INTRODUCTION TO UNIX

1
INTRODUCTION TO UNIX

• SHELL PROGRAMMING, COMPUTATION NUMBER
  PROCESSING
• SESSION 4

2
Multiline commands

• A command line entered at the shell may be longer
  than the width of the terminal if you are typing
  a complex pipeline expression
• UNIX provides a continuation mechanism which can
  be used to go on to the next line without
  processing the current input
• The \ operator escapes the NEWLINE and allows
  you to format complex commands for more
  readability

3
Multiline commands

• You may also type past the end of a line and most
  systems will continue your command on the next
  line
• In some cases, the shell will ignore the NEWLINE
  such as when you have begun a quoted command
  argument and pressed NEWLINE before closing the
  quotes
• cat/etc/profile \

4
Multiline commands

• To indicate that you are continuing a command
  line, the shell will use the PS2 prompt gt
  instead of the PS1 prompt
• The here Documents argument is an example of a
  command line argument which usually flows across
  multiple lines

5
Multiline commands

• The ltlthereDocument operator provides input data
  in a similar fashion to the file redirection
  operatorlt except that the data is entered right
  in the command string

6
Multiline commands

• Using ltlthereDocument
• cat - ltltend
• gt hello this is a test
• gt this is still a test
• gt end
• hello this is a test
• this is still a test

7
Multiline commands

• Using ltlthereDocument
• cat - ltltend
• gtMy login id is LOGNAME
• gt end
• My login name is hal

8
Multiline commands

• Using ltlthereDocument
• cat - ltltmarker
• gt echo There are ls HOME l wc-l
• gt files in HOME
• gt marker
• There are 23 files in /usr/hal

9
Storing shell commands in files

• Commands may be stored in a file and executed in
  the same way as they would be if there were
  directly entered via the terminal
• Command files may be executed by using the file
  as an argument for the sh command

10
Storing shell commands in files

• cat cmd.file
• echo LOGNAME
• pwd
• sh cmd.file
• hal
• /usr/hal
• Command files may be made directly executable
  using the chmod command

11
Storing shell commands in files

• chmod u x cmd.file
• cmd.file
• hal
• /usr/hal
• Command files or shell scripts can include all
  functions that can be performed directly from the
  keyboard

12
Storing shell commands in files

• Local variables and path changes may take place
  within the shell script which will not affect
  your environment when the script finishes
• cat cmd3.file
• pwd
• echo Changing directory.....
• cd /usr/hal

13
Storing shell commands in files

• pwd
• cmd3.file
• /usr/bob
• Changing directory....
• /usr/hal
• pwd
• /usr/bob

14
Storing shell commands in files

• Shell scripts may be used as commands within
  other shell scripts but locally defined variables
  will not be passed unless the exportcommand is
  used
• Shell programs saved in files should include
  comments to remind the user of what they do and
  how they are set up

15
Storing shell commands in files

• Comments are prefixed by a operator and
  everything after the is ignored by the shell
• echo hello this is a comment
• hello

16
The if operator

• The if operator provides a conditional test in
  a shell script and introduces a multiline command
  sequence that closes when the fi operator is
  used
• Using the if fi operators
• if true
• gt then

17
Storing shell commands in files

• gt echo hello
• gt fi
• hello
• if false
• gt then
• gt echo hello
• gt fi

18
Storing shell commands in files

• note true returns a value of zero while false
  returns a non-zero value
• The else operator provides a second leg for
  the if construction

19
Storing shell commands in files

• if false
• gt then
• gt echo hello
• gt else
• gt echo goodbye
• gt fi
• goodbye

20
Storing shell commands in files

• The elif (else if) operator provides additional
  nested if-type constructions
• if false
• gt then
• gt echo hello
• gt elif true
• gt then

21
Storing shell commands in files

• gt echo goodbye
• gt fi
• goodbye

22
The testcommand

• The test operator allows a comparison between
  two numbers of or returns a true/false value if a
  specified file exists/does not exist
• The test operator is used in conjunction with
  the if construction and may be implemented in
  two fashions

23
The testcommand

• if test VAR
• gt then
• gt echo defined
• gt fi
• if HOME
• gt then

24
The testcommand

• gt echo defined
• gt fi
• defined
• The test operator has a number of different
  arguments for testing files including

25
The testcommand

• -f filename (true exists)
• -r filename (true exists readable)
• -w filename (true exists writeable)
• -x filename (true exists executable)
• -d dirname (true exists is a dir.)
• -s filename (true exists is gt 0 bytes)

26
The testcommand

• DIR pwd
• if DIR HOME
• gt then
• echo In home directory!
• gt fi
• In home directory!
• Note the operator is used only between
  strings and not for numbers, also the ! (not
  equal) operator may be used

27
The testcommand

• The test operator has numeric operators for
  making comparisons including
• -eq (equals)
• -ne (not equals)
• -gt (greater than)
• -lt (less than)
• -le (less than or equal)

28
The testcommand

• -o (or)
• -a (and)
• mkdir /tmp/SS
• RET?
• if RET -eq 0
• gt then
• gt echo mkdir succeeded

29
The testcommand

• gtelse
• gt echo mkdir failed
• gt fi
• mkdir succeeded

30
The exit command

• The exit command is used to immediately end the
  execution of a shell script it may also take an
  argument that will become the value that the
  script returns back to the shell
• Using the exit command
• if true
• gt then
• gt exit 6

31
The exit command

• gt fi
• gtVAL?
• gt echo VAL
• 6

32
The exprcommand

• The expr (expression) command takes numbers and
  arithmetic operators as arguments and computes
  the result
• the standard arithmetic operators are used (, -,
  , /, ) and only integers may be processed
• expr 4 5
• 9
• expr 3 \4 2 V 2

33
The exprcommand

• 13
• note the and / operators must be preceded
  by a \ to keep the shell from interpreting them
  incorrectly in this context

34
The for operator

• The for operator provides looping capability
  within shell scripts so that recursive operations
  can be programmed
• The for operator can be used in the following
  ways
• for VAL in 1 2 3 4
• gt do

35
The for operator

• gt echo VAL
• gt done
• 1
• 2
• 3
• 4
• for FILE in

36
The for operator

• gt do
• gt echo FILE
• gt done
• file1
• textfile
• datafile

37
The while operator

• The while operator combines features of both
  for and if
• If the test is true then the do-done loop is
  performed
• If the test proves false, the loop is terminated

38
The while operator

• while !-f textfile
• gt do
• gt echo Trying to create file
• gt touch textfile
• gt done
• VAL1
• while VAL -lt 11
• gt do

39
The while operator

• gt touch fileVAL
• gt VALexpr VAL 1
• gt done
• note the operator until may be substituted for
  while so that the loop is executed as long as
  the test is false

40
The case operator

• The case operator acts like a series of
  if-elif-elif-...elif-fi operators by matching a
  character string and executing a list of commands
  while unmatched strings are ignored
• The case operator is used in the following
  fashion

41
The case operator

• case LOGNAME in
• gt hal)
• gt echo hello hal, whats up?
• gt
• gt marysue)
• gt echo hi, how are you?
• gt
• gt jim)
• gt echo hello jim, whats doing?

42
The case operator

• gt
• gt )
• gt echo hello LOGNAME
• gt
• gt esac
• hello hal, whats up?

43
The printf command and output from shell scripts

• The printf command is used to get more complex
  forms of character output from a shell script it
  provides a string-oriented subset of the
  capabilities of the C Languages printf(3)
  subroutine
• The command takes two kinds of arguments
• A formatting specification

44
The printf command and output from shell scripts

• A list of strings to be printed
• printf this is a string s\n 123456
• this is a string 123456
• Strings may be left-justified, truncated, set to
  a specific width, and tabs and newlines may be
  specified

45
The .profile and /etc/profile scripts

• The .profile and /etc/profile shell scripts
  are good examples of how command files can be
  used to tailor your environment
• The /etc/profile script is executed as soon as
  a user logs onto the system and provides a set of
  default environmental settings for the user
• The .profile script resides in the users home
  directory and contains settings for that
  particular users needs

46
The .profile and /etc/profile scripts

• Examples of shell scripts may be found in the
  following UNIX system files /usr/bin/calendar,
  /usr/bin/spell, /bin/basename, and
  /usr/bin/uuto.

47
The .profile and /etc/profile scripts

• The . operator provides a means of running a
  shell script under the current shell rather than
  in its own subshell since changes made in
  subshells do not propagate back to the parent
  shell
• This can be useful if you are testing
  modifications to your .profile script

48
Command line arguments

• Operators are provided for use in shell scripts
  to process command line arguments in the same
  fashion as other system provided commands
• The argument contains the number of command
  line parameters in a shell script
• The argument holds the current value of the
  parameters

49
Command line arguments

• cat - gt echo.args
• echo
• for VAR in
• do
• echo VAR
• done
• chmod ux echo.args

50
Command line arguments

• echo.args one two three
• 3
• one
• two
• three

51
Command line arguments

• Each command line argument can be used to pass
  parameters into the shell script for use the
  set operator may also be used within a shell
  script to set default values for use

52
Errors and error messages in using shell scripts

• Shell scripts can be run with several options to
  provide for error tracing and debugging
• The-x operator provides a trace function to
  allow a shell script writer to follow the
  sequence of a command execution
• The -v (verbose) option provides more
  information about each command as it is executed
  in the script

53
Understanding UNIX system documentation

• The UNIX Users manual is the official
  documentation for the UNIX system and contains,
  somewhere inside, all commands, tools, subroutine
  libraries, file formats, utilities, etc.
• It is sort of similar to the bible in that
  everything is there, you just have to learn how
  to understand and interpret it

54
Understanding UNIX system documentation

• The manual is a reference document and cannot be
  used to learn the UNIX system, you must already
  understand UNIX to read and interpret the manual

55
Layout of the Users manual

• Manual sections
• Commands and application programs
• commands and application programs supplied with
  the standard UNIX implementation including most
  of the commands that we have discussed in class

56
Layout of the Users manual

• System Calls
• primarily used by software developers for use in
  C or Fortran programs to use in new programs
• Subroutines
• also used mostly by software developers for
  inclusion in new programs

57
Layout of the Users manual

• File Formats
• this section documents the format of all
  important UNIX files such as /etc/passwd and
  terminfo
• Miscellaneous
• other, harder to classify areas are documented in
  this section including troff and terminal
  settings

58
Layout of the Users manual

• Games
• games and other fun programs are documented in
  this section although your particular system may
  not have these implanted
• Special Files
• this section provides documentation of device
  interface files including disks, tapes, and
  terminals as well as local area networks

59
Layout of the Users manual

• System Maintenance Procedures
• information about booting the system, diagnosing
  hardware problems and other system administrator
  jobs contained in this section

60
Referring to the manual section of a command

• Manual pages are identified by a topic or command
  name followed by a manual section reference in
  parenthesis and all commands and topics are
  arranged alphabetically in their section
• Examples of headings include
• pwd(1), init(1M), man(1), term(5)

61
A typical Man page

• Man page sections include
• Heading
• command name (both left and right side), release
  information (center)
• Name
• name of the command in full form
• Synopsis
• short summary of how to use the command with
  syntax options

62
A typical Man page

• Description
• more detailed description of the command and all
  its options
• Note
• additional comments not suited for the
  description section
• Warnings
• discusses potential problems which can arise when
  using the command

63
A typical Man page

• See also
• gives related commands or other relevant
  information pertaining to the use of the command
• Files
• gives the path names of databases and files which
  are affected by or which are used by this command
• Diagnostics
• gives a short description of error messages which
  may be generated by this command

64
A typical Man page

• Bugs
• provides warnings about unexpected and
  undesirable problems with this command

65
The permuted index

• The Permuted Index lists each word of the name
  section of each manual page as an aid to locating
  the correct section of the UNIX manual
• The alphabetic listing appears in the middle of
  the page
• The manual page listing is on the right side of
  the page

66
The permuted index

• The words which precede the entry are on the side
  of the page

67
The online mansystem

• The command man is available on larger systems
  to provide access to the actual manual pages from
  your terminal
• Care must be taken that the proper TERM setting
  is specified so that the output to your terminal
  is correct

68
The online mansystem

• Manual pages are often stored in their troff
  source format and are normally processed by
  troff -man or nroff -man before being
  displayed on your terminal

69
Online help command

• UNIX SVR3 provides an online help facility with
  its own menus and submenus
• To enter this facility from its own menu, enter
  the command help and follow the instructions
  provided

70
Online help command

• help may also be entered by using its subsystem
  commands directly from a command line
• locate
• usage
• starter
• glossary

71
NUMBER PROCESSING UNDER UNIX

• Computation tools under UNIX are primarily line
  oriented and are more like programming languages
• Very few on-screen calculators, like those found
  in MS-DOS productivity tools, are available under
  UNIX except for the X-Windows environment

72
NUMBER PROCESSING UNDER UNIX

• The tools that are available work at variety of
  levels, from the simple 'expr' operator to the C
  programming language

73
ELECTRONIC SPREADSHEETS

• The standard SVR4 release of UNIX does not
  include an electronic spreadsheet
• Lotus 1-2-3 and many other spreadsheets have been
  ported to UNIX
• Spreadsheet software may be purchased from third
  party vendors

74
SHELL REPRISE

• Fairly complex computational tasks can be
  accomplished using shell programming and the
  pipes, filters and 'expr' operator
• A few special purpose statistical and numerical
  computing programs have been designed but most
  have not been successful enough to include in the
  standard releases of UNIX

75
SHELL REPRISE

• The 'stat' package was designed for use with the
  shell pipeline but it is not normally included in
  most UNIX releases

76
THE 'DC' AND 'BC' CALCULATORS

• The 'dc' and 'bc' calculators are powerful
  line-oriented numerical processing tools
• The 'dc' (desk calculator) operator uses "reverse
  polish" notation (postfix notation) which
  requires the user to enter the numbers to be
  processed, followed by the process operator
• The 'dc' (desk calculator) is
• Stack-oriented
• Any number base
• Any precision level

77
THE 'DC' AND 'BC' CALCULATORS

• The 'bc' (before calculator) operator uses the
  more standard "infix notation" similar to what
  you learned in grade school where you enter a
  number, followed by a numeric operator, then the
  second number
• Procedure oriented
• Local subroutines and variables
• Logical operators and statements
• Any precision level
• Often used as a preprocessor to 'dc'

78
THE 'DC' COMMAND

• The 'dc' operator reads its commands and values
  from standard input, from a file, or both
• When 'dc' reads its commands from a file, it
  continues until all input has been processed
  (EOF) and then returns to standard input for more
  commands

79
THE 'DC' COMMAND

• When 'dc' reads its commands from standard input,
  it continues until a CTRL-D is entered which ends
  its execution
• When 'dc' receives a 'q' (quit) command from
  either the keyboard or a file, it terminates

80
THE 'DC' COMMAND

• Instructions to 'dc' may be numbers or operators
• Numbers may contain decimal points and negative
  numbers are preceded by the '_' (underscore)
  operator numbers are immediately pushed onto the
  'dc' stack

81
THE 'DC' COMMAND

• dc 3 4pq
• 12
• dc
• 3
• 4
• p
• 12
• q

82
THE 'DC' COMMAND

• The arithmetic operators '' (addition), '-'
  (subtraction), '/' (division), ''
  (multiplication), '' (remainder), and ''
  (exponentiation) act on the first two numbers in
  the stack
• The result of an operation is placed back on the
  stack, replacing the two numbers
• The 'p' (print) operator displays the top value
  on the stack but does not change it

83
THE 'DC' COMMAND

• 'dc' can accept commands and values on separate
  lines or multiple commands and values on single
  lines delimited by white space these modes may
  be intermixed
• dc
• 5 6
• 5
• / p
• 6
• q

84
THE 'DC' COMMAND

• Several operations in a row may be performed
  since the result of the last operation is placed
  back on the stack and the next operation will use
  that value and the one below it
• dc
• 3
• 4
• 7
• -
• p
• -8

85
THE 'DC' COMMAND

• Computations performed by 'dc' retain as many
  decimal places as needed
• dc
• 2.345 5.4567 p
• 7.8017
• q

86
THE 'DC' COMMAND

• Other commands in 'dc' include
• 'c' (clear stack)
• 'd' (duplicate top element of stack)
• 'f' (print all elements of stack in order)

87
THE 'DC' COMMAND

• Variables in 'dc
• The 'dc' command provides 26 register variables
  (a-z) to hold values needed for calculations
• Register names are lower case alphabetic
  characters and can be used in the following way
• 's' (save), top of stack in register "a"
• 'l' (get), register "a" to top of stack

88
THE 'DC' COMMAND

• Register elements may be reversed by or moved out
  of the way by placing them in unused registers

89
THE 'DC' COMMAND

• dc
• 2.34
• 4.56
• p
• 4.56
• st
• p
• 2.34
• lt
• p
• 4.56
• q

90
THE 'DC' COMMAND

• The 's' and 'l' operators may also be used with
  "auxiliary stacks" by using upper case alphabetic
  characters (A-Z) as names these stacks preserve
  the order of the values just as the main stack
  does
• Character strings may also be stored on the stack
  by using the ' ' brackets and stored strings
  can be taken from the stack and executed using
  the 'x' operator

91
THE 'DC' COMMAND

• Character strings must be explicitly removed
  after use or unexpected results may occur
• Other commands for 'dc' include
• '!' (bang), the shell escape operator
• 'v' (square root)
• 'i' (number base), for input
• 'o' (number base), for output

92
THE 'BC' COMMAND

• The 'bc' calculator is a simplified numerical
  calculation programming language processor which
  acts as a front-end to 'dc
• The 'bc' calculator reads from standard input and
  writes to standard output so that redirection
  from a file is allowed
• Unlike 'dc', when 'bc' reads its input from a
  file, it exits when it reads the (EOF) marker

93
THE 'BC' COMMAND

• The 'bc' calculator may also take a filename as
  an argument in which case it processes the
  commands in the file and then returns to standard
  input (keyboard) for additional commands
• The 'bc' calculator uses "infix" or the standard
  notation that most people learn in grade school
  (a b c)

94
THE 'BC' COMMAND

• The 'bc' calculator provides the user with the
  use of variables (a-z) and the concept of number
  arrays
• Variables are assigned using any lower case
  alphabetic character and may be referenced at any
  time just like numbers and they retain their
  value until reassigned

95
THE 'BC' COMMAND

• w value
• bc
• y4
• 3y
• 7

96
THE 'BC' COMMAND

• Arrays of numbers may be defined by using the '
  ' brackets to indicate the array index
• s23.3
• The 'bc' command performs its calculations in
  integer mode unless the 'scale' operator is used
  to indicate the number of decimal places required

97
THE 'BC' COMMAND

• bc6.456/5.6781scale36.456/5.5671.137

98
THE 'BC' COMMAND

• Different base numbers may be used by setting the
  input base 'ibase', and the output base 'obase'
  bcibase210019obase8100111

99
THE 'BC' COMMAND

• The '' and the '--' operators are used to
  increment and decrement the value of a variable
  bcs4s4--ss3

100
THE 'BC' COMMAND

• bcs4t--s3.3t33.3
• bc
• s4
• t --s 3.3
• t4
• 3.3

101
THE 'BC' COMMAND

• Other 'bc' statements and operators are provided
  including additional numeric operators, logical
  operators and the 'if', 'for, 'while' and 'break'
  statements
• The following operators are provided to change
  the value of a variable directly

102
THE 'BC' COMMAND

• '-' (subtract from)'' (add to)'' (multiply
  by)'/' (divide by)'' (divide remainder)''
  (exponentiate by)

103
THE 'BC' COMMAND

• Sequences of operations may be grouped together
  by using ' ' brackets which return whatever
  values that each individual component would
  return
• Logical operators may be used with the loop and
  test operators ('if', 'for', 'while')

104
THE 'BC' COMMAND

• '' (is equal)'lt' (is less than or equal)'gt'
  (is more than or equal)'!' (is not equal)'gt'
  (is greater than)'lt' (is less than)

105
THE 'BC' COMMAND

• bcs3if ( s 3 ) s 2s5

106
THE 'BC' COMMAND

• bcs4while ( s gt 0 ) ss - 14321

107
THE 'BC' COMMAND

• bcfor ( s 4 s gt 0 --s ) s4321

108
THE 'BC' COMMAND

• The 'break' statement allows exit from a loop
  before the condition part tests false,
  terminating only the innermost loop
• bcfor ( s 4 s gt 0 --s ) if ( s lt 2 )
  breaks43

109
THE 'BC' COMMAND

• The 'bc' processor allows the creation of
  functions identified by a single alphabetic
  character (a-z)
• External variables may be used within functions
  and their values may be changed as a result of
  the function

110
THE 'BC' COMMAND

• Local variables may be declared using the auto
  operator and used within the function without
  changing the value of existing external variables
  with the same name

111
THE 'BC' COMMAND

• bc
• define x (a, b)
• auto s
• for (s a sltb s)
• s
• return (22)
• x (3,6)
• 3
• 4
• 5
• 22

112
THE 'BC' COMMAND

• The 'bc' processor also provides a math library
  which can be loaded with the '-l' command line
  option
• 's(x)' (sine of x)'c(x)' (cosine of
  x)'e(x)' (exponential of x)'l(x)' (log of
  x)'a(x)' (arctangent of x)'j(n,x)' (Bessel
  function of x)

113
THE 'AWK' COMMAND

• The 'awk' command (named for Aho, Weinberger,
  Kernighan) is a powerful tool for both
  computation and pattern processing tasks which
  scans a list of input files for lines that match
  a set of specified patterns and then performs a
  set of specified actions on those lines

114
THE 'AWK' COMMAND

• the 'awk' command uses elements of 'bc', and the
  C programming language with features of shell
  programming
• Interpreted like 'bc'
• Field variables (1, 2 etc.) like shell
• Printing and control operators like C

115
THE 'AWK' COMMAND

• The 'awk' command is extremely sophisticated in
  its uses while being terse and arcane in its
  documentation

116
THE UNIX PROCESS

• INTRODUCING THE UNIX PROCESS

117
INTRODUCING THE UNIX PROCESS

• A process or task is an executing program some
  processes continue as long as you are logged on
  to the system while others exist for the duration
  necessary to complete their task

118
INTRODUCING THE UNIX PROCESS

• Some commands are internal to the shell ('cd' and
  'echo' for example) and do not generate a
  separate process when executed
• Command strings with pipeline operators may
  generate more than one process when they are run

119
TIME-SHARING IN THE UNIX SYSTEM

• Under the control of the kernel, the multiple
  tasks are switched several times a second to give
  the user the impression that they are being run
  simultaneously
• Under heavy loads or when processes are creating
  a problem response time will slow down and users
  may become aware that they are sharing the system
  

120
CONTROLLING PROCESS PRIORITY

• While most processes have equal priority, that is
  they are given equal time by the kernel, certain
  processes may need to be given more time than
  others to be able to operate effectively
• Only the superuser may raise the priority of a
  process any user may lower the priority of their
  own processes (default 10) using the 'nice'
  command

121
CONTROLLING PROCESS PRIORITY

• nice cat /etc/passwd
• nice -14 pr printfile
• nice --10 cat bigdocfile

122
BACKGROUND PROCESSES

• Most often, the 'nice' command is used in
  conjunction with a process running in background
  mode to allow the task to be executed while the
  user continues to work on the shell
• The user may create as many background processes
  as they wish

123
BACKGROUND PROCESSES

• Processes may be monitored by using the 'ps'
  command
• nice cat /etc/passwd gt scratch1
• 1234
• nice ls -al gt files1 2gt error1
• 1235

124
LOGGING OFF ...

• Normally, processes that are being run in the
  background will be killed when you log off the
  system since they are associated with your login
  shell
• The 'nohup' (no hangup) command will allow a
  process to continue to run after the user has
  logged off

125
LOGGING OFF ...

• When using 'nohup' with a pipeline command, all
  elements of the pipeline must be preceded by
  'nohup'
• If no output file is specified (via redirection)
  then 'nohup' will create its own output file
  (nohup.out) for the user

126
LOGGING OFF ...

• nohup cat /etc/passwd
• 1234
• sending output to nohup.out
• nohup cat file1 nohup wc gt out1
• 1235

127
PARENTS AND CHILDREN

• Processes are said to be 'born' when they begin
  and 'die' when they end
• When one process spawns another process, the
  older process is known as the 'parent' while the
  newly created process is called the 'child'
  process

128
PARENTS AND CHILDREN

• Normally, when a parent process is killed, its
  associated child processes are also terminated
• The 'nohup' command allows an existing child
  process to be 'inherited' by 'init', process
  number 1
• A parent process may have multiple children but
  child processes may have only one parent process

129
THE 'PS' COMMAND

• The 'ps' (process status) allows a user to
  display information about processes that are
  currently alive
• The 'ps' command with no arguments will display
  processes associated with your login session
• ps

130
THE 'PS' COMMAND

• The '-f' option provides more information about
  each process for the user including the UID (user
  id), PID (process id), PPID (parent process id),
  C (resource use index), TTY (terminal executing),
  STIME (time started), and COMMAND (process
  executed)
• ps -f

131
ACTIVITY OF OTHER USERS

• The 'ps' command may also be used to give you
  information concerning the processes of other
  users by using the '-u' option followed by a
  valid user id

132
ACTIVITY OF OTHER USERS

• The '-a' operator will show all user started
  processes currently operating a the system
• ps -u hal
• ps -af
• ps -uf hal

133
SYSTEM PROCESSES

• The 'ps' option '-e' will give information about
  all processes operating on a system including
  system processes

134
SYSTEM PROCESSES

• This information can be useful in diagnosing
  problems with a system once you are familiar with
  the processes which should be present and how
  much activity they should be receiving from the
  cpu
• ps -ef

135
DIAGNOSING PROBLEMS WITH PROCESSES

• Using the 'ps -ef' command and options, problem
  with a system may be recognized and corrected by
  the system administrator
• When the system response time begins to slow down
  or when processes seem to have an extremely large
  number of children, this may indicate a problem
  an application may show a number of indications
  of failure

136
DIAGNOSING PROBLEMS WITH PROCESSES

• Its process will die prematurely and/or keep
  attempting to respawn (restart)
• The process will spawn too many children and
  begin to slow up system response
• A process may consume inordinate amounts of cpu
  time due to a program error (loop) or an improper
  priority setting

137
KILLING A PROCESS

• A process may be terminated by using the 'kill'
  command with the PID of the offending process as
  its argument
• A user may kill any process they own while the
  superuser may kill any process except processes
  with PID's 1, 2, 3, 4

138
KILLING A PROCESS

• The 'ps' command should be run again to see that
  the process was killed and that its children were
  not inherited by another parent (grandparent)
  process
• Multiple processes may be killed at the same time
• kill 1234 1235 1236

139
SIGNALS

• When a process is killed, it is sent a
  termination "signal" which it may ignore if there
  are already problems with that process
• The normal 'kill' signal is '15' which tell the
  process to terminate

140
SIGNALS

• An "unconditional" kill signal ('9') can be sent
  to processes that ignore the '15' sent by the
  standard kill command
• kill -9 1234 1235 1236

141
PROCESSES THAT RESPAWN

• The '/etc/inittab' file
• Some processes will automatically restart when
  you kill them these processes are listed int the
  'inittab' file
• Field three of each entry in the file indicates
  if the process listed it to restart when
  terminated
• To terminate a runaway process, you must edit the
  'inittab' file, changing the 'respawn' entry to
  'off'

142
PROCESSES THAT RESPAWN

• After editing the file, use the 'telinit q'
  command to instruct 'init' to reread the table
  and stop respawning the offending process
• Why the first 'ps' takes longer
• Under SVR4, 'ps' maintains a table in the
  '/etc/ps_data' file to enable it to speed up the
  response time for 'ps'

143
PROCESSES THAT RESPAWN

• If the command has not been run for some time or
  if the system has been rebooted, 'ps' may
  automatically rebuild the table and take a bit
  longer to respond

144
PROCESSES THAT RESPAWN

• Waiting and defunct processes
• When a process spawns a child, it will normally
  wait for the child to complete and go out of
  existence
• If the process is run in the background, however,
  the child may finish and the parent may not
  acknowledge its completion, leaving it marked as
  a ltdefunctgt process when viewed by 'ps'

145
PROCESSES THAT RESPAWN

• A certain number of these ltdefunctgt processes
  represents no problem an excessive number
  indicates a problem

146
PROCESSES THAT RESPAWN

• The '/proc' directory
• A new feature in SVR4, the '/proc' directory
  contains virtual memory images' of the processes
  that are running on the machine
• The file size listed by the 'ls -l' command
  indicate the actual memory size used by the
  process

147
PROCESSES THAT RESPAWN

• '/proc' currently provides little value for UNIX
  users but it will provide the basis for future
  developments in memory-mapped file systems