Under some rare conditions, you may get a GRUB loader corruption. This post illustrates how to re-install the GRUB loader on CentOS/RHEL 5 or 6. How do you know GRUB has corrupted Below are some of the symptoms you would see when there is a GRUB loader corruption. 1. The GRUB menu is not shown when booting the server 2. Boot the server into rescue mode using installation DVD, and check the header of the booting diskIf the GRUB loader is corrupted: # file -s /dev/sda /dev/sda: x86 boot … [Read more...] about CentOS / RHEL 5,6 : How to reinstall GRUB loader from rescue mode
So, here is the situation - pvcreate and vgcreate command throws errors shown below. # pvcreate /dev/sdd1 Can't open /dev/sdd1 exclusively. Mounted filesystem? # vgcreate vg1 /dev/sdd1 Can't open /dev/sdd1 exclusively. Mounted filesystem? Unable to add physical volume '/dev/sdd1' to volume group 'vg1'. Probable Cause of the error LVM will only create a pv label on a device if it is not currently in use. There are some of the other various causes for this issue, which include's: The … [Read more...] about pvcreate error : Can’t open /dev/sdx exclusively. Mounted filesystem?
The device node name of a disk (/dev/sda, /dev/hda, /dev/vda, etc.) may change in some situations. For example, after switching cables around or upgrading certain packages, sda & sdc could swap places. This causes problems when /etc/fstab references filesystems by the disk names. It is not safe to use block device node names like /dev/sda1 and /dev/vdb2 to refer to filesystems in /etc/fstab. Instead, use filesystem UUIDs (universally unique identifiers) or labels. Either of these allows for … [Read more...] about CentOS / RHEL : How to change the UUID of the filesystem
The following post shows the procedure to boot CentOS/RHEL/OEL 5 and 6 systems into different kernel installed. CentOS/RHEL/OEL 5 and 6 operating system uses GRUB as the default boot loader. When you install a kernel using either rpm, up2date or yum application, the kernel package creates an entry in the boot loader configuration file for that new kernel. However, rpm does not configure the new kernel to boot as the default kernel, up2date and yum does. You must do this manually when … [Read more...] about Change default kernel (boot with old kernel) in CentOS/RHEL/OEL 5 and 6
Question: How to install Apache and configure Apache httpd to run as a service? Answer: Installing the Apache package If you have the apache package downloaded, you can install it using rpm command as root user. # rpm -ivh httpd If you have yum repository configured, use the recommended way of installing Apache httpd, i.e. with "yum install" command. # yum install httpd NOTE: To get a specific version replace httpd with the version you would like. Example: … [Read more...] about CentOS / RHEL : How to install and start the Apache httpd service
What is LVM tag In a case where you want that only a particular set of logical volumes to be activated and available during boot, lvm tags can come in handy. Lvm tags can allow these tags to be marked beforehand and the effect achieved. Configuration file Navigate to the section show below in the configuration file /etc/lvm/lvm.comf : # vi /etc/lvm/lvm.conf # If volume_list is defined, each LV is only activated if there is a # match against the list. # # "vgname" and … [Read more...] about CentOS / RHEL : How to add, delete and display LVM tags
What is LVM Logical volume manager (LVM) introduces an extra layer between the physical disks and the file system allowing file systems to be : - resized and moved easily and online without requiring a system-wide outage. - Using discontinuous space on disk - meaningful names to volumes, rather than the usual cryptic device names. - span multiple physical disks Linux LVM is very similar to HP-UX LVM and provides many other advanced features like snapshots, cluster support (GFS2, OCFS and … [Read more...] about RedHat / CentOS : A beginners guide to LVM
Multipathing Overview A path is a connection between a server and the underlying storage. The path can be severed due to many reasons like faulty HBA, faulty cable etc. To avoid such single point of failures, multipathing exists. Multipathing ensures that the system uses multiple physical paths to provide redundancy and increased throughput. There are many vendor specific multipathing implementations like EMC's powerpath and Symantecs VxDMP. What is Device Mapper multipath Device Mapper … [Read more...] about Beginners guide to Device Mapper (DM) multipathing