20.1 Process Table

   

---

The process table is a kernel data structure that keeps records of all processes in memory. Each process has information associated with it that resides in the process table. You can use the ps command to list process attributes in tabular form containing different fields. Some of the fields in the process are shown in Table 20-1.

Table 20-1. Process Attributes in the Process Table

Field	Description
PID	Process ID
PPID	Process ID of the parent
STAT	Current process state
UID	User who created the process
GID	Group ID of the owner
C or CPU	Processor utilization
PRI	Priority of the process
NI	Nice value used in the priority calculation
ADDR	The memory address of the process
SZ	Size in physical pages of the process image
WCHAN	Event for which the process is waiting
STIME	Starting time of the process
TTY	Controlling terminal of the process
TIME	Cumulative execution time of the process
COMM	The command that started the process
MAX	Maximum number of open files allowed

At system startup, the swapper process is created that has a process ID of 0. The swapper process initiates the init process that has a PID of 1. The init process is then responsible for creating other processes using the fork system call.

The kernel has a scheduling mechanism used to determine which process will be executed during a given time slice. The state of a process is represented by a process context that contains information about process data and register values. When a time slice for a process is finished, its context is saved, and the next process is started.

---

   

Top