System Admin Q & A – XVIII

Ques 1: – What is xinetd & why we required xinetd services in linux ?

Ans: – xinetd, the eXtended InterNET Daemon, is an open-source daemon which runs on many Linux and Unix systems and manages Internet-based connectivity.xinetd performs the same function as inetd: it starts programs that provide Internet services. Instead of having such servers started at system initialization time, and be dormant until a connection request arrives, xinetd is the only daemon process started and it listens on all service ports for the services listed in its configuration file. When a request comes in, xinetd starts the appropriate server. Because of the way it operates, xinetd (as well as inetd) is also referred to as a super-server.

Ques 2: – What is use of initrd?

Ans: – The initial RAM disk (initrd) is an initial root file system that is mounted prior to when the real root file system is available. The initrd is bound to the kernel and loaded as part of the kernel boot procedure. The kernel then mounts this initrd as part of the two-stage boot process to load the modules to make the real file systems available and get at the real root file system. The initrd contains a minimal set of directories and executables to achieve this, such as the insmod tool to install kernel modules into the kernel.

Ques 3: – What are Physical Exents & Logical Extents in LVM ?

Ans: – Each physical volume is divided chunks of data, known as physical extents, these extents have the same size as the logical extents for the volume group. Each PV consists of a number of fixed-size physical extents (PEs); similarly, each LV consists of a number of fixed-size logical extents (LEs). (LEs and PEs are always the same size, the default in LVM 2 is 4 MB.) An LV is created by mapping logical extents to physical extents.

Ques 4: – How to find whether you are working physical or virtual linux Server ?

Ans: – Using the command dmidecode we can determine whether I am working on phyical or virtual linux server.

Sample Output :

 # dmidecode | grep -i -e "kvm" -e "vmware"
 Manufacturer: VMware, Inc. 
 Product Name: VMware Virtual Platform 
 Serial Number: VMware-56 4d d3 dd d9  43 5f e4-9d ea c0 99 d0 5e 21 c1 
 Description: VMware SVGA II

Ques 5: – How to find model & serial number of Linux Servers ?

Ans: – : With help of dmidecode command we find the model & serial number of linux Servers as shown below :

# dmidecode -t system
# dmidecode 2.9
 SMBIOS  2.6 present. 
 Handle  0x0100, DMI type 1, 27 bytes
 System  Information
 Manufacturer:  HP
 Product  Name: ProLiant DL360 G7
 Version:  Not Specified
 Serial  Number: USE000A11M
 UUID:  30000000-3000-5000-4000-300000000000
 Wake-up  Type: Power Switch
 SKU  Number: 579237-B21
 Family:  ProLiant 
 Handle  0x2000, DMI type 32, 11 bytes
 System  Boot Information
 Status:  No errors detected

Ques 6: – What is Open vSwitch?

Ans: – Open vSwitch is a production quality open source software switch designed to be used as a vswitch in virtualized server environments. A vswitch forwards traffic between different VMs on the same physical host and also forwards traffic between VMs and the physical network. Open vSwitch supports standard management interfaces (e.g. sFlow, NetFlow, RSPAN, CLI), and is open to programmatic extension and control using OpenFlow and the OVSDB management protocol.

Open vSwitch as designed to be compatible with modern switching chipsets. This means that it can be ported to existing high-fanout switches allowing the same flexible control of the physical infrastructure as the virtual infrastructure. It also means that Open vSwitch will be able to take advantage of on-NIC switching chipsets as their functionality matures.

Ques 7: – What virtualization platforms can use Open vSwitch?

Ans: – : Open vSwitch can currently run on any Linux-based virtualization platform (kernel 2.6.18 and newer), including: KVM, VirtualBox, Xen, Xen Cloud Platform, XenServer. As of Linux 3.3 it is part of the mainline kernel. The bulk of the code is written in platform- independent C and is easily ported to other environments.

Ques 8: – Which are the important configuration files for Linux DNS server ?

Ans: – BIND uses /etc/named.conf as its main configuration file, the /etc/rndc.conf file as the configuration file for name server control utility rndc, and the /var/named/ directory for zone files and the like.

Ques 9: – What is Trunk Port ?

Ans: – A Trunk Link, or ‘Trunk‘ is a port configured to carry packets for any VLAN. These type of ports are usually found in connections between switches. These links require the ability to carry packets from all available VLANs because VLANs span over multiple switches.

Ques 10: – What is VLAN and its advantages ?

Ans: – VLAN refers to Virtual Local Area Network is a virtual LAN that extends its functionalities beyond a single LAN. Through VLAN a network is divided into different logical segments known as broadcast domains. The computers in the VLAN acts as they are connected with the same LAN segment even they are located on the different network segments. In the VLAN, computers can move from one location to another and they can still be the part of the same VLAN. VLAN offers many advantages over the traditional local area network.

The main advantages of the VLAN includes high performance, simplified network administration, security, low cost and the creation of the virtual groups to avoid the collision and data loss in the network. VLAN controls the bandwidth allocations and provides the flexibility and ease of work to the users.In the VLAN, the computers do not need to be physically located at the same place. Though it is a logical entity it is created and configured through the software.

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