21⟩ How we find WWN numbers of HBA cards in Linux Server?
We can find the WWN numbers of HBA cards using the command 'systool -c fc_host -v | grep port_name'
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“Linux Administrator related frequently asked questions by expert members with experience in Linux OS. These questions and answers will help you strengthen your technical skills, prepare for the new job test and quickly revise the concepts”
43 Linux Administrator Questions And Answers
22⟩ How to scan newly asssigned luns on linux box without rebooting?
There are two ways to scan newly assigned luns :
Method 1: if sg3 rpm is installed , then run the command 'rescan-scsi-bus.sh'
Method 2: Run the Command , echo " - - - " > /sys/class/scsi_host/hostX/scan
23⟩ How to upgrade Kernel in Linux?
We should never upgrade Linux Kernel , always install the new New kernel using rpm command because upgrading a kenel can make your linux box in a unbootable state.
24⟩ How to enable a service at a particular run level?
We can enable a service using the Command 'chkconfig <Service-Name> on -level 3′
25⟩ Which services are enabled at a particular run level in linux server?
With the help of command 'chkconfig -list | grep 5:on' we can list all the service that are enabled in run level5. For other run levels just replace 5 with the respective run level.
26⟩ How to check which ports are listening in my Linux Server?
Use the Command 'netstat -listen' and 'lsof -i'
27⟩ How to check default route and routing table?
By using the Commands 'netstat -nr' and 'route -n' we can see the default route and routing tables.
28⟩ How to check and verify the status the bond interface?
By using the command 'cat /proc/net/bonding/bond0′ , we can check which mode is enabled and what lan cards are used in this bond. In this example we have one only one bond interface but we can have multiple bond interface like bond1,bond2 and so on.
29⟩ What are the different modes of network bonding in Linux?
☛ balance-rr or 0 - round-robin mode for fault tolerance and load balancing.
☛ active-backup or 1 - Sets active-backup mode for fault tolerance.
☛ balance-xor or 2 - Sets an XOR (exclusive-or) mode for fault tolerance and load balancing.
☛ broadcast or 3 - Sets a broadcast mode for fault tolerance. All transmissions are sent on all slave interfaces.
☛ 802.3ad or 4 - Sets an IEEE 802.3ad dynamic link aggregation mode. Creates aggregation groups that share the same speed & duplex settings.
☛ balance-tlb or 5 - Sets a Transmit Load Balancing (TLB) mode for fault tolerance & load balancing.
☛ balance-alb or 6 - Sets an Active Load Balancing (ALB) mode for fault tolerance & load balancing.
30⟩ Explain Network Bonding?
Network bonding is the aggregation of multiple Lan cards into a single bonded interface to provide fault tolerance and high performance. Network bonding is also known as NIC Teaming.
31⟩ What are the default ports used for SMTP,DNS,FTP,DHCP,SSH and squid?
Service: Port
SMTP: 25
SSH: 22
Squid: 3128
DNS: 53
FTP: 20 (data transfer) , 21 ( Connection established)
DHCP: 67/UDP(dhcp server) , 68/UDP(dhcp client)
32⟩ How to check and mount nfs share?
Using 'showmount' command we can see what directories are shared via nfs e.g 'showmount -e <ip address of nfs server>'.Using mount command we can mount the nfs share on linux machine.
33⟩ How to share a directory using nfs?
To share a directory using nfs , first edit the configuration file '/etc/exportfs' , add a entry like
'/<directory-name> <ip or Network>(Options)' and then restart the nfs service.
34⟩ Why LVM is required in Linux?
LVM stands for Logical Volume Manager, to re-size filesystem's size online we required LVM partition in Linux. Size of LVM partition can be extended and reduced using the lvextend & lvreduce commands respectively.
35⟩ How To check memory stats and CPU stats in Linux?
Using 'free' & 'vmstat' command we can display the physical and virtual memory statistics respectively.With the help of 'sar' command we see the CPU utilization & other stats.
36⟩ Tell me what does Sar provides and at which location Sar logs are stored?
Sar Collect, report, or save system activity information. The default version of the sar command (CPU utilization report) might be one of the first facilities the user runs to begin system activity investigation, because it monitors major system resources. If CPU utilization is near 100 percent (user + nice + system), the workload sampled is CPU-bound.
37⟩ How to increase the size of LVM partition?
☛ Use the lvextend command (lvextend -L +100M /dev/<Name of the LVM Partition> , in this example we are extending the size by 100MB.
☛ resize2fs /dev/<Name of the LVM Partition>
☛ check the size of partition using 'df -h' command
38⟩ How to reduce or shrink the size of LVM partition?
The logical Steps to reduce size of LVM partition :
☛ Umount the filesystem using umount command,
☛ use resize2fs command , e.g resiz2fs /dev/mapper/myvg-mylv 10G
☛ Now use the lvreduce command , e.g lvreduce -L 10G /dev/mapper/myvg-mylv
Above Command will shrink the size & will make the filesystem size 10GB.
39⟩ How to create partition from the raw disk?
Using fdisk utility we can create partitions from the raw disk.Below are the steps to create partition from the raw dsik :
☛ fdisk /dev/hd* (IDE) or /dev/sd* (SCSI)
☛ Type n to create a new partition
☛ After creating partition , type w command to write the changes to the partition table.
40⟩ Where kernel modules are located?
The '/lib/modules/kernel-version/' directory stores all kernel modules or compiled drivers in Linux operating system. Also with 'lsmod' command we can see all the installed kernel modules.
