Explanation of the output of the "ntpq -p" command :Sample Output : -------[root@server ~]# ntpq -premote refid st t when poll reach delay offset jitter*10.1.0.9 LOCAL(0) 11 u 186 512 377 123.355 45.573 8.832[root@server ~]# -------Columns Defined:remote: peers specified in the ntp.conf file* = current time source# = source selected, distance exceeds maximum valueo = source selected, Pulse Per Second (PPS) used+ = source selected, included in final setx = source false ticker. = source selected from end...
Thursday, 26 May 2011
Tuesday, 17 May 2011
Setup an iSCSI target using tgtadm in Red Hat Enterprise Linux 5?
Posted on 10:05 by Unknown
SCSI uses a client-server architecture. A "client" (ie: your system) is an initiator, it initiates requests. A "server" (ie: your storage device) is a target, it has something you want and answers requests from the initiator(s). Initiators come in two varieties: software and hardware. A software initiator is just a driver that handles all requests and pairs the network interfaces driver and the SCSI drivers together to make it all work. Using a software initiator any system with an ethernet card can act as an iSCSI initiator. A hardware initiator...
Configuring iSCSI initiator on rhel 5
Posted on 09:58 by Unknown
SCSI uses a client-server architecture. A "client" (ie: your system) is an initiator, it initiates requests. A "server" (ie: your storage device) is a target, it has something you want and answers requests from the initiator(s). Initiators come in two varieties: software and hardware. A software initiator is just a driver that handles all requests and pairs the network interfaces driver and the SCSI drivers together to make it all work. Using a software initiator any system with an ethernet card can act as an iSCSI initiator. A hardware initiator...
Configuring iSCSI initiator with multipathing ?
Posted on 09:56 by Unknown
For configurations where both paths to the iSCSI target travel over different networks-or-subnets 1. Config the first path through one of you network interfaces:# service iscsid start# chkconfig iscsid on# iscsiadm -m discovery -t st -p -P 1# iscsiadm -m discovery -t st -p -l 2. After logging into the target you should see new SCSI block devices created, verify this by executing fdisk -l:# partprobe# fdisk -l 3. Config the second path through eth1:# iscsiadm -m discovery -t st -p -P 1# iscsiadm -m discovery -t st -p -lFor configurations...
What is Fibre Channel?
Posted on 09:42 by Unknown
What is Fibre Channel?Fibre Channel (FC) is a transport protocol commonly used in storage networks. A common misunderstanding is that FC and fiber optic infrastructure such as host bus adaptor cards and fiber optic cables are the one-in-the-same. This is incorrect. FC is a protocol, like TCP/IP, and can be used over fiber optic cables or over copper. FC is commonly used to transport SCSI commands over fibre optic or copper cables in a Storage Area Network (SAN.)A SAN is simply that: a storage network. A traditional LAN connects computers and devices...
What is cluster ?
Posted on 09:37 by Unknown
What is cluster ?Ans : A cluster is two or more interconnected computers that create a solution to provide higher availability, higher scalability or both. The advantage of clustering computers for high availability is seen if one of these computers fails, another computer in the cluster can then assume the workload of the failed computer. Users of the system see no interruption of access. Clustering software : Red Hat Cluster suitePlatform : Red Hat Enterprise Linux 4,5,6Storage : SCSI, SAN, NASStorage Protocols : iSCSI(pronounced "eye-scuzzy)...
Monday, 16 May 2011
"cluster is not quorate. refusing connection"
Posted on 18:50 by Unknown
Guys,Environment : Red Hat Enterprise Linux 5.6, RHCSError : subject lineIssue : I am not sure while I got this error in the system log since quorate is enabled and working fine on non-firewalled machine where SELinux is also disabled. For the two node cluster, all the cluster.conf are same. One node was connected to the cluster and other didn't.Resolution : 1. Make sure : chkcofing cman off; chkcofing clvmd off; chkcofing rgmanager off;2. Make sure all cluster.conf fules are same.3. Check if iptables are temporary off4. Start cman, clvmd and rgmanager...
Tuesday, 10 May 2011
How add FTP user from backend in linux?
Posted on 18:34 by Unknown
Use following commands :Environment : RHEL 6, vsftpd[root@vm91 ~]# useradd -m testing -G users,ftp,wheel -s /bin/bash[root@vm91 ~]# passwd testingChanging password for user testing.New password: BAD PASSWORD: it is based on a dictionary wordBAD PASSWORD: is too simpleRetype new password: passwd: all authentication tokens updated successfully.[root@vm91 ~]#[root@vm91 ~]# ll -dr /home/*|grep testingdrwx------. 2 testing testing 4096 May 11 06:58 /home/testing[root@vm91 ~]#Test the settings :You may get following error : [kmaiti@kmaiti ~]$ ftp IP_FTP_server...
Thursday, 5 May 2011
How to make persistant static route
Posted on 13:45 by Unknown
Environment : All RHELSteps :1. vi /etc/sysconfig/network-scripts/route-ethX and add following :---GATEWAY=xxx.xxx.xxx.xxxNETMASK=yyy.yyy.yyy.yyyADDRESS=zzz.zzz.zzz.zzz---NB: Replace the address here.2. service network restart3. If you use bond0 device : add following entries in /etc/sysconfig/network-scripts/route- ---default via X.X.X.X dev bond010.10.10.0/24 via X.X.X.X dev bond0---NB: X.X.X.X is the gateway IP addresstry...
How to create network bonding device?
Posted on 13:43 by Unknown
Environment : RHEL 6Steps : 1. vi /etc/modprobe.conf and add : alias bond bonding 2. vi /etc/sysconfig/network-scripts/ifcfg-bond and add :---DEVICE=bond0IPADDR=192.168.1.1NETMASK=255.255.255.0ONBOOT=yesBOOTPROTO=noneUSERCTL=noBONDING_OPTS=""---NB : N -> 0,1, ...2. Let two ethernet cards are there like : eth0 and eth1 :They will look like :----DEVICE=eth<0/1>BOOTPROTO=noneONBOOT=yesMASTER=bondSLAVE=yesUSERCTL=no----3. Make sure "bonding" kernel module is present on server: lsmod | grep bonding; modprobe bonding;4. Restart the service...
How to analysis coredump using GDB tool?
Posted on 06:20 by Unknown
Hello,Usually particular program or kernel creates core dump/vmcore file. You need to enable coredump on the linux machine. To collect the vmcore file(memory dump using crash kernel) you need to install kexec/kdump utils in the machine.Once setup is done, you can install GDB like : #yum install gdb1. Analysis coredump generated by process/binary :a)Install the particular package which contains that binary. Check the version to make it similar if you want to analysis the coredump file on another system.b) Install -debuginfo- on the machine of that...
Wednesday, 4 May 2011
What is Proxy and Reverse Proxy?
Posted on 07:18 by Unknown
Web Proxies :A proxy server is a gateway for users to the Web at large. Users configure the proxy in their browser settings, and all HTTP requests are routed via the proxy. Proxies are typically operated by ISPs and network administrators, and serve several purposes: for example, * to speed access to the Web by caching pages fetched, so that popular pages don't have to be re-fetched for every user who views them. * to enable controlled access to the web for users behind a firewall. * to filter or transform web content.Reverse Proxies :A...
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