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Tools

Config & Log Files

Open the cluster configuration file and the log files in a terminal, file browser or text editor, find and read the logs, and which applications KafkIO opens.

KafkIO keeps your cluster configurations in one file and writes what it does to log files, both in folders you rarely need to visit. When you do (to back up or bulk-edit your clusters, or to look at what went wrong), the Tools menu takes you straight there, so you never have to remember where the folders are.

Opening the configuration

Tools ▸ Show Config In opens the folder that holds clusters.json, the file with all your cluster configurations, or the file itself:

KafkIO's Tools menu open with Show Config In highlighted and its submenu listing Terminal, File Browser and Text Editor. Below Show Config In are Show Logs In, JKS Converter, Network Tool and Sample Docker Compose. Behind the menu, Storefront Dev is connected and a duplicated Storefront Dev (Consumers) tab is open. 1 2 3 4
The Show Config In submenu.
  1. Tools ▸ Show Config In.
  2. Terminal opens a terminal window whose current folder is the one holding clusters.json, ready for cp, git or a script.
  3. File Browser opens that folder in your file manager with clusters.json selected (on Linux, the file is selected in Nautilus, Dolphin and Caja; other file managers just open the folder).
  4. Text Editor opens clusters.json itself, in whatever application your system opens .json files with. If none is set up, Windows asks you to pick one.

Next to clusters.json you'll find clusters.json.bak, the version before KafkIO's last save. The folder is the config folder of KafkIO's data folder (for example %LOCALAPPDATA%\com.certak\kafkio\config on Windows), or, in Memory Stick Mode, the folder the KafkIO program is in: the menu always opens the file KafkIO is really using. What's in the file, how to edit it safely and where it lives on each system are in Where configurations are stored.

Warning: clusters.json holds your clusters' passwords and keys in plain text. If you open it in an editor, quit KafkIO first when you intend to change it (KafkIO rewrites the file on many actions), and don't attach it to a ticket or e-mail as it is.

Your preferences aren't in this folder: they're kept in the operating system's store for Java preferences (see What's left behind), and you save them to a file with the Preferences dialog's Export preferences to file button instead.

Opening the logs

Tools ▸ Show Logs In does the same for KafkIO's log files:

KafkIO's Tools menu open with Show Logs In highlighted and its submenu listing Terminal, File Browser and Text Editor. Above it is Show Config In; below it JKS Converter, Network Tool and Sample Docker Compose. 1 2 3 4
The Show Logs In submenu.
  1. Tools ▸ Show Logs In.
  2. Terminal opens a terminal in the logs folder, handy for grep or tail -f on the newest file.
  3. File Browser opens the logs folder.
  4. Text Editor opens the most recently written log file (the one KafkIO is writing to now) in the application your system uses for .log files; on macOS that's usually Console. If there's no log file yet, it opens the folder instead.

The same newest log file opens from the View Logs button of every error dialog and of the bug-report form, so you rarely need the menu to look at what just failed. The logs folder is:

SystemFolder
Windows%LOCALAPPDATA%\com.certak\kafkio\logs
macOS~/Library/Application Support/kafkio/logs
Linux~/.local/share/kafkio/logs

Memory Stick Mode doesn't move the logs: they stay in this folder on the computer you run KafkIO on.

Reading the logs

Each line has a time stamp, the time since KafkIO started, the thread, the level (INFO, WARN, ERROR, or DEBUG in debug mode) the class and method that wrote it, and the message, with the stack trace under errors. Files are named by date (kafkio_2026-10-25_3.log), and KafkIO starts a new one each time it starts, each day and every 20 MB, keeping the 20 most recent, so a problem from earlier today or yesterday is usually still there. Search for ERROR near the time the problem happened.

For more detail, such as the Kafka client's own DEBUG messages, start KafkIO from a terminal with the --debug option (Command-Line Options), repeat what failed, then open the newest file with Show Logs In ▸ Text Editor. More on using the logs with the Event Log to diagnose connection problems is in Troubleshooting Connections.

Warning: logs can contain host names, topic names and parts of messages. Read a log through before you post it anywhere public, and send only the part around the problem.

Which terminal and file browser open

KafkIO uses your system's own applications:

SystemTerminalFile Browser
WindowsA new Command Prompt window (or Windows Terminal, if that's your default terminal application)File Explorer
macOSTerminalFinder
LinuxThe terminal that /etc/alternatives/x-terminal-emulator points to (GNOME Terminal, Konsole, Xfce Terminal or another)The file manager of your desktop (Nautilus, Dolphin, Caja, Nemo, Thunar), otherwise whatever xdg-open chooses

Choosing a different terminal

There is no setting for this in Preferences: Terminal always opens the system's terminal as above. If you prefer another one, open the folder with File Browser and start your terminal from there, or copy the path from the tables above.

On Linux distributions without /etc/alternatives/x-terminal-emulator (it's a Debian and Ubuntu convention, so Fedora, Arch and others often lack it), Terminal shows Could not detect terminal automatically using '/etc/alternatives/x-terminal-emulator'. Please define a custom terminal in the preferences. Despite the wording, there's no such preference to set; use File Browser instead, or create the link if your distribution supports it (for example sudo ln -s /usr/bin/gnome-terminal /etc/alternatives/x-terminal-emulator).

Note: if nothing opens at all (no terminal, file browser or editor), KafkIO usually doesn't show an error; the reason is written to the log as Could not open console, Could not open folder or Could not open file.