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 does not share physical extents with other PVs. You can find the extent and device of an LV using the command given below; # lvdisplay -m Steps involved 1. Unmount the directory . # umount … [Read more...] about CentOS / RHEL : Move a Physical Volume from an existing Volume Group to another Volume Group
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 switch to "rescue" mode. Make sure that no users are accessing files on the active volume. # umount /data01 2. Mark the volume group inactive Marking the volume group … [Read more...] about CentOS / RHEL : How to move a Volume Group from one system to another
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 should not be considered a replacement for more RAM. Swap space is located on hard drives, which have a slower access time than physical memory. Swap space can be a dedicated swap partition … [Read more...] about The ultimate Linux interview questions : swap
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 method. Installing the environment group "Server with GUI" 1. Check the available environment groups : # yum grouplist Loaded plugins: langpacks, product-id, … [Read more...] about CentOS / RHEL 7 : How to Install GUI
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 to display your available network interfaces. # ip addr 1: lo: [LOOPBACK,UP,LOWER_UP] mtu 65536 qdisc noqueue state … [Read more...] about CentOS / RHEL 7 : Configuring static IP adress using network interface configuration files
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 has the ability to do any of the three at any time. The configuration in the snmpd.conf file (/etc/sma/snmp/snmpd.conf) will indicate which versions allowed. - By default the rocommunity and … [Read more...] about CentOS / RHEL : How to determine which SNMP version is being used
Creating network interface alias for network boot or jumpstart installation at OBP
Question : How to create a network interface alias at OBP for jumpstart installation or network boot. Solution : Sometimes when we want to do a jumpstart installation or a network boot the default network interface which is selected is not connected to the network. The command 'boot net - install' fails to run in this case. The workaround is to create a new alias for the network interface which we know has network connectivity. Example : 1. Halt the system to the OBP (ok) prompt, … [Read more...] about Creating network interface alias for network boot or jumpstart installation at OBP
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 are 3 ways you can create the user. 1. command line 2. Interactive 3. Manually 1. Command … [Read more...] about CentOS / RHEL 6 : Install and Configure SNMPv3
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 restrictions specified in the file /etc/security/time.conf. So the desired login windows must be defined in that file. Example Policy Using an … [Read more...] about CentOS / RHEL : How to restrict SSH login by time of day
How to run savecore (crash dump) manually in Solaris
If savecore did not successfully run to retrieve system core image(crash dump) from the dump device during reboot following a system panic it is possible to attempt to retrieve the crash dump manually from the command line. The kernel core image gets copied into the dump device configured by the dumpadm command as part of the panic recovery code. The default dump device is primary swap space. Often, the kernel core image may remain intact for some time after the panic. First, ensure there is … [Read more...] about How to run savecore (crash dump) manually in Solaris