RLIMITSTACK

RLIMITSTACK (RLIMIT_STACK in POSIX) is a resource limit that defines the maximum size of a thread’s stack. It is part of the suite of RLIMIT resources used to control a process’s memory usage and is accessed through system interfaces such as getrlimit and setrlimit.

The stack for a thread grows downward as the thread allocates stack frames. The limit restricts how large that per-thread stack can become. If a thread attempts to grow beyond the soft limit, the growth is constrained and, when the limit is reached, memory access faults can occur, typically resulting in a signal such as a segmentation fault that terminates the offending thread or process. The soft limit (rlim_cur) may be raised up to the hard limit (rlim_max); increasing the hard limit generally requires privileges. In practice, the hard limit can often be lowered by a non-privileged user, while raising it usually requires administrative permission.

Setting and querying the limit are done with the rlimit structure and the functions getrlimit and setrlimit. The structure contains rlim_cur (soft limit) and rlim_max (hard limit). A value of RLIM_INFINITY denotes no limit, though actual applicability may be bounded by address space constraints of the operating system.

Default values for RLIMIT_STACK vary by operating system and architecture. On many Linux systems, the main thread stack is on the order of a few to several tens of megabytes, commonly with a soft limit around 8 MB. The limit is an important consideration for applications with deep or intensive recursion, multithreaded programs, and security hardening, since overly large or misconfigured stacks can lead to resource exhaustion or instability.

See also RLIMIT_AS, setrlimit, getrlimit, and pthreads.