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30 .\" @(#)1.6.t 8.5 (Berkeley) 6/1/94
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32 .Sh 2 "Resource controls
33 .Sh 3 "Process priorities
34 .PP
35 The system gives CPU scheduling priority to processes that have not used
36 CPU time recently. This tends to favor interactive processes and
37 processes that execute only for short periods.
38 The instantaneous scheduling priority is a function of CPU usage
39 and a settable priority value used in adjusting the instantaneous
40 priority with CPU usage or inactivity.
41 It is possible to determine the settable priority factor currently
42 assigned to a process (PRIO_PROCESS),
43 process group (PRIO_PGRP),
44 or the processes of a specified user (PRIO_USER),
45 or to alter this priority using the calls:
46 .DS
47 .Fd getpriority 2 "get program scheduling priority
48 prio = getpriority(which, who);
49 result int prio; int which, who;
50 .DE
51 .DS
52 .Fd setpriority 3 "set program scheduling priority
53 setpriority(which, who, prio);
54 int which, who, prio;
55 .DE
56 The value \fIprio\fP is in the range \-20 to 20.
57 The default priority is 0; lower priorities cause more
58 favorable execution.
59 The
60 .Fn getpriority
61 call returns the highest priority (lowest numerical value)
62 enjoyed by any of the specified processes.
63 The
64 .Fn setpriority
65 call sets the priorities of all the
66 specified processes to the specified value.
67 Only the super-user may lower priorities.
68 .Sh 3 "Resource utilization
69 .PP
70 The
71 .Fn getrusage
72 call returns information describing the resources used by the
73 current process (RUSAGE_SELF),
74 or all its terminated descendent processes (RUSAGE_CHILDREN):
75 .DS
76 .Fd getrusage 2 "get information about resource utilization
77 getrusage(who, rusage);
78 int who; result struct rusage *rusage;
79 .DE
80 The information is returned in a structure defined in \fI<sys/resource.h>\fP:
81 .DS
82 .TS
83 l s s s
84 l l l l.
85 struct rusage {
86 struct timeval ru_utime; /* user time used */
87 struct timeval ru_stime; /* system time used */
88 int ru_maxrss; /* maximum core resident set size: kbytes */
89 int ru_ixrss; /* integral shared memory size (kbytes*sec) */
90 int ru_idrss; /* unshared data memory size */
91 int ru_isrss; /* unshared stack memory size */
92 int ru_minflt; /* page-reclaims */
93 int ru_majflt; /* page faults */
94 int ru_nswap; /* swaps */
95 int ru_inblock; /* block input operations */
96 int ru_oublock; /* block output operations */
97 int ru_msgsnd; /* messages sent */
98 int ru_msgrcv; /* messages received */
99 int ru_nsignals; /* signals received */
100 int ru_nvcsw; /* voluntary context switches */
101 int ru_nivcsw; /* involuntary context switches */
102 };
103 .TE
104 .DE
105 .Sh 3 "Resource limits
106 .PP
107 The resources of a process for which limits are controlled by the
108 kernel are defined in \fI<sys/resource.h>\fP, and controlled by the
109 .Fn getrlimit
110 and
111 .Fn setrlimit
112 calls:
113 .DS
114 .Fd getrlimit 2 "get maximum system resource consumption
115 getrlimit(resource, rlp);
116 int resource; result struct rlimit *rlp;
117 .DE
118 .DS
119 .Fd setrlimit 2 "set maximum system resource consumption
120 setrlimit(resource, rlp);
121 int resource; struct rlimit *rlp;
122 .DE
123 The resources that may currently be controlled include:
124 .DS
125 .TS
126 l l.
127 RLIMIT_CPU /* cpu time in milliseconds */
128 RLIMIT_FSIZE /* maximum file size */
129 RLIMIT_DATA /* data size */
130 RLIMIT_STACK /* stack size */
131 RLIMIT_CORE /* core file size */
132 RLIMIT_RSS /* resident set size */
133 RLIMIT_MEMLOCK /* locked-in-memory address space */
134 RLIMIT_NPROC /* number of processes */
135 RLIMIT_NOFILE /* number of open files */
136 .TE
137 .DE
138 .ne 1i
139 Each limit has a current value and a maximum defined
140 by the \fIrlimit\fP structure:
141 .DS
142 .TS
143 l s s s
144 l l l l.
145 struct rlimit {
146 quad_t rlim_cur; /* current (soft) limit */
147 quad_t rlim_max; /* hard limit */
148 };
149 .TE
150 .DE
151 .PP
152 Only the super-user can raise the maximum limits.
153 Other users may only
154 alter \fIrlim_cur\fP within the range from 0 to \fIrlim_max\fP
155 or (irreversibly) lower \fIrlim_max\fP.
156 To remove a limit on a resource,
157 the value is set to RLIM_INFINITY.