Unix Command Interface and commands


  • Unix command interface  is a separate program referred to as shell.
  • The shell provides the user interface between the user and the Kernel.
  • Unix commands and Utilities , like the shell , are also separate programs.
  • They are part of a Unix distribution , and are considered part of Unix but not part of the Kernel.


Unix System Services

  • Unix Provides a number  of system services such as system administration , system reconfiguration and file system maintenance.
  • Other services include

    • Customization of system parameters
    • Rebuilding of kernel with user device
    • Creation and definition of user accounts.
    • Setup and maintenance of access control parameters for files and peripherals.
    • Most service are built in to the kernel as system calls.


Unix System calls


  • System calls provide a programming interface that allows user programs  to access Kernel function.
  • There are a large number of system calls that perform functions to manage system resources such as memory , disk storage , and peripherals.
  • System calls are defined in a run time library that provides a mapping of the system call interface to the Kernel routines that platform the system functions.
  • The shell also provides functionality equivalent to many of the system calls.


System Usage Accounting Services

Unix provides some general accounting services.

As each process terminations , an accounting record is mode available discoing the resources used by the process.

  • Name of the process
  • Amount of user and system CPU time used
  • Elapsed time
  • Average amount of memory used.
  • Number of disk I/O operations done
  • UID and GID of the process
  • Terminal from which process was Started.