The CPU average load value is a very important metric to understand the behavior of a Linux system, and especially its current and recent past status. Many times there is confusion between this term and percentage of CPU usage, but differences are important. In this article I will try to explain the true meaning of both and how to tell if a Linux box is overloaded or underutilized.
I am a strong supporter of simplicity and the principle that less is more, but as far as security and performance of information systems is concerned, we must be able to strike a balance between keeping things simple and exposing ourselves as little as possible to potential threats while trying to obtain the maximum performance of all system elements involved.
It is a common practice that the various distributions of Linux, and even the images used to launch Linux virtual server instances as in the case of AWS AMI’s, implement by default an extremely simple partitioning scheme consisting in a single partition that covers the entire disk. It is in this only partition where the root filesystem (/) is mounted and in which all the directories that configure the file hierarchy of a Linux operating system are placed.
But one of the features of Linux is precisely that it allows you to be highly flexible in placing each of these directories on different partitions or on different disks if necessary.
One of the most common and tedious tasks of a sysadmin is to prevent file systems become completely full, because when a server runs out of space the consequences are unpredictable. Depending on how you structured the root file system and if it is divided into different partitions or volumes, those consequences will be more or less severe, but in any case undesirable.
Less than two days after it was detected a vulnerability (CVE-2014-6271) that affects the Bash shell on Linux, Unix and Mac OS X, a patch was released that solves this issue only partially, which forced to report a new vulnerability (CVE-2014-7169) still pending. This issue has quickly gained a simple name by which it will be remembered for a long time: Shellshock or Shell Shock.
The simplest and shortest method to measure the number of processors present on a Linux box, which is also widely extended as it’s part of coreutils is:
