redhat man page for sysinfo

SYSINFO(2)						     Linux Programmer's Manual							SYSINFO(2)

NAME
       sysinfo - returns information on overall system statistics

SYNOPSIS
       #include <sys/sysinfo.h>

       int sysinfo(struct sysinfo *info);

DESCRIPTION
       Until Linux 2.3.16, sysinfo used to return information in the following structure:

	      struct sysinfo {
		   long uptime; 	    /* Seconds since boot */
		   unsigned long loads[3];  /* 1, 5, and 15 minute load averages */
		   unsigned long totalram;  /* Total usable main memory size */
		   unsigned long freeram;   /* Available memory size */
		   unsigned long sharedram; /* Amount of shared memory */
		   unsigned long bufferram; /* Memory used by buffers */
		   unsigned long totalswap; /* Total swap space size */
		   unsigned long freeswap;  /* swap space still available */
		   unsigned short procs;    /* Number of current processes */
		   char _f[22]; 	    /* Pads structure to 64 bytes */
	      };

       and the sizes were given in bytes. Since Linux 2.3.23 (i386), 2.3.48 (all architectures) the structure is

	      struct sysinfo {
		   long uptime; 	    /* Seconds since boot */
		   unsigned long loads[3];  /* 1, 5, and 15 minute load averages */
		   unsigned long totalram;  /* Total usable main memory size */
		   unsigned long freeram;   /* Available memory size */
		   unsigned long sharedram; /* Amount of shared memory */
		   unsigned long bufferram; /* Memory used by buffers */
		   unsigned long totalswap; /* Total swap space size */
		   unsigned long freeswap;  /* swap space still available */
		   unsigned short procs;    /* Number of current processes */
		   unsigned long totalhigh; /* Total high memory size */
		   unsigned long freehigh;  /* Available high memory size */
		   unsigned int mem_unit;   /* Memory unit size in bytes */
		   char _f[20-2*sizeof(long)-sizeof(int)]; /* Padding for libc5 */
	      };

       and the sizes are given as multiples of mem_unit bytes.

       sysinfo	provides  a simple way of getting overall system statistics.  This is more portable than reading /dev/kmem.  For an example of its
       use, see intro(2).

RETURN VALUE
       On success, zero is returned.  On error, -1 is returned, and errno is set appropriately.

ERRORS
       EFAULT pointer to struct sysinfo is invalid

CONFORMING TO
       This function is Linux-specific, and should not be used in programs intended to be portable.

       The Linux kernel has a sysinfo system call since 0.98.pl6.  Linux libc contains a sysinfo() routine since 5.3.5, and glibc  has	one  since
       1.90.

SEE ALSO
       proc(5)

Linux 2.0							    1997-08-25								SYSINFO(2)