Tuesday, 10 July 2012



Unix/Linux System Admin Interview Questions And Answers 8

Q: - How to detect CPU architecture/bitmode (32-bit or 64-bit) for Linux ?
cat /proc/cpuinfo | grep flags
you will find one of them with name "tm(transparent mode)" or
"rm(real mode)" or "lm(long mode)"

1. rm tells ,it is a 16 bit processor
2. tm tells, it is a 32 bit processor
3. lm tells, it is a 64 bit processor
Q: - What is the difference between SSH and Telnet ?
The Primary difference between SSH and Telnet is of security i.e in ssh data transfer between the systems is in encrypted form so it is difficult for the hackers to understand what is going on network.
 In Telnet data transfer between the systems is in plain text. 
SSH uses a public key for authentication while Telnet does not use any authentication.
Due to the security measures that were necessary for SSH to be used in public networks, each packet contains less data to make room for the data of the security mechanisms. In order to transmit the same amount of data, you would need to take-up a lot more bandwidth. This is called overhead..
SSH adds a bit more overhead to the bandwidth compared to Telnet.
Q: - What is difference between AT and CRON? 
Cron command is used to schedule the task daily at the same time repeatedly ,
at command is used to schedule the task only once i.e to run only one time.

Q: - What is network bonding in Linux and steps to configure network bonding ?
 Network interface card (NIC) bonding (also referred to as NIC teaming) is the bonding together of two or more physical NICs so that they appear as one logical device. This allows for improvement in network performance by increasing the link speed beyond the limits of one single NIC and increasing the redundancy for higher availability. For example, you can use two 1-gigabit NICs bonded together to establish a 2-gigabit connection to a central file server.
When bonded together, two or more physical NICs can be assigned one IP address. And they will represent the same MAC address. If one of the NICs fails, the IP address remains accessible because it is bound to the local NIC rather than to a single physical NIC.
Steps to configure :
Step #1: Create a bond0 configuration file
Red Hat Linux stores network configuration in /etc/sysconfig/network-scripts/ directory. First, you need to create bond0 config file:
# vi /etc/sysconfig/network-scripts/ifcfg-bond0
Append following lines to it:
DEVICE=bond0
IPADDR=192.168.1.20
NETWORK=192.168.1.0
NETMASK=255.255.255.0
USERCTL=no
BOOTPROTO=none
ONBOOT=yes
Replace above IP address with your actual IP address. Save file and exit to shell prompt.
Step #2: Modify eth0 and eth1 config files:
Open both configuration using vi text editor and make sure file read as follows for eth0 interface
# vi /etc/sysconfig/network-scripts/ifcfg-eth0
Modify/append directive as follows:
DEVICE=eth0
USERCTL=no
ONBOOT=yes
MASTER=bond0
SLAVE=yes
BOOTPROTO=none
Open eth1 configuration file using vi text editor:
# vi /etc/sysconfig/network-scripts/ifcfg-eth1Make sure file read as follows for eth1 interface:
DEVICE=eth1
USERCTL=no
ONBOOT=yes
MASTER=bond0
SLAVE=yes
BOOTPROTO=none
Save file and exit to shell prompt.
Step # 3: Load bond driver/module
Make sure bonding module is loaded when the channel-bonding interface (bond0) is brought up. You need to modify kernel modules configuration file:
# vi /etc/modprobe.conf
Append following two lines:
alias bond0 bonding
options bond0 mode=balance-alb miimon=100
Step # 4: Test configuration
First, load the bonding module:
# modprobe bonding
Restart networking service in order to bring up bond0 interface:
# service network restart
Verify everything is working:
# less /proc/net/bonding/bond0Output:
Bonding Mode: load balancing (round-robin)
MII Status: up
 MII Polling Interval (ms): 0
 Up Delay (ms): 0
 Down Delay (ms): 0


 Slave Interface: eth0
 MII Status: up
 Link Failure Count: 0
 Permanent HW addr: 00:0c:29:c6:be:59
Slave Interface: eth1
 MII Status: up
 Link Failure Count: 0
 Permanent HW addr: 00:0c:29:c6:be:
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