getrusage(S)

Synopsis

   #include <sys/time.h>
   #include <sys/resource.h>
   

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

Description

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.

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

   struct  rusage {
           struct timeval ru_utime;        /* user time used */
           struct timeval ru_stime;        /* system time used */
           long    ru_maxrss;
   #define ru_first        ru_ixrss
           long    ru_ixrss;               /* XXX: 0 */
           long    ru_idrss;               /* XXX: sum of rm_asrss */
           long    ru_isrss;               /* XXX: 0 */
           long    ru_minflt;              /* any page faults not requiring I/O */
           long    ru_majflt;              /* any page faults requiring 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 */
   #define ru_last         ru_nivcsw
   };

The fields 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(S) system call). Also, see ``Notices''.

ru_ixrss

Currently returns 0.

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. Note: it does not take sharing into account. Also, see ``Notices''.

ru_isrss

Currently returns 0.

ru_minflt

The number of page faults serviced which did not require any physical I/O activity. Also, see ``Notices''.

ru_majflt

The number of page faults serviced which required physical I/O activity. This could include page ahead operations by the kernel. Also, see ``Notices''.

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(S) request.

ru_oublock

The number of times the file system had to perform output in servicing a write(S) 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

Errors

EINVAL

The who argument is not a valid value.

EFAULT

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

An invalid address for the r_usage argument may result in a core dump as opposed to returning EFAULT.

References

Notices

The numbers ru_inblock and ru_oublock account only for real I/O, and are approximate measures at best. Data supplied by the caching 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(S) and write(S) system calls. 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(S) or write(S) 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.

Standards conformance