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itec 400 Unix Processes

itec 400 Unix Processes. George Vaughan Franklin University. Topics. What is a process? Life cycle of a process Process States Monitoring Processes Signals Managing Processes cron Utility. Unix Processes. What is a process? an executing program that has its own address space.

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itec 400 Unix Processes

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  1. itec 400Unix Processes George Vaughan Franklin University

  2. Topics • What is a process? • Life cycle of a process • Process States • Monitoring Processes • Signals • Managing Processes • cron Utility

  3. Unix Processes • What is a process? • an executing program that has its own address space. • Each process has its own unique ID (called the process id). • Every process (with very few exceptions) are created by a parent process

  4. User Processes • When you log into a Unix/Linux system, a shell process is started on your behalf. • When you execute a command (like ‘ps’), another process is created for that command: >ps PID TTY TIME CMD 12325 pts/1 00:00:00 bash 12367 pts/1 00:00:00 ps

  5. User Processes • Assume you write a one-line script named ‘test01’: sleep 10 #my one-line script • When you run ‘test01’, 2 processes are created: • a new shell process is created which executes the script • a process is created to run sleep. Sleep runs within the context of the new shell - not the parent shell (login shell). • when your script ends, the script shell terminates • this means the parent shell (the login shell) won’t be affected by the script • Example (using 2 telnet sessions): PID TTY TIME CMD 1434 pts/0 00:00:00 bash <= Login shell from telnet #1 12594 pts/2 00:00:00 bash <= Login shell from telnet #2 12663 pts/2 00:00:00 bash <= Script shell from telnet #2 12664 pts/2 00:00:00 sleep <= sleep from script on telnet #2 12665 pts/0 00:00:00 ps <= ps on telnet #1

  6. What is a process? • Book’s definition: “A process is a single executable program that is running in its own address space.” • Note that a command may spawn other processes. • All user processes are descendents of init. • Typical of a single user to have more than one active process.

  7. What is a process? • Almost all system processes are descendents of init. • There are a few processes that are created ‘by hand’ during system startup. • In Solaris hand crafted processes are: • scheduler • init • pager • fsflush

  8. What is a process? • The kernel keeps track of process state information, such as: • address space map • current state of process • priority • process owner • list of open files • etc.

  9. Life cycle of a process • All processes are created from another process (i.e. all processes have a parent, except init). • Parent process creates a copy of itself using fork() - see manpage • In child copy, fork returns 0. • In parent copy, fork returns PID of child • This is how parent and child can tell who is who.

  10. 0001 #include <stdio.h> 0002 #include <sys/types.h> 0003 #include <unistd.h> 0004 0005 main() 0006 { 0007 printf ("PARENT: process ID is: %d, BEFORE fork()\n", getpid()); 0008 pid_t procID = fork(); 0009 if (procID != 0) { /* Am I the PARENT process? */ 0010 printf ("PARENT: process ID is: %d. ", getpid()); 0011 printf ("Sleep 30 sec...\n"); 0012 sleep(30); 0013 printf("PARENT: process just woke up\n"); 0014 } 0015 else { /* I must be the CHILD process */ 0016 printf (" CHILD: process ID is: %d. ", getpid()); 0017 printf ("Sleep 60 sec...\n"); 0018 sleep(60); 0019 printf(" CHILD: process just woke up\n"); 0020 } 0021 printf ("Process: %d has just terminated\n", getpid()); 0022 } Line 8: process forks into 2 processes Line 9: Test to see if we are the parent process Lines 10-13: This code is executed only by parent Lines 16-19: This code is executed only by child Line 21: This line is executed by both the parent and the child. OUTPUT (telnet session 1): >ex1000 PARENT: process ID is: 14028, BEFORE fork() CHILD: process ID is: 14029. Sleep 60 sec... PARENT: process ID is: 14028. Sleep 30 sec... PARENT: process just woke up Process: 14028 has just terminated CHILD: process just woke up Process: 14029 has just terminated OUTPUT (telnet session 2); >ps -u vaughang PID TTY TIME CMD 13295 pts/40 0:00 ksh 6704 pts/6 0:00 ksh 14032 pts/40 0:00 ps 14029 pts/6 0:00 ex1000  Child Process 14028 pts/6 0:00 ex1000  Parent Process 13281 pts/9 0:00 ksh 14001 pts/4 0:00 vi 6687 pts/4 0:00 ksh Example ex1000.c

  11. Life cycle of a process • The child process may then overwrite its own address space with the desired program using exec() - see manpage. • Although child runs new program, it does so within the inherited environment of the parent. • The child process will continue to run until it exits or is terminated. exit() - see man page • When a process ends, it sends a signal to parent process.

  12. 0001 #include <stdio.h> 0002 #include <sys/types.h> 0003 #include <unistd.h> 0004 0005 main() 0006 { 0007 printf ("ex1010 PARENT: process ID is: %d, BEFORE fork()\n", getpid()); 0008 pid_t procID = fork(); 0009 if (procID != 0) { /* Am I the PARENT process? */ 0010 printf ("ex1010 PARENT: process ID is: %d\n", getpid()); 0011 } 0012 else { /* I must be the CHILD process */ 0013 printf ("ex1010 CHILD: process ID is: %d\n", getpid()); 0014 execl("ex1020", (char *) 0); 0015 } 0016 printf ("ex1010 Process: %d has just terminated\n", getpid()); 0017 } ------------------------------------------------------------------ 0001 #include <stdio.h> 0002 #include <unistd.h> 0003 0004 main() { 0005 printf("ex1020 process ID is: %d\n", getpid()); 0006 } ex1010: Line 8: fork() occurs here Line 9: Check to see if I am parent or child Line 8-10: These lines are only executed by parent Line 12: process must be child Lines13-15: These lines are only executes by child Line 14: Child executes “execl()” which will now execute ex1020 ex1020: Line 5: print out that this process is now executing 1020 OUTPUT: >ex1010 ex1010 PARENT: process ID is: 14410, BEFORE fork() ex1010 CHILD: process ID is: 14411 ex1010 PARENT: process ID is: 14410 ex1010 Process: 14410 has just terminated ex1020 process ID is: 14411 How come we don’t see?: ex1010 Process: 14411 has just terminated ex1010.c and ex1020.c

  13. Fork Run-able Running Exiting Process States Ready exit Scheduled Deleted Parent Process Paused Waiting on Resource Resource Available Blocked (Sleeping) See last slide for References

  14. Process States • Fork Event: • A Process makes an exact copy of itself • New process inherits environment from parent • Child process has new PID • Child process has unique address space • The child overwrites address space with image of desired program. See exec().

  15. Process States • Run-able State: • This state represents a queue • All processes that are run-able are on the queue. • Many processes can be in the run-able state. • Run-able means that the process is not waiting for any resources • The process is just waiting its turn to become the “running process”.

  16. Process States • “Running” State • Process is executing in CPU • Only ‘n’ processes can be running on system with ‘n’ CPU's. • Process will remain in this state until: • Process exceeds CPU time-slice • if so, process moves to run-able state • Process needs resource to continue (I/O) • if so, process is moved to blocked state • Process is pre-empted by a higher priority process. • if so, process moves to run-able state.

  17. Process States • Blocked “Sleeping” State: • A process moves to this state when it is waiting for a resource • Many processes maybe in this state (queue). • Maybe waiting on I/O, page fault, etc.

  18. Process States • Exiting State: • A process moves into the ‘Exiting’ state when exit() is invoked. • Parent process is notified and parent acknowledges termination of child (see wait()). • Abnormal situations: • If a parent refuses to acknowledge termination of child process, the child process becomes a zombie process. • If parent process already terminated, grand-parent process adopts child process and acknowledges termination (Unix). • If parent no longer exists, kernel makes child a process of init - init then adopts and acknowledges termination of child process (Linux).

  19. Monitoring Processes • uptime >uptime 11:08pm up 16 day(s), 14:49, 58 users, load average: 3.46, 3.07, 1.77 • fields • current time • elapsed time the system has been up • current number of users • average number of job in the run-able state over the last 1, 5 and 15 minutes

  20. Monitoring Processes • ps - list active processes (Solaris [bsd version]) >/usr/ucb/ps aux | more USER PID %CPU %MEM SZ RSS TT S START TIME COMMAND rhodes06 25983 27.2 36.3 52776 8365008? R 23:00:47 14:16 a.out rhodes06 25980 27.0 33.7 52764 8338936? R 23:00:41 14:27 a.out rhodes06 25982 8.6 0.1 1448 904 ? S 23:00:47 4:47 a.out rhodes06 25981 8.4 0.1 1448 904 ? O 23:00:41 4:51 a.out rhodes06 25979 8.4 0.1 1448 896 ? S 23:00:41 4:32 a.out rhodes06 25984 7.8 0.1 1448 728 ? S 23:00:47 4:55 a.out • Fields: • USER: logname • PID: Process ID • %CPU, %MEM: percentage of cpu and memory used by processes • SZ: Total virtual memory size in pages • RSS: Resident Set Size (size resident in memory) in bytes • TT: Associated TTY line • S: process status (R=runnable, S=sleeping, O=active, Z=zombie, T=stopped) • TIME: cumulative cpu time

  21. Monitoring Processes • top - show top consuming processes (Solaris) >top | more last pid: 29652; load averages: 3.82, 3.73, 3.60 23:38:00 261 processes: 249 sleeping, 2 running, 8 stopped, 2 on cpu Memory: 1024M real, 15M free, 2934M swap in use, 341M swap free PID USERNAME THR PRI NICE SIZE RES STATE TIME CPU COMMAND 25983 1961 1 10 0 1027M 83M run 18:15 28.89% a.out 25980 1961 1 11 0 1027M 78M cpu/0 19:52 23.51% a.out 25984 1961 1 32 0 1448K 720K sleep 6:06 8.71% a.out 25982 1961 1 32 0 1448K 896K sleep 5:59 8.47% a.out 25979 1961 1 33 0 1448K 888K run 6:16 7.89% a.out • Fields • PID, USERNAME, SIZE, RES, STATE, TIME, CPU, COMMAND: nothing new • THR: # of executing threads in the process • PRI: prioirity • NICE: nice value

  22. Monitoring Processes • pstree - shows parent-child process relationships $ pstreeinit-+-atd |-cannaserver |-cpumemusage_app |-crond |-cserver |-deskguide_apple |-dhcpcd |-gconfd-1 |-gdm---gdm-+-X | `-gnome-session |-gnome-name-serv |-gnome-smproxy |-gnome-terminal-+-2*[bash] | |-bash---pstree | `-gnome-pty-helpe

  23. Signals • Process level interrupt • Can be used for: • inter-process commutation • user at terminal can send signals to kill, interrupt, suspend processes with special key strokes • signals can be sent with kill command • kernel can send signals on abnormal events (division by zero, invalid address, etc.) • More than 30 types of signals…

  24. Signals • Types of signals:

  25. Managing Processes • kill - kill a process: • user can kill process owned by user • root can kill any process • must specify PID • can specify signal level (e.g. kill -9 12345) • signal 15 is the default • see man page for more details…

  26. Managing Processes • Foreground process • process currently associated with keyboard. interactive process • Background process • a process that was kicked off with ‘&’ at end of command line • can have many background processes • to see active background processes, type: jobs • to bring background job to forground, type: fg %n (where n is the background job number - not PID).

  27. 0001 >cat bigJob 0002 while : ; 0003 do 0004 echo bigJob $1 is alive 0005 sleep 5 0006 done 0007 >bigJob John & 0008 [1] 5823 0009 >bigJob John is alive 0010 0011 bigJob John is alive 0012 bigJob Alice & 0013 bigJob John is alive 0014 [2] 5830 0015 bigJob Alice is alive 0016 bigJob John is alive 0017 bigJob Alice is alive 0018 bigJob John is alive 0019 bigJob Alice is alive 0020 jobs 0021 0022 [2] + Running bigJob Alice & 0023 [1] - Running bigJob John & 0024 bigJob John is alive 0025 bigJob Alice is alive 0026 bigJob John is alive 0027 bigJob Alice is alive 0028 kill %1 0029 [1] - Terminated bigJob John & 0030 bigJob Alice is alive 0031 jobs 0032 [2] + Running bigJob Alice & 0033 bigJob Alice is alive 0034 fg %2 0035 bigJob Alice 0036 bigJob Alice is alive 0037 bigJob Alice is alive 0038 ^D Managing Processes

  28. Managing Processes • nohup • “no hang-up” • a mechanism for running a program, even if you want to logout. • Usually used for large programs • Example: nohup bigJob & • Automatically invokes “nice”

  29. Managing Processes • nice • A method of running a command that may be cpu intensive that will be friendly to other processes. • Affects (lowers) process priority. • Can be used with foreground and background jobs • nohup automatically invokes nice.

  30. Managing Processes • at • a method for specifying a command or script to be executed at a specific time. • Used for “one-shot” scheduling. • For repetitive tasks, use crontab. • example: at 4am < myFile

  31. cron Utility • A Unix facility to schedule repeating tasks (scripts) • cron command starts crond deamon. • crond reads crontab file. • A unique crontab file is created on a per user basis.

  32. cron Utility • Format of crontab entry minutes hours day-of-month month weekday command

  33. cron Utility • Create file with entries • Use crontab to install entries • Use crontab -l to check entries 0001: $ cat cronfile 0002: 0,5,10,15,20,25,30,35,40,45,50,55 * * * * date >> ~/trash/output 0003: $ crontab cronfile 0004: $ crontab -l 0005: # DO NOT EDIT THIS FILE - edit the master and reinstall. 0006: # (cronfile installed on Tue Feb 25 21:52:24 2003) 0007: # (Cron version -- $Id: crontab.c,v 2.13 1994/01/17 03:20:37 vixie Exp $) 0008: 0,5,10,15,20,25,30,35,40,45,50,55 * * * * date >> ~/trash/output

  34. cron Utility • check output for progress • remove crontab entries • check removal with crontab -l 0012: $ cat output 0013: Tue Feb 25 21:55:00 EST 2003 0014: Tue Feb 25 22:00:00 EST 2003 0015: Tue Feb 25 22:05:01 EST 2003 0016: Tue Feb 25 22:10:00 EST 2003 0017: $ crontab -r 0018: $ crontab -l 0019: no crontab for gvaughan

  35. cron Utility • Look at cron log (must be root) 0021: tail /var/log/cron 0022: 0023: Feb 25 22:15:00 localhost CROND[3002]: (mailman) CMD (/usr/bin/python -S /var/mailman/cron/gate_news) 0024: Feb 25 22:15:00 localhost CROND[3003]: (gvaughan) CMD (date >> ~/trash/output) 0025: Feb 25 22:15:41 localhost crontab[3013]: (gvaughan) DELETE (gvaughan) 0026: Feb 25 22:15:46 localhost crontab[3014]: (gvaughan) LIST (gvaughan) 0027: Feb 25 22:16:01 localhost CROND[3020]: (mailman) CMD (/usr/bin/python -S /var/mailman/cron/qrunner)

  36. References • http://rabbit.eng.miami.edu/class/een521/processstates.html • http://jan.netcomp.monash.edu.au/OS/l8_2.html • Essential System Administration, Aeleen Frisch, 2002 • Linux Administration Handbook, Evi Nemeth, et. al., 2002 • The UNIX Programming Environment - Kernighan and Pike, 1984 • The Design of the Unix Operating System - Maurice J. Bach, 1986

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