The Problem On CentOS/RHEL 6, a disk has issue and mdadm command shows /dev/md5 was active, degraded state . # mdadm -Q --detail /dev/md5 /dev/md5: Version : 0.90 Creation Time : Wed Apr 12 09:50:21 2017 Raid Level : raid1 Array Size : 10485696 (10.00 GiB 10.74 GB) Used Dev Size : 10485696 (10.00 GiB 10.74 GB) Raid Devices : 2 Total Devices : 1 Preferred Minor : 5 Persistence : Superblock is persistent Update Time : Mon Jun 5 14:47:09 2017 State : active, degraded Active Devices … [Read more...] about mdadm Command Shows State : active, degraded
Archives for December 2018
How to Re-generate initramfs and vmlinuz for Rescue Kernel with Current Kernel in CentOS/RHEL 7
We want to re-generate initramfs and vmlinuz for the Rescue Kernel in our CentOS/RHEL 7 system. How can this be done using the current kernel from which the system is booted up? During the boot process, when the kernel image and initramfs image get loaded, initramfs starts the first process on the system, which is systemd with the process ID 1. This systemd process further takes over control in the final stages of system booting and performs the following operations: Reads the … [Read more...] about How to Re-generate initramfs and vmlinuz for Rescue Kernel with Current Kernel in CentOS/RHEL 7
Understanding Failover in a Pacemaker Cluster
This post provides an introduction to creating a Pacemaker cluster running a service that will fail over from one node to another when the node on which the service is running becomes unavailable. By working through this procedure, you can learn how to create a service in a two-node cluster and you can then observe what happens to that service when it fails on the node on which it running. This example procedure configures a two node Pacemaker cluster running an Apache HTTP server. You can … [Read more...] about Understanding Failover in a Pacemaker Cluster
Understanding Pacemaker Cluster Tools and Processes
This post provides an introduction to the tools and processes you use to create a Pacemaker cluster. It is intended for users who are interested in seeing what the cluster software looks like and how it is administered, without needing to configure a working cluster. This example requires a single node running CentOS/RHEL 7 and it requires a floating IP address that resides on the same network as the statically assigned IP address for that node. Note: Ensure that the name of the node on which … [Read more...] about Understanding Pacemaker Cluster Tools and Processes
Simple Steps to use LogMiner for finding high redo log generation
LogMiner is a tool that lets you use SQL statements to analyze events in the database log. With LogMiner, you can track transactions as they are processed or locate specific functions that result in data modifications. LogMiner was introduced with Oracle8i. LogMiner can be used, along with audit trails, to determine what has happened in your Oracle database. In this post, we will see simple steps for mining the redo logs, for instance, to troubleshoot excessive redo generation. 1. Enable … [Read more...] about Simple Steps to use LogMiner for finding high redo log generation
How to create a new lv using an existing volume group that is managed by pacemaker cluster (CentOS/RHEL 7)
1. In order to create a new lv in an existing vg, execute the lvcreate command on the node which has lvm resource running. [root@node2 ~]# pcs status Cluster name: nakul Last updated: Tue Oct 4 01:20:49 2016 Last change: Tue Oct 4 01:20:45 2016 Stack: corosync Current DC: node1.example.com (1) - partition with quorum Version: 1.1.12-a14efad 2 Nodes configured 3 Resources configured Online: [ node1.example.com node2.example.com ] Full list of resources: fence … [Read more...] about How to create a new lv using an existing volume group that is managed by pacemaker cluster (CentOS/RHEL 7)
Beginners Guide to “journalctl” – How To Use Journalctl to View and Manipulate Systemd Logs
Using the system journal By default, newer systemd based linux systems now uses two logging services for the system logs: systemd-journald, which is configured to only keep logs in memory rsyslogd, which gets messages sent to it by systemd-journald (and others) and stores them on disk. To view messages in the system journal, a tool called journalctl can be used. If used without any parameters it will show the full contents of the system journal, presented in a pager (by default less is … [Read more...] about Beginners Guide to “journalctl” – How To Use Journalctl to View and Manipulate Systemd Logs
How can I increase the log level of winbind or samba without restarting the services in Linux
The user doesn't want to restart winbind or samba to increase the log levels. The user needs increased logging while a problem is occurring but increasing the log level through the smb.conf requires a restart of the services which can temporarily fix an issue and requires the user to wait for another occurrence to get the logs needed. How can we increase the log levels without restarting the services? Increasing the log level of winbind or samba without restarting the services Increasing the … [Read more...] about How can I increase the log level of winbind or samba without restarting the services in Linux
How to find the size of a MySQL database
The easiest method is to query the INFORMATION_SCHEMA. For Example: SELECT ENGINE, COUNT(*), SUM(DATA_LENGTH), SUM(INDEX_LENGTH) FROM information_schema.TABLES WHERE TABLE_SCHEMA='menagerie' GROUP BY ENGINE; Additionally here is a potentially faster example to estimate the db size (InnoDB only and if you do not use compressed tables) since it doesn't use INFORMATION_SCHEMA.TABLES : select sum( CLUST_INDEX_SIZE + OTHER_INDEX_SIZE)* @@innodb_page_size / 1024 / 1024 "Estimated size in Mb" … [Read more...] about How to find the size of a MySQL database
How to run Apache httpd server from a non-root user in CentOS/RHEL 7
The user wants to run Apache httpd server from a non-root user in CentOS/RHEL 7. How this can be achieved with the help a service under systemd? Configuring Apache httpd server to run from a non-root user (Using systemd service) The /run/httpd file ownership and permissions are changed by systemd on startup because of the /usr/lib/tmpfiles.d/httpd.conf file. This is installed with the httpd package and doesn't require the httpd.service to be enabled. If a non-root user tries to start the … [Read more...] about How to run Apache httpd server from a non-root user in CentOS/RHEL 7