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 […]
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 […]
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 […]
LVM VG Metadata Corruption with ‘Checksum error’
The Problem “Checksum errors” are reported when running LVM commands on CentOS/RHEL server. # vgs /dev/mapper/cx0009_lun45: Checksum error /dev/mapper/cx0009_lun48: Checksum error VG #PV #LV #SN Attr VSize VFree vg00 1 7 0 wz–n- 279.12G 159.12G vgcommrmandb 1 6 0 wz–n- 20.00G 44.00M vgcotsoracle 1 1 0 wz–n- 20.00G 4.00M vgcotsorapit 1 1 0 wz–n- 50.00G […]
How to Rebuild the “initramfs” with Multipath in CentOS/RHEL 6 and 7
The initramfs contains kernel modules for all hardware that is required to boot, as well as the initial scripts required to proceed to the next stage of booting. On CentOS/RHEL system, the initramfs contains a complete operational system (which may be used for troubleshooting purposes). Occasionally, the initramfs image may get damaged as well. If […]
After Reboot RAID1 Disk Gets Removed/Out of Sync (CentOS/RHEL)
The Problem A faulty disk was replaced in CentOS/RHEL 6 machine. RAID1 was rebuilt and the server was rebooted. After reboot, disk got removed/out of sync from RAID. RAID had to be rebuilt after every reboot. RAID rebuilt before reboot. # mdadm –detail /dev/md1 /dev/md1: Version : 0.90 Creation Time : Fri Feb 8 10:20:51 […]
How to Configure Proxy in CentOS/RHEL/Fedora
What is a Proxy Server A proxy server is a server that acts as an intermediary for requests from clients seeking resources on the internet or an external network. Think of it as a go-between who makes requests on behalf of the client, ensuring that anyone outside of your network does not know the details […]
How to configure xhost to be persistent across reboots in Linux
Introduction The xhost command is the Linux X-Windows server access control program. Depending on the arguments used, xhost grants or denies user/host access (connections) to the local X-server, thereby allowing or denying users/hosts the ability to display X-Windows-based applications e.g. xclock, graphical installers etc. The purpose of this post is to describe how to configure […]
How to set children-max for udev Service in CentOS/RHEL 7
This post will outline steps to set children-max in CentOS/RHEL 7 temporarily and permanently. Temporary set children-max for udev Service To change temporarily, without rebooting: # systemctl status systemd-udevd.service … Status: “Processing with ## children at max”
How to persistently set nr_requests using UDEV rules
The nr_requests is a parameter for block device, it controls maximum requests may be allocated in the block layer for read or write requests, the default value is 128. Occasionally, it may be suggested to adjust the value, generally speaking: Increasing the value will improve the I/O throughput, but will also increase the memory usage. […]