This post describes how to move a Physical Volume from an existing Volume Group to another existing Volume Group. This facilitates the move of data in the PV to the new VG without doing any manual migration. Before moving a PV, you should make sure that the Logical Volumes created on top of such PVs […]
Archives for August 2016
CentOS / RHEL : How to move a Volume Group from one system to another
To move a whole volume group from one system to another, the vgexport and vgimport commands can be used. Below example involves the steps to move a volume group named “data_vg” from one system to another. The logical volume from this volume group is initially mounted at /data01. 1. Un-mount the file system If required […]
The ultimate Linux interview questions : swap
What is swap space? Swap space in Linux is used when the amount of physical memory (RAM) is full. If the system needs more memory resources and the physical memory is full, inactive pages in memory are moved to the swap space. While swap space can help machines with a small amount of RAM, it […]
CentOS / RHEL 7 : How to Install GUI
For the new installation of RHEL 7, GUI doesn’t come with the default installation. If you do not click on the “Software Selection” link and pick “server with GUI” then there will be no GUI after reboot, only “Base Environment ” will be installed. To enable GUI after system installation, you can use the following […]
CentOS / RHEL 7 : Configuring static IP adress using network interface configuration files
There are various ways you can configure an IP address in RHEL 7. The posts discusses the use of network interface configuration files to configure the IP address. Each physical network device has an associated network interface configuration file. Network interface configuration files are located in the /etc/sysconfig/network-scripts directory. 1. Use the ip addr command […]
CentOS / RHEL : How to determine which SNMP version is being used
Question :1. What command shows what SNMP Protocol version(s) [1, 2c, 3] I am running on my system? 2. How do change the SNMP version in use? Answer : There is no command to show the current running SNMP version. The snmpd daemon will not show as running in any one particular version, as it […]
CentOS / RHEL 6 : Install and Configure SNMPv3
Steps to configure SNMPv3 1. Install the required packages Install the 2 required packages namely, 1. net-snmp-utils 2. net-snmp-devel # yum install net-snmp net-snmp-utils net-snmp-devel net-snmp-utils is required to use the utility snmpwalk. 2. Configure SNMP version 3 user We need to turn off the agent when running net-snmp-create-v3-user command. # service snmpd stop There […]
CentOS / RHEL : How to restrict SSH login by time of day
Question: How to enforce a policy that allows new ssh logins at perticular time of the day only. Outside these access windows no new ssh logins are to be permitted. Solution : PAM Resource Description Login times can be controlled using the Linux Plugin Authentication Method (PAM) pam_time.so module. The pam_time.so module enforces the login […]
RHEL 7 – RHCSA Notes : Create hard and soft links.
RHEL 7 – RHCSA Notes (Cheat Sheets) Soft links As shown in the diagram soft links or symbolic links simply points to another file. It only contains the pathname of the file to which it is pointing 1. Creation method # touch file # ln -s file link # ls -l -rw-r–r– 1 root root […]
CentOS / RHEL 7 : How to boot into Rescue Mode or Emergency Mode
The post explains how to bootup RHEL 7 system into rescue mode or emergency mode. In RHEL7, both rescue mode and emergency mode are systemd targets which replaced the concept of runlevels in previous linux versions. Rescue mode Rescue mode is equivalent to single user mode and requires the root password. Rescue mode allows you […]