Yes, you will need to restart the SCM Agent after increasing the logging level in the HAgent.arg file.
If your agent is on a Windows machine, you can restart it from the "Administrative Tools" -> Services window.
If your agent is on a Linux or Unix box, and is running as a multi-user agent, it will need to be restarted by the "root" user. If you will check with your system administrator, you will likely have a script somewhere that restarts the agent.
More information on starting the SCM Agent can be found here: https://docops.ca.com/ca-harvest-scm/13-0/en/installing/install-ca-harvest-scm-on-unix-linux-and-zlinux/install-the-agent-on-unix-linux-and-zlinux#InstalltheAgentonUNIX,Linux,andzLinux-StarttheAgent
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