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Top Forums UNIX for Beginners Questions & Answers Interpreting Linux's free command output Post 303010964 by omega3 on Thursday 11th of January 2018 05:32:04 AM
Old 01-11-2018
Interpreting Linux's free command output

I have two questions on Linux's free command. Below, I have provided output from my home laptop (fedora 26 ) which has 16GB Physical RAM and a production server (RHEL 7.4) which has 24GB RAM.


Question1. What exactly does the buffer/cache column say in free command's output ? buffer/cache is only 1GB in my home laptop but it is 18GB in production server below.


Question2. To know the free RAM available to the system, Can I trust the 'available' column rather than the 'free' column ?
In my home laptop, the 'free' column shows 13GB and available shows 14GB
But, in my production server, when the free command shows just 2GB , the available command shows 9 GB


My Home Laptop with 16 GB RAM (Fedora 26)
Code:
[sysadmin@keithspc ~]$ cat /etc/redhat-release
Fedora release 26 (Twenty Six)
[sysadmin@keithspc ~]$
[sysadmin@keithspc ~]$ uname -a
Linux keithspc 4.12.8-300.fc26.x86_64 #1 SMP Thu Aug 17 15:30:20 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
[sysadmin@keithspc ~]$
[sysadmin@keithspc ~]$ free -h
              total        used        free      shared  buff/cache   available
Mem:            15G        854M         13G        385M        1.0G         14G
Swap:          7.8G          0B        7.8G
[sysadmin@keithspc ~]$
[sysadmin@keithspc ~]$ free -m
              total        used        free      shared  buff/cache   available
Mem:          15939         854       14073         385        1011       14362
Swap:          8034           0        8034
[sysadmin@keithspc ~]$

A production Server (VM) with 24GB RAM (RHEL 7.4)
Code:
[root@manhprod187 ~]# cat /etc/redhat-release
Red Hat Enterprise Linux Server release 7.4 (Maipo)
[root@manhprod187 ~]#
[root@manhprod187 ~]# uname -a
Linux manhprod187 3.10.0-693.5.2.el7.x86_64 #1 SMP Fri Oct 13 10:46:25 EDT 2017 x86_64 x86_64 x86_64 GNU/Linux
[root@manhprod187 ~]#
[root@manhprod187 ~]# free -h
              total        used        free      shared  buff/cache   available
Mem:            23G        3.3G        2.0G         10G         18G        9.0G
Swap:          2.0G        1.4G        674M
[root@manhprod187 ~]#
[root@manhprod187 ~]# free -m
              total        used        free      shared  buff/cache   available
Mem:          23948        3471        2002       11006       18473        9194
Swap:          2063        1389         674
[root@manhprod187 ~]#

 

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SYSADMIN(1)						      General Commands Manual						       SYSADMIN(1)

NAME
sysadmin - responsible for everything imaginable that may or may not have to do with the system you're using. Contraction of "system" and "administrator" SYNOPSIS
sysadmin [-ab] [-cd] [-ef] etc...... DESCRIPTION
sysadmin takes care of everything, is generally harangued, must be supplied with coffee, chocolate, and alcohol in order to function prop- erly, cannot be exposed to direct sunlight, and must not be allowed to have a life. sysadmin is not intended as a user interface routine; other programs provide user-friendly front ends; sysadmin is used by everyone who can track him [her] down. With no flags, sysadmin reads its standard input up to an EOF, or a line which sysadmin wishes to parse, and then proceeds to ignore it entirely and read news all day. When invoked with the -w option, sysadmin reads standard input and responds according to terms of job description. OPTIONS
-bofh Go into Bastard Operator From Hell mode. This option causes sysadmin to use tools stored in the /usr/lib/bofh directory to parse the standard input and route user tasks appropriately. -cd causes sysadmin to become caffeine-deprived, resulting in system slowdowns. -b causes the sysadmin to function normally while augmenting the standard input with beer(5). Can be used with the -t option as well, depending upon which version of sysadmin you are running. -t causes the sysadmin to smoke tobacco, which can result in significant performance improvement, provided you are running the correct version of sysadmin. -Cfile Specify an alternate configuration file (sysadmin.cf is the standard). -dX set debuggin value to X. -fFullname Set the full name of the sysadmin. -Bf Create the sysadmin.cf configuration freeze file. -lname Sets the name of the "luser" person (that is, originator of a given request). -l can only be used by "trusted" users (who are listed in sysadmin.cf). NOTES
The -t option should not be used with a version of sysadmin which is not capable of parsing tobacco input. Though the functionality of this command may seem similar to the -b option, it should not be confused with that or the related -c option. 25 September 1995 SYSADMIN(1)
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