Which of the following commands is used to set restrictions on the size of a core file that is created for a user when a program crashes?

`core` is not a standard command for managing core file size limits; it refers to the core dump file itself.

`edquota` is used to edit user disk quotas, not general resource limits like core file size.

The `ulimit` command allows an administrator or user to view or set shell resource limits. Specifically, `ulimit -c` is used to control the maximum size of a core file that can be created upon a program crash.

`quota` is used to display disk quota information, not to set resource limits for core files.