We have seen how to create variables – integer, float, or character types, each variable is given a unique name and you can store one item under that name. Often, however, we need several similar items to be grouped under a single name. For example, marks scored by a student in different subjects, the salaries […]
Archives for July 2021
Control Structures of C – for, while and do loops, if then else statements, switch statements
Here we learn about the control structures of C. The compiler normally takes the program line by line and executes them in a sequence ( one after another ). But this may not always be the case. Based on certain conditions existing in the data, we may want to change the data – Then we […]
Fundamentals of C Variables, data types, arithmetic expressions and Library functions
C has evolved from a succession of programming languages developed by Bell Laboratories in the early 1970s. The increasing popularity of the unix operating system, which has C as its “Standard” programming language, further enhanced the usefulness of C making it arguably the most popular of the programming languages. We now start with the fundamentals […]
How to calculate recommended value of vm.min_free_kbytes Kernel Tuning Parameter
/proc/sys/vm/min_free_kbytes: This controls the amount of memory that is kept free for use by special reserves including “atomic” allocations (those which cannot wait for reclaim). Setting vm.min_free_kbytes too low prevents the system from reclaiming memory. This can result in system hangs and OOM-killing multiple processes. However, setting this parameter to a value that is too […]
how to rotate Tang Server Keys and update the Clevis Client
This post explains how to rotate Tang Server Keys and update the Clevis Client. Note, below is an example hence all certificates, keys and device names/uuid’s are fictional. Change the keys on the tang server 1. Check existing key: # ls -la /var/db/tang total 8 dr-xrws—. 2 tang tang 84 Jun 26 11:24 . drwxr-xr-x. […]
What Are Dirty Pages in Linux
Question: What are dirty pages and what is their purpose? Whenever application/database process needs to add virtual page into physical memory but no free physical pages are left OS must clear-out remaining old pages. Now if old page had not been written at all then this one does not need to be saved it can […]
How RHEVM Monitor Storage Health
This post will illustrate how RHEVM monitors storage health in detail. Monitor Storage Pool Manager Health The Storage Pool Manager (SPM) is a management role assigned to one of the hosts in a data center enabling it to manage the storage domains of the data center. RHEVM check SPM availability and metadata integrity at every […]
How does Sanlock Work in RedHat Virtualization
In RHV, KVM Host uses Sanlock to detect the connectivity with Storage domain. When Sanlock enables, it will open wdmd daemon(watchdog multiplexing daemon) and send keepalive with certain heartbeat. sanlock IO to storage does not complete within a fixed time, sanlock stop sending keepalive to wdmd. When it is timeout,the wdmd daemon controlling /dev/watchdog will […]
RHV – Understanding “Resilience Policy” for VM live migration
In RHV web portal, Select “Compute” -> “Cluster” -> Select one cluster object -> click “Edit” -> click “Migration Policy”, there is a control called “Resilience Policy”, this note explains how “Resilience Policy” controls VM live migration during an outage. Basically “Resilience Policy” controls how virtual machines running on the host in “Non-operational” state in […]
How To Change Engine Database Password for RHVM Engine
This post illustrates steps to change engine database password for RHVM engine. 1. Before modification, you can run below commands to check the current ENGINE_DB_PASSWORD for RHEVM engine interacting with the engine database. By default, ENGINE_DB_PASSWORD is a random string which is auto-generated by engine-config during the setup process. The ENGINE_DB_PASSWORD is used by below […]