Improve Robustness of Agent Foreground and Background Execution Modes

[vikman90]

Parent Issue: #241

Description

The Wazuh agent currently has issues handling its execution modes when run with --run (foreground) or --start (background) flags. Specifically, launching the agent in foreground with ./wazuh-agent --run can sometimes print the following message:

wazuh-agent already running

This message typically indicates that an instance of the agent is already running. However, it may also appear if the agent's previous process terminated unexpectedly, which leads to unreliable behavior.

Proposed Solution

1. Separate --run and --start behavior:
   • --run: Should only launch the agent in the foreground without checking if an instance is already running.
   • --start: Should launch the agent in the background and include checks to ensure no other instance of the agent is running.
2. PID file handling:
   When using --start, the agent should:
   • Check for the existence of a PID file.
   • If a PID file exists, verify if it corresponds to a currently running agent process.
   • If no running process is found or the PID file does not exist, perform a fork and execute the agent in background mode (--run).
3. Systemd Compatibility:
   • Ensure that the modified behavior aligns with Systemd’s service management for proper control over the agent's lifecycle.

[sdvendramini]

12/11/2024

I've started reproducing the problem and researching different approaches to solve this issue.