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.