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%sccs.include.redist.roff%
@(#)1.6.t 8.3 (Berkeley) 05/20/94
.Sh 2 "Resource controls .Sh 3 "Process priorities
The system gives CPU scheduling priority to processes that have not used CPU time recently. This tends to favor interactive processes and processes that execute only for short periods. The instantaneous scheduling priority is a function of CPU usage and a settable priority value used in adjusting the instantaneous priority with CPU usage or inactivity. It is possible to determine the settable priority factor currently assigned to a process (PRIO_PROCESS), process group (PRIO_PGRP), or the processes of a specified user (PRIO_USER), or to alter this priority using the calls: .Fd getpriority 2 "get program scheduling priority prio = getpriority(which, who); result int prio; int which, who; .Fd setpriority 3 "set program scheduling priority setpriority(which, who, prio); int which, who, prio; The value prio is in the range -20 to 20. The default priority is 0; lower priorities cause more favorable execution. The .Fn getpriority call returns the highest priority (lowest numerical value) enjoyed by any of the specified processes. The .Fn setpriority call sets the priorities of all the specified processes to the specified value. Only the super-user may lower priorities. .Sh 3 "Resource utilization
The .Fn getrusage call returns information describing the resources utilized by the current process (RUSAGE_SELF), or all its terminated descendent processes (RUSAGE_CHILDREN): .Fd getrusage 2 "get information about resource utilization getrusage(who, rusage) int who; result struct rusage *rusage; The information is returned in a structure defined in <sys/resource.h>:
| struct rusage { |
| struct timeval ru_utime; /* user time used */ |
| struct timeval ru_stime; /* system time used */ |
| int ru_maxrss; /* maximum core resident set size: kbytes */ |
| int ru_ixrss; /* integral shared memory size (kbytes*sec) */ |
| int ru_idrss; /* unshared data memory size */ |
| int ru_isrss; /* unshared stack memory size */ |
| int ru_minflt; /* page-reclaims */ |
| int ru_majflt; /* page faults */ |
| int ru_nswap; /* swaps */ |
| int ru_inblock; /* block input operations */ |
| int ru_oublock; /* block output operations */ |
| int ru_msgsnd; /* messages sent */ |
| int ru_msgrcv; /* messages received */ |
| int ru_nsignals; /* signals received */ |
| int ru_nvcsw; /* voluntary context switches */ |
| int ru_nivcsw; /* involuntary context switches */ |
| }; |
The resources of a process for which limits are controlled by the kernel are defined in <sys/resource.h>, and controlled by the .Fn getrlimit and .Fn setrlimit calls: .Fd getrlimit 2 "get maximum system resource consumption getrlimit(resource, rlp) int resource; result struct rlimit *rlp; .Fd setrlimit 2 "set maximum system resource consumption setrlimit(resource, rlp) int resource; struct rlimit *rlp; The resources that may currently be controlled include:
| RLIMIT_CPU /* cpu time in milliseconds */ |
| RLIMIT_FSIZE /* maximum file size */ |
| RLIMIT_DATA /* data size */ |
| RLIMIT_STACK /* stack size */ |
| RLIMIT_CORE /* core file size */ |
| RLIMIT_RSS /* resident set size */ |
| RLIMIT_MEMLOCK /* locked-in-memory address space */ |
| RLIMIT_NPROC /* number of processes */ |
| RLIMIT_NOFILE /* number of open files */ |
| struct rlimit { |
| quad_t rlim_cur; /* current (soft) limit */ |
| quad_t rlim_max; /* hard limit */ |
| }; |
Only the super-user can raise the maximum limits. Other users may only alter rlim_cur within the range from 0 to rlim_max or (irreversibly) lower rlim_max. To remove a limit on a resource, the value is set to RLIM_INFINITY.