Mode switching

A user process undergoes a mode switch when it needs access to system resources. This is implemented through the system call interface or by interrupts such as page faults.

There are two modes:

• User mode
• Kernel mode

Processor time spent in user mode (application and shared libraries) is reflected as user time in the output of commands such as the vmstat, iostat, and sar commands. Processor time spent in kernel mode is reflected as system time in the output of these commands.