NetBSD/share/doc/psd/05.sysman/1.6.t

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.\" $NetBSD: 1.6.t,v 1.2 1998/01/09 06:54:45 perry Exp $
.\"
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.\" Copyright (c) 1983, 1993, 1994
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.\" @(#)1.6.t 8.5 (Berkeley) 6/1/94
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.\"
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.Sh 2 "Resource controls
.Sh 3 "Process priorities
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.PP
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.
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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),
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or to alter this priority using the calls:
.DS
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.Fd getpriority 2 "get program scheduling priority
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prio = getpriority(which, who);
result int prio; int which, who;
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.DE
.DS
.Fd setpriority 3 "set program scheduling priority
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setpriority(which, who, prio);
int which, who, prio;
.DE
The value \fIprio\fP is in the range \-20 to 20.
The default priority is 0; lower priorities cause more
favorable execution.
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The
.Fn getpriority
call returns the highest priority (lowest numerical value)
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enjoyed by any of the specified processes.
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The
.Fn setpriority
call sets the priorities of all the
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specified processes to the specified value.
Only the super-user may lower priorities.
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.Sh 3 "Resource utilization
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.PP
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The
.Fn getrusage
call returns information describing the resources utilized by the
current process (RUSAGE_SELF),
or all its terminated descendent processes (RUSAGE_CHILDREN):
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.DS
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.Fd getrusage 2 "get information about resource utilization
getrusage(who, rusage);
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int who; result struct rusage *rusage;
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.DE
The information is returned in a structure defined in \fI<sys/resource.h>\fP:
.DS
.TS
l s s s
l l l l.
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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 */
};
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.TE
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.DE
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.Sh 3 "Resource limits
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.PP
The resources of a process for which limits are controlled by the
kernel are defined in \fI<sys/resource.h>\fP, and controlled by the
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.Fn getrlimit
and
.Fn setrlimit
calls:
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.DS
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.Fd getrlimit 2 "get maximum system resource consumption
getrlimit(resource, rlp);
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int resource; result struct rlimit *rlp;
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.DE
.DS
.Fd setrlimit 2 "set maximum system resource consumption
setrlimit(resource, rlp);
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int resource; struct rlimit *rlp;
.DE
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The resources that may currently be controlled include:
.DS
.TS
l l.
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 */
.TE
.DE
.ne 1i
Each limit has a current value and a maximum defined
by the \fIrlimit\fP structure:
.DS
.TS
l s s s
l l l l.
struct rlimit {
quad_t rlim_cur; /* current (soft) limit */
quad_t rlim_max; /* hard limit */
};
.TE
.DE
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.PP
Only the super-user can raise the maximum limits.
Other users may only
alter \fIrlim_cur\fP within the range from 0 to \fIrlim_max\fP
or (irreversibly) lower \fIrlim_max\fP.
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To remove a limit on a resource,
the value is set to RLIM_INFINITY.