Program Versus Process - Unix Systems - Lecture Slides, Slides of Advanced Operating Systems

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Chapter 10: Managing Linux

Processes

2

Introduction

• Program versus process
• Daemon versus user processes
• Viewing processes
  • The ps command
  • The top command (view, kill, priority, etc.)
• PID and PPID
• Process status (sleeping, running, Zombie,

etc.)

• Process priority and nice value

4

Killing Processes

• 64 types of kill signals can be used

with the kill command

• To kill a tree of processes, you need to

kill the parent process

• Some processes can ignore some kill

signals except SIGKILL (9)

• To kill several processes with the

same name use the killall command

5

Common Kill Signals

7

Process priority

• PRI dictates number of time slices a process gets which can not be changed directly
• Use nice and renice command to change the priority indirectly
• Ex: $nice – n -20 ps – l
• EX: $renice +10 PID

8

Scheduling Processes

• Using two daemons
  • at for scheduling processes to run once
  • cron for scheduling processes to be run repetitively
• Two files are used to allow/deny users access to either one.
• These files are stored in /etc and named x.allow or x.deny (if both exit only allow is processed)
• at options include – l, -c, -d, & -f
• The crontab command can use options: -e to edit, -r to remove and – l to list cron table entries

10

Scheduling Processed (cont)