Linux system admin interview questions

1.What is the best RAID level?
RAID 0 for performance
RAID 5 for High availability
RAID 6 even better HA if the budget is fine

2.What is MAC address and How to check the MAC address in linux?
A mac address means media access control address.It is a unique address assigned to almost all networking hardware such as Ethernet cards, router etc.
Most layer 2 network protocols use one of three numbering spaces which are designed to be globally unique.

Linux Command to see MAC address:
Ifconfig is used to configure network interfaces.
$ /sbin/ifconfig grep HWaddr

Output: eth0 Link encap:Ethernet HWaddr 00:0F:EA:91:04:07

OR
$ /sbin/ifconfig
eth0 Link encap:Ethernet HWaddr 00:0F:EA:91:04:07 <<< THIS IS THE MAC ADDRESS
inet addr:192.168.1.1 Bcast:192.168.1.255 Mask:255.255.255.0
inet6 addr: fe80::20f:eaff:fe91:407/64 Scope:Link

OR as a root user type following command:
# grep eth0 /var/log/dmesg

eth0: RealTek RTL8139 at 0xc000, 00:0f:ea:91:04:07, IRQ 18 <<< this line 2 component from this side is MAC address
eth0: Identified 8139 chip type 'RTL-8100B/8139D'
eth0: link up, 100Mbps, full-duplex, lpa 0x45E1

3.how to assign a permanent IP to a client which is presently in DHCP in Linux?
/sbin/ifconfig eth0 192.168.10.1 netmask 255.255.255.0 broadcast 192.168.10.255
In this command we are assigning 192.168.10.1 IP to ethernet interface(NIC card) eth0.

Also in redhat linux terminal you can type comand "setup" & launch a Wizard type interface in which u can choose network & configure IP

You can use the GUI tool /usr/bin/neat - Gnome GUI network administration tool. It handles all interfaces and configures for both static assignment as well as dynamic assignment using DHCP.

4. How to exclude some ip address range in DHCP?
To exclude the range of IP address in a subnet is to split the address range of subnet into two.
Example:
subnet 1.1.1.0 netmask 255.255.255.0
{
range 1.1.1.10 1.1.1.15
range 1.1.1.21 1.1.1.40
}

so in the above example automatically the IP 16-20 will be excluded from the list.

5.What is the default serial number of DNS ?
Are based on ISO dates. Every time the data in the database is changed, the serial number must be increased in order that the slave servers know the zone has changed

6.how to pull the data to the secondary nis server from master server?
ypxfr is a pull command which runs on each slave server to make that server import the map from master nis server

7.what file need to be changed in nis client if you are changing the machine from one subnetwork to other subnetwork?
/etc/yp.conf

8.how to see memory usage?
Commands "top" and "free -m"

9.how to increase the filesystem ?
Using command # fdisk