Tehnical Interview

What are all the components in a PC or Server?
PC: chassi, system board, psu, cpu, ram, hdd, fans, cables, graphics card, dvd, monitor, keyboard/mouse
Server: same with deduction of a extra graphics card (is one on the system board), and addition of hdd controller, possibly backplane, no cd/dvd, extra nic, double cpu, ram, psu, fans, remote monitoring/console.

 

What protocol is used by ping? – ICMP (this is a sneaky question – an obvious fault is to go for TCP or UDP)

 

How many IDE devices can you have in a PC? – two per channel (usually 4)
How many can you have on each channel? What are they called? – 2 / master and slave
What is the resolution in Windows 2000 safe mode? – 800×600 or 640×480?- see this link on mydigitallife or this post on tom’s hardware.
What is a MAC address? – Media Access Control – a unique identifier for network devices. Used by many protocols.
What is the name of the Ethernet plug? – RJ45
How do you recognize a broken hard drive without software or removing it from the machine? – 1) Noise (tick tack sound of the arm getting stuck/hitting something) 2) Any leds on the disk, system board, controller 3) Any vibration or anything from the disk?
How do you find the first disk in a linux OS? – Look under /dev/ for a disk like /dev/sda(SATA) /dev/hda (PATA). Then /dev/sda1 is the first partition.
Name two devices needed to make a network: switch and router (well, network card (NIC) and router should do it, or a switch and network card.. depends how big you want to make it, really i guess you can have a network with a crossover cable and two nics).
What is BIOS? Basic input/output system. Responsible for initializing hardware, POST/startup diagnostics, boot the OS and varies hardware settings.
What is the bit rate of a serial interface of a network device? – the default apparently in hyperterminal – 9600 (this might be tricky, in my experience this varies between the devices – max is probably 115200bps). Maybe what they are asking for is what is the default speed of a Cisco switch’s aux or console port? If so, the answer is 9600.
What is the port used for HTTP? – 80
What is the difference between PCIe and PCI? – PCI-e is newer than PCI and PCI-x. The slots look different and they are not compatible.
How many primary partitions can you have in DOS?
 – Four primary and maximum one active per disk. See this link for some explanations. Unsure at this stage what the exact question was.
What does HTTP stand for? Hypertext Transfer Protocol
What controls GPU CPU Mem at boot up?


What is ROM?
 Read Only Memory – Used for storing data that you do not want somebody to write to.

Length of cat5 transmission? 100m


What does NIC stand for? 
Network Interface Card

 

What is the standard type of filesystems now? disk filesystem and network filesystems
How would you create an EXT4 filesystem on the first partition of the first SCSI drive? 
mkfs.ext4 /dev/sda1   mkfs -t ext3 /dev/sda6
How would you install lilo?  I used to install lilo on the MBR
How do you get IP info from Linux or Windows? “ip addr” or “ifconfig” in Linux and “ipconfig” in Windows.
What is the subnet mask for a Class B Network?
 255.255.0.0

 

You have 100 broken computers, how do you proceed.

There are lots of ways to approach this one, how far can you take it?

Same room same rack?

  1. Get an overview – where are they, what kind of hardware, importance, severity of problem, the wider you can make this the better. To have this done automagically is important and speeds up troubleshooting immensely. Consider monitoring softwares like nagios, ganglia, cactii. They not only monitor hardware but can also services.
  2. What’s the status of the central components? Network, power, etc.
  3. Hopefully not all have the same problem, try to find certain groups of them that have the same obvious error.
  4. Maybe there are more than one underlying issues, but they appear to be the same – or gives the same problem.
  5. Maybe there is one problem on one computer that is causing problem for all the rest. For example bad ethernet/fibre channel card or cable can cause network interruptions on the whole network or SAN.
  6. Maybe a service and there is something in that software on one node that is causing this issue. Like a job that runs on many machines but it broke on one machine and that caused the rest to break.
  7. Look in logs of the systems/services.
  8. Run a diagnostic CD PXE on computers like ultimateboot CD to look for hardware errors. Server vendors may have their own diagnostic tools. memtest86 is a good boot CD for memory testing (probably best to test memory that way, the least amount of memory locked by the OS)
  9. For severe hardware problems you can look in the POST of the machine, check leds on them, but for 100 machines this might be more of a last resort.
  10. If you suspect the problem is SW – again try to find something they have in common – same manufacturer, same softwares/patches installed. Maybe this software has a monitoring part that can tell you more. Check the logs.
  11. When did the problem start? At the same time as a power outage, after a patch deployment, etc.
  12. Are they all physically close? Anything else gone down?

 

How do you see what happens during boot of the OS in Linux?
Answer: output of command dmesg and also in /var/log/syslog
Where do you find the logs in Linux?
     /var/log

 

How do you mount a disk?    Answer: mount
Every boot?
   Answer: fstab
How do you see what version of the kernel is running?
Answer:  uname -v (-r gives 2.6.x etc)
How do you put an image on a pc?    Answer: pxeboot as an example

 

How do you turn a room into a data center?

floor strong enough to hold the weight of all the equipment?
physical security – bar windows, access control(keys), cameras, guards, iris scan cctv
ventilation – perforated tiles?
cooling
anti-fire
racks
UPS – electrical work

 

What is the difference between a switch and a router
Switches create a network. Routers connect networks. A router links computers to the Internet, so users can share the connection. A router acts as a dispatcher, choosing the best path for information to travel so it’s received quickly.

Router Store IP address in Routing table

network switch stores MAC addresses in a lookup table.

Router – Connecting two or more networks

Switch – Connecting two or more nodes in the same network or different network

 

 

 

 

– Explain how to add a new harddrive in Linux (Start from the scratch with holding the hdd in your hand)

 

SATA drives are connected via a dedicated cable of seven conductors of which there are two pairs dedicated to data with the remaining 3 being ground. SATA drives represent the predominat and current technology.

Linux SATA naming convention: /dev/sda, /dev/sdb, …

 

IDE based systems, can support two drives on each ribbon cable. The cable is attached to either the Primary or Secondary IDE controller. A “jumper” is pressed onto two pins (thus connecting the two pins) on the drive to define the drive as a “Master” or a “Slave” drive. Each cable can support one master and one slave drive. Typically new desktop systems have one hard drive connected as a Master on the Primary controller and one CD-Rom on the second cable configured as a master.

Linux IDE naming convention: /dev/hda, /dev/hdb, …

 

SCSI drives will have jumpers positioned to assign a SCSI device ID number typically numbered 1-8. A sticker on the top of the drive will often show a diagram of jumper placement for drive assignment.

Linux SCSI naming convention: /dev/sda, /dev/sdb, …

 

 

To determine the path that your system has assigned to the new hard drive, open a terminal and run: sudo lshw -C disk

 

– What does DNS stand for and whats its purpose

 

– What file in a Linux file system is responsible for DNS (resolve.conf)

 

– What file in a Linux file system is responsible for the IP configuration (/etc/network/interfaces)

 

– What does nslookup do

In simple terms, it is a tool that can provide information by interrogating DNS servers either locally on your network or externally assuming the required DNS server responsible (or knowledgeable) about the requested domain is contactable from where you are operating – over the Internet for example. To access the nslookup utility, drop out to a cmd prompt window.

 

 

– How to get into safe boot (runlevel 3)  init3  telinit 3

 

– If you do “ls” in the root directory, which folders are you going to see

All structure /bin  sbin etc dev vat tmp usr home boot opt mnt media svr

 

– What protocol is “ping”

using  ICMP echo request and echo response are the two operation codes of ICMP used to implement

 

– What three commands are you using, when a machine is running slow (maybe various – told him I’d start with “uptime” “free -m” “smartctl” – he was fine with that)

 

– What is the difference between bin and sbin

(user binaries bin  / system binaries  sbin)

 

– What is /usr/ containing (unix system resources)

 

– What is /var/ containing (variables)

 

– What components do I need to build a basic server,

Chassis , Motherboard

CPU, RAM, Hard Drive ,network card if not included with mobo

RAID configuration, you’ll probably want to add a proper RAID controller to that list.

RAID controller card, PSU-Power Supply  ,BACKUP PSU, video card?

 

how to configure a network card under Linux (ifconfig),

 

troubleshoot a computer that its video card is not working,

– What level of knowledge I had with Linux also with scripting or other programming languages.

 

 

about IPv4,

 

what is a net mask and what is it used for

 

what is DNS.

 

difference between IDE connectors and SATA.

 

Can you please describe the boot sequence of a plain PC ? (The answer is the detailed sequence from pressing the power button until the 1st boot device)

 

-Where the date is stored?

 

What is the Master Boot Record ?

 

How the Computer knows which one is the bootable device?

 

What is Permissions 644 stands for ?

 

How you can change the ownership of a folder or a single file?

 

 

 

If you do not have an ssh connection, neither ipmi , how you can copy a file? (telnet)

 

You are a team leader and you have 2 workers. Describe the procedure of racking 100 servers.

(By my opinion, this question has to do with leadership skills and to check if you have experience with racking servers etc. I don’t think that there is a 100% correct answer here, hence it depends.

But in general anyone who has worked in a datacenter has the necessery skills and basic knowleage of how to do that.)

 

What are the benefits of two network cards?

 

 

If you “team” two network cards will you get the sum of 1+1=2 gigabits?

How do you recover the root password if you forgot it? / What is a live cd? /

What is single user mode.

 

 

How you can sniff a network activity of a network port on the same lan?

 

 

What is hub?

 

What is traceroute? how does it works?

 

What is dns?

 

How a provides knows which domain points to which ip?

 

Lets suppose that your browser of your home computer opens the websites very slowlly. How will you troubleshoot this situation?

 

 

Virtualization

 

    What is the “Ring -1”? Which flag should be available into the processor in order to support virtualization technologies?

 

    What are the differences between “Full Virtualization” and “Paravirtualization”?

Full virtualization is called “full” because the entire system’s resources are abstracted by the virtualization software layer. Paravirtualization is called “para” because only a portion of the system’s resources, or partial amount, is abstracted. Application programming interfaces (APIs) enable communication or provide assistance in certain situations. Paravirtualization requires that the guest operating system running on the host server be modified so that it recognizes the virtualization software layer, while fully virtualized workloads do not require any change or modification to their guest operating system

 

Paravirtualization

Paravirtualization refers to communication between the guest OS and the hypervisor to improve performance and efficiency.

Involves modifying the OS kernel to replace non-virtualizable instructions with hyper calls that communicate directly with the virtualization layer hypervisor. (Virtualized Resources and Non-Virtualized Resources).

 

The hypervisor also provides hyper call interfaces for other critical kernel operations such as memory management, interrupt handling, and timekeeping.

 

Full virtualization

It is a virtualization technique used to provide a virtual machine environment which is a complete simulation of the underlying hardware.

 

All operating systems and applications which can run natively on the hardware can also be run in the virtual machine;

The guest OS need not be modified;

Guest OS do not aware the existence of VM;

Each VM is independent of each other.

 

What is an hypervisor?

A hypervisor or virtual machine monitor (VMM) is a piece of computer software, firmware or hardware that creates and runs virtual machines. A computer on which a hypervisor runs one or more virtual machines is called a host machine, and each virtual machine is called a guest machine.

 

 

    Explain step by step how to create a new VM (LVM storage) using the xen CLI

 

 

    You need to provide High Availability and failover to your virtualized infrastructure. What do you propose?