getrusage —
get information about resource utilization
Standard C Library (libc, -lc)
#include <sys/resource.h>
#define	RUSAGE_SELF	 0
  
  #define	RUSAGE_CHILDREN	-1
int
  
  getrusage(int
    who, struct rusage
    *rusage);
getrusage() returns information describing the resources
  used by the current process, or all its terminated child processes. The
  who parameter is either
  RUSAGE_SELF or
  RUSAGE_CHILDREN. The buffer to which
  rusage points will be filled in with the following
  structure:
struct rusage {
        struct timeval ru_utime; /* user time used */
        struct timeval ru_stime; /* system time used */
        long ru_maxrss;          /* max resident set size */
        long ru_ixrss;           /* integral shared text memory size */
        long ru_idrss;           /* integral unshared data size */
        long ru_isrss;           /* integral unshared stack size */
        long ru_minflt;          /* page reclaims */
        long ru_majflt;          /* page faults */
        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 fields are interpreted as follows:
  - ru_utime
- the total amount of time spent executing in user mode.
- ru_stime
- the total amount of time spent in the system executing on behalf of the
      process(es).
- ru_maxrss
- the maximum resident set size used (in kilobytes).
- ru_ixrss
- an “integral” value indicating the amount of memory used by
      the text segment that was also shared among other processes. This value is
      expressed in units of kilobytes * ticks-of-execution.
- ru_idrss
- an integral value of the amount of unshared memory residing in the data
      segment of a process (expressed in units of kilobytes *
      ticks-of-execution).
- ru_isrss
- an integral value of the amount of unshared memory residing in the stack
      segment of a process (expressed in units of kilobytes *
      ticks-of-execution).
- ru_minflt
- the number of page faults serviced without any I/O activity; here I/O
      activity is avoided by “reclaiming” a page frame from the
      list of pages awaiting reallocation.
- ru_majflt
- the number of page faults serviced that required I/O activity.
- 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.
- ru_oublock
- the number of times the file system had to perform output.
- ru_msgsnd
- the number of IPC messages sent.
- ru_msgrcv
- the number of IPC messages received.
- 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.
The numbers ru_inblock and
  ru_oublock account only for real I/O; data supplied by
  the caching mechanism is charged only to the first process to read or write
  the data.getrusage() returns -1 on error. The possible errors
  are:
  - [EINVAL]
- The who parameter is not a valid value.
- [EFAULT]
- The address specified by the rusage parameter is not
      in a valid part of the process address space.
Thegetrusage() function call appeared in
  4.2BSD.
There is no way to obtain information about a child process that has not yet
  terminated.