The cron command issues a settaskid to ensure that each cron, at, and batch job executes in a separate task, with the appropriate default project for the submitting user. The at and batch commands also capture the current project ID, which ensures that the project ID is restored when running an at job.
The su command joins the target user's default project by creating a new task, as part of simulating a login.
To switch the user's default project by using the su command, type the following:
# su - user