Week_Eight_Nine_Revision

Week_Eight_Nine_Revision

1. What is a file system?

   • A file system is the way files are stored and organised. Can be described as a type of database of files and directories.  It enables:  1. Simplified access to data.   2. The OS to keep track of how files are organised and how any available space is managed on a disk.   - It supplies structure to transform simple block device into sophisticated hierarchy of files and sub-directories that users can understand.  - In Linux the file system is a hierarchical directory structure that descends from the root directory (/).       - All partitions are contains under the root directory.  - All objects such as devices (monitor, keyboard) and directories are treated as files. Theses are sorted in the (/dev) directory.  
   • Two Types of File Systems: 1. Disk File System; = Mounted on a local computer 2. Network File System (NFS); = Mounted on a different partition of a local computer / remote computer.

2. Advantages/Reasons for partitioning a hard-disk

   • A file system uses disk partitions to enable: 1. Better organisation and productivity.  2. Security of data. 3. Backup of data. 4. If real memory runs out then Linux virtual memory can move pieces of memory to and from a disk storage - called Swapping.  5. Multiple OS's can be configured. - Each partition can contain an independent file system with multiple partitions available on a single physical disk.  STORAGE SPACE = Collection of storage devices. FILE-SYSTEM = Block Structure for a specific partition. 
   • - fdisk enables this to operate by use of Command-Line tool.  - It can run only as root.- Can access only IDE and SCSI hard drives. 

3. How is a file stored on a hard disk?

   • 1. The file is decomposed into fixed size blocks 2. Each block is then stored at a disk location

4. What is NIS?

   • NIS  = Network Information Service.  - It is a client/server protocol that centralizes user and group IDs 
   • What is the main function it provide?
     • - It provides database access so that network computers can share configuration information (or any other relevant info required).  For example; /etc/passwd /etc/shadow /etc/group

5. An example of 2 config files used to generate NIS MAPS

   • Maps are databases that store shared configuration information which is related to NIS networks. Each map stores key-value pairs which are generated from the Master Config files. For Example: user login and encrypted password.  Config File #1: /etc/passed Config File #2: /etc/shadow 

6. Three Types of host servers that NIS consists of:

   • NIS uses RPC to allocate and manage shared resources between NIS clients and servers.  RPC portmapper MUST run on both NIS client and server.
   • 1. NIS Master Server
     • - This contains NIS maps and makes them available over the network.
   • 2. NIS Slave Servers
     • - This can be used to distribute NIS master server's load evenly if load is heavy.
   • 3. NIS Clients
     • - All hosts in a NIS-Based network. Including Master and Slave servers. 

7. What is the key function of DHCP?

   • DHCP = Dynamic Host Configuration Protocol. - The DHCP server leases IP addresses for a specified period and assigns these to client computer dynamically.  - This is NOT useful when all computers in a network stay connected permanently. - Used to assign IP addresses automatically for each network host. I.E each host does NOT need configured separately. 

8. Explain the stages required for a computer to be assigned an IP address from a DHCP server

   • DHCP employs a connectionless service model with uses UDP. 
   • 1. Discovery
     • Client creates and sends a message to everyone on the network asking for an IP Address. 
   • 2. Offer
     • 1. The server receives the DHCP discover message - (An IP address lease request).  2. The server maintains a record of available and used IP addresses   - (Server checks what IP Addresses are available and reserves an available IP for the client).  3. The server makes a lease offer to the client by sending a DHCP offer message.   - (This offer is broadcast to EVERY device on the network because the client does not yet have an IP address  meaning the serer does not known where to find the client). 
   • 3. Request
     • - Following the offer the client MUST REPLY to the server to make a request for the offered IP address.  - Although the client can receive multiple DHCP offers from multiple DHCP servers the client can only accept ONE.  (Any unrequested IPs are returned to the server pool of available IP addresses).  
   • 4. Acknowledge
     • 1. The DHCP server then receives the DHCP request from the client. 2. The must confirm to the client that it can start using the IP address  - (Within the negotiated parameters).  

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