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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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SYSTEMD-CRYPTSETUP-GENERATOR(8) 			   systemd-cryptsetup-generator 			   SYSTEMD-CRYPTSETUP-GENERATOR(8)

NAME
systemd-cryptsetup-generator - Unit generator for /etc/crypttab SYNOPSIS
/lib/systemd/system-generators/systemd-cryptsetup-generator DESCRIPTION
systemd-cryptsetup-generator is a generator that translates /etc/crypttab into native systemd units early at boot and when configuration of the system manager is reloaded. This will create systemd-cryptsetup@.service(8) units as necessary. systemd-cryptsetup-generator implements systemd.generator(7). KERNEL COMMAND LINE
systemd-cryptsetup-generator understands the following kernel command line parameters: luks=, rd.luks= Takes a boolean argument. Defaults to "yes". If "no", disables the generator entirely. rd.luks= is honored only by initial RAM disk (initrd) while luks= is honored by both the main system and the initrd. luks.crypttab=, rd.luks.crypttab= Takes a boolean argument. Defaults to "yes". If "no", causes the generator to ignore any devices configured in /etc/crypttab (luks.uuid= will still work however). rd.luks.crypttab= is honored only by initial RAM disk (initrd) while luks.crypttab= is honored by both the main system and the initrd. luks.uuid=, rd.luks.uuid= Takes a LUKS superblock UUID as argument. This will activate the specified device as part of the boot process as if it was listed in /etc/crypttab. This option may be specified more than once in order to set up multiple devices. rd.luks.uuid= is honored only by initial RAM disk (initrd) while luks.uuid= is honored by both the main system and the initrd. If /etc/crypttab contains entries with the same UUID, then the name, keyfile and options specified there will be used. Otherwise, the device will have the name "luks-UUID". If /etc/crypttab exists, only those UUIDs specified on the kernel command line will be activated in the initrd or the real root. luks.name=, rd.luks.name= Takes a LUKS super block UUID followed by an "=" and a name. This implies rd.luks.uuid= or luks.uuid= and will additionally make the LUKS device given by the UUID appear under the provided name. rd.luks.name= is honored only by initial RAM disk (initrd) while luks.name= is honored by both the main system and the initrd. luks.options=, rd.luks.options= Takes a LUKS super block UUID followed by an "=" and a string of options separated by commas as argument. This will override the options for the given UUID. If only a list of options, without an UUID, is specified, they apply to any UUIDs not specified elsewhere, and without an entry in /etc/crypttab. rd.luks.options= is honored only by initial RAM disk (initrd) while luks.options= is honored by both the main system and the initrd. luks.key=, rd.luks.key= Takes a password file name as argument or a LUKS super block UUID followed by a "=" and a password file name. For those entries specified with rd.luks.uuid= or luks.uuid=, the password file will be set to the one specified by rd.luks.key= or luks.key= of the corresponding UUID, or the password file that was specified without a UUID. rd.luks.key= is honored only by initial RAM disk (initrd) while luks.key= is honored by both the main system and the initrd. SEE ALSO
systemd(1), crypttab(5), systemd-cryptsetup@.service(8), cryptsetup(8), systemd-fstab-generator(8) systemd 237 SYSTEMD-CRYPTSETUP-GENERATOR(8)
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