System Usage Accounting Services in UNIX
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.