Tribblix: manual page: getrusage.3c

GETRUSAGE(3C) Standard C Library Functions GETRUSAGE(3C)

NAME

getrusage - get information about resource utilization

SYNOPSIS

#include <sys/resource.h>

int getrusage(int who, struct rusage *r_usage);

DESCRIPTION

The getrusage() function provides measures of the resources used by
the current process, its terminated and waited-for child processes,
or the current light weight process (LWP). If the value of the who
argument is RUSAGE_SELF, information is returned about resources used
by the current process. If the value of the who argument is
RUSAGE_CHILDREN, information is returned about resources used by the
terminated and waited-for children of the current process. If the
child is never waited for (for instance, if the parent has
SA_NOCLDWAIT set or sets SIGCHLD to SIG_IGN), the resource
information for the child process is discarded and not included in
the resource information provided by getrusage(). If the value of the
who argument is RUSAGE_LWP, information is returned about resources
used by the current LWP.

The r_usage argument is a pointer to an object of type struct rusage
in which the returned information is stored. The members of rusage
are as follows:

struct timeval ru_utime; /* user time used */
struct timeval ru_stime; /* system time used */
long ru_maxrss; /* maximum resident set size */
long ru_idrss; /* integral resident set size */
long ru_minflt; /* page faults not requiring physical
I/O */
long ru_majflt; /* page faults requiring physical I/O */
long ru_nswap; /* swaps */
long ru_inblock; /* block input operations */
long ru_oublock; /* block output operations */
long ru_msgsnd; /* messages sent */
long ru_msgrcv; /* messages received */
long ru_nsignals; /* signals received */
long ru_nvcsw; /* voluntary context switches */
long ru_nivcsw; /* involuntary context switches */

The structure members are interpreted as follows:

ru_utime
The total amount of time spent executing in user mode.
Time is given in seconds and microseconds.

ru_stime
The total amount of time spent executing in system
mode. Time is given in seconds and microseconds.

ru_maxrss
The maximum resident set size. Size is given in pages
(the size of a page, in bytes, is given by the
getpagesize(3C) function). See the NOTES section of
this page.

ru_idrss
An "integral" value indicating the amount of memory in
use by a process while the process is running. This
value is the sum of the resident set sizes of the
process running when a clock tick occurs. The value is
given in pages times clock ticks. It does not take
sharing into account. See the NOTES section of this
page.

ru_minflt
The number of page faults serviced which did not
require any physical I/O activity. See the NOTES
section of this page.

ru_majflt
The number of page faults serviced which required
physical I/O activity. This could include page ahead
operations by the kernel. See the NOTES section of
this page.

ru_nswap
The number of times a process was swapped out of main
memory.

ru_inblock
The number of times the file system had to perform
input in servicing a read(2) request.

ru_oublock
The number of times the file system had to perform
output in servicing a write(2) request.

ru_msgsnd
The number of messages sent over sockets.

ru_msgrcv
The number of messages received from sockets.

ru_nsignals
The number of signals delivered.

ru_nvcsw
The number of times a context switch resulted due to a
process voluntarily giving up the processor before its
time slice was completed (usually to await
availability of a resource).

ru_nivcsw
The number of times a context switch resulted due to a
higher priority process becoming runnable or because
the current process exceeded its time slice.

RETURN VALUES

Upon successful completion, getrusage() returns 0. Otherwise, -1 is
returned and errno is set to indicate the error.

ERRORS

The getrusage() function will fail if:

EFAULT
The address specified by the r_usage argument is not in a
valid portion of the process' address space.

EINVAL
The who parameter is not a valid value.

ATTRIBUTES

NOTES

The ru_maxrss, ru_ixrss, ru_idrss, and ru_isrss members of the rusage
structure are set to 0 in this implementation.

The numbers ru_inblock and ru_oublock account only for real I/O, and
are approximate measures at best. Data supplied by the cache
mechanism is charged only to the first process to read and the last
process to write the data.

The way resident set size is calculated is an approximation, and
could misrepresent the true resident set size.

Page faults can be generated from a variety of sources and for a
variety of reasons. The customary cause for a page fault is a direct
reference by the program to a page which is not in memory. Now,
however, the kernel can generate page faults on behalf of the user,
for example, servicing read(2) and write(2) functions. Also, a page
fault can be caused by an absent hardware translation to a page, even
though the page is in physical memory.

In addition to hardware detected page faults, the kernel may cause
pseudo page faults in order to perform some housekeeping. For
example, the kernel may generate page faults, even if the pages exist
in physical memory, in order to lock down pages involved in a raw I/O
request.

By definition, major page faults require physical I/O, while minor
page faults do not require physical I/O. For example, reclaiming the
page from the free list would avoid I/O and generate a minor page
fault. More commonly, minor page faults occur during process startup
as references to pages which are already in memory. For example, if
an address space faults on some "hot" executable or shared library,
this results in a minor page fault for the address space. Also, any
one doing a read(2) or write(2) to something that is in the page
cache will get a minor page fault(s) as well.

There is no way to obtain information about a child process which has
not yet terminated.

July 2, 2004 GETRUSAGE(3C)