I believe the Sentinel functions to work as follows:
Each sentinel has 1 of 3 states and within this state it picks a random Status, Function, and Current Subroutine, belonging to that state. It finally picks an additional random Directive, which is independant of state. I have created a table below to show the possibilities. Hope it makes sense 
Spoiler ahead!
Sentinel Functions - Spoiler!
| State | Status | Function | Current Subroutine | Directive |
|---|---|---|---|---|
 |
Investigate | Support | Investigate | Directive |
| Investigating… | Support Unit | [ Lifeform Search ] | Civilisation Destruction | |
| Searching… | Rapid Response | [ Anomaly Detection ] | Suppress Sentience | |
| Inspecting… | Active Suppression | [ Event Processing ] | Locate Beauty | |
| Scanning… | Anomaly Destruction | [ Trend Analysis ] | Portal Deletion | |
| Auditing… | Combat Support | [ Boundary Test ] | Lifeform Immobilisation | |
| Probing… | Breach Repair | [ Waveform Analysis ] | Civilisation Delay | |
| Reviewing… | Anomaly Repair | [ Preparing Alarm ] | Sow Division | |
| Analysing… | De-escalation | [ Depth Testing ] | Harvest Data | |
| Studying… | Counter Attack | [ Temporal Analysis ] | Observe All | |
| Anomaly Detected… | Advanced Combat | [ Boundary Reinforcement ] | Replicate Sentinels | |
| Detecting Breach… | Retaliation | [ Safeguard Deployment ] | Sanitisation | |
| Oversight Initiated… | Rapid Suppression | [ Ocular Testing ] | Spread Decay | |
| Observing… | Retribution | [ Low Frequency Ping ] | Reinforce Boundaries | |
| Irregularity Detected… | Anomaly Neutralisation | [ Probability Sort ] | Traveller Detection | |
| Analysis Required… | Sentience Destruction | [ Data Siphon ] | Sow Discord | |
| Sensors Deployed… | Prevent Sentience | |||
| Predator Suppression | ||||
 |
Patrol | Patrol | Patrol | Herbivore Protection |
| Patrolling… | Ambient Protection | [ Patrol ] | Mineral Protection | |
| Uploading Report… | Active Patrol | [ Idle ] | Botanical Protection | |
| Cruising… | Anomaly Suppression | [ Route Optimisation ] | Specimen Collection | |
| Watchful… | Intelligence Suppression | [ Path Optimisation ] | Specimen Preservation | |
| Registering Activity… | Field Scout | [ Kinetic Recovery ] | Data Harvest | |
| Sensors Ready… | Anomaly Hunt | [ Self-Analysis ] | Surveillance | |
| Patrolling… | Area Suppression | [ Background Diagnostics ] | Lifeform Supervision | |
| Patrolling… | Boundary Protection | [ Fuel Cell Cleaning ] | Sentience Degradation | |
| Patrolling… | Boundary Enforcement | [ Defragmenting ] | Delta Wave Detection | |
| Low Power Mode | Breach Detection | [ Long-Distance Scanner ] | Memory Protection | |
| Recharging | Anomaly Ward | [ Short-Range Scanner ] | Encryption Block | |
| Reconnecting… | Passive Enforcement | [ Portal Detection ] | Load Balancing | |
| Processing… | Oversight Patrol | [ Patrol Iteration ] | Null Checker | |
| Optimising… | Ambient Protection | [ Distributed Analysis ] | Innocence Preservation | |
| Awaiting Orders… | Mobile Aegis | [ … /// … /// … /// … ] | Universal Detranslation | |
| Digital Cartography | ||||
 |
Alert | Guard | Alert | Leyline Mapping |
| High Alert | Guard Duty | [ Weapon Deployment ] | Calculate Probabilities | |
| Combat | Security | [ Active Pursuit ] | Sacrifice to Atlas | |
| Requesting Assistance | Local Defence | [ Signalling Reinforcements ] | Authenticate Threats | |
| Engaging | Active Defence | [ Preemptive Destruction ] | Anomaly Spoofing | |
| Targeting | Escort | [ Target Prediction ] | Data Interception | |
| Target Acquired | Localised Suppression | [ Ammo Fabrication ] | ||
| Repairing Breach | Sentry | [ Field Suppression ] | ||
| Repairing Anomaly | Active Protection | [ Trend Analysis ] | ||
| Cleansing Anomaly | Guardian | [ Seal Breach ] | ||
| BREACHED | Active Oversight | [ Anomaly Repair ] | ||
| Combat | Local Overwatch | [ RED RED RED ] | ||
| Weapons Deployed | Active Protection | [ A T L A S ] | ||
| Targeting | Area Defence | [ Firing Eye ] | ||
| Combat | Specific Patrol | [ Hardpoint Repair ] | ||
| High Alert | Anomaly Buffer | [ Hunting ] |
For full tables of Sentinel data found in the localisation files, see here.