alibaba/arthas · error · IllegalArgumentException

Too many line numbers, maximum is 256.

Error message

Too many line numbers, maximum is 256.

What it means

Thrown by parseLines() in the `line` command when the accumulated distinct line numbers exceed MAX_LINE_COUNT (256, defined at LineCommand.java:41). Each unique line number is enhanced with bytecode instrumentation, so Arthas caps the count to bound overhead.

Source

Thrown at core/src/main/java/com/taobao/arthas/core/command/monitor200/LineCommand.java:302

                if (value.length() == 0) {
                    continue;
                }
                if (value.indexOf('-') >= 0) {
                    throw new IllegalArgumentException("Line range syntax is not supported in the first version: "
                            + value);
                }
                final int lineNumber;
                try {
                    lineNumber = Integer.parseInt(value);
                } catch (NumberFormatException e) {
                    throw new IllegalArgumentException("Invalid line number: " + value);
                }
                if (lineNumber <= 0) {
                    throw new IllegalArgumentException("Line number must be greater than 0: " + value);
                }
                result.add(lineNumber);
                if (result.size() > MAX_LINE_COUNT) {
                    throw new IllegalArgumentException("Too many line numbers, maximum is " + MAX_LINE_COUNT + ".");
                }
            }
        }
        if (result.isEmpty()) {
            throw new IllegalArgumentException("The --line option is required unless --list-lines is used.");
        }
        return result;
    }

    private void listLines(CommandProcess process) {
        try {
            Instrumentation instrumentation = process.session().getInstrumentation();
            Set<Class<?>> classes = GlobalOptions.isDisableSubClass
                    ? SearchUtils.searchClass(instrumentation, getClassNameMatcher())
                    : SearchUtils.searchSubClass(instrumentation, SearchUtils.searchClass(instrumentation,
                            getClassNameMatcher()));
            if (classes.size() > maxNumOfMatchedClass) {
                process.end(-1, "The number of matched classes is " + classes.size()

View on GitHub (pinned to 21cf2e9ba5)

Solutions

1. Reduce the --line list to 256 or fewer unique numbers.
2. Narrow the set to the lines you actually need to inspect.
3. Run multiple `line` commands in sequence if you must watch more lines, rather than one giant spec.

Example fix

// before
line --class X --line 1,2,3,...,300
// after
line --class X --line 51,56,60   // keep <= 256 unique lines

static final int MAX_LINE_COUNT = 256;
static String sanitizeLineSpec(String spec) {
    Set<Integer> uniq = new LinkedHashSet<>();
    for (String p : spec.split(",")) { String v=p.trim(); if(!v.isEmpty()) uniq.add(Integer.valueOf(v)); }
    if (uniq.size() > MAX_LINE_COUNT)
        throw new IllegalArgumentException("Too many lines: " + uniq.size());
    return uniq.stream().map(String::valueOf).collect(java.util.stream.Collectors.joining(","));
}

null

null

When it happens

Trigger: Running `line --class X --line` with a comma-separated list containing more than 256 unique line numbers (e.g. generated ranges expanded manually), or repeatedly calling with a large generated spec.

Common situations: Programmatically building a line list that exceeds the cap; trying to watch every line of a large method; misunderstanding that the cap counts unique lines, not spec strings.

Related errors

• Invalid line number: {}
• Line number must be greater than 0: {}
• sizeLimit must be greater than 0.
• Time fragment index is expected, please type -i to specify
• 必须提供 path 或 cursor

AI-assisted analysis of alibaba/arthas@21cf2e9ba5 (2026-08-14). Data as JSON: /api/errors/25636c79e271670b. Report an issue: GitHub.