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The goal of ARPANET, the precursor to the global Internet, was to exploit new computer technologies to meet the needs of military command and control against nuclear threats, achieve survivable control of US nuclear forces, and improve military tactical and management decision making.
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free(1) [xfree86 man page]

FREE(1) 							   User Commands							   FREE(1)

NAME
free - Display amount of free and used memory in the system SYNOPSIS
free [options] DESCRIPTION
free displays the total amount of free and used physical and swap memory in the system, as well as the buffers and caches used by the ker- nel. The information is gathered by parsing /proc/meminfo. The displayed columns are: total Total installed memory (MemTotal and SwapTotal in /proc/meminfo) used Used memory (calculated as total - free - buffers - cache) free Unused memory (MemFree and SwapFree in /proc/meminfo) shared Memory used (mostly) by tmpfs (Shmem in /proc/meminfo) buffers Memory used by kernel buffers (Buffers in /proc/meminfo) cache Memory used by the page cache and slabs (Cached and SReclaimable in /proc/meminfo) buff/cache Sum of buffers and cache available Estimation of how much memory is available for starting new applications, without swapping. Unlike the data provided by the cache or free fields, this field takes into account page cache and also that not all reclaimable memory slabs will be reclaimed due to items being in use (MemAvailable in /proc/meminfo, available on kernels 3.14, emulated on kernels 2.6.27+, otherwise the same as free) OPTIONS
-b, --bytes Display the amount of memory in bytes. -k, --kibi Display the amount of memory in kibibytes. This is the default. -m, --mebi Display the amount of memory in mebibytes. -g, --gibi Display the amount of memory in gibibytes. --tebi Display the amount of memory in tebibytes. --pebi Display the amount of memory in pebibytes. --kilo Display the amount of memory in kilobytes. Implies --si. --mega Display the amount of memory in megabytes. Implies --si. --giga Display the amount of memory in gigabytes. Implies --si. --tera Display the amount of memory in terabytes. Implies --si. --peta Display the amount of memory in petabytes. Implies --si. -h, --human Show all output fields automatically scaled to shortest three digit unit and display the units of print out. Following units are used. B = bytes K = kibibyte M = mebibyte G = gibibyte T = tebibyte P = pebibyte If unit is missing, and you have exbibyte of RAM or swap, the number is in tebibytes and columns might not be aligned with header. -w, --wide Switch to the wide mode. The wide mode produces lines longer than 80 characters. In this mode buffers and cache are reported in two separate columns. -c, --count count Display the result count times. Requires the -s option. -l, --lohi Show detailed low and high memory statistics. -s, --seconds delay Continuously display the result delay seconds apart. You may actually specify any floating point number for delay using either . or , for decimal point. usleep(3) is used for microsecond resolution delay times. --si Use kilo, mega, giga etc (power of 1000) instead of kibi, mebi, gibi (power of 1024). -t, --total Display a line showing the column totals. --help Print help. -V, --version Display version information. FILES
/proc/meminfo memory information BUGS
The value for the shared column is not available from kernels before 2.6.32 and is displayed as zero. Please send bug reports to <procps@freelists.org> SEE ALSO
ps(1), slabtop(1), top(1), vmstat(8). procps-ng 2016-06-03 FREE(1)

Check Out this Related Man Page

Sys::Statistics::Linux::MemStats(3pm)			User Contributed Perl Documentation		     Sys::Statistics::Linux::MemStats(3pm)

NAME
Sys::Statistics::Linux::MemStats - Collect linux memory information. SYNOPSIS
use Sys::Statistics::Linux::MemStats; my $lxs = Sys::Statistics::Linux::MemStats->new; my $stat = $lxs->get; DESCRIPTION
Sys::Statistics::Linux::MemStats gathers memory statistics from the virtual /proc filesystem (procfs). For more information read the documentation of the front-end module Sys::Statistics::Linux. MEMORY INFORMATIONS
Generated by /proc/meminfo. memused - Total size of used memory in kilobytes. memfree - Total size of free memory in kilobytes. memusedper - Total size of used memory in percent. memtotal - Total size of memory in kilobytes. buffers - Total size of buffers used from memory in kilobytes. cached - Total size of cached memory in kilobytes. realfree - Total size of memory is real free (memfree + buffers + cached). realfreeper - Total size of memory is real free in percent of total memory. swapused - Total size of swap space is used is kilobytes. swapfree - Total size of swap space is free in kilobytes. swapusedper - Total size of swap space is used in percent. swaptotal - Total size of swap space in kilobytes. swapcached - Memory that once was swapped out, is swapped back in but still also is in the swapfile. active - Memory that has been used more recently and usually not reclaimed unless absolutely necessary. inactive - Memory which has been less recently used and is more eligible to be reclaimed for other purposes. On earlier kernels (2.4) Inact_dirty + Inact_laundry + Inact_clean. The following statistics are only available by kernels from 2.6. slab - Total size of memory in kilobytes that used by kernel for data structure allocations. dirty - Total size of memory pages in kilobytes that waits to be written back to disk. mapped - Total size of memory in kilbytes that is mapped by devices or libraries with mmap. writeback - Total size of memory that was written back to disk. committed_as - The amount of memory presently allocated on the system. The following statistic is only available by kernels from 2.6.9. commitlimit - Total amount of memory currently available to be allocated on the system. METHODS
new() Call "new()" to create a new object. my $lxs = Sys::Statistics::Linux::MemStats->new; It's possible to set the path to the proc filesystem. Sys::Statistics::Linux::MemStats->new( files => { # This is the default path => '/proc', meminfo => 'meminfo', } ); get() Call "get()" to get the statistics. "get()" returns the statistics as a hash reference. my $stat = $lxs->get; EXPORTS
No exports. SEE ALSO
proc(5) REPORTING BUGS
Please report all bugs to <jschulz.cpan(at)bloonix.de>. AUTHOR
Jonny Schulz <jschulz.cpan(at)bloonix.de>. COPYRIGHT
Copyright (c) 2006, 2007 by Jonny Schulz. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. perl v5.14.2 2012-03-09 Sys::Statistics::Linux::MemStats(3pm)

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