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RedHat 9 (Linux i386) - man page for sysinfo (redhat section 2)

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)