What causes "Failed to write %s" in hashicorp/terraform?

Check and fix write permissions on the file and directory: `chmod u+w `.

Failed to write

Error message

Failed to write %s

What it means

Thrown by processFile when the -write flag is set, formatting changed the file, and os.WriteFile fails to write the reformatted bytes back to disk. This is a write-permission or disk-capacity failure on the target file path.

Solutions

Check and fix write permissions on the file and directory: `chmod u+w <path>`.
Free disk/inode space if the volume is full (`df -h`, `df -i`).
Ensure the working directory is not on a read-only mount; remount rw or copy files to a writable location.

Example fix

$ chmod u+w main.tf && terraform fmt -write main.tf

Defensive patterns

Strategy: validation

Validate before calling

// Verify writability before running fmt -write.
func isWritable(path string) bool {
    fi, err := os.Stat(path)
    if err != nil { return false }
    return fi.Mode().Perm()&0200 != 0
}

Prevention

Ensure files are checked out writable before fmt (avoid read-only VCS workspaces).
Run fmt as the file owner or a user with write access.
Check disk space before large batch -write operations.

When it happens

Trigger: Running `terraform fmt -write` (default for files) on a file whose path is read-only, on a full disk, on a read-only filesystem, or where the user lacks write permission. Also fires if the directory was removed mid-operation.

Common situations: Files checked into a read-only VCS checkout; Docker volume mount mounted ro; CI running as a user without write access to the module directory; full disk / inode exhaustion.

Related errors

AI-assisted analysis of hashicorp/terraform@d32a084675 (2026-08-11). Data as JSON: /api/errors/54d3e1db3379825d. Report an issue: GitHub.

Appendix: source

Thrown at internal/command/fmt.go:206

	// it. If not, the formatter is likely to make drastic changes that would
	// be hard for the user to undo.
	_, syntaxDiags := hclsyntax.ParseConfig(src, path, hcl.Pos{Line: 1, Column: 1})
	if syntaxDiags.HasErrors() {
		diags = diags.Append(syntaxDiags)
		return diags
	}

	result := c.formatSourceCode(src, path)

	if !bytes.Equal(src, result) {
		// Something was changed
		if c.list {
			fmt.Fprintln(w, path)
		}
		if c.write {
			err := os.WriteFile(path, result, 0644)
			if err != nil {
				diags = diags.Append(fmt.Errorf("Failed to write %s", path))
				return diags
			}
		}
		if c.diff {
			diff, err := bytesDiff(src, result, path)
			if err != nil {
				diags = diags.Append(fmt.Errorf("Failed to generate diff for %s: %s", path, err))
				return diags
			}
			w.Write(diff)
		}
	}

	if !c.list && !c.write && !c.diff {
		_, err = w.Write(result)
		if err != nil {
			diags = diags.Append(fmt.Errorf("Failed to write result"))
		}

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