Managing Linux Processes: Understanding Types, Viewing, and Killing Processes, Slides of Advanced Operating Systems

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Chapter 10

Managing Linux Processes

Objectives

• Categorize the different types of processes on a Linux system
• View processes using standard Linux utilities
• Illustrate the difference between common kill signals
• Describe how binary programs and shell scripts are executed

Linux Processes

• Program: Structured set of commands stored in an executable file - Executed to create a process
• Process: Program running in memory and on CPU
• User process: Process begun by user on a terminal
• Daemon process: System process
  • Not associated with a terminal

Linux Processes (continued)

• Process ID (PID): Unique identifier assigned to a process
• Child process: Process started by another process (parent process)
• Parent process: Process that has started other processes (child processes)
• Parent Process ID (PPID): Parent process’s PID

Linux Processes (continued)

Figure 10-2: Process genealogy

Viewing Processes

• ps command: View processes
  • Most common process viewing utility
  • No arguments: Lists all processes running in current shell - PID, terminal, command that started process, CPU time
  • – f (full) option: More complete information
    • User identifier (UID), PPID, start time, CPU utilization

Viewing Processes (continued)

• Process priority (PRI): Determines how many processor time slices process will receive - Higher value means lower priority
• Nice value (NI): Indirectly represents priority
  • Higher value means lower priority

Viewing Processes (continued)

Table 10-1: Common options to the ps command

Killing Processes

• kill signal: Sent to a process by kill command
  • 64 types of kill signals
    • Affect processes in different ways
• kill command: Kills all instances of a process by command name - To kill a process, give kill signal and PID - If no kill signal given, SIGTERM assumed

Killing Processes (continued)

Table 10-2: Common administrative kill signals

Killing Processes (continued)

• killall command: Kills all instances of a process by command name - Uses process name instead of PID
• Can use top command to kill processes

Process Execution

• Three main types of executable commands
  • Binary programs
  • Shell scripts
  • Shell functions

Process Execution (continued)

Figure 10-3: Process forking

Running Processes in the Background

• Foreground processes: BASH shell must wait for termination
• Background processes: BASH shell does not wait for termination - & metacharacter - Upon execution, user receives BASH shell prompt immediately