Process limits - key elements

The kernel imposes resource limits to ensure fair allocation of system resources among contending processes. These limits guarantee that a random process does not monopolize ownership of resources. There are 16 different types of resource limits, and the task structure points to an array of type struct rlimit, in which each offset holds the current and maximum values for a specific resource.

/*include/uapi/linux/resource.h*/
struct rlimit {
  __kernel_ulong_t        rlim_cur;
  __kernel_ulong_t        rlim_max;
};
These limits are specified in include/uapi/asm-generic/resource.h

 #define RLIMIT_CPU        0       /* CPU time in sec */
 #define RLIMIT_FSIZE      1       /* Maximum filesize */
 #define RLIMIT_DATA       2       /* max data size */
 #define RLIMIT_STACK      3       /* max stack size */
 #define RLIMIT_CORE       4       /* max core file size */
 #ifndef RLIMIT_RSS
 # define RLIMIT_RSS       5       /* max resident set size */
 #endif
 #ifndef RLIMIT_NPROC
 # define RLIMIT_NPROC     6       /* max number of processes */
 #endif
 #ifndef RLIMIT_NOFILE
 # define RLIMIT_NOFILE    7       /* max number of open files */
 #endif
 #ifndef RLIMIT_MEMLOCK
 # define RLIMIT_MEMLOCK   8       /* max locked-in-memory   
 address space */
 #endif
 #ifndef RLIMIT_AS
 # define RLIMIT_AS        9       /* address space limit */
 #endif
 #define RLIMIT_LOCKS      10      /* maximum file locks held */
 #define RLIMIT_SIGPENDING 11      /* max number of pending signals */
 #define RLIMIT_MSGQUEUE   12      /* maximum bytes in POSIX mqueues */
 #define RLIMIT_NICE       13      /* max nice prio allowed to 
 raise to 0-39 for nice level 19 .. -20 */
 #define RLIMIT_RTPRIO     14      /* maximum realtime priority */
 #define RLIMIT_RTTIME     15      /* timeout for RT tasks in us */
 #define RLIM_NLIMITS      16