The Problem There is only one Network card on machine but ifconfig shows 2 interface by name virbr0 and lxcbr0. How to remove or disable them permanently if not using them. # ifconfig .... lxcbr0 Link encap:Ethernet HWaddr 82:61:68:AC:39:0F inet addr:10.116.186.1 Bcast:0.0.0.0 Mask:255.255.255.0 inet6 addr: fe80::8061:68ff:feac:390f/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:5 errors:0 … [Read more...] about How to Remove virbr0 and lxcbr0 Interfaces on CentOS/RHEL 6,7
Non-Uniform Memory Access or Non-Uniform Memory Architecture (NUMA) is a physical memory design used in SMP (multiprocessors) architecture, where the memory access time depends on the memory location relative to a processor. Under NUMA, a processor can access its own local memory faster than non-local memory, that is, memory local to another processor or memory shared between processors. In a NUMA system, processors, memory, and I/O are grouped together into cells. The latency and bandwidth … [Read more...] about How to Disable NUMA in CentOS / RHEL 6,7
Non-Uniform Memory Access or Non-Uniform Memory Architecture (NUMA) is a physical memory design used in SMP (multiprocessors) architecture, where the memory access time depends on the memory location relative to a processor. Under NUMA, a processor can access its own local memory faster than non-local memory, that is, memory local to another processor or memory shared between processors. In a NUMA system, processors, memory, and I/O are grouped together into cells. The latency and bandwidth … [Read more...] about How to find if NUMA configuration is enabled or disabled?
The Problem pvcreate command fails while using multipath device with below error even when the device is present. # fdisk -l /dev/mapper/mpatha Disk /dev/mapper/mpatha: 51.6 GB, 51624542208 bytes, 100829184 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk label type: dos Disk identifier: 0x5d7fc634 Device Boot Start End Blocks Id System /dev/mapper/mpatha1 32 100829183 … [Read more...] about pvcreate Fails With Error: “Device /dev/mapper/mpatha Not Found (or Ignored By Filtering).”
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
Question: Is it possible to limit yum so that it lists or installs only security updates? How to patch the system only with security errata? Install the yum-security plugin It is now possible to limit yum to install only security updates (as opposed to bug fixes or enhancements) by installing the yum-security plugin. Contrary to RHEL 7, in RHEL 6 the yum-security plugin is not part of yum. So to install the plugin use : # yum install yum-plugin-security listing available erratas To … [Read more...] about CentOS / RHEL 6 : How to list or install only security updates with yum