Processes and Job Control

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Processes and Job Control

• CSCI 2467 Spring 2007
• Instructor Michael Ruth
• Computer Science Department
• University of New Orleans
• mruth_at_cs.uno.edu

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Any Questions Before We Move On?

• The two topics of today
• Ken Thompson was born in New Orleans, LA
• Not surprisingly currently at Google
• We spoke earlier of a Content-based Image
  Retrieval
• SIMPLicity engine at Penn State, which was
  developed at Stanford
• http//wang14.ist.psu.edu/cgi-bin/zwang/regionsear
  ch_show.cgi
• I can never seem to remember all of your
  questions please send them to mevia email
• Any other questions before we move on?

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Topics

• Quoting metacharacters
• Control codes
• The Unix Process
• Process Definitions
• Process environment
• Process execution
• Process Management
• Other Useful Commands
• Touch
• Aliases
• History
• Grep

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Quoting Metacharacters

• Sometimes you may need to quote a metacharacter
• For example, suppose we wish to find all files
  that begin with .
• . and .. are metacharacters?
• We can quote a single metacharacter using a \
  just before it
• Ex ls a \.
• Suppose we need to quote a sequence of
  metacharcters
• We quote using ltmetacharactersgt
• Ex ls a

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Control Codes

• Control codes are a way to send signals of
  certain types to the system
• The following summarizes some of the most
  commonly used control codes
• ctrl-D
• Signals the end of a file you are entering from
  the terminal if typed at the beginning of a line
  or if typed twice elsewhere in a line
• ctrl-Z
• Suspends a process or job but does not terminate
  it
• Well discuss later why this is important
• ctrl-C
• Cancels a command or interrupts a running program
• ctrl-U
• Clears the command line
• ctrl-S
• Freezes the process
• ctrl-Q
• Unfreezes the process

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The Unix Process Model

• A program is an executable file residing on disk
  in a directory
• A process is an instance of running a program
• Every time you issue a command, Unix starts a new
  process, and suspends the current process (the
  shell) until the new process completes
• Each process is uniquely identified on each
  system with a process identification number or
  PID
• Every process has an environment in which it
  operates in

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Process Environment

• There is a notion of each process having its own
  memory space
• There is also a notion of timesharing
• However, at this juncture, well focus on
  environment variables and setting them
• Environment Variables
• Name value pairs which are used for possibly
  application specific reasons

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Manipulating the Environment

• For a list of all name-value pairs
• env
• For a specific environment value
• echo ltnamegt
• To set an environment value
• export ltnamegtltvaluegt

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Permanence and Env Vars

• Using export saves the variables temporarily
• When you log off they vanish
• We need to be able to set them so that they
  persist even after logging out
• We do this by putting the export statement in one
  of the following files
• .cshrc
• Called every time a process is created/started
• Do NOT insert text outputting commands
• Too much can slow execution of all command
• .login
• Run just after cshrc upon login (once only)
• Put aliases or environment value stuff here
• Activate changes in either by either logging out
  then back in or
• Use source command like so
• Ex source .login

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Process Execution

• A process may be in the foreground, in the
  background, or be suspended
• In general the shell does not return the UNIX
  prompt until the current process has finished
  executing
• Some processes take a long time to run and hold
  up the terminal

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The background

• Backgrounding a long process has the effect that
  the UNIX prompt is returned immediately, and
  other tasks can be carried out while the original
  process continues executing
• To perform this
• ltcommand linegt
• The result of which looks something like
• num-one num-two
• num-one is the job id
• num-two is the process id

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Bringing it back

• Suppose we want to bring the background process
  back into the foreground
• We can get a list of jobs by running
• jobs
• This will give a list of items such as
• ltjob idgt ltJob statusgt ltthe commandlinegt
• To bring something back into the foreground
• fg ltjob idgt
• If there is no job id, then the last backgrounded
  job is brought to the foreground

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Suspending processes

• Why?
• We can suspend processes in the foreground by
  using ctrl-Z
• To suspend a background process, we need its job
  number
• stop ltjob idgt

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Resuming Processes

• The bg command is used to resume a process in the
  background
• bg ltjob idgt
• The fg command resumes a suspended process in the
  foreground
• fg ltjob idgt

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Scheduling Processes

• Additionally, we can schedule processes to run at
  a specific time in the future
• at command does this
• at job TIME
• This is useful when we need to run things at a
  specific time (think of concurrency issues)

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Attaining Process Status

• To see information about your processes, with
  their associated PID and status
• ps
• Some useful options
• -e
• List all processes currently running on this
  machine
• -f
• Generate a full listing
• -l
• Generate a long listing

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Example of running ps
PID TTY TIME CMD 3880 pts/10
000 ksh 3883 pts/10 000 ps
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Example of running ps -e
PID TTY TIME CMD 0 ?
055 sched 1 ? 000 init 2 ?
000 pageout 3 ? 1925
fsflush 121 ? 000 sysevent 7 ?
004 svc.star 9 ? 013
svc.conf 125 ? 011 picld 103 ?
006 ipmon 204 ? 000
ttymon 96 ? 000 pfild 221 ?
000 rpc.nisd 712 ? 000
sendmail 852 ? 000 rpc.ttdb 130
? 010 nscd
PID TTY TIME CMD 195 ?
000 sac 134 ? 001 kcfd 189 ?
002 rpcbind 241 ? 000
nfs4cbd 196 ? 003 statd 205
console 000 sh 220 ? 001
ypserv 202 ? 000 lockd 206 ?
000 utmpd 381 ? 000
in.rarpd 227 ? 000 ypbind 719 ?
000 dtlogin 249 ? 006
nfsmapid 450 ? 000 vold 256 ?
000 cron
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Example of running ps -f
UID PID PPID C STIME TTY TIME
CMD mruth 3938 3935 0 030854 pts/8
000 ps -f mruth 3935 3934 0 030849
pts/8 000 sh -i
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Example of running ps -l
F S UID PID PPID C PRI NI ADDR
SZ WCHAN TTY TIME CMD 0 O 11743
3946 3943 0 50 20 ? 163
pts/8 000 ps 0 S 11743 3943 3942
0 50 20 ? 176 ? pts/8
000 ksh
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Sometimes you want to place nice

• You can set the priority of a process by using
  the nice command
• Yes, I know everyone should be nice right?
• This command allows us to improve/degrade the
  priority of a process
• Unless you are a superuser you cannot improve the
  priority of a process
• The syntax is as follows
• nice -n ltcommand linegt
• Where n is a number
• positive degrades the priority, negative numbers
  improve the priority
• Range goes from -20 (highest priority) to 19
  (lowest).

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When its time not to be nice

• There may be many reasons why we want to kill a
  process
• To kill a job when it is in the foreground
• ctrl-C
• To kill a job when it is in the background
• kill ltprocess idgt
• kill -9 ltprocess idgt

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Other useful commands

• There are a number of commands that are highly
  useful
• There are many, many more. We will cover what we
  need to cover as we need to cover it
• However, there are a few which cannot be skipped
• Touch
• Touch resets the access and modification times of
  the file we touch
• Alternatively creates the file if it doesnt
  exist
• stty
• Set terminal options
• -a outputs all the settings for the terminal
• stty option value
• EX stty erase 'H'

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AKA (aliases)

• Aliases are used to rename commands, and
  sometimes to include options
• Syntax alias cmdnew command
• This allows us to enforce rules upon ourselves
• EX alias rm"rm -i"
• However, this is a double edge sword we could
  things make our own life worse

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Those that dont study History

• In Unix, we cant simply use the up button to
  get the command we just typed in
• Of course, theres a much more complex system in
  place
• Using the history command
• The syntax history
• Lists all recent commands
• fc s ltcommand numbergt
• Reruns the command given by the number
• Can we save more commands in the list?
• Yes, but you shouldnt need to do this man fc/env

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grep

• Finds lines in a file matching a character
  pattern
• Syntax grep - icvn pattern file
• Options of interest
• -i Ignores case
• -c Lists count of lines that contain pattern
• -v Lists all lines except those with pattern
• -n Lists line number for each found pattern
• The pattern is a regular expression and the file
  is the file you are interested in
• This command will certainly help each of you
  understand Regular expressions b/c its quick.

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script

• What if you wanted to log your usage at the
  shell?
• Use the script command
• script ltfilenamegt
• It waits until the EOF is encountered (ctrl-d)

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The future

• Shell Programming Regular Expressions
• Homework 1 is coming next week!!!
• Krewe du Vieux is this weekend! (2/3 _at_ 7pm)
• Introduction to C Programming

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Questions?