When using iSCSI and LVM, sometimes we have to manually enable iSCSI disk that used as a physical volume in LVM. This is because LVM service is started earlier than iSCSI service so the iSCSI disk containing the physical volume is not present yet. Solution to this problem is to enable lvmetad in /etc/lvm/lvm.conf. The lvmetad is “LVM metadata daemon” that acts as in-memory cache of LVM metadata gathered from devices as they appear in the system. Whenever a block device appears and has PV label on it, it is automatically scanned via an udev rule. This update the lvmetad daemon with the LVM metadata found. Once the VG is complete (all the PVs making up the VG are present), the VG is activated. The lvmetad daemon is required for this LVM event-based autoactivation to work and the iSCSI disk must be present in the system after boot time.
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In this short tutorial I will show how to check TCP/UDP open port or services in FreeBSD box. For checking open port or services which uses port in FreeBSD simply issue the following commands.
check TCP connection
sockstat -Ptcp check UDP connection
sockstat -PudpCombine with grep to search port used by specific service or service which using specific port.
use grep to get service or port
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DRBD refers to block devices designed as a building block to form high availability cluster. This is done by mirroring a whole block device via an assigned network. DRBD can be understood as network based RAID-1. (DRBD)
Sometimes we have a disk failure on hard drive which contains DRBD backing device. The following steps can be used to replace or recover the failed drive.
detach drbd resource from broken backing storage
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Split Brain in DRBD is a condition where each host think that resource in another host is outdated, thus synchronization won’t be occured. This condition often occurs because of network or power failure which is indicated by these variables:
log: Split-Brain detected, dropping connection connection-state: StandAlone/WFConnection To manually recover the cluster from split brain condition, the following steps is required.
on victim connection state must be StandAlone
# drbdadm disconnect <resource> set victim as secondary
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It is usual task to find someone computer by its MAC address when there is an issue related to his computer in the local network. The common case is IP conflict or network abuse. But, if the MAC Address shows that machine is one of many scattered VMware virtual machine out there, how do we find it?
vSphere Client If you have an VMware ESX or ESXi server, vSphere Client is tool to manage your virtual machines from remote computer. But, vSphere Client cannot tell the MAC Address of virtual machines from version 10 or higher and to find virtual machine based on MAC Address we must open the virtual machine Setting one by one. It is still possible when there are few virtual, but it is exhausting when we have many virtual machine.
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Zimbra is a well known collaboration suite which includes email, calendaring, file sharing, activity streams, social communities and more. The most popular product from Zimbra is Zimbra Collaboration Server. Zimbra Collaboration Server comes with two version: Network Edition and Open Source Edition (FOSS). This documentation shows a simple way to install Zimbra Collaboration Server Open Source Edition in CentOS 6.5.
Getting Started Prepare the system
# yum update Disable SELinux
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Quantum Espresso is a software for electronic-structure calculations and materials modeling at the nanoscale. The installation of Quantum Espresso is quite easy because it includes external libraries which it needs. But we are encouraged to install Quantum Espresso using our own machine optimized external libraries such as Basic Linear Algebra Subprograms (BLAS), Linear Algebra Package (LAPACK), Scalable LAPACK (SCALAPACK), and Fastest Fourier Transform in the West (FFTW).
External Libraries There are several repositories or development teams which provide external libraries. For example is Netlib which provides BLAS, LAPACK, and SCALAPACK. But, for machines with Intel processor, maybe the best external libraries out there is Intel® Math Kernel Library which has a non-commercial version as standalone or included in Intel® Parallel Studio XE 2013 for Linux that can be downloaded in Intel Non-Commercial Software Development. Intel® Math Kernel Library provides BLAS, LAPACK, SCALAPACK, and even FFTW interfaces.
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Icinga is a well-known server or network monitoring that runs in many Unix/Linux distribution. Server/Network monitoring is an essential part of Network Operations Center because by monitoring network engineers can always get the feedback and status from network and production servers. This is a simple documentation of Icinga installation in Scientific Linux 6.4 server.
Getting started Before we install icinga, it best to keep our system updated.
# yum update Search icinga package using yum search in RPMForge repository.
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Cacti is a network graphic monitoring tools which used the potential of RRDTool. RRDTool is a data logging and graphing system for time series data. Cacti can show us a real time performance of network or servers which make this software become one of the most popular open source monitoring software. Getting Started Always update your box before we install new software.
# yum update Install dependencies for cacti.
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