Everything KafkIO stores lives in two places on each computer: a data folder for your clusters, templates, certificates and logs, and the operating system's store for Java preferences. This page lists what is where, so you can back it up, move it to another computer, or remove it. From inside KafkIO, the quickest way to the right folder is Tools ▸ Show Config In or Show Logs In (Config & Log Files).
The data folder
KafkIO creates its data folder in your user profile the first time it starts. It belongs to your user account, so each person who uses KafkIO on a shared computer has their own clusters and logs.
| System | Data folder |
|---|---|
| Windows | %LOCALAPPDATA%\com.certak\kafkio (for example
C:\Users\you\AppData\Local\com.certak\kafkio) |
| macOS | ~/Library/Application Support/kafkio |
| Linux | ~/.local/share/kafkio, or $XDG_DATA_HOME/kafkio if you set
XDG_DATA_HOME |
On Windows the folder is under AppData\Local, not AppData\Roaming, so it doesn't
follow you to other computers on a domain with roaming profiles. Inside it:
| Folder | What's in it |
|---|---|
config |
clusters.json, your cluster configurations, and clusters.json.bak, the
version before KafkIO's last save. If you upgraded from a version before 2.1.7 you may also find
the old clusters.yml, which is no longer used. |
message_templates |
Your produce message templates,
as plain text files: key.name.txt, value.name.txt and
headers.name.txt. Created the first time KafkIO lists or saves templates. |
ssl |
ct_truststore.jks, the certificates you added under
Trusted certificates
in Preferences. |
logs |
Log files, one series per day: kafkio_2026-10-25_0.log,
kafkio_2026-10-25_1.log and so on. A new file starts each time KafkIO starts, each day
and every 20 MB, and the 20 most recent are kept
(Reading the logs). |
mb |
Two small lock files KafkIO uses to notice it's already running (Running more than one instance). Leave them alone. |
What is stored where
| What | Where |
|---|---|
| Clusters, with their connection, security, Schema Registry, Kafka Connect and ksqlDB settings and saved credentials | config/clusters.json
(The clusters.json file) |
| Favourite topics | Also in clusters.json, in each cluster's favourites entry, so they travel
with the cluster (Favourites) |
| Message templates | message_templates, shared by every cluster |
| Certificates added in Preferences | ssl/ct_truststore.jks |
| Logs | logs |
| Preferences, and things KafkIO remembers itself (window size and position, side pane widths, an update you chose to ignore) | The Java preferences store (below) |
| A saved proxy password | Your operating system's keychain: Windows Credential Manager, macOS Keychain or the Linux Secret Service (Proxy authentication) |
Truststores, keystores, certificates, krb5.conf and other files a cluster or
preference points to |
Wherever you keep them: KafkIO stores only their full path, not a copy |
| Topic dumps and exported preferences | The file or folder you choose when you save them |
clusters.json and clusters.json.bak hold your clusters'
passwords and keys in plain text, and logs can contain host names, topic names and parts of messages.
Treat the data folder like a password file when you copy or share it.Preferences
Preferences aren't in the data folder. KafkIO keeps them in Java's preferences store for your user account,
under the node com/certak/kafkio:
| System | Preferences |
|---|---|
| Windows | The registry key
HKEY_CURRENT_USER\Software\JavaSoft\Prefs\com\certak\kafkio |
| macOS | A property list file under ~/Library/Preferences |
| Linux | ~/.java/.userPrefs/com/certak/kafkio/prefs.xml |
Don't edit these by hand. To see every stored value, copy them to another computer or start again, use the
Preferences window's Show preferences, Export preferences to
file, import and Reset preferences buttons, or the
--reset-preferences option when KafkIO won't start
(Managing Preferences).
In Memory Stick Mode
Memory Stick Mode (Windows and Linux) moves part of this into
KafkIO's program folder, the folder that holds kafkio.jar: KafkIO\app on Windows and
lib/app on Linux, inside the folder you extracted KafkIO to.
| What | In Memory Stick Mode |
|---|---|
| Clusters (and favourites) | clusters.json and clusters.json.bak in
the program folder |
| Certificates added in Preferences | ct_truststore.jks in the program
folder |
| Preferences | The computer's preferences store as usual, plus a copy in
kafkio.xml in the program folder, loaded when KafkIO starts |
Message templates, logs, mb | Unchanged: the data folder on the computer you're using |
While the mode is on, Tools ▸ Show Config In opens the program folder, so it always
takes you to the clusters.json KafkIO is really using. Turning the mode on or off copies
clusters.json and ct_truststore.jks between the two locations and leaves the
originals where they were (Turning it on).
Backing up and moving to another computer
Quit KafkIO first, so it doesn't rewrite clusters.json while you copy it. Then keep:
config/clusters.json(in Memory Stick Mode, the one in the program folder).- The
message_templatesfolder, if you use templates. ssl/ct_truststore.jks, if you added certificates in Preferences.- A preferences export from Export preferences to file, if you changed preferences.
- The certificate, keystore and
krb5.conffiles your clusters refer to, which aren't in the data folder.
To restore, or to set up another computer, quit KafkIO there and copy the files into the same folders of its
data folder (creating them if KafkIO hasn't run yet), then import the preferences. Paths to certificate and
keystore files are stored as they were on the old computer: if they differ, fix them with
Edit Cluster. Copying clusters.json replaces the whole cluster list;
how to merge lists or share a subset with a colleague is in
Sharing configurations
between machines. You don't need to keep the logs, mb or clusters.json.bak.
Removing everything
Uninstalling KafkIO leaves the data folder and preferences in place, so a reinstall picks up where you left
off. To remove all trace of KafkIO, for example before handing the computer on, delete the data folder, reset
the preferences (or delete the registry key or file above), and remove a saved proxy password from your keychain. If you used Memory Stick Mode, delete clusters.json, clusters.json.bak,
ct_truststore.jks and kafkio.xml from the program folder too
(What's left behind).