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Top Forums UNIX for Beginners Questions & Answers Interpreting Linux's free command output Post 303010968 by drysdalk on Thursday 11th of January 2018 07:36:35 AM
Old 01-11-2018
Hi,

Taking your questions in turn:

1. Buffers and cache are essentially types of memory that, whilst they are in use, could be freed up if the system required memory for some other purpose. These are types of memory that are mostly used to hold things which either are yet to be written or have recently been read from disk, in order to accelerate file I/O. So if ever a process genuinely needs more memory than is sitting absolutely unused (which is the total in the 'free' column) more can be obtained by flushing out certain things from the buffers and/or cache.

2. The 'free' column shows you the memory on the system which is genuinely 100% unused - so not in use by a process, and not part of the buffers, cache or shared memory pool. The 'available' column consists of the 'free' memory, plus whatever memory from other categories (mainly the buffers and cache) which could be easily freed up if required. So you can take 'available' as a trustworthy figure as the amount of free memory that applications could use if they needed to.

Hope this helps.
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FREE(1) 							Linux User's Manual							   FREE(1)

NAME
free - Display amount of free and used memory in the system SYNOPSIS
free [-b|-k|-m|-g] [-c count] [-l] [-o] [-t] [-s delay] [-V] DESCRIPTION
free displays the total amount of free and used physical and swap memory in the system, as well as the buffers used by the kernel. The shared memory column should be ignored; it is obsolete. OPTIONS -b Display the amount of memory in bytes. -c count Display the result count times. Requires the -s option. -g Display the amount of memory in gigabytes. -k Display the amount of memory in kilobytes. This is the default. -l Show detailed low and high memory statistics. -m Display the amount of memory in megabytes. -o Display the output in old format, the only difference being this option will disable the display of the "buffer adjusted" line. -s Continuously display the result delay seconds apart. You may actually specify any floating point number for delay, usleep(3) is used for microsecond resolution delay times. -t Display a line showing the column totals. -V Display version information. FILES
/proc/meminfo memory information AUTHORS
Written by Brian Edmonds. Send bug reports to <albert@users.sf.net> SEE ALSO
ps(1), slabtop(1), top(1), vmstat(8). Cohesive Systems 5 Oct 2009 FREE(1)
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