What causes "could not write output" in Y2Z/monolith?

Check free disk space and write quota on the destination volume.

could not write output

Error message

could not write output

What it means

This panic comes from `output.write(&result).expect("could not write output")` in main.rs:286 (the STDIN-pipe branch). `Output::write` propagates `io::Error` from `write_all`/`flush` on either stdout or the destination file. The output object was created successfully, but writing/flushing the rendered monolithic document bytes failed, so the program panics after all fetching work has already completed.

Solutions

Check free disk space and write quota on the destination volume.
Avoid piping output into commands that close early (`head`); use `monolith - > file.html` or capture to a file first.
Verify the destination file/mount is writable and not locked by another process.
Re-run without piping stdout; if the panic was EPIPE on stdout, redirect to a file.
For automation, wrap the call so a panic exit (code 101) is detected and retried or reported.

Example fix

// before (shell)
monolith - -o page.html | head -c 100   # closes pipe -> "could not write output" panic

// after (shell)
monolith - -o page.html   # write fully to file, no truncated pipe consumer

Defensive patterns

Strategy: try-catch

Validate before calling

#!/usr/bin/env bash
df -h . | awk 'NR==2 {exit ($5+0 > 95 ? 1 : 0)}' || { echo "disk nearly full"; exit 1; }
monolith - -o page.html || code=$?
[ "$code" = "101" ] && echo "output write panicked (disk/pipe?)"

Try / catch

match std::panic::catch_unwind(|| {
    output.write(&result)
}) {
    Ok(Ok(())) => {},
    Ok(Err(e)) => eprintln!("write failed: {}", e),
    Err(_) => eprintln!("panicked while writing output (disk full or closed pipe?)"),
}

Prevention

Don't pipe monolith output into commands that exit early (head, less -F); redirect to a file instead.
Monitor free disk space when saving large pages.
Avoid writing output to network/removable mounts that can drop mid-write.
Detect panic exit code 101 in automation to distinguish write failures from fetch failures.

When it happens

Trigger: The destination file became unwritable after creation (disk full mid-write, quota exceeded, permission revoked), or writing to stdout failed because the pipe was closed early (e.g. `monolith - | head -n 1` causing SIGPIPE/EPIPE) or stdout redirected to a full/unwritable target.

Common situations: Disk filled up while saving a very large page; output piped into `head`, `less -F`, or a process that exits early, closing the pipe; NFS/network mounts dropping mid-write; tmpfs quota exceeded; antivirus or backup software locking the file on Windows.

Related errors

AI-assisted analysis of Y2Z/monolith@a6fc8d0095 (2026-09-05). Data as JSON: /api/errors/74386054a1423203. Report an issue: GitHub.

Appendix: source

Thrown at src/main.rs:286

    let session: Session = Session::new(cache, cookies, options);

    // Retrieve target from source and output result
    if cli.target == "-" {
        // Read input from pipe (STDIN)
        let data: Vec<u8> = read_stdin();

        match create_monolithic_document_from_data(session, data, None, None) {
            Ok((result, title)) => {
                // Define output
                let mut output = Output::new(
                    &destination.unwrap_or(String::new()),
                    &title.unwrap_or_default(),
                    output_format,
                )
                .expect("could not prepare output");

                // Write result into STDOUT or file
                output.write(&result).expect("could not write output");
            }
            Err(error) => {
                if !silent {
                    print_error_message(&format!("Error: {}", error));
                }

                exit_code = 1;
            }
        }
    } else {
        match create_monolithic_document(session, cli.target) {
            Ok((result, title)) => {
                // Define output
                let mut output = Output::new(
                    &destination.unwrap_or(String::new()),
                    &title.unwrap_or_default(),
                    output_format,
                )

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