Unix Tutorial

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CHAPTER 8 <strong>Unix</strong> Processes Management When you execute a program on your UNIX system, the system creates a special environment for that program. This environment contains everything needed for the system to run the program as if no other program were running on the system. Whenever you issue a command in UNIX, it creates, or starts, a new process. When you tried out the lscommand to list directory contents, you started a process. A process, in simple terms, is an instance of a running program. The operating system tracks processes through a five digit ID number known as the pid or process ID . Each process in the system has a unique pid. Pids eventually repeat because all the possible numbers are used up and the next pid rolls or starts over. At any one time, no two processes with the same pid exist in the system because it is the pid that UNIX uses to track each process. Starting a Process: When you start a process (run a command), there are two ways you can run it: Foreground Processes Background Processes Foreground Processes: By default, every process that you start runs in the foreground. It gets its input from the keyboard and sends its output to the screen. You can see this happen with the ls command. If I want to list all the files in my current directory, I can use the following command: $ls ch*.doc This would display all the files whose name start with ch and ends with .doc: ch01-1.doc ch010.doc ch02.doc ch03-2.doc ch04-1.doc ch040.doc ch05.doc ch06-2.doc ch01-2.doc ch02-1.doc TUTORIALS POINT Simply Easy Learning
The process runs in the foreground, the output is directed to my screen, and if the ls command wants any input (which it does not), it waits for it from the keyboard. While a program is running in foreground and taking much time, we cannot run any other commands (start any other processes) because prompt would not be available until program finishes its processing and comes out. Background Processes: A background process runs without being connected to your keyboard. If the background process requires any keyboard input, it waits. The advantage of running a process in the background is that you can run other commands; you do not have to wait until it completes to start another! The simplest way to start a background process is to add an ampersand ( &) at the end of the command. $ls ch*.doc & This would also display all the files whose name start with ch and ends with .doc: ch01-1.doc ch010.doc ch02.doc ch03-2.doc ch04-1.doc ch040.doc ch05.doc ch06-2.doc ch01-2.doc ch02-1.doc Here if the ls command wants any input (which it does not), it goes into a stop state until I move it into the foreground and give it the data from the keyboard. That first line contains information about the background process - the job number and process ID. You need to know the job number to manipulate it between background and foreground. If you press the Enter key now, you see the following: [1] + Done ls ch*.doc & $ The first line tells you that the ls command background process finishes successfully. The second is a prompt for another command. Listing Running Processes: It is easy to see your own processes by running the ps (process status) command as follows: $ps PID TTY TIME CMD 18358 ttyp3 00:00:00 sh 18361 ttyp3 00:01:31 abiword 18789 ttyp3 00:00:00 ps One of the most commonly used flags for ps is the -f ( f for full) option, which provides more information as shown in the following example: $ps -f UID PID PPID C STIME TTY TIME CMD amrood 6738 3662 0 10:23:03 pts/6 0:00 first_one amrood 6739 3662 0 10:22:54 pts/6 0:00 second_one amrood 3662 3657 0 08:10:53 pts/6 0:00 -ksh TUTORIALS POINT Simply Easy Learning
Page 1 and 2: Unix Tutorial
Page 3 and 4: ABOUT THE TUTORIAL Unix Tutorial UN
Page 5 and 6: Renaming Directories: .............
Page 7 and 8: Extended Shell Scripts: ...........
Page 9 and 10: Example: ..........................
Page 11 and 12: Trapping Signals: .................
Page 13 and 14: The main concept that unites all ve
Page 15 and 16: New UNIX password:******* Retype ne
Page 17 and 18: CHAPTER 2 Unix File Management All
Page 19 and 20: Displays all the files whose name s
Page 21 and 22: 4. Fourth Column: represents file n
Page 23 and 24: CHAPTER 3 Unix Directories Adirecto
Page 25 and 26: Creates the directories docs and pu
Page 27 and 28: CHAPTER 4 Unix File Permission Setu
Page 29 and 30: $ls -l testfile -rw-rwxrwx 1 amrood
Page 31 and 32: The SUID and SGID bits will appear
Page 33 and 34: Note - The shell initialization pro
Page 35 and 36: The default secondary prompt is > (
Page 37 and 38: CHAPTER 6 Java Basic Utilities So f
Page 39 and 40: laserp-574 grace 82744 Nov 7 11:28
Page 41 and 42: CHAPTER 7 Unix Pipes and Filters Yo
Page 43: This pipe sorts all files in your d
Page 47 and 48: $kill -9 6738 Terminated Parent and
Page 49 and 50: CHAPTER 9 Unix Communication When y
Page 51 and 52: prompt on Turns prompt on. Dir List
Page 53 and 54: No Plan. Check all the logged in us
Page 55 and 56: ~ ~ ~ ~ ~ ~ ~ ~ "testfile" [New Fil
Page 57 and 58: Command CTRL+d CTRL+d CTRL+f CTRL+u
Page 59 and 60: ^G U U J Press CNTRL and G keys at
Page 61 and 62: IMPORTANT: Here are the key points
Page 63 and 64: POSIX shell ( sh) The different C-t
Page 65 and 66: CHAPTER 12 Unix- Using Variables Av
Page 67 and 68: NAME="Zara Ali" unset NAME echo $NA
Page 69 and 70: Command-Line Arguments: The command
Page 71 and 72: CHAPTER 14 Unix - Using Arrays Ashe
Page 73 and 74: CHAPTER 15 Unix - Basic Operators T
Page 75 and 76: val=`expr $b / $a` echo "b / a : $v
Page 77 and 78: else echo "$a -ge $b: a is not grea
Page 79 and 80: != Checks if the value of two opera
Page 81 and 82: ] is true. -x file Check if file is
Page 83 and 84: Right shift == String comparison fo
Page 85 and 86: -r file Checks if file is readable
Page 87 and 88: Example: #!/bin/sh a=10 b=20 if [ $
Page 89 and 90: There is only one form of case...es
Page 91 and 92: CHAPTER 17 Unix - Shell Loops Loops
Page 93 and 94: done This will produce following re
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4) juice 5) appe 6) all 7) none #?
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CHAPTER 18 Unix - Loop Control So f
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1 0 1 5 The continue statement: The
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\n new line \r carriage return \t h
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CHAPTER 20 Unix - Quoting Mechanism
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The Double Quotes: Try to execute t
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CHAPTER 21 Unix - IO Redirections M
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EOF 3 $ This is a simple lookup pro
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CHAPTER 22 Unix - Shell Functions F
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echo "Return value is $ret" This wo
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CHAPTER 23 Unix - Manpage Help All
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CHAPTER 24 Unix - Regular Expressio
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Try out the following address range
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sys:x:3:3:sys:/dev:/bin/sh sync:x:4
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[0-9] Matches a single number [a-zA
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(555)555-1213 (555)555-1214 (666)55
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dev /etc /lib /boot /home /mnt /pro
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$du -h /etc 5k /etc/cron.d 63k /etc
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CHAPTER 26 Unix - User Administrati
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$ groupdel developer This removes o
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CHAPTER 27 Unix - System Performanc
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CHAPTER 28 Unix - System Logging Un
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The combination of facilities and l
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Unix - Signals and Traps CHAPTER 29
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Trapping these signals is quite eas
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CHAPTER 30 Unix - Useful Commands T
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Ispell Emacs ex, edit Emacs Emacs C
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Command Dbx Gdb Make Nm Size Strip
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Reset Reset terminal mode Script Ke
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