Why do I see a user named _system_ and what its role?
The _system_ user is an internal user which is used by Artifactory to run different tasks.
For example, authentication tasks – If you are running Artifactory HA, the authentication with other nodes will be performed by the _system_ user.
Another tasks that are performed by this user are cleanup operations, when a policy for cleaning unique tags is configured (due to the maximum unique tags value inside a repository) – the old tags will be cleaned up by the _system_ user. IF you are using different cleanup user plugins such as buildCleanup or artifactCleanup, the cleanup tasks will also be performed by the _system_ user.
Next time you encounter such actions by _system_ user, you may want to check any of the above.