setup script that overwrote or omitted them; the same root cause as the Invalid output_of_set error (bad set output) but with '=' lines that simply lacked these keys.

Related errors

AI-assisted analysis of nodejs/node@1b2de5e052 (2026-08-13). Data as JSON: /api/errors/8ecd1ef8c9b5bc20. Report an issue: GitHub.