Lecture 7 Unix Processes

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Lecture 7Unix Processes
CSCE 510 Systems Programming

• Topics
• Tsearch revisited
• Gcc
• Ar implementation
• make
• Time functions

September 6, 2005
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• Last Time
• File times
• Ar archive formats
• Tsearch (Example tsearch.ex.c)
• Ar implementation
• Last Times Slides that we did not get to
• Make (briefly today)
• Time functions (Example time.c)
• Today
• Processes
• Gnu Debugger

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Time.c

• include lttime.hgt
• include ltstdio.hgt
• main()
• time_t now
• struct tm bdtime, bdt_ptr
• char buf1024
• now time(NULL)
• printf("the number of seconds since the Epoch
  is ld\n", now)
• printf("the current time is s\n",
  ctime(now))
• bdt_ptr localtime(now)
• strftime(buf, 1024, "a b d H m j y u
  Z", bdt_ptr)
• printf("s\n", buf)

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User and Group IDs (UIDs, GIDs)

• /etc/password
• /etc/group
• root user ID 0 ( superuser)
• man -k userid
• man -k groupid
• man -k group grep name

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Process IDs

• Process IDs unique identifier that identifies
  the process
• start low and get larger as machine stays up
  longer
• Start over on reboot
• All processes except for one or two are created
  by fork (vfork) system call
• pid
• ps
• fixed PIDs
• process 0 - scheduler
• process 1 - init
• process 2 -

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Creating Processes

• fork

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Process Terminology

• parent, child
• orphan
• exit status of a child check by parent using
  system call wait
• zombie

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PID syscalls

• PID syscalls
• getpid()
• getppid()

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Group ID Functions

• Group IDs getgid(), getpgid()
• supplementary groups
• setgroups(int ngroups, int gidset)
• int getgroups(int gidsetsize, int grouplist)

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• Effective, real, saved UID
• int setuid(uid_t euid)
• set uid,gid on exec

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Memory layout of Unix Processes

• arguments to main
• environment
• stack
• heap
• bss -
• initialized data
• text segment

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Dumping pointers

• dumpaddr(char label, void address)
  fprintf(stdout,"p s\n", address, label)
• dumpaddr("Global addresses global", global)

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Example printargs.c

• / This example shows how to access command line
  arguments /
• include main(int argc,char argv)
• int i
• for(i0 i lt argc i)
• printf("argvd""s""\n", i, argvi)

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The Environment

• Environment
• argv style list of strings of the form
  "namevalue"
• extern char environ

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Example printenv.c

• / This example shows how to access environment
  variables /
• include extern char environ
• main()
• char p
• for(penviron p ! NULL p)
• fprintf(stderr,"s\n", p)

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Environment manipulation functions

• char getenv(name)
• setenv(name, value, overwrite)
• void unsetenv(name)
• int putenv (string)

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Notes on Environment Functions

• putenv- removes old entry if it exists
• setenv-does not remove old entry if overwrite 0
  
• What happens when we try to stuff in a longer new
  value?
• What happens when we try to add a new name?

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Standard fork Skeleton

• Creating new processes fork
• Standard fork Skeleton
• if((p fork()) lt 0)
• / error /
• else if (p 0) / child process code /
• else / parent process code /

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• Fork example parentChildren.c
• include
• main()
• int pid, pid2, status
• if ((pid fork()) lt 0) fatal("Cannot fork")
• else if (pid 0) / Child code /
• printf("Child code\n")
• if ((pid fork()) lt 0)fatal("Cannot fork")
• else if (pid 0) / Child of Child code /
• printf("Child of Child code\n") sleep(1)
  exit(30)
• else / Parent of Child code /
• printf("Parent of Child code\n") sleep(5)
  exit(31)
• else / Parent Code /
• while( pid2 wait(status) gt 0)
• printf("\n pidd \n return value d \n status
  4x, status
• shiftedd\n", pid, pid2, status, statusgtgt8)
  

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• vfork
• wait4
• Exec family

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