System Admin Q & A – XXI

Ques 1: – What is the difference between hard link and soft link ?

Ans: – When you delete a file it removes one link to the underlying inode. The inode is only deleted (or deletable/over-writable) when all links to the inode have been deleted.

A symbolic link is a link to another name in the file system.
Once a hard link has been made the link is to the inode. deleting renaming or moving the original file will not affect the hard link as it links to the underlying inode. Any changes to the data on the inode is reflected in all files that refer to that inode.

Note: Hard links are only valid within the same File System. Symbolic links can span file systems as they are simply the name of another file.

Ques 2: – How Set the password expiry for a user ?

Ans: – In Linux, chage command is used to configure the password expiry information for a user. The expiry information for all the accounts is stored in /etc/shadow file. The chage command can only be used on Linux system which uses /etc/shadow file to store the user password information. chage command requires root privilege except for ‘-l’ option.

Ques 3: – What is relay host in Mail Server ?

Ans: -If the machine needs to pass mail to another mail server to get out to the Internet, the hostname of the mail server should be defined as the Relay Host. If a Relay Host is defined, mail to all domains not defined as a mail route or virtual domain will be forwarded to the machine defined as Relay Host. Generally, this option is used to relay outgoing mail.

Ques 4: – What is iscsi Server in Linux ?

Ans: – ISCSI stands for Internet scsi , is a network protocol which allows SCSI-3 commands to be encapsulated in TCP streams and transmitted over IP. Generally , it is used in conjuction with Gigabit Ethernet or 10-Gigabit Ethernet technology as way to build-wide area Storage Area Network (SAN) using inexpensive hardware in place of more expensive Fibre Channel equipment.

Ques 5: – Define the working of ISCSI Server ?

Ans: – : A Remote disk server is Configured as an iSCSI target. The target will serve out one or more disks , each disk or logical unit , will have its own logical unit number(LUN). A typical target normally listens for connections on the default iSCSI port , tcp/3260 , although tcp/860 is sometimes used as an alternative in the reserved port range by some implementations. A Client that wants to access a disk runs an iSCSI initiator.

The initiator is configured to find and log in to the iSCSI target and access one or more of its LUNs.The disks accessed will then show up on the client as a normal scsi disks in the order in which they connect (/dev/sd*). The disks then can be used as if they were locally-attached disks : they can be partitioned, registered as LVM physical volumes , formatted with ext3/ext4 filesystems and so on.

Ques 6: – What is domain delegation in DNS (bind) ?

Ans: – Domain delegation means if you have a sub-domain and want to forward all dns queries another name server. In this case, let’s say is the sub-domain. The idea is that you want to create DNS records for the sub-domain (say and manage those DNS records through a different DNS name server.

Delegating the subdomain to another NS – being

geo IN NS

del IN A

Ques 7: – What is the use of Multicast address in RedHat cluster ?

Ans : – Red Hat Cluster nodes communicate among each other using multicast addresses.

Therefore, each network switch and associated networking equipment in a Red Hat Cluster must be configured to enable multicast addresses and support IGMP (Internet Group Management Protocol). Ensure that each network switch and associated networking equipment in a Red Hat Cluster are capable of supporting multicast addresses and IGMP; if they are, ensure that multicast addressing and IGMP are enabled. Without multicast and IGMP, not all nodes can participate in a cluster, causing the cluster to fail.

Ques 8: – What is CNAME record in DNS ?

Ans: – CNAME stands for Canonical Name. CNAME is a type of resource record in the Domain Name System (DNS) that specifies that the domain name is an alias of another, canonical domain name.

Ques 9: – What is Satellite Network Server in Linux ?

Ans: – Redhat offers Red Hat Network (RHN) is a family of systems management services operated by Red Hat that makes updates, patches, and bug fixes of packages included within Red Hat Linux and Red Hat Enterprise Linux available to subscribers. Other available features include the deployment of custom content to, and the provisioning, configuration, reporting, monitoring of client systems.

Ques 10: – What is the use of pvmove command in Linux ?

Ans: – pvmove allows us to move the allocated physical extents (PEs) on SourcePhysicalVolume to one or more other physical volumes (PVs).

You can optionally select a subset of the allocated physical extents on SourcePhysicalVolume by giving colon-separated lists and/or ranges of physical extents, or by specifying the source LogicalVolume optionally with colon-separated lists and/or ranges of logical extents.

In this case only these extents are moved to free (or specified) extents on DestinationPhysicalVolume(s). If no DestinationPhysicalVolume is specifed, the normal allocation rules for the volume group are used.

Ques 11: – What is LVM Snapshots ?

Ans: – A snapshot volume is a special type of volume that presents all the data that was in the volume at the time the snapshot was created. we can backup that volume without having to worry about data being changed while the backup is going on, and we don’t have to take the database volume offline while the backup is taking place.