Change the base TCP port

The CAT Control applet runs up to four rigctld-compatible TCP servers on consecutive ports starting from a configurable base. Change the base port when the default conflicts with another application on your system.

Before you start

• AetherSDR must be connected to the radio. The CAT applet requires an active radio connection.
• Open the CAT Control applet by clicking the CAT tray button on the right sidebar if it is not already visible.

Steps

1. In the CAT Control applet, locate the Base: label and its text field at the bottom of the applet.
2. Click the Base: field and type the new port number. Valid range: 1024–65535. Default: 4532.
3. Press Enter or Tab to confirm. If the value is outside the valid range, it snaps back to 4532.
4. The new base port is saved immediately to CatTcpPort.
5. If Enable TCP is currently active, all four servers restart automatically on the new ports (base, base+1, base+2, base+3). No further action is needed.

What each control does

Control	Kind	Default
Base:	Text field	4532
Enable TCP	Toggle button	Off
Enable TTY	Toggle button	Off
A/B/C/D channel rows	Indicator	(stopped)
## Tips

• Choose a base port that leaves the next three consecutive ports free. For example, a base of 4532 uses 4532, 4533, 4534, and 4535.
• If you change the port while Enable TCP is off, the servers will start on the new port the next time you click Enable TCP.
• On Linux and macOS, click Enable TTY to expose each channel as a virtual serial port. Point your logging software to the corresponding symlink path displayed below each channel label.
• In v26.5.3, PTY symlinks are created per-user under $XDG_RUNTIME_DIR/aethersdr/cat-A through cat-D on Linux, or ~/Library/Caches/AetherSDR/cat-A through cat-D on macOS. This change from the previous /tmp/AetherSDR-CAT-* location fixes a security vulnerability (GHSA-qxhr-cwrc-pvrm) and uses atomic symlink replacement to prevent time-of-check/time-of-use (TOCTOU) race conditions.

Troubleshooting

• Servers do not restart after changing the port — Confirm you pressed Enter or Tab to finish editing the Base: field. Clicking away without committing the edit may not apply the change.
• Port field snaps back to 4532 — The value entered was outside the 1024–65535 range. Enter a value within that range.
• Server fails to start on the new port — Another application may already be using that port or one of the three consecutive ports. Choose a different base port.
• PTY symlinks do not appear — Enable TTY is available on Linux and macOS only. Confirm you clicked Enable TTY and that AetherSDR has write access to the per-user runtime directory. On Linux this is typically $XDG_RUNTIME_DIR/aethersdr/; on macOS ~/Library/Caches/AetherSDR/.

Related

• Enable CAT TCP so N1MM, Log4OM, WSJT-X can control the radio
• Autostart CAT servers with AetherSDR
• Check how many external clients are connected to each channel