UNIX COMP-145

LECTURE 5: UNIX PROCESSES

TEXT: S. DAS, “YOUR UNIX: THE ULTIMATE GUIDE”, 2ND EDITION, MCGRAW HILL, 2006

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UNIX OPERATING SYSTEM

• THE UNIX PROCESS STRUCTURE• PROCESS INITIALIZATION SEQUENCE• PROCESS CONTROL COMMANDS• RUNNING SHELL SCRIPTS IN BACKGROUND• PROCESS SIGNALING AND EXIT STRUCTURE• EXECUTE &TERMINATE PROCESSES• SCHEDULE A PROCESS TO RUN

AUTOMATICALLY

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THE PROCESS

• AN INSTANCE OF A PROGRAM IN EXECUTION. • IDENTIFIED BY A UNIQUE PID (PROCESS-ID). • CREATED BY ANOTHER PROCESS AS ITS CHILD• ONE PROCESS CAN BE PARENT OF MULTIPLE

CHILDREN• CAN BE KILLED OR STOPPED BY SENDING IT A

SIGNAL

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THE PROCESS CYCLE

• PARENT FORKS A CHILD BY 1ST REPLICATING ITS OWN PROCESS IMAGE AND LOGGING THE CHILD IN THE PROCESS TABLE.

• CHILD EXECUTES (OVERWRITES) THIS IMAGE WITH THAT OF ANOTHER PROGRAM.

• WHILE CHILD IS RUNNING, PARENT MAY WAIT FOR CHILD TO COMPLETE EXECUTION (IF A CHILD EXECUTING IN

FOREGROUND) CONTINUE WITH ITS OTHER TASKS (IF A CHILD EXECUTING IN

FOREGROUND)

• PROCESS TERMINATES AND PARENT PICKS UP EXIT STATUS OF CHILD. Until Parent picks up exit status of child, process called a ZOMBIE,

because process not removed

• KERNEL REMOVES ENTRY FOR DEAD CHILD FROM PROCESS TABLE.

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THE PROCESS CYCLE (contd)

• IF PARENT PROCESS DIES BEFORE A CHILD PROCESS CHILD PROCESS CALLED AN ORPHAN PROCESS init BECOMES PARENT OF CHILD,

AS IT IS FOR MOST DAEMONS ORPHAN PROCESSES CONTINUE TO OPERATE UNTIL ITS

KILLED OR ENDS NORMALLY.

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MORE ON THE PROCESS

• BUILT IN SHELL COMMANDS DO NOT FORK SEPARATE A PROCESS FOR EXAMPLE: cd or pwd

• SHELL SCRIPTS USE SUB-SHELLS TO RUN COMMANDS IN SCRIPT

• SIGNALS: USED BY KERNEL TO COMMUNICATE WITH A PROCESS kill -s, OR GENERATED THROUGH YOUR keyboard

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PROCESS ATTRIBUTES INHERITED BY CHILD

• Real User ID (UID) and Group (GID)• Effective UID and GID• Current directory• File descriptors• umask value• Environment variables

• PID Process ID – referred to as “pid” When born, logged in Process Table with unique number Used to track and kill a process Stored in variable $$ To see or show value of $$ use echo $$

• PPID Parent PID, referred to as “p-pid” Can be used to kill a child process but only be used if 1 child spawned

$ ps PID TT STAT TIME COMMAND64199 p3 S 0:00.00 -ksh (ksh)64218 p3 R+ 0:00.00 ps$

PROCESS ATTRIBUTES NOT INHERITED BY CHILD

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PROCESS CONTROL COMMANDS

• ps (PROGRAM STATUS)• kill (TERMINATE PROCESS)

• DISPLAY ENVIRONMENTSPECIFIES A LIST OF DIRECTORIES TO SEARCH.

$ ps –e

PID TT STAT TIME COMMAND64199 p3 S 0:00.00 -ksh (ksh)64304 p3 R+ 0:00.00 ps –e

PROGRAM STATUS (ps)

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• DISPLAY COMMAND-LINE AND ENVIRONMENT INFO ABOUT SWAPPED OUT PROCESSES. UID OF USE MUST BE 0.

$ ps –f

PID TT STAT TIME COMMAND64199 p3 S 0:00.00 -ksh (ksh)64305 p3 R+ 0:00.00 ps –f

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PROGRAM STATUS (ps) (contd)

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• DISPLAY DETAILED PROCESS LISTING

$ ps –lUID PID PPID CPU PRI NI VSZ RSS MWCHAN STAT TT TIME COMMAND83641 75606 75605 0 20 0 1996 540 pause S p3 0:00.00 -ksh (ksh)83641 75610 75606 0 96 0 5776 992 - R+ p3 0:00.00 ps –l

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PROGRAM STATUS (ps) (contd)

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RUNNING JOBS IN THE BACKGROUND

• APPEND & (AMPERSAND) TO THE END OF A SHELL OR COMMAND SHELL OPERATOR TO RUN IN BACKGROUND FREES KEYBOARD AND SCREEN FOR USE.

$ sort empl.lst > junk2 &

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RUNNING JOBS IN THE BACKGROUND (contd)

• PREPEND nohup (NO HANG UP) IN FRONT OF A SHELL OR COMMAND SHELL OPERATOR TO NOT TERMINATE THE COMMAND

RUNNING IN BACKGROUND EVEN IF THE SESSION ENDS

$ nohup sort empl.lst > junk2 &

UNIKE & , USE nohup WITH EACH COMMAND IN A PIPELINE, E.G.

$ nohup grep directory | nohup sort > empl_directors_sorted&

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PROCESS SIGNALING AND EXIT STRUCTURE

• JOB CONTROL USES <job_id> AS IT RELATES TO PGID MOVE JOBS BETWEEN FOREGROUND AND

BACKGROUND COMMANDS

fg bg suspend (OUTPUT TO TERMINAL) jobs (LISTS CURRENTLY ACTIVE JOBS) kill (TERMINATES JOBS) ctl-z (SUSPENDS CURRENT FOREGROUND

JOB)

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EXECUTE & TERMINATE PROCESSES

• JOB CONTROL COMMANDS START A COMMAND IN THE BACKGROUND$ find / -name a.out –print > files_to_remove 2>dev/null &[1] 1287$ ls -lR / > system_list 2>dev/null &[2] 1288$ du -s /usrs1/* > disk_usage &[3] 1289

• STOP OUTPUT TO THE TERMINAL + SUSPEND JOB SUSPENDS JOB WHEN TRIES TO WRITE TO TERMINAL$ stty tostop

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EXECUTE & TERMINATE PROCESSES (contd)

• USE OF JOB CONTROL FUNCTIONS USING JOB NUMBER MOVE TO FOREGROUND

$ fg %1

SUSPENDS ONLY A FOREGROUND JOB$ [ctl-z]

USING JOB NUMBER RETURN JOB 1 TO BACKGROUND $ bg %1

WHEN JOB ENDS NORMALLY GET $ [2]- Exit 1 ls -lR / > system_list 2>dev/null

WHEN JOB NEEDS TO BE KILLED MANUALLY USE <job_id> $ kill %2[1] + Terminated ls -lR / > system_list 2>dev/null

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• kill <pid> or <job_id>Pid SPECIFIES THE PROCESS THAT THE OS IS TO KILLTHE RESULT IS NOT REVERSIBLE.

$ kill 154339$ kill %1

TERMINATE PROCESSES

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DAEMON IN UNIX

• SCRIPTS THAT LACK TERMINAL CONTROL $ lpsched

$ mail, mailx, cron

• ps –e SHOWS cron DAEMON RUNNING.• PROGRAMS INVOKED BY LAUNCHING A SHELL

OR SUB-SHELL SHELL SCRIPTS SUB-SHELL READS & EXECUTES EACH STATEMENT IN

SCRIPT

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SCHEDULE A PROCESS TO RUN AUTOMATICALLY

• cron vs crontab cron

KERNEL STARTED DAEMON STARTED EACH MINUTE TO EXECUTE WHAT IS IN A USER’S

crontab FILE crontab

TAKES AS INPUT A USER EDITED FILE USED TO INSERT JOBS TO BE EXECUTED BY cron DAEMON crontab –r (REMOVES CONTENT FROM A

USER’S crontab FILE) crontab –l (LISTS CONTENT OF USER’S

crontab FILE) crontab <file> (LISTS CONTENT OF USER’S

crontab FILE)

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SCHEDULE A PROCESS TO RUN AUTOMATICALLY (contd)

• CRONTAB file’s entry syntax:minutes, hours, days of month, month, days of week, command

o MINUTES: 00 TO 59, CAN BE EXPRESSED AS A RANGE E.G., 00-15, or 0,15,30,45

o HOURS : 0 TO 23, # of hourso DAY IN MONTH: 0 TO MAX # DAYS IN MONTHo MONTH: 1 TO 12o DAYS OF WEEK: 0 TO 6, WHERE 0=SUNDAYo USE ASTERISK (*) TO INDICATE ALLo USE COMMA (,) TO INDICATE A SET OF VALUESo USE HYPHEN (-) TO INDICATE A RANGE OF VALUES

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SCHEDULE A PROCESS TO RUN AUTOMATICALLY (contd)

• EXAMPLES OF ENTRIES IN A crontab FILEminutes, hours, days of month, month, days of week, command

00-10 17 10,20,30 * 1,3 find / -newer .last_time -print >backuplist

(EXECUTE THE COMMAND EITHER 3 DAYS OF THE MONTH OR MONDAY AND WEDNESDAY OF EACH MONTH)

55 17 * * 4 find / -newer .last_time -print >backuplist

(EXECUTE THE COMMAND EVERY THURSDAY AT 5:55 PM) 0,30 * * * * find / -newer .last_time -print >backuplist

(EXECUTE THE COMMAND EVERY 3O MINUTES ON THE HALF HOUR)

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• UTILITY FOR ONE TIME EXECUTION at <time> - SAME DATE, FORMAT hhmm OR hh:mmat –t <time2>- SCHEDULED, FORMAT [[CC]YY]MMDDhhmm[.SS]

$ at 15:08at> empawk2.sh > rep.lst

at –l - LISTS ITEMS IN “at” QUEUEat -r <job_id> - reMOVES ITEM FROM “at” QUEUEat –m <time>

• EXECUTE AS A BATCH JOB IN “at” QUEUE BATCH JOBS ARE RUN WHEN RESOURCE UTILIZATION LEVELS ARE

LOW, HAVE LOWER PRIORITY THAN USER FOREGROUND JOBS SUBMITS JOB TO RUN IN BATCH QUEUE

batch < empawk22.sh

SCHEDULE A PROCESS TO RUN AUTOMATICALLY (contd)

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SUMMARY

• PROCESS CYCLE WHAT PARENT OR CHILD CAN DO WHILE OTHER IS RUNNING

• PROGRAM STATUS COMMAND• RUNNING A PROCESS

BACKGROUND FOREGROUND TERMINATE A PROCESSES

• CRON AND RELATED COMMANDS