This document discusses Unix process states, zombie processes, running jobs in the background, and killing processes with signals. It covers the following key points: 1. Process states include running, waiting, zombie, and runnable. A zombie process is one whose parent hasn't issued a wait call, while an orphan has no living parent process. 2. Background jobs run without user intervention using the & operator or nohup command. The jobs command lists background jobs. 3. The kill command terminates processes by sending signals. It can target processes by PID or send a specific signal number.

1. Introduction to Unix and OS
Module 2 Continued……
Dr. Girisha G S
Dept. of CSE
SoE,DSU, Bengaluru
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2. Agenda
• Process States and Zombies
• Running jobs in background
• Killing processes with Signals
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3. Process States
1 Runnable Sate :
2. Running State :
3. Waiting (or sleeping)/Suspended State:
4. Zombie state :
Process states are :
Figure. Process State Diagram
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4. Zombie Process
A zombie process is one which has exited, but its parent hasn't yet issued a wait()
system call to observe its termination state
Orphan Process
Process whose parent process no more exists i.e. either finished or terminated without
waiting for its child process to terminate is called an orphan process.
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5. Running Jobs in Background
Foreground Job: The process that is connected to the terminal is called
the foreground job
E.g. A foreground process begins by typing a command at the prompt. For
example, type ls to see a simple listing of the files in the current directory
Background Job: Process that runs behind the scenes (i.e., in the background) and
without user intervention
E.g. sorting a large file in the background
Jobs
- This command lists jobs running in the background
E.g $ jobs
[3]+ running grep ‘director emp.dat &
[2]- running sort employee.data>sortedlist.data &
[1] supended wc –l hugefile.txt
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6. 2. nohup- no hangup
- nohup command permits execution of the process even after the user has
logged out.
- Use & with it as well
E.g. $nohup sort emp.lst &
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sending output to nohup.out
Two ways of starting jobs in background
1. With shell’s & operator
The shell’s & operator used to run a job in the background
E.g. Sort a file called ‘foo’ and place the results in a file called ‘bar’
$ sort <foo >bar &
550 //jobs PID
- This method run in the background but the process will be killed if you logout.
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7. Killing processes with Signals
- Some times you want or need to terminate a process.
- The following are some reasons for stopping a process
• Its using too much CPU time
• It is running too long without producing the expected
output
• Its no longer useful
How to get out of these situations?
• Use kill command to stop the background process
• press <ctrl-c> to stop a command that is not in the background
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8. Kill – premature termination of a process
- Kill command is used to terminate a process
- Issuing a kill command sends a signal to a process
- Unix programs can send or receive more than 20 signals each of
which is represented by a number
- Use kill -l to list all signal names and numbers
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9. Two forms of using kill command
Kill PIDs
– uses one or more PIDs as arguments
Kill -Number PIDs
- Uses signal number as option and PID as arguments
Examples
1. kill a process whose PID is 123
$ kill 123
2. Kill a process with signal number 9 whose PID is 123
$ kill -9 123
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