RLIMITCPU

RLIMIT_CPU is a per-process resource limit that constrains the amount of CPU time a process may consume. It is part of the POSIX resource limits interface (struct rlimit), and consists of two fields: rlim_cur (the soft limit) and rlim_max (the hard limit). Values are expressed in seconds; a value of RLIM_INFINITY indicates no limit. The timer measures CPU time spent in both user and kernel modes.

When a process uses CPU time beyond the soft limit, the kernel delivers a SIGXCPU signal to the process. The signal may be caught or ignored; if the process continues to run, CPU time continues to accumulate. If the hard limit is reached, the kernel terminates the process, typically by sending a SIGKILL.

Limits are set and queried via the setrlimit and getrlimit system calls. They apply to the process and may apply to its threads depending on the operating system. Many shells expose the soft CPU limit via ulimit -t, allowing users to set a time-out per command.

RLIMIT_CPU is used to prevent runaway processes, enforce quotas, or isolate resource consumption in sandboxing or job control. It interacts with the scheduling and signal facilities of the kernel, and may be combined with other limits such as RLIMIT_AS or RLIMIT_FSIZE for broader containment.

See also: setrlimit, getrlimit, RLIMIT_AS, SIGXCPU.