How to accurately determine memory (RAM) information Post: 302262284

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Top Forums UNIX for Dummies Questions & Answers How to accurately determine memory (RAM) information Post 302262284 by fiori_musicali on Thursday 27th of November 2008 01:41:07 AM

11-27-2008

Registered User

How to accurately determine memory (RAM) information

I'm writing a shell script to display as much useful information on physical and virtual memory availability and usage as possible. I need a CLI tool to print these numbers for me.

The utilities that I know to give out some statistics are the following:

free
top
vmstat
sysctl

In Linux there's also /proc/meminfo

I'm however using OpenBSD which doesn't by default utilize /proc, and I want the script to apply in as many different environments as possible, relying on the most common basic utilities. The command "free" isn't installed on OpenBSD out-of-the-box, so I've excluded that. sysctl seems the best bet at the moment, aside from the fact that I have to do some wildcarding/conditionals for my script to apply to both Linux and BSD kernels (for example in Linux the first level key for some parameters is "kernel" whereas in OpenBSD it's "kern").

sysctl also displays the amount of physical memory wrong:

hw.physmem=469037056
hw.usermem=467742720

I have 512MB of RAM on that machine. What's up with that? I've also seen it reported by some users that sysctl incorrectly displays the machine to have 2147483648 bytes of physical memory, even when the actual amount by far exceeds this. I'm not sure if this was a Mac-related or a universal issue.

Where does /proc/meminfo fetch its content from? What about free, top, vmstat? Surely there's some cross-referencing somewhere?

Lower the level, the better, as long as it's reachable by scripting.

fiori_musicali

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LEARN ABOUT LINUX

sysctl

SYSCTL(8)																 SYSCTL(8)

NAME

       sysctl - configure kernel parameters at runtime

SYNOPSIS

       sysctl [-n] [-e] variable ...
       sysctl [-n] [-e] [-q] -w variable=value ...
       sysctl [-n] [-e] [-q] -p [filename]
       sysctl [-n] [-e] -a
       sysctl [-n] [-e] -A

DESCRIPTION

       sysctl is used to modify kernel parameters at runtime.  The parameters available are those listed under /proc/sys/.  Procfs is required for
       sysctl support in Linux.  You can use sysctl to both read and write sysctl data.

PARAMETERS

       variable
	      The name of a key to read from.  An example is kernel.ostype.  The '/' separator is also accepted in place of a '.'.

       variable=value
	      To set a key, use the form variable=value where variable is the key and value is the value to set it  to.   If  the  value  contains
	      quotes or characters which are parsed by the shell, you may need to enclose the value in double quotes.  This requires the -w param-
	      eter to use.

       -n     Use this option to disable printing of the key name when printing values.

       -e     Use this option to ignore errors about unknown keys.

       -N     Use this option to only print the names. It may be useful with shells that have programmable completion.

       -q     Use this option to not display the values set to stdout.

       -w     Use this option when you want to change a sysctl setting.

       -p     Load in sysctl settings from the file specified or /etc/sysctl.conf if none given.  Specifying - as filename means reading data from
	      standard input.

       -a     Display all values currently available.

       -A     Display all values currently available in table form.

EXAMPLES

       /sbin/sysctl -a
       /sbin/sysctl -n kernel.hostname
       /sbin/sysctl -w kernel.domainname="example.com"
       /sbin/sysctl -p /etc/sysctl.conf

FILES

       /proc/sys
       /etc/sysctl.conf

SEE ALSO

       sysctl.conf(5)

BUGS

       The -A parameter behaves just as -a does.

AUTHOR

       George Staikos, <staikos@0wned.org>

								    21 Sep 1999 							 SYSCTL(8)