RLIMITDATA

RLIMIT_DATA is a per-process resource limit used on many Unix-like systems to cap the size of a process's data segment. The data segment includes the program’s initialized and dynamically allocated data, such as the heap. It does not cover the code segment or the stack. The limit is expressed in bytes and is managed through the standard resource limit interfaces (getrlimit and setrlimit) and can also be viewed or modified via shell utilities such as ulimit.

The limit features soft and hard boundaries. The soft limit can be reached during normal execution, and further growth of the data segment (for example, by increasing the heap via brk/sbrk) may fail with an allocation error (typically ENOMEM). The hard limit controls the maximum value to which the soft limit can be raised and can only be increased by privileged processes. If the limit is exceeded, the operating system prevents further expansion of the data region.

Platform variations exist. On many systems, RLIMIT_DATA is available for compatibility but may be limited in effect on modern memory management. In Linux, memory usage is frequently governed more by RLIMIT_AS (address space) than by RLIMIT_DATA, and allocations via mmap may be outside the data segment limit. Some platforms may ignore RLIMIT_DATA or treat it differently in practice.

Default values for RLIMIT_DATA vary by system and configuration. In some environments it may be unlimited by default, while in others it can be restricted to help contain memory usage for untrusted or long-running processes. Tools used to enforce limits include setrlimit, ulimit, and related process-control mechanisms, often employed in sandboxing and resource-control contexts.

See also RLIMIT_AS, RLIMIT_STACK, getrlimit, setrlimit, and ulimit.