RLIMITRSS

RLIMIT_RSS is a POSIX resource limit that specifies the maximum resident set size (RSS) a process may occupy. RSS is the portion of a process’s memory that is currently resident in physical RAM, excluding swapped-out pages and memory that is not loaded. The limit is designed to be queried and modified with the getrlimit and setrlimit system calls, using a struct rlimit where the soft limit (rlim_cur) and the hard limit (rlim_max) are expressed in bytes.

In practice, RSS-based limits are defined as part of a broader set of memory-related controls. Soft limits can be raised up to the hard limit, or lowered to restrict memory usage. However, the effectiveness of RLIMIT_RSS depends on the operating system and memory management policies. On many Linux systems, RLIMIT_RSS is not actively enforced, and modern memory limitations are more reliably achieved using RLIMIT_AS (address space limit) or memory cgroups. BSD variants historically used RSS limits more directly, but enforcement can vary by implementation and kernel version.

Because RSS measures only the memory currently resident in RAM, it does not account for memory that is swapped out or not yet allocated, and it can be a poor indicator of a process’s total memory footprint in systems with dynamic paging or complex memory usage patterns. For robust memory control on contemporary systems, administrators often rely on RLIMIT_AS or containerization and cgroups rather than RLIMIT_RSS alone.

See also: getrlimit, setrlimit, RLIMIT_AS, RLIMIT_STACK, RLIMIT_DATA, VmRSS, cgroups.