Linux

The Basics A key aspect of Red Hat cluster design is that a system must be configured with at least one fencing device to ensure that the services that the cluster provides remain available when a node in the cluster encounters a problem. Fencing is the mechanism that the cluster uses to resolve issues and failures that occur. When you design your cluster services to take advantage of fencing, you can ensure that a problematic cluster node will be cut off quickly and the remaining nodes in the … [Read more...] about Understanding Fencing in a Red Hat High Availability Cluster

We will be setting up VNC for a new user, using the account name of john as an example. 1. Create the VNC user accounts as root: $ su - # useradd john # passwd john 2. Edit the server configuration file /etc/sysconfig/vncservers, and append john on VNCSERVERS line and set VNCSERVERARGS. # vi /etc/sysconfig/vncservers VNCSERVERS="1:aa 2:john" VNCSERVERARGS[1]="-geometry 640x480" VNCSERVERARGS[2]="-geometry 640x480" Account john will have a 640 by 480 screen resolution. 3. … [Read more...] about How to Setup VNC Server for New User in CentOS/RHEL 5

This post describes how to access VNC server which is already installed and configured on a CentOS/RHEL server: vnc-server for CentOS/RHEL 5 tigervnc-server for CentOS/RHEL 6 Before starting, it is assumed that the access the VNC console via vncviewer is possible: # vncviewer [Server IP]:5901 But the below message is received when tried to access using URL: http://[Server IP]:5901 over web broswer: RFB 003.008 The Steps VNC for HTTP access uses a port number other than the … [Read more...] about How to Access VNC Server Through A Web Browser in CentOS/RHEL

The script stop_cluster.sh should get executed during system bootup/shutdown. Email notification should be sent to confirm the execution of the script. If the script is placed in /etc/rc.d/ directory (For example /etc/rc.d/rc3.d/sample-testmail) it would not get executed because it is not a service started by SysV. Even if the script is moved to rc0.d it would be executed during the shutdown. To make SysV run a script, make it the SysV way, and for that merge the start script and stop script … [Read more...] about How to Configure a script to execute during system shutdown and startup in CentOS/RHEL/Fedora

The Problem VNC server failed with "A VNC server is already running as :X" while vncserver restart. VNC server is not starting and getting the following error. # service vncserver restart Shutting down VNC server: 3:testuser 5:testuser2 [FAILED] Starting VNC server: 3:ctmagt70 New 'test1:3 (testuser)' desktop is test1:3 Starting applications specified in /tsc/apps/testuser/.vnc/xstartup Log file is /tsc/apps/testuser/.vnc/tscpinf001:3.log 5:testuser2 A VNC server is already running … [Read more...] about VNC server failed with “A VNC server is already running as :X” while vncserver restart

By default, VNC starts up only a simple window manager and a terminal window. To enable a full Red Hat desktop environment over VNC, we need to configure vncserver to either start GNOME or KDE environments. Follow the steps outlined below to set a default desktop environment over VNC in a CentOS/RHEL 5,6 system. 1. Edit the file ${HOME}/.vnc/xstartup file to run gnome-session for GNOME or startkde for KDE instead of twm as shown below: - To start bare minimum desktop, use the below … [Read more...] about How to Configure vncserver to start GNOME or KDE by default in CentOS/RHEL 5,6

What is NIS (Network Information Service) The Network Information Service or NIS (originally called Yellow Pages or YP) consists of a client-server directory service protocol for distributing system configuration data such as user and hostnames between computers on a computer network. NIS enables to create user accounts that can be shared across all systems over the network. The user account is created only on the NIS server. NIS clients verify the necessary username and password data from the … [Read more...] about How to configure NIS (Network Information Service) Master and Slave servers in CentOS/RHEL 5,6

The audit package ties into the Linux kernel audit subsystem. The audit system audits system calls and other kernel level events, not user-space events, so we need to audit the execve() system call which is what starts executing new programs. For the example in this post, we have taken the CentOS/RHEL system, but the steps remain more or less the same for other *NIX distributions as well. For CentOS/RHEL 7 Apply audit rules into the system 1. To keep the rules persistent after reboot or … [Read more...] about How to audit all Commands run on a Linux system using auditd