System Admin Q & A – XVI

Ques 1: – What is RCRON and where to use RCRON ?

Ans: – rcron is a powerful tool that helps system administrators in setting up cron jobs redundancy and failover over groups of machines. RCRON ensure that a job installed on several machines will only run on the active one at any time. High Availability using RCRON ( One Node will be stamped as Active and Second Node will be stamped as Passive ) , Same cron configuration will be on both , only difference would be active/passive state in a file.

For automatic Switching of active/passive state , we will be using KEEPALIVED Daemon , which utilizes the keepalive signal for communication between 2 nodes. After a signal is sent, if no reply is received the link is assumed to be down.

Ques 2: – What is Content Negotiation ?

Ans: – Load Balancing Clusters operate by having all workload come through one or more load balancing front-ends, which then distribute it to a collection of back end servers. If a node in a load-balancing cluster becomes inoperative, the load balancing software detects the failure and redirects requests to other cluster nodes. Red Hat Cluster Suite provides load- balancing through LVS (Linux Virtual Server).

Ques 3: – What is Puppet ?

Ans: – Puppet is a configuration Tool which is use to automate administration tasks.Puppet Agent(Client) sends request to Puppet Master (Server) and Puppet Master Push Configuration on Agent.

Ques 4: – What is Facter in Puppet ?

Ans: – Sometime you need to write manifests on conditional experession based on agent specific data which is available through Facter. Facter provides information like Kernel version,Dist release, IP Address, CPU info and etc.You can defined your facter also.

Ques 5: – What is Storage Clusters ?

Ans: -Storage clusters provide a consistent file system image across servers in a cluster, allowing the servers to simultaneously read and write to a single shared file system. With a cluster-wide file system, a storage cluster eliminates the need for redundant copies of application data and simplifies backup and disaster recovery. Red Hat Cluster Suite provides storage clustering through Red Hat GFS(Global File System).

Ques 6: – How to enable proxy settings in RSYNC and APT (ubuntu) ?

Ans: – Proxy Settings in RSYNC

# export  RSYNC_PROXY="http://:”
#  export RSYNC_PROXY="http://proxy.nextstep4it.com:8080”

Proxy settings for APT : Edit /etc/apt/apt.conf

Acquire::http::Proxy “http://:“;

Ques 7: – What is Virtual Hosting in Apache ?

Ans: – The term Virtual Hosting refers to the practice of running more than one web site (such as site1.nextstep4it.com and site2.nextstep4it.com) on a single machine. In Apache there are two types of virtual hosting.

1: IP Based Virtual Hosting

2: Name-Based Virtual Host

Ques 8: – What is Glusterfs ?

Ans: – GlusterFS is an open source network / cluster filesystem and based on a stackable user space design. It is used to achieve high availability of storage(i.e real time replication of files) across two linux machines using GlusterFS. Although glusterfs found its application in different areas like cloud computing, streaming media services, and content delivery networks.

Ques 9: – What is mutt and how to send mails using mutt from linux console ?

Ans: – Mutt is a small but powerful text-based e-mail client for Unix like operating systems. With mutt command one can send and read emails. Mutt supports both maildir & mbox mail formats. Mutt is compatible with POP & IMAP protocols.

Syntax :

# mutt -s “Subject of the Mail”  recipient-address@domain.com <  /dev/null

Ques 10: – What is Storage Clusters ?

Ans: -Storage clusters provide a consistent file system image across servers in a cluster, allowing the servers to simultaneously read and write to a single shared file system. With a cluster-wide file system, a storage cluster eliminates the need for redundant copies of application data and simplifies backup and disaster recovery. Red Hat Cluster Suite provides storage clustering through Red Hat GFS(Global File System).

System Admin Q & A – XV

Ques 1: – What is Virtualization ?

Ans: – Virtualization (or virtualisation), in computing, is the creation of a virtual (rather than actual) version of something, such as a hardware platform, operating system, a storage device or network resources.

Ques 2: – what are the key features of NFSv4 ?

Ans: – NFSv4 comes with several new features:

Advanced security management
Kerberos
SPKM
LIPKEY
Firewall friendly
Advanced and aggressive cache management
Non Unix compatibility (Windows)
Easy to administer (Replication, migration)
Crash recovery (Client and server sides

Ques 3: – What are the types of hardware virtualization?

Ans: – Full virtualization: Almost complete simulation of the actual hardware to allow software, which typically consists of a guest operating system, to run unmodified Partial virtualization: Some but not all of the target environment is simulated. Some guest programs, therefore, may need modifications to run in this virtual environment.

Paravirtualization: A hardware environment is not simulated; however, the guest programs are executed in their own isolated domains, as if they are running on a separate system. Guest programs need to be specifically modified to run in this environment.

Ques 4: – What are the benefits of virtualization?

Ans: – Virtualization is a creation of virtual machines and to manage them from one place. It allows the resources to be shared with large number of network resources. Virtualization is having lots of benefits and they are as follows:

It helps in saving lots of cost and allows to easily maintaining it, in less cost.
It allows multiple operating systems on one virtualization platform.
It removes the dependency of heavy hardware to run the application.
It provides consolidating servers that are used for crashing of a server purpose
It reduces the amount of space being taken by data centers and company data.

Ques 5: – What is the location of postfix mailserver Queue ?

Ans: -By default, the Postfix mail queues are located in the /var/spool/postfix directory. Each message queue is created as a separate subdirectory within this directory. Each message is stored as a separate file in the subdirectory, using a unique identifier for the filename.

Ques 5: – What is the Difference Between Qemu and KVM ?

Ans: – QEMU : Itis a generic and open source machine emulator and virtualizer. When used as a machine emulator, QEMU can run OS and programs made for one machine (e.g. an ARM board) on a different machine (e.g. your own PC). By using dynamic translation, Qemu achieves very good performance.

KVM (Kernel Virtual Machine ) : KVM is a Linux kernel module that allows a user space program to utilize the hardware virtualization features of various processors.

Ques 6: – What is Content Negotiation ?

Ans: – Content Negotiation refers to the technique Web clients and servers use to select how to present a resource , such as a document , that is available in several different formats.

Ques 7: – What does /etc/skell directory contains?

Ans: – The /etc/skel directory contains files and directories that are automatically copied over to a new user’s home directory when such user is created by the useradd or adduser command.

Ques 8: – What is the difference between /dev/dsk and /dev/rdsk in Solaris ?

Ans: – In Solaris whenever we create a new slice using format command a raw physical slice or a Raw Device will be created which is addressed as /dev/rdsk/c#d#s# where # is the number for slice.

After formatting it with newfs command the slice will be addressed as /dev/dsk/c#d#s# which can now be used for mounting.

eg.

#newfs /dev/rdsk/c0d0s4

#mkdir /oracle
#mount /dev/dsk/c0d0s4 /oracle

After mounting /dev/dsk/c#d#s# is called as Block Device

/dev actually contains logical device names which are links (Shortcuts in windows terminology) to actual physical devices in /devices directory.arate system. Guest programs need to be specifically modified to run in this environment.

Ques 9: – What is sticky bit in Solaris?

Ans: -Sticky Bit is a permission bit that protects the files with in a Directory. If the directory has sticky bit set, a file can only be deleted by the owner of the file, or root. This Prevents a user from deleting other users files from public directories . The sticky bit is displayed as the letter t in the execute field for ‘others’.

System Admin Q & A – XIV

Ques 1: – What is Puppet ?

Ans: – Puppet is a configuration Tool which is use to automate administration tasks.Puppet Agent(Client) sends request to Puppet Master (Server) and Puppet Master Push Configuration on Agent. Communtication between the master and agent is done by exchaning the certificates.

Ques 2: – What is the use of etckeeper-commit-post and etckeeper-commit-pre on Puppet Agent ?

Ans:- etckeeper-commit-post: In this configuration file you can define command and scripts which executes after pushing configuration on Agent

etckeeper-commit-pre: In this configurati-on file you can define command and scripts which executes before pushing configuration on Agent

Ques 3: – What does IntelliMirror do?

Ans: – It helps to reconcile desktop settings, applications, and stored files for users, particularly those who move between workstations or those who must periodically work offline.

Ques 4: – What’s the major difference between FAT and NTFS on a local machine?

Ans: – FAT and FAT32 provide no security over locally logged-on users. Only native NTFS provides extensive permission control on both remote and local files.

Ques 5: – What’s the difference between standalone and fault-tolerant DFS (Distributed File System) installations?

Ans:- The standalone server stores the Dfs directory tree structure or topology locally. Thus, if a shared folder is inaccessible or if the Dfs root server is down, users are left with no link to the shared resources. A fault-tolerant root node stores the Dfs topology in the Active Directory, which is replicated to other

Ques 6: – What is Server Load Balancing ?

Ans: – Server Load Balancing (SLB) provides network performance and content delivery by implementing a series of algorithms and priorities to respond to the specific requests made to the network. In simple terms, SLB distributes clients to a group of servers and ensures that clients are not sent to failed servers.

Ques 7: – What do you mean a File System?

Ans: – File System is a method to store and organize files and directories on disk. A file system can have different formats called file system types. These formats determine how the information is stored as files and directories.

Ques 8: – Which Environment is most suitable for fibre Channel SANS ?

Ans: – Typically, Fibre Channel SANs are most suitable for large data centers running business-critical data, as well as applications that require high-bandwidth performance such as medical imaging, streaming media, and large databases. Fibre Channel SAN solutions can easily scale to meet the most demanding performance and availability requirements.

Ques 9: – What is ‘inode’ ?

Ans: – All UNIX files have its description stored in a structure called ‘inode’. The inode contains info about the file-size, its location, time of last access, time of last modification, permission and so on. Directories are also represented as files and have an associated inode.

Ques 10: – What is Health Check in refer to load balancer ?

Ans: – The Health Check feature of the load balancer that allows you to set parameters to perform diagnostic observations on the performance of web servers and web server farms associated with each appliance. Health checking allows you to determine if a particular server or service is running or has failed. When a service fails health checks, the SLB(server load balancing) algorithm will stop sending clients to that server until the service passes health checks again.

Ques 11: – What is SAN?

Ans: -A storage area network (SAN) is defined as a set of interconnected devices (e.g. disks and tapes) and servers that are connected to a common communication and data transfer infrastructure such as a fibre channel. The common communication and data transfer mechanism for a given deployment is commonly known as the storage fabric. The purpose of the SAN is to allow multiple servers access to a pool of storage in which any server can potentially access any storage unit.

System Admin Q & A – XIII

Ques 1: – What Are Organizational Units in Active Directory ?

 Ans: – An organizational unit (OU) is a versatile container object used to organize objects within a domain into logical administrative groups. These logical administrative groups can include just one type of object or multiple types depending on how an administrator wants to structure it. Think of an OU like a large box that can contain many things, including other boxes (other OUs called sub-OUs), and those boxes can then contain additional boxes (additional sub-OUs) as well.

Ques 2: – What are Trees in Active Directory?

Ans: -A tree is a grouping or hierarchical arrangement of one or more Windows 2000 / 2003 domains that allows global resource sharing. A tree may consist of a single Windows 2000 domain or multiple domains in a contiguous namespace.
You can create a larger tree (contiguous namespace) by joining multiple domains in a hierarchical structure, since all domains within a single tree share a common namespace and a hierarchical naming structure. Following naming conventions, the domain name of a child domain is the name of that child domain appended with the name of the parent domain.

Ques 3: – What are the process states in Unix?

Ans: – As a process executes it changes state according to its circumstances. Unix processes have the following states

Running : The process is either running or it is ready to run .
Waiting : The process is waiting for an event or for a resource.
Stopped : The process has been stopped, usually by receiving a signal.
Zombie : The process is dead but have not been removed from the process table.

Ques 4: – What Are Forests in Active Directory ?

Ans: A forest is a grouping of one or more trees. As noted with our example of tailspintoys.com and nwtraders.com, each of those is a tree within our forest even though their naming conventions are not related.

It does not matter if each Tree is made up with a single, or multiple domains. Forests allow organizations to group together divisions that do not use the same naming scheme, and may need to operate independently, but still need to communicate with the entire organization via transitive trusts, and share the same schema and configuration container. The first domain in the forest is called the forest root domain. The name of that domain refers to the forest, such as nwtraders.msft. By default, the information in Active Directory is shared only within the forest. This way, the forest is a security boundary for the information that is contained in the instance of Active Directory.

Ques 5: – What is the difference between Active and Passive FTP ?

Ans: – Active FTP : Client says to server port 21, that it want to start a FTP session. Server confirms from port 21 and initates a connection from a new dynamic port to the client. (note: client firewalls etc don’t know which port, so it is sometimes blocked as it is considered unwanted, and unrequested)

Passive FTP : Client says to server port 21, that they want to start a FTP session. Server confirms and tells the client to connect to specified dynamic port (8674 for instance) for FTP data transfer. Client connects to server port 8674, and server replies. (note: the server reply isn’t blocked because the firewall has logged that the client has at some point communicated with server on port 8674)

Ques 6: – What is inode ?

Ans: – All UNIX files have its description stored in a structure called ‘inode’. The inode contains info about the file-size, its location, time of last access, time of last modification, permission and so on. Directories are also represented as files and have an associated inode.

Ques 7: – Explain Zombie Process ?

Ans: – Zombie is a process state when the child dies before the parent process. In this case the structural information of the process is still in the process table.

Ques 8: – What is Curl and use of Curl ?

Ans: – Curl is a command line tool to transfer data from or to a server, using one of the supported protocols. The command is designed to work without user interaction. curl offers a busload of useful tricks like proxy support, user authentication, FTP upload, and much more.
We can use curl command to use :

  •  Troubleshoot http/ftp/cdn server problems.
  • Check or pass HTTP/HTTPS headers.
  • Upload / download files using ftp protocol or to cloud account.
  • Debug HTTP responses and find out exactly what an Apache/Nginx/Lighttpd/IIS server is sending to you without using any browser add-ons or 3rd party applications.

Ques 9: – What is netcat ?

Ans: – Netcat or nc is a simple Linux or Unix command which reads and writes data across network connections, using TCP or UDP protocol. We use this tool to open up a network pipe to test network connectivity, make backups, bind to sockets to handle incoming / outgoing requests and much more.

In this example, We tell nc to listen to a port # 4005 and execute /usr/bin/w command when client connects and send data back to the client:

#nc -l -p 4005 -e /usr/bin/w

System Admin Q & A – XII

Ques 1: – What are major and minor numbers in Linux ?

Ans: – When accessing a device file, the major number selects which device driver is being called to perform the input/output operation. This call is being done with the minor number as a parameter and it is entirely up to the driver how the minor number is being interpreted.

e.g :

 #  ls -l /dev/sda
brw-rw---- 1 root disk 8, 0 root  9 07:56 /dev/sda

Here , 8 is the device number and 0 is the minor device number.

Ques 2: – What is Nested virtualization & How to enable this in KVM ?

Ans: – Nested virtualization refers to running virtual machines (VMs) inside other VMs, usually for testing purposes.

To enable nested Virtualization , set this kernel module “kvm-intel.nested=1”

Ques 3: – What is Shorewall?

Ans:Shorewall is a opensource gateway/firewall configuration tool for Linux. Shorewall, is high-level tool for configuring Netfilter. We describe our firewall/gateway requirements using entries in a set of configuration files. Shorewall reads those configuration files and with the help of the iptables, iptables-restore, ip and tc utilities, Shorewall configures Netfilter and the Linux

Ques 4: – What is NAT ?

Ans:Network Address Translation(NAT) generally involves re-writing the source and/or destination addresses of IP packets as they pass through a firewall.There are two two types of natting.

i) DNAT
ii) SNAT

Ques 5: – What are SRV record in DNS ?

Ans: – A Service record (SRV record) is a specification of data in the Domain Name System defining the location, i.e. the hostname and port number, of servers for specified services.
An SRV record has the form:

_service._proto.name TTL class SRV priority weight port target
  • service: the symbolic name of the desired service.
  • proto: the transport protocol of the desired service; this is usually either TCP or UDP.
  • name: the domain name for which this record is valid.
  • TTL: standard DNS time to live field.
  • class: standard DNS class field (this is always IN).
  • priority: the priority of the target host, lower value means more preferred.
  • weight: A relative weight for records with the same priority.
  • port: the TCP or UDP port on which the service is to be found.
  • target: the canonical hostname of the machine providing the service.

An example SRV record in textual form that might be found in a zone file might be the following:

_sip._tcp.example.com. 86400 IN SRV 0 5 5060 sipserver.example.com.

Ques 6: – What is a Veritas Cluster server or VCS cluster ?

Ans: – VERITAS Cluster Server (VCS) from Symantec connects multiple, independent systems into a management framework for increased availability. Each system, or node, runs its own operating system and cooperates at the software level to form a cluster. VCS links commodity hardware with intelligent software to provide application failover and control. When a node or a monitored application fails, other nodes can take predefined actions to take over and bring up services elsewhere in the cluster.

Ques 7: – What are On-Off & Persistent Resources in Veritas Cluster ?

Ans: – On-Off:- VCS starts and stops On-Off resources as required. For example, VCS imports a disk group when required, and deports it when it is no longer needed.

Persistent:- These resources cannot be brought online or taken offline. For example, a network interface card cannot be started or stopped, but it is required to configure an IP address. A Persistent resource has an operation value of none. VCS monitors Persistent resources to ensure their status and operation. Failure of a Persistent resource triggers a service group failover

Ques 8: – What are the Active directory requirements to install Exchange Server 2007?

Ans:

  1. Domain functional level at least windows server 2000 native or higher
  2. Schema Master must be run on windows 2003 server with sp1
  3. At least one Domain Controller, in each domain with windows server 2003 sp1
  4. At least one global catalog server in Active Directory Site which hosts exchange Server 2007
  5. 4:1 ratio of Exchange processor to global catalog server processors

Ques 9: – What are Veritas Cluster or VCS User Account Privileges ?

Ans:

Cluster Administrator :- Full Privileges

Cluster Operator :- All cluster, service group, and resources-level operations.

Cluster Guest  :- Read-only access: new users created as cluster guest accounts by default.

Group Administrator :- All service group operations for a specified service group, except deleting service group.

Group Operator :- Bring service groups and resources online and take offline, temporarily freeze or unfreeze service groups

Ques 10: – What is Transition in Exchange Server 2007?

Ans: – Transition is the scenario in which you upgrade an existing Exchange organization to Microsoft Exchange Server 2007. To perform the transition, you must move data from the existing Exchange servers to new Exchange 2007 servers. For example, when upgrading from an Exchange Server 2003 or Exchange 2000 Server organization to an Exchange 2007 organization, you perform a transition. When transitioning to Exchange 2007, you cannot perform an in-place server upgrade on an existing Exchange server. Instead, you must install a new Exchange 2007 server into the existing organization, and then move data to the new Exchange 2007 server

System Admin Q & A – XI

Ques 1: – 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 2: – 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 3: – 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 4: – 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.

Ques 5: – What are VLAN’s Classifications ?

Ans: –VLAN can be classified into the following types.

  • Layer1 VLAN: It is based on the ports that belongs the VLAN.
  • Layer2VLAN: It is based on the MAC address of the computer. Layer2 VLAN is also based on the protocol type.
  • Layer3VLAN: It is based on the layer3 header. The IP address and the subnet mask are used to determine and classify the VLAN membership.
  • High Layer VLAN: The membership of the VLAN is determined by using the service of applications or the combination of both.

Ques 6: – What could DUP mean when using ping?

Ans: – DUP means duplicate packet.ping will report duplicate and damaged packets. Duplicate packets should never occur, and seem to be caused by inappropriate link-level retransmissions. Duplicates may occur in many situations and are rarely (if ever) a good sign, although the presence of low levels of duplicates may not always be cause for alarm.

Damaged packets are obviously serious cause for alarm and often indicate broken hardware somewhere in the ping packet’s path (in the network or in the hosts).

Ques 7: – What is IP Masquerade ?

Ans: – IP Masquerade is a networking function in Linux similar to the one-to-many (1:Many) NAT (Network Address Translation) servers found in many commercial firewalls and network routers. For example, if a Linux host is connected to the Internet via PPP, Ethernet, etc., the IP Masquerade feature allows other “internal” computers connected to this Linux box (via PPP, Ethernet, etc.) to also reach the Internet as well. Linux IP Masquerading allows for this functionality even though these internal machines don’t have an officially assigned IP address.

 MASQ allows a set of machines to invisibly access the Internet via the MASQ gateway. To other machines on the Internet, the outgoing traffic will appear to be from the IP MASQ Linux server itself. In addition to the added functionality, IP Masquerade provides the foundation to create a HEAVILY secured networking environment. With a well built firewall, breaking the security of a well configured masquerading system and internal LAN should be considerably difficult to accomplish.

Ques 8: – What is GFS2 filesystem ?

Ans: – GFS2 is a shared file system used by Red Hat Cluster node member simultaneously. GFS2
allows all nodes to have direct concurrent access to the same shared block storage. In addition, GFS2 can also be used as a local filesystem. The principle component to allow such access is lock management. GFS2 uses DLM or Distributed Lock Management to achieve this. Also clustered LVM is used to communicate LVM meta data changes across nodes.

Ques 9: – What is fencing in clustering and why it is required ?

Ans: – Fencing is the process of isolating a node of a computer cluster when the former is malfunctioning. Isolating a node means ensuring that I/O can no longer be done from it. Fencing is typically done automatically, by cluster infrastructure such as shared disk file systems, in order to
protect processes from other active nodes modifying the resources during node failures.

Fencing is required because it is impossible to distinguish between a real failure and a
temporary hang. If the malfunctioning node is really down, then it cannot do any
damage, so theoretically no action would be required (it could simply be brought back
into the cluster with the usual join process).

However, because there is a possibility that a malfunctioning node could itself consider the rest of the cluster to be the one that is malfunctioning, a race condition could ensue, and cause data corruption. Instead, the system has to assume the worst scenario and always fence in case of problems

System Admin Q & A – X

Ques 1: – What is SAN ?

Ans: – storage area network (SAN) is defined as a set of interconnected devices (e.g. disks and tapes) and servers that are connected to a common communication and data transfer infrastructure such as a fibre channel. The common communication and data transfer mechanism for a given deployment is commonly known as the storage fabric. The purpose of the SAN is to allow multiple servers access to a pool of storage in which any server can potentially access any storage unit.

Ques 2: – WHAT ARE THE BENEFITS OF FIBRE CHANNEL SANS?

Ans: – Fibre Channel SANs are the de facto standard for storage networking in the corporate data center because they provide exceptional reliability, scalability, consolidation, and performance. Fibre Channel SANs provide significant advantages over direct-attached storage through improved storage utilization, higher data availability, reduced management costs, and highly scalable capacity and performance.

Ques 3: – What are key differnces between open source zimbra and network edition of zimbra server?

Ans: – Clustering/High-Availability feature is available in network edition of zimbra server. Hot Backup is also possible in zimbra network edition Email Archiving & Discovery is not possible in opensource zimbra server. Real-time backup and restore is also possible in network edition of zimbra server

Ques 4: – Explain the functionality of PING.

Ans: – Ping Is particularly used to check if the system is in network or not. It also gives packet lost information. In windows ping command is written as ping ip_address. The output returns the data packets information. The number of packets sent, received and lost is returned by PING.

Ques 5: – What is NetBIOS protocol?

Ans: – NetBIOS (Network Basic Input/Output System) Protocol allows applications on separate computers to communicate over a LAN. It runs over TCP/IP giving each computer in the network a NetBIOS name and IP address. E.g. It can be used for computers running Windows 2000 (or before) to join a computer network running Windows 2000 (or later).

Ques 6: – How do u force a user to change password on next login in linux?

chage -d 0 “User”

Ques 7: – Explain traffic monitoring on a switched network ?

Ans: – Two popular methods that are specifically designed to allow a network analyst to monitor traffic are:

Port mirroring — the switch sends a copy of network packets to a monitoring network connection.

SMON — “Switch Monitoring” is described by RFC 2613 and is a protocol for controlling facilities such as port mirroring.

Another method to monitor may be to connect a layer-1 hub between the monitored device and its switch port. This will induce minor delay, but will provide multiple interfaces that can be used to monitor the individual switch port

Ques 8: – When u try to create a file, u got a error that “No space available”. But actually space available on volume? How do u resolve this issue?

Ans: – Try this df -i list inode information instead of block usage [Perhaps are you out of inodes on this file system.], To “rectify it”, remove unwanted files or move them somewhere else.

Ques 9: – How do u findout the users who are NOT logged in for more than 30 days? which file u will check?

Ans: – last , lastlog, /var/log/wtmp

System Admin Q & A – IX

Ques 1: – How many WebLogic Servers can I have on a multi-cpu machine?

Ans: – There are many possible configurations and each has its own advantages and disadvantages. BEA WebLogic Server has no built-in limit for the number of server instances that can reside in a cluster. Large, multi-processor servers such as Sun Microsystems, Inc.

 Sun Enterprise 10000, therefore, can host very large clusters or multiple clusters. In most cases, WebLogic Server clusters scale best when deployed with one WebLogic Server instance for every two CPUs. However, as with all capacity planning, you should test the actual deployment with your target web applications to determine the optimal number and distribution of server instances. See Performance Considerations for Multi-CPU Machines for additional information.

Ques 2: – What happens when a failure occurs and the stub cannot connect to a Web Logic Server instance?

Ans: – When the failure occurs, the stub removes the failed server instance from its list. If there are no servers left in its list, the stubb uses DNS again to find a running server and obtain a current list of running instances. Also, the stub periodically refreshes its list of available server instances in the cluster, this allows the stub to take advantage of new servers as they are added to the cluster.

Ques 3: – What is the difference between an application server and a Web server?

Ans: – A Taking a big step back, a Web server serves pages for viewing in a Web browser, while an application server provides methods that client applications can call. A little more precisely, you can say that:

A Web server exclusively handles HTTP requests, whereas an application server serves business logic to application programs through any number of protocols.

Ques 4: – What does apachectl graceful do?

Ans: – It sends a SIGUSR1 for a restart, and starts the apache server if it?s not running.

Ques 5: – How do I configure Tomcat to work with IIS and NTLM?

Ans: – Follow the standard instructions for when the isapi_redirector.dll

Configure IIS to use “integrated windows security”

In server.xml, make sure you disable tomcat authentication:

<Connector port=”8009″ enableLookups=”false” redirectPort=”8443″ protocol=”AJP/1.3″ tomcatAuthentication=”false” />

Ques 6: – Explain the concepts of Tomcat Servlet Container ?

Ans: – A servlet container is a specialized web server that supports servlet execution.

* It combines the basic functionality of a web server with certain Java/servlet specific optimizations and extensions (such as an integrated Java runtime environment, and the ability to automatically translate specific URLs into servlet requests).
* Individual servlets are registered with a servlet container, providing the container with information such as the functionality, the URL used for identification.
* The servlet container then initializes the servlet as necessary and delivers requests to the servlet as they arrive.
* Many containers can dynamically add and remove servlets from the system, allowing new servlets to quickly be deployed or removed without affecting other servlets running from the same container.
* Servlet containers are also referred to as web containers or web engines.

Ques 6: – What is Virtualization ?

Ans: – Virtualization (or virtualisation), in computing, is the creation of a virtual (rather than actual) version of something, such as a hardware platform, operating system, a storage device or network resources.

Ques 7: – what are the key features of NFSv4 ?

Ans: – NFSv4 comes with several new features:

  • Advanced security management
  • Kerberos
  • SPKM
  • LIPKEY
  • Firewall friendly
  • Advanced and aggressive cache management
  • Non Unix compatibility (Windows)
  • Easy to administer (Replication, migration)
  • Crash recovery (Client and server sides

Ques 8: – What are the types of hardware virtualization?

Ans: – Full virtualization: Almost complete simulation of the actual hardware to allow software, which typically consists of a guest operating system, to run unmodified Partial virtualization: Some but not all of the target environment is simulated. Some guest programs, therefore, may need modifications to run in this virtual environment.

Paravirtualization: A hardware environment is not simulated; however, the guest programs are executed in their own isolated domains, as if they are running on a separate system. Guest programs need to be specifically modified to run in this environment.

Ques 9: – What are the benefits of virtualization?

Ans: – Virtualization is a creation of virtual machines and to manage them from one place. It allows the resources to be shared with large number of network resources. Virtualization is having lots of benefits and they are as follows:

  • It helps in saving lots of cost and allows to easily maintaining it, in less cost.
  • It allows multiple operating systems on one virtualization platform.
  • It removes the dependency of heavy hardware to run the application.
  • It provides consolidating servers that are used for crashing of a server purpose
  • It reduces the amount of space being taken by data centers and company data.

Ques 10: – What is the location of postfix mailserver Queue ?

Ans: –By default, the Postfix mail queues are located in the /var/spool/postfix directory. Each message queue is created as a separate subdirectory within this directory. Each message is stored as a separate file in the subdirectory, using a unique identifier for the filename.

System Admin Q & A – VIII

Ques 1: – How to make DHCP server to release IP imidiately if all ips in scope are already assigned ?

i)By reducing lease period

ii) By extending end ip address in the pool

iii) By deleting assigned ip addresses

Ques 2: – Unable to access file share on file server using it’s name (share name) , what can be the solution ?

Ans: – After verifiying DNS funcionality you should check whether host A record for that share has been existed or not. It should be checked on DNS server in forward lookup zone. If does not exist manually create it. or use ipconfig /registerdns command to allow client to dynamically update its host A record (works only if dynamic updates are allowed)

Ques 3: – What is DDNS and why do I need it?

Ans: – Dynamic DNS (described in RFC 2136) allows servers to dynamically update and create records in DNS. Dynamic DNS is used by the Exchange server to create server records and other entries used by the Exchange Servers for things like message routing. In a simple Exchange organization, DDNS is not strictly necessary, but makes administration much easier.

Ques 4: – What is a border server?

Ans: – A border server is an Exchange server that communicates with external servers. In a single server organization, your server is by default a border server. In a multi-server configuration, you may have one or more dedicated servers that communicate directly or indirectly with foreign servers and then pass the mail to other internal Exchange servers.

Ques 5: – How do I restrict a user or domain from sending mail to my users?

Ans: – First, add the address or domain you wish to filter to the Filtering Tab of the Message Delivery Global Settings. Next, you need to apply the filter to the SMTP virtual server you wish to filter. (Administrative Group | Server | Protocols | SMTP | <SMTP Virtual Server> | Properties | Advanced | <select the IP address for which you wish to enable filtering> | Edit | Apply Filter). Normally, you would only want to apply message filtering to the border SMTP servers (servers that communicate directly with External servers).

Ques 6: – What is HTTP Tunneling

Ans: – HTTP Tunneling is a security method that encryptes packets traveling throught the internet. Only the intended reciepent should be able to decrypt the packets. Can be used to Create Virtual Private Networks. (VPN)

Ques 7: – You wish to create a link to the /data directory in bob’s home directory so you issue the command ln /data /home/bob/datalink but the command fails. What option should you use in this command line to be successful.

Ans: – Use the -F option
In order to create a link to a directory you must use the -F option

Ques 8: – What command should you use to check the number of files and disk
space used and each user’s defined quotas?

Ans: – repquota

The repquota command is used to get a report on the status of the
quotas you have set including the amount of allocated space and amount
of used space.

System Admin Q & A – VII

Ques 1: – What are the different modes in network bonding ?

Ans: – There are different modes in network bonding :
mode=0 (Balance-rr) – This mode provides load balancing and fault tolerance.
mode=1 (active-backup) – This mode provides fault tolerance.
mode=2 (balance-xor) – This mode provides load balancing and fault tolerance.
mode=3 (broadcast) – This mode provides fault tolerance.
mode=4 (802.3ad) – This mode provides load balancing and fault tolerance.
mode=5 (balance-tlb) – Prerequisite: Ethtool support in the base drivers for retrieving the speed of each slave.
mode=6 (Balance-alb) – Prerequisite: Ethtool support in the base drivers for retrieving the speed of each slave.

Ques 2: – What’s the difference between TCP &UDP ?

Ans: – TCP is a Transmission Control Protocol.
UDP is a User Datagram Protocol.
There are four major differences between UDP and TCP:
1. TCP can establishes a Connection and UDP cannot.
2. TCP provides a stream of unlimited length, UDP sends small packets.
3.TCP gurantees that as long as you have a connection data sent will arrive at the destination, UDP provides not guarantee delivery.
4.UDP is faster for sending small amounts of data since no connection setup is required, the data can be sent in less time then it takes for TCP to establish a connection.

Ques 3: – What are the fields of the password file?

Ans: – The /etc/passwd contains one entry per line for each user (or user account) of the system. All fields are separated by a colon (:) symbol. Total seven fields as follows.

An example record may be:

systemadmin
The fields, in order from left to right, are:

  1. The first field is the user name, i.e. the string a user would type in when logging into the operating system: the logname. Each record in the file must have a unique user name field.
  2. The second field stores information used to validate a user’s password; however in most modern uses this field is usually set to “x” (or some other indicator) with the actual password information being stored in a separate shadow password file. Setting this field to an asterisk “*” is the typical way to deactivate an account to prevent it being used.
  3. The third field is the user identifier, the number that the operating system uses for internal purposes. It does not have to be unique.
  4. The fourth field is the group identifier. This number identifies the primary group of the user; all files that are created by this user may initially be accessible to this group.
  5. The fifth field, called the Gecos field, is commentary that describes the person or account. Typically, this is a set of comma-separated values including the user’s full name and contact details.
  6. The sixth field is the path to the user’s home directory.

The seventh field is the program that is started every time the user logs into the system. For an interactive user, this is usually one of the system’s command line interpreters (shells).

Ques 4: – What is DDNS and why do I need it?

Ans: – Dynamic DNS (described in RFC 2136) allows servers to dynamically update and create records in DNS. Dynamic DNS is used by the Exchange server to create server records and other entries used by the Exchange Servers for things like message routing. In a simple Exchange organization, DDNS is not strictly necessary, but makes administration much easier.

Ques 5: – What do I need in order to install Exchange 2003?

Ans: – A partial list includes:
DNS (preferably DDNS)
Active Directory 2000 or 2003
Permissions to update the Schema
Hardware sufficient to run Exchange 2003

Windows 2000 SP3 applied to all DCs, GC, and all (future) E2K2 servers, or Windows 2003.

Ques 6: – What is POSIX? Name 2 POSIX-oriented operating systems?

Ans: – Portable Operating System Interface is the collective name of a family of related standards specified by the IEEE to define the application programming interface (API). HP-UX, Solaris, AIX etc

Ques 7: – When u try to create a file, u got a error that “No space available”. But actually space available on volume? How do u resolve this issue?

Ans: – Try this df -i list inode information instead of block usage [Perhaps are you out of inodes on this file system.], To “rectify it”, remove unwanted files or move them somewhere else.]

Ques 8: – whats is called 1.5 stage in boot process of linux?

Ans: – The 1.5 boot loader is stored (if needed) in the MBR or the boot partition.The great thing about GRUB is that it includes knowledge of Linux file systems. Instead of using raw sectors on the disk, as LILO does, GRUB can load a Linux kernel from an ext2 or ext3 file system. It does this by making the two-stage boot loader into a three-stage boot loader.

Stage 1 (MBR) boots a stage 1.5 boot loader that understands the particular file system containing the Linux kernel image.Examples include reiserfs_stage1_5(to load from a Reiser journaling file system) or e2fs_stage1_5(to load from an ext2 or ext3 file system). When the stage 1.5 boot loader is loaded and running, the stage 2 boot loader can be loaded.”

So Basically,

Stage 1 Boot loader is MBR
Stage 2 Boot loader is GRUB
Stage 1.5 Boot loader is e2fs_stage1_5

(Basically this module will load the knowledge of Filesystem to Grub to read the kernel)

System Admin Q & A – VI

Ques 1: – What is MTU ?

Ans: – The MTU is the “Maximum Transmission Unit” used by the TCP protocol. TCP stands for Transmission Control Prototcol. The MTU determines the size of packets used by TCP for each transmission of data. Too large of an MTU size may mean retransmissions if the packet encounters a router along its route that can’t handle that large a packet. Too small of an MTU size means relatively more overhead and more acknowledgements that have to be sent and handled. The MTU is rated in “octets” or groups of 8 bits. The so-called “official” internet standard MTU is 576, but the standard rating for ethernet is an MTU of 1500.

Ques 2: – What does nslookup do? Explain its two modes.

Ans: – Nslookup is used to find details related to a Domain name server. Details like IP addresses of a machine, MX records, servers etc. It sends a domain name query packet to the corresponding DNS.

Nslookup has two modes. Interactive and non interactive. Interactive mode allows the user to interact by querying information about different hosts and domains.

Non interactive mode is used to fetch information about the specified host or domain.
Interactive mode:

Nslookup [options] [server]

Ques 3: – Explain RPM (Red Hat Package Manager) features

Ans: – RPM is a package managing system (collection of tools to manage software packages).
Features:

RPM can verify software packages.
RPM can be served as a powerful search engine to search for software’s.
Components, software’s etc can be upgraded using RPM without having to reinstall them
Installing, reinstalling can be done with ease using RPM
During updates RPM handles configuration files carefully, so that the customization is not lost.

Ques 4: – daemon is used for scheduling of the commands?

Ans: – The crontab command is used for scheduling of the commands to run at a later time. SYNTAX

crontab [ -u user ] file
crontab [ -u user ] { -l | -r | -e }

Options
-l List – display the current crontab entries.
-r Remove the current crontab.
-e Edit the current crontab using the editor specified by the VISUAL or EDITOR environment variables.

When user exits from the editor, the modified crontab will be installed automatically. Each user can have their own crontab, and though these are files in /var, they are not intended to be edited directly. If the –u option is given than the crontab gives the name of the user whose crontab is to be tweaked. If it is given without this then it will display the crontab of the user who is executing the command.

Ques 5: – What is LD_LIBRARY_PATH?

Ans: – LD_LIBRARY_PATH is an environment variable. It is used for debugging a new library or a non standard library. It is also used for which directories to search. Path to search for directories needs to given. The variable can be set by using setenv—LD_LIBRARY_PATH–$PATH.

Ques 6: – What is LMHOSTS file?

Ans: – It’s a file stored on a host machine that is used to resolve NetBIOS to specific IP addresses.

Ques 7: – Describe a TCP connection sequence?

Ans: – The TCP three-way handshake describes the mechanism of message exchange that allows a pair of TCP devices to move from a closed state to a ready-to-use, established connection. Connection establishment is about more than just passing messages between devices to establish communication. The TCP layers on the devices must also exchange information about the sequence numbers each device wants to use for its first data transmission, as well as parameters that will control how the connection operates.

The former of these two data exchange functions is usually called sequence number synchronization, and is such an important part of connection establishment that the messages that each device sends to start the connection are called SYN (synchronization) messages.
You may recall from the TCP fundamentals section that TCP refers to each byte of data individually, and uses sequence numbers to keep track of which bytes have been sent and received. Since each byte has a sequence number, we can acknowledge each byte, or more efficiently, use a single number to acknowledge a range of bytes received.

Ques 8: – How to delete the files older than 7 days in linux/unix ?

 find /your_directory -mtime +7 -exec rm -f {} \;

Ques 9: – What the Purpose of VLAN?

Ans: – VLANs can enhance network security. VLANs increase the number of broadcast domains while decreasing their size. Network adds, moves, and changes are achieved by configuring a port into the appropriate VLAN.

A group of users needing high security can be put into a VLAN so that no users outside of the VLAN can communicate with them. As a logical grouping of users by function, VLANs can be considered independent from their physical or geographic locations.

Ques 10: – How to enable timestamp with history command in Linux ?

Ans: – History is a common command for shell to list out all the executed commands. It is very useful when it comes to investigation on what commands was executed that tear down the server. With the help of last command, you be able to track the login time of particular user as well as the the duration of the time he/she stays login

HISTTIMEFORMAT takes format string of strftime. Check out the strftime manual to choose and construct the timestamp that suit your taste

# export HISTTIMEFORMAT="%F %T"

System Admin Q & A – V

Ques 1: – Write a command to find all of the files which have been accessed within the last 30 days.

find / -type f -atime -30 > files.txt

This command will find all the files under root, which is ‘/’, with file type is file. ‘-atime -30′ will give all the files accessed less than 30 days ago. And the output will put into a file call files.txt.

Ques 2: – What is difference between ARP and RARP ?

Ans: – The address resolution protocol (ARP) is used to associate the 32 bit IP address with the 48 bit physical address, used by a host or a router to find the physical address of another host on its network by sending a ARP query packet that includes the IP address of the receiver. The reverse address resolution protocol (RARP) allows a host to discover its Internet address when it knows only its physical address.

Ques 3: – What command is used to remove the password assigned to a group ?

# gpasswd -r

The gpasswd command is used to change the password assigned to a group. Use the -r option to remove the password from the group.

Ques 4: – What is NETBIOS and NETBEUI ?

Ans: – NETBIOS is a programming interface that allows I/O requests to be sent to and received from a remote computer and it hides the networking hardware from applications.
NETBEUI is NetBIOS extended user interface. A transport protocol designed by microsoft and IBM for the use on small subnets.

Ques 5: – What does nslookup do? Explain its two modes ?

Ans: – Nslookup is used to find details related to a Domain name server. Details like IP addresses of a machine, MX records, servers etc. It sends a domain name query packet to the corresponding DNS.

Nslookup has two modes. Interactive and non interactive. Interactive mode allows the user to interact by querying information about different hosts and domains.

Non interactive mode is used to fetch information about the specified host or domain.

Interactive mode:

Nslookup [options] [server]

Ques 6: – How to disable USB in grub ?

Ans: – Open the Grub configuration file

#vi /boot/grub/menu.lst

Add “nousb” at the end of the Kernel Line. Like the following

kernel /vmlinuz-2.6.18-128.1.1.el5 ro root=LABEL=/ console=tty0 console=ttyS1,19200n8 nousb

Ques 7: – What is the main advantage of creating links to a file instead of copies of the file ?

Ans: – The main advantage is not really that it saves disk space (though it does that too) but, rather, that a change of permissions on the file is applied to all the link access points. The link will show permissions of lrwxrwxrwx but that is for the link itself and not the access to the file to which the link points. Thus if you want to change the permissions for a command, such as su, you only have to do it on the original. With copies you have to find all of the copies and change permission on each of the copies.

Ques 8: – What command would you type to use the cpio to create a backup called backup.cpio of all the users’ home directories ?

 find /home | cpio -o > backup.cpio

The find command is used to create a list of the files and directories contained in home. This list is then piped to the cpio utility as a list of files to include and the output is saved to a file called backup.cpio.

Ques 9: – You would like to temporarily change your command line editor to be vi. What command should you type to change it ?

Ans: – set -o vi

The set command is used to assign environment variables. In this case, you are instructing your shell to assign vi as your command line editor. However, once you log off and log back in you will return to the previously defined command line editor.

Ques 10: – You have two files each ten lines long. What text filter could you use to combine the two files so that each line of the output contains the corresponding line from each file ?

Ans: – join
The join text filter will display one line for each pair of input lines from two files.