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Operating Systems Linux Red Hat Concept of free –m command in Linux Post 302758705 by sixstrings on Sunday 20th of January 2013 02:02:32 PM
Old 01-20-2013
Code:
             total       used       free     shared    buffers     cached
Mem:          3816       3569        247          0        118       2397
-/+ buffers/cache:       1053       2763
Swap:         3823         13       3810

ok, this is the output for my laptop.

The free command is used to display the amount of free and used memory on a system. The -m option tells free to print the output in MB.

My laptop has 4Gb currently.

Linux attempts to utilize all of the memory on the system and not leave any sitting idle, like some other operating systems have done over time. Memory will be used for the OS and applications, but the remainder will be used as "buffers and cache". The kernel will keep items in memory that are needed often or are predicted to be needed for faster access. The memory used for "buffers and cache" is available for applications or the OS to use. If required, it is quickly flushed and used.

To find the actual available memory on my system, take the last number on the Mem line (247) and add it to the last number on the Mem line (2397). So currently, I have about 3G of memory available.

Most of this information is available via the manpage and simple google searches. Take a look and you should have all of your questions answered.
 

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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)
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