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Unix Background

Unix Background

• Kernel - the master control program which performs the general low-level functions of mediating between the UNIX system utilities and the system hardware eg
  • locating the program and data files on disk,

  • loading the programs and data into main memory,

  • scheduling processes to be worked on by the CPU,

  • reading user input from terminal and writing user output to terminals and printers.

• Shell - special program acts as a command interpreter
  • a layer above the kernel ie users don't work directly with the kernel but rather programs and commands call upon kernel services.

• Process - when a command, or a shell or an application program executes it is called a process.

• Daemons are essentially processes which are not attached to a shell so they run in the background and serve the user or system community eg
  • utilities which run in the background all the time waiting for someone to send mail

  • or a file to the printer and they are begun when the system is booted.

NFS

• allows application transparent sharing of file systems or directories among nodes on a network.

• is implemented using the machine/vendor independent remote procedure call (RPC) mechanism, whose protocols are described using the external data representation (XDR) package

• allows the user to share files with other systems, reducing the overhead on disk space and also reducing the chances of having several versions of the same software around the network.

NFS Server

• Exports file systems to make them available for application transparent sharing with NFS clients

• Reads or writes files in response to NFS client requests

• Maintains no state information about its client's open files

• May remove its client's open file

• May serve NFS clients of other NFS servers

• May communicate with its NFS clients through Ethernet router nodes

• Does not cache NFS client write requests

NFS Client

• Mounts shared file systems or directories exported by the NFS server

• Files are read or written via request made to the NFS server

• Maintains all state information about its open files

• May not necessarily use root privileges to access NFS file systems

• May have many NFS servers

• May communicate with NFS servers through Ethernet router nodes

• Performs any file system write caching

NFS Server/Client Interaction

• Server makes file systems available

• Server starts NFS and mount daemons

• Client issues NFS mount request

• Server's mount daemon returns a pointer:
  • ie to the requested file system or directory if that file system has been exported to that client

• Client places the file handle in the kernel's mount table
  • all future references beyond the mount point are passed to the NFS daemon running on the server

• NFS read ahead/write behind is handled by the client's block I/O daemon

NIS

• NIS - Network Information service

• An interface to NFS - easier to maintain.
  • NFS is used for file systems, NIS is used for individual files also it is dedicated to the purpose.

• NIS Servers and Clients
  • A NIS client - host which makes use of the NIS network service.

  • A NIS slave server - provides the NIS network service.

  • A NIS master server - provides NIS service, updates NIS maps and propagates NIS maps to NIS slave servers.

• Used for the administration of network-wide databases, 2 programs:
  • YPBINDPROG - for finding a NIS server

  • YPPROG - accessing the NIS databases.

Currently Installed Software

• Languages
  • C

  • C++

  • FORTRAN77

  • FORTRAN90

  • HPF

• Parallel Software Development:
  • Parallel Libraries: PVM

  • Parallel Program Analysis: XPVM

  • Graphical Programming: HeNCE

  • Debugging: Conventional Debugger - XDBX, Parallel Debugger - Xmdb

  • Source Analysis / Transformation: Enterprise (to be replaced)

  • Code Profiling: Enterprise (to be replaced)

• Cluster Management:
  • DQS

• Document Delivery:
  • Mosaic

  • Netscape