python/cpython · error

error when writing to '%s'

Error message

error when writing to '%s'

What it means

Build-time error from Programs/_freeze_module.c: after writing the frozen module's C source, ferror(outfile) reports a stream error — typically ENOSPC (disk full) or an I/O error on the output file. The file is closed and write_frozen() returns -1, failing the freeze step.

Source

Thrown at Programs/_freeze_module.c:210

       which in turn should cause the EOL style match the C library's text mode */
    FILE *outfile = fopen(outpath, "w");
    if (outfile == NULL) {
        fprintf(stderr, "cannot open '%s' for writing\n", outpath);
        return -1;
    }

    fprintf(outfile, "%s\n", header);
    char *arrayname = get_varname(name, "_Py_M__");
    if (arrayname == NULL) {
        fprintf(stderr, "memory error: could not allocate varname\n");
        fclose(outfile);
        return -1;
    }
    write_code(outfile, marshalled, arrayname);
    free(arrayname);

    if (ferror(outfile)) {
        fprintf(stderr, "error when writing to '%s'\n", outpath);
        fclose(outfile);
        return -1;
    }
    fclose(outfile);
    return 0;
}

int
main(int argc, char *argv[])
{
    const char *name, *inpath, *outpath;

    _PyImport_FrozenBootstrap = no_modules;
    _PyImport_FrozenStdlib = no_modules;
    _PyImport_FrozenTest = no_modules;
    PyImport_FrozenModules = NULL;
    _PyImport_FrozenAliases = aliases;

View on GitHub (pinned to bc6749cc3b)

Solutions

1. Free disk space (`df -h`) and rerun the build
2. Build on a filesystem with adequate free space; clean previous build dirs (`git clean -fdx` carefully)
3. If on a network mount, remount/reconnect and rerun

# shell: require free space before the freeze stage
# [ "$(df -Pk "$OUT" | awk 'NR==2{print $4}')" -gt 1048576 ] || { echo 'need >1GB free'; exit 1; }

When it happens

Trigger: The output filesystem fills up while write_code() emits the (large) marshalled-data array; I/O errors on the target device; network filesystems dropping mid-write.

Common situations: CI runners or VMs with small /tmp or workspace disks filling during a CPython build; building on NFS/SMB mounts that fail transiently.

Related errors

• cannot open '%s' for reading
• cannot fstat '%s'
• could not allocate %ld bytes
• read too short: got %ld instead of %ld bytes
• cannot open '%s' for writing

AI-assisted analysis of python/cpython@bc6749cc3b (2026-08-14). Data as JSON: /api/errors/c6100ffa3878492f. Report an issue: GitHub.