scis.regis.edu ● scis@regis.edu

CS 468: Advanced UNIXClass 4

Dr. Jesús BorregoRegis University

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Topics

•Controlling Processes•Periodic Processes•Process Management•Q&A•Midterm

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Process

•A running program•Used to control resource allocation by the

OS•When a process is created, a table is

made in a Process Table•Process consists of address space and

memory pages allocated to the process•Address space has code, variables, stacks,

virtual memory pointers, and other data

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Processes

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A process can be defined as:

Source: Operating Systems: Internals and Design Principles (7th. Ed.) by William Stallings

Process data structures

•Address space map for process•Process state•Execution priority•Resources allocated and in use•File descriptors and network ports used•Process signal mask•Process owner

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Processes

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Threads

•Created by a fork in a process•Inherits from parent•Can have multiple threads executing

concurrently•Multicore and multiprocessor systems

benefit multithreading

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Attributes

•PID – unique process ID•PPID – parent PID•UID – user ID; who created the process•EUID – effective UID – reflects resources the

process can have; same as UID in most casesGID – group ID

•EGID – effective GID•Niceness – how the process interacts with

others•Control terminal – linkages to standard I/O

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Process lifecycle

•Created with fork•Process execution begins with exec•Process terminates with a call to exit

▫Provides return code (0 is success)▫Parent receives return code to

acknowledge child’s death•If parent dies first, child is “adopted” by

init

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Signals

•Interrupt request for processes•Can be used to communicate among

processes•Can kill, interrupt, or suspend processes•Can be originated by kernel when

unhandled exceptions occur•When received, a handler is called (if

handler is defined); otherwise, kernel takes action

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Kill signal

•Used to terminate a process•Can be used by normal users to kill their

own processes•Root access is required for other

processes•Kill receives a signal, a numeric value

(see previous slide)•In some systems, killall terminates init –

system shutdown

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Monitoring processes•To monitor processes:

ps•Shows PID, UID,

priority, control terminal

•Can include memory used, CPU utilization, status

•See example of ps aux on page 131

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Dynamic Monitoring

•ps captures a snapshot of the system▫At that particular time

•top – top processes using the system every 10 seconds (default)

•topas – AIX version•prstat – Solaris version

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/proc File System

•The /proc directory contains information about the system state

•The kernel creates the directory•Information is organized by

subdirectories named by the PID▫/proc 1 is the init process directory

•Predefined directories are shown in Table 5.7 (next slide)

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Tracing signals and system calls•Linux provides visibility into a process

with strace▫Shows every system call and every signal

received•Similar: truss (AIX, Solaris), and tusc

(HPUX)•Example of strace is shown on page 137

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Scheduling Commands

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•To schedule scheduled processes: cron daemon

•Starts when system boots up and terminates when shutdown

•Receives configuration files (crontab) with commands and times to execute▫User crontabs located /var/spool/cron▫One for root, up to one per user

•Executes lines with sh

crontab File Format

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•#comments•Six field line:

▫Minute, hour, day of month, month, weekday (separated by white space)

▫Command (passed to shell in entirety)•% represent new lines

▫Command receives characters up to first %

Time Formats

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•* - wild card•Single integers – matches exactly•Two integers separated by dash – range•Ranges followed by slash and step:

▫1-10/2 1 to 10, in 2 increments•Comma separated list of values

35 10 * * 1-3 10:35 am Monday to Wednesday

crontab Management

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•To create or replace your user’s crontab:crontab filename

•To check out crontab and edit:crontab -e

•To list contents of crontab:crontab -l

•To remove crontab:crontab –r

•Roots can add username to above

Applications of cron

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•Preinstalled: ▫Daily scripts in /etc/cron.daily▫Weekly scripts in /etc/cron.weekly

•Reminders: periodic tasks•Filesystem cleanup

▫Removing obsolete files•Network file synchronization•Log file cleanup

Process Management

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•Kernel controls process access to RAM and CPU:▫Scheduler – allocates CPU time to a

processes, based on scheduling algorithm▫Memory Manager – allocates memory

space to each process and protects it from external source access

CPU Utilization

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Scheduling of processes

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Source: Operating Systems: Internals and Design Principles (7th. Ed.) by William Stallings

Executable file layout

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Magic Number and Main Header

Section One Header

Section Two Header

Section One

Section Two

First Processes

•PID 0 (sched) – created at boot•PID 0 executes fork and exec twice to

create processes 1 (init) and 2 (pageout)

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Process 1

fork/exec fork/exec

process 48 process 12

process 34

fork/exec

Process States

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RunningZombie

dRunnabl

eIdle

Sleeping

Suspended

Initialize

Signal Signal

Exit

Wait on Event

EventOccurs

AllocatedCPU

Process Composition

•Code Area – executable portion of the process

•Data Area – static data used by process•Stack Area – Temporary data•User Area – Housekeeping process

information•Page Tables – Memory management

system

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User Area

•One per process•Accessible by the kernel•Fields included:

▫Signal handling record▫File descriptor record▫CPU access record

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Process Table

•One entry for each process•Created in kernel’s data region•Contain:

▫PID and PPID▫UID and GID▫Process state▫Location of code, data, stack, user area▫Pending signal set

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Midterm

•2 hour•Take home•Due by Friday midnight•Email in a Word document to

jborrego@regis.edu

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Questions?

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