apache/cassandra · error · IllegalArgumentException

Can not parse replication factor from %s

Error message

Can not parse replication factor from %s

What it means

When a single plain-string RF argument is given to nodetool cms, it is parsed with Integer.parseInt; failure to parse produces IllegalArgumentException('Can not parse replication factor from %s') naming the offending argument.

Source

Thrown at src/java/org/apache/cassandra/tools/nodetool/CMSAdmin.java:179

            if (args.isEmpty())
                throw new IllegalArgumentException("Replication factor is empty");

            Map<String, Integer> parsedRfs = new HashMap<>(args.size());
            for (String rf : args)
            {
                if (!rf.contains(":"))
                {
                    if (args.size() > 1)
                        throw new IllegalArgumentException("Simple placement can only specify a single replication factor across all data centers");
                    int parsedRf;
                    try
                    {
                        parsedRf = Integer.parseInt(args.get(0));
                    }
                    catch (Throwable t)
                    {
                        throw new IllegalArgumentException(String.format("Can not parse replication factor from %s", args.get(0)));
                    }
                    probe.getCMSOperationsProxy().reconfigureCMS(parsedRf);
                    return;
                }
                else
                {
                    String[] splits = rf.split(":");
                    if (splits.length > 2)
                        throw new IllegalArgumentException(String.format("Can not parse replication factor %s", rf));
                    String dc = splits[0];
                    int parsedRf;
                    try
                    {
                        parsedRf = Integer.parseInt(splits[1]);
                    }
                    catch (Throwable t)
                    {
                        throw new IllegalArgumentException(String.format("Can not parse replication factor from %s", args.get(0)));

View on GitHub (pinned to 88fd0f6a0e)

Solutions

1. Pass a plain positive integer: nodetool cms 3
2. Trim whitespace and remove stray characters from the argument
3. Use dc:rf syntax if you meant per-DC factors: nodetool cms dc1:3

Example fix

// before
nodetool cms 3.5
// after
nodetool cms 3

String arg = args[0].trim();
if (!arg.matches("\\d+"))
    throw new IllegalArgumentException("RF must be a plain integer, got: " + args[0]);
int rf = Integer.parseInt(arg);

try {
    int rf = Integer.parseInt(args.get(0));
} catch (NumberFormatException e) {
    // show usage with valid RF examples
}

When it happens

Trigger: Running 'nodetool cms three', 'nodetool cms 3.5', or 'nodetool cms " 3"' — the single argument without ':' that is not a valid integer.

Common situations: Typos or letters in the RF; shell quoting adding whitespace; pasting 'dc1=3' style syntax; locales/scripts passing decimal numbers.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

• Replication factor should not be set if previous operation i
• Replication factor is empty
• Simple placement can only specify a single replication facto
• Failed to initialize command line hierarchy
• Unknown CLI layout:

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/e88cf266ae3240c3. Report an issue: GitHub.