> For the complete documentation index, see [llms.txt](https://docs.auterion.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.auterion.com/vehicle-operation/settings-and-maintenance/security-and-access-control.md).

# Security & Access Control

This page summarizes the most relevant security and access control methods.

## Storing of Sensitive Information

### PX4 Logging

`SDLOG_BACKEND` controls where flight log data is written — to the FMU SD card, over MAVLink to the companion computer, or both. Note that on the Skynode S, SD card logging is unavailable and only logging on the companion side is possible. The content of the FMU SD card is unencrypted, while the companion computer is encrypted.

`SDLOG_NO_POS_DAT` allows position and GPS data to be excluded from logs entirely, which is useful in privacy-sensitive or operationally sensitive deployments where recording the vehicle's flight path is undesirable. Note that flight logs originating from flights with `SDLOG_NO_POS_DAT` are often missing crucial information for incident analysis.

### PX4 Mission, Safe Points and Geofence Storage

`SYS_DM_BACKEND` controls the storage backend used by PX4's dataman module, which persistently stores operationally sensitive data including mission waypoints, mission state, geofence polygons, and safe points. Setting the backend to RAM rather than file means this data is never written to disk and is lost on power cycle, which can be desirable in deployments where residual mission data on the vehicle poses a security concern.

Skynode S does not have an SD card and thus the data is always only stored in RAM.

### PX4 Secure Mode

The PX4 parameter `COM_SEC_MODE_EN` enables secure mode, which protects operationally sensitive information by automatically purging GCS-related data after landing. This includes deleting the Home position, mission, and land approaches, resetting the local position origin, and disabling the serial console — ensuring that details about the GCS location cannot be reconstructed from the vehicle after a flight.

## Access Control

### Production Image

Skynode releases ship with two image variants: a development image and a production image. On the production image, the MAVLink shell is password protected, the UART debug port is changed to read only, and parameter changes are blocked by default — the PX4 parameter `MAV_PARAM_LOCK` must be explicitly set to allow them. The development image has no such restrictions and is intended for integration and testing only; it should not be used in deployed vehicles.

## PX4 Parameter Summary

<table><thead><tr><th width="189">Parameter Name</th><th width="248">Values</th><th>Function</th></tr></thead><tbody><tr><td><code>BAT_CRIT_THR</code></td><td>minValue: 0.05<br>maxValue: 0.5<br>increment: 0.01<br>default: 0.07</td><td>Sets the threshold when the battery will be reported as <strong>critically</strong> low. This has to be lower than the <strong>low</strong> threshold. This threshold commonly will trigger RTL.</td></tr><tr><td><code>BAT_EMERGEN_THR</code></td><td>minValue: 0.03<br>maxValue: 0.5<br>increment: 0.01<br>default: 0.05</td><td>Sets the threshold when the battery will be reported as <strong>dangerously</strong> low. This has to be lower than the <strong>critical</strong> threshold. This threshold commonly will trigger landing.</td></tr><tr><td><code>BAT_LOW_THR</code></td><td>minValue: 0.12<br>maxValue: 0.5<br>increment: 0.01<br>default: 0.15</td><td>Sets the threshold when the battery will be reported as <strong>low</strong>. This has to be higher than the <strong>critical</strong> threshold. This threshold commonly will trigger landing.</td></tr><tr><td><code>CA_SV_CS0_TRIM</code><br><code>CA_SV_CS1_TRIM</code><br><code>CA_SV_CS2_TRIM</code><br><code>CA_SV_CS3_TRIM</code><br><code>CA_SV_CS4_TRIM</code><br><code>CA_SV_CS5_TRIM</code><br><code>CA_SV_CS6_TRIM</code><br><code>CA_SV_CS7_TRIM</code></td><td>minValue: -1.0<br>maxValue: 1.0<br>default: 0.0</td><td><p>Control Surface X trim, where X can be from 0->7.</p><p></p><p>Can be used to add an offset to the servo control.<br><br>NOTE: Do not use for PWM servos. Use the PWM CENTER parameters instead (e.g., PWM_MAIN_CENT, PWM_AUX_CENT) instead. This parameter can only be set if all PWM Center parameters are set to default.</p></td></tr><tr><td><code>COM_DLL_EXCEPT</code></td><td><p><code>0</code>: Mission</p><p><code>1</code>: Auto modes</p><p><code>2</code>: Offboard</p><p><code>3</code>: External Mode</p><p><code>4</code>: Altitude Cruise</p></td><td><p>Datalink loss exceptions.</p><p>Specify modes in which ground control station connection loss is ignored and no failsafe action is triggered. See also COM_RCL_EXCEPT.</p></td></tr><tr><td><code>COM_LOW_BAT_ACT</code></td><td><p><code>0</code>: Warning</p><p><code>2</code>: Land mode</p><p><code>3</code>: Return at critical level, land at emergency level</p><p><code>4</code>: Return at critical level, terminate at emergency level</p></td><td><p>Battery failsafe mode.</p><p>Action the system takes at critical battery. See also BAT_CRIT_THR and BAT_EMERGEN_THR for definition of battery states.</p></td></tr><tr><td><code>COM_RC_IN_MODE</code></td><td><p><code>0</code>: RC only</p><p><code>1</code>: MAVLink only</p><p><code>2</code>: RC or MAVLink with fallback</p><p><code>3</code>: RC or MAVLink keep first</p><p><code>4</code>: Disable manual control</p><p><code>5</code>: Prio: RC > MAVL 1 > MAVL 2</p><p><code>6</code>: Prio: MAVL 1 > MAVL 2 > RC</p><p><code>7</code>: Prio: RC > MAVL 2 > MAVL 1</p><p><code>8</code>: Prio: MAVL 2 > MAVL 1 > RC</p></td><td><p>Manual control input source configuration.</p><p>Selects stick input selection behavior: either a traditional remote control receiver (RC) or a MAVLink joystick (MANUAL_CONTROL message)</p><p>Priority sources are immediately switched to whenever they get valid.</p></td></tr><tr><td><code>COM_RC_LOSS_T</code></td><td>minValue: 0<br>maxValue: 35<br>increment: 0.1<br>default: 0.5</td><td><p>Manual control loss timeout.</p><p>The time in seconds without a new setpoint from RC or Joystick, after which the connection is considered lost. This must be kept short as the vehicle will use the last supplied setpoint until the timeout triggers. Ensure the value is not set lower than the update interval of the RC or Joystick.</p></td></tr><tr><td><code>COM_WIND_MAX_ACT</code></td><td><p><code>0</code>: None</p><p><code>1</code>: Warning</p><p><code>2</code>: Hold</p><p><code>3</code>: Return</p><p><code>4</code>: Terminate</p><p><code>5</code>: Land</p></td><td><p>High wind failsafe mode.<br></p><p>Action the system takes when a wind speed above the specified threshold is detected. See COM_WIND_MAX to set the failsafe threshold. If enabled, it is not possible to resume the mission or switch to any auto mode other than RTL or Land if this threshold is exceeded. Taking over in any manual mode is still possible.</p></td></tr><tr><td><code>EKF2_AGP0_CTRL</code><br><code>EKF2_AGP1_CTRL</code></td><td>minValue: 0<br>maxValue: 3</td><td>Auxiliary global position sensor 0 aiding.<br>Set bits in the following positions to enable: 0 : Horizontal position fusion 1 : Vertical position fusion</td></tr><tr><td><code>EKF2_GPS_CTRL</code></td><td>minValue: 0<br>maxValue: 15<br>default: 7</td><td>GNSS sensor aiding.<br>Set bits in the following positions to enable: 0 : Longitude and latitude fusion 1 : Altitude fusion 2 : 3D velocity fusion 3 : Dual antenna heading fusion</td></tr><tr><td><code>GF_ACTION</code></td><td><p><code>0</code>: None</p><p><code>1</code>: Warning</p><p><code>2</code>: Hold mode</p><p><code>3</code>: Return mode</p><p><code>4</code>: Terminate</p><p><code>5</code>: Land mode</p></td><td><p>Geofence violation action.</p><p>Note: Setting this value to 4 enables flight termination, which will kill the vehicle on violation of the fence.</p></td></tr><tr><td><code>GF_MAX_HOR_DIST</code></td><td>minValue: 0<br>maxValue: 10000<br>default: 0.0</td><td><p>Max horizontal distance from Home.</p><p>Maximum horizontal distance in meters the vehicle can be from Home before triggering a geofence action. Disabled if 0.</p></td></tr><tr><td><code>GF_MAX_VER_DIST</code></td><td>minValue: 0<br>maxValue: 10000<br>default: 0.0</td><td><p>Max vertical distance from Home.</p><p>Maximum vertical distance in meters the vehicle can be from Home before triggering a geofence action. Disabled if 0.</p></td></tr><tr><td><code>MAV_SYS_ID</code></td><td>minValue: 1<br>maxValue: 250<br>default: 1</td><td>MAVLink system ID.</td></tr><tr><td><code>NAV_DLL_ACT</code></td><td><p><code>0</code>: Disabled</p><p><code>1</code>: Hold mode</p><p><code>2</code>: Return mode</p><p><code>3</code>: Land mode</p><p><code>5</code>: Terminate</p><p><code>6</code>: Disarm</p></td><td><p>Set GCS connection loss failsafe mode.</p><p>The GCS connection loss failsafe will only be entered after a timeout, set by COM_DL_LOSS_T in seconds. Once the timeout occurs the selected action will be executed.</p></td></tr><tr><td><code>NAV_RCL_ACT</code></td><td><p><code>1</code>: Hold mode</p><p><code>2</code>: Return mode</p><p><code>3</code>: Land mode</p><p><code>5</code>: Terminate</p><p><code>6</code>: Disarm</p><p><code>7</code>: Hold mode (no failsafe)</p></td><td><p>Set manual control loss failsafe mode.</p><p>The manual control loss failsafe will only be entered after a timeout, set by COM_RC_LOSS_T in seconds.</p></td></tr><tr><td><code>RTL_DESCEND_ALT</code></td><td>minValue: 0<br>increment: 0.5<br>default: 30.0</td><td><p>Return mode loiter altitude.</p><p>Descend to this altitude (above destination position) after return, and wait for time defined in RTL_LAND_DELAY. Land (i.e. slowly descend) from this altitude if autolanding allowed. VTOLs do transition to hover in this altitude above the landing point.</p></td></tr><tr><td><code>RTL_LAND_DELAY</code></td><td>minValue: -1<br>increment: 0.5<br>default: 0.0</td><td><p>Return mode delay.</p><p>Delay before landing (after initial descent) in Return mode. If set to -1 the system will not land but loiter at RTL_DESCEND_ALT.</p></td></tr><tr><td><code>RTL_RETURN_ALT</code></td><td>minValue: 0<br>increment: 0.5<br>default: 60.0</td><td><p>Return mode return altitude.</p><p>Default minimum altitude above destination (e.g. home, safe point, landing pattern) for return flight. The vehicle will climb to this altitude when Return mode is engaged, unless it currently is flying higher already. This is affected by RTL_MIN_DIST and RTL_CONE_ANG.</p></td></tr><tr><td><code>COM_SEC_MODE_EN</code></td><td>0: disabled<br>1: enabled</td><td>Purges GCS-related data after landing to protect operationally sensitive information.</td></tr><tr><td><code>MAV_PARAM_LOCK</code></td><td>0: Whitelist in restricted, full otherwise<br>1: Only whitelist<br>2: Full access</td><td>Prevents modification of parameters except for white-listed ones.</td></tr><tr><td><code>SDLOG_BACKEND</code></td><td>bit 0: FMU SD card<br>bit 1: Companion computer</td><td>Selects where flight log data is written — FMU SD card, Companion computer (streamed over MAVLink), or both.</td></tr><tr><td><code>SDLOG_NO_POS_DAT</code></td><td>0: disabled<br>1: enabled</td><td>Excludes position and GPS data from flight logs.</td></tr><tr><td><code>SYS_DM_BACKEND</code></td><td><p>0: Default storage</p><p>1: RAM storage</p></td><td>Place to store Mission, Safe Points and Geofences. Default storage for Skynode X and N is the SD card, for Skynode S this parameter has no effect.</td></tr></tbody></table>