ulimit switches and values

hard or soft

The -H and -S options specify that the hard or soft limit is set for the given resource.
A hard limit cannot be increased once it is set; a soft limit may be increased up to the value of the hard limit.
If neither -H nor -S is specified, both the soft and hard limits are set.

values

The value of limit can be a number in the unit specified for the resource or one of the special values hard, soft, or unlimited, which stand for the current hard limit, the current soft limit, and no limit, respectively.

---

REFERRERS
ResourceLimits