Processes

• • •

Objectives

–

to become familiar with Unix processes Contents

– – – – – – –

processes & daemons Nice levels User limits System resources signals batch queues cron jobs Practicals

–

to run and control several Unix processes

•

Summary

The Unix Kernel

ksh chmod cron management who mail hardware file sysadm oracle processes pageout init

Programs & Processes

• •

A program is an executable file

–

for example:

/bin/bash –

a program may be executed by more than one process A process is an instance of a program being executed

– –

a process may execute more than one program during its lifetime for example:

mingetty  login  bash

•

SVR4 Unix supports three types of processes

– – – –

real time processes (always run before all others) system processes (run if no real time processes) standard processes each process category has its own priority levels

Daemons & Zombies

• •

Daemon processes provide system functionality

– –

detached from terminal stdout redirected to console or log file Zombies are completed processes

– –

still holding onto resources cleaned up when parent does a wait or exits

Key Attributes of a Process

• • • • •

Every process is identified by a unique number

–

its process id (pid) Every process has an owner and a group

–

the effective UID and GID define the processes access to the system The kernel allocates a control block for every process

– –

there is a finite number of these process control blocks an individual user can be restricted to just a few processes Each process uses memory

– –

code segment is read only and re-entrant data and stack segments are writeable The kernel uses a paged virtual memory system

– –

writeable memory pages may be paged out to the swap file code pages are discarded and reloaded from the executable program

Running Processes

• •

A fork is Unix terminology for creating a child process

– –

current process is duplicated to create the new child child has a different PID otherwise identical Exec replaces the current process with new program

– – –

usually done by a child process after a fork there is an

exec

command in the shell sometimes called "chaining"

$

ps

PID TTY TIME COMMAND 191 01 0:01 /bin/sh 207 01 0:00 ps $

exec ps

PID TTY TIME COMMAND 191 01 0:01 ps

bash ps

Login:

Checking on Processes

• •

Use the ps command to examine processes

-f -l -e -a -t

terminal

-u

user

full listing long listing every process all interesting process (ignores daemons, login shells) all processes attached to named terminal all processes owned by named user Key columns in output listings

PID

process ID

PPID UID TTY CMD S

parent process ID owning user controlling terminal command used to run process process state (

-l

listing only) R runnable, O on processor, S sleeping, Z zombie

Process priority

•

Nice-Levels

From –19 to +20 -19 highest priority (system choking) +20 lowest priority (wait for all other processes to complete)

• • •

Use the nice command to set priority to application

# nice –15 ls Will set nicelevel –15 to ls command

Use renice command to change priority to running process

# renice 10 422 Will change nicelevel to 10 for process 422

Getpriority & Setpriority

–

If you are programming C/C++

•

Mother and Child

–

If mother is changed all childs will inherent nice levels

User resources control

•

ulimit (User resource limits)

- shows a list of all current limits #

ulimit –a core file size

(blocks, -c) 0

data seg size file size

(kbytes, -d) unlimited (blocks, -f) unlimited

max locked memory max memory size open files pipe size stack size cpu time max user processes virtual memory

(kbytes, -l) 32 (kbytes, -m) unlimited (-n) 1024 (512 bytes, -p) 8 (kbytes, -s) unlimited (seconds, -t) unlimited (-u) 768 (kbytes, -v) unlimited

Setting ulimits

•

Set ulimit

– Systemwide is set in

/etc/profile

– On particular users in ~/.bashrc or ~/.bash_profile

– Controlled by PAM modules /etc/security/limits.conf – PAM limits description in README.pam_limit

Examples)

# Limits of physical memory:

ulimit -m 98304

# Limits of virtual memory:

ulimit -v 98304 Important Not all shells support ulimit directives. PAM (for instance,

pam_limits) offers comprehensive adjustment possibilities if you depend on encompassing settings for these restrictions.

System resources control

•

sysctl files

–

Adjust all kinds of kernel parameters SuSE config file: Direct config file: /etc/sysconfig/sysctl /etc/sysctl.conf

Memory filesystem:

–

/proc/sys reloading sysctl (the slow way)

# SuSEconfig -

show all parameters

# sysctl –a -

show all parameters, as a table!

# sysctl –A -

Load from /etc/sysctl.conf or other specified file

# sysctl -p /etc/sysctl.conf

-

you can also do an echo

# echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_all Look in /proc/sys for parameters!

Exercise - Looking at Processes

• •

Can you identify the daemon processes?

Can you follow the process tree for the ps command?

$

ps -ef

UID PID PPID STIME TTY TIME CMD root 1 0 09:22:31 ? 0:13 /sbin/init ...

root 42 1 09:24:45 tty1 0:00 ttymon root 47 1 09:25:03 ? 0:02 cron hawkeye 81 1 10:02:04 console 0:03 -ksh hawkeye 121 81 10:22:43 console 0:01 vi datafile hawkeye 101 81 10:18:00 console 0:02 make myprog hawkeye 122 121 10:23:01 console 0:01 ksh hawkeye 125 122 10:24:31 console 0:01 ps -ef

Signals

•

Signals are used to communicate with a running process

– – – –

processes define how to react to signals most signals ignored by default some cause process termination signals defined by name (or number)

•

Hardware related program faults also cause signals

– –

bus (memory) error divide by zero

•

System administrators usually use signals to eliminate a process

Sending Signals

•

Use the

kill

command to send signals

HUP (1) INT (2) QUIT (3) KILL (9) TERM (15)

terminal hang up (powered off) user pressed interrupt (^C) key user pressed quit (^\) key kill immediately (process cannot ignore and dies immediately) terminate program (default)

•

Users can only signal processes they own

#

ps -fu trapper

UID PID PPID STIME TTY TIME CMD trapper 92 1 10:02:04 tty1 0:03 -ksh trapper 97 92 10:18:00 tty1 0:02 myprog #

kill 97

#

ps -fu trapper | grep myprog

trapper 97 92 10:18:00 tty1 0:02 myprog #

kill -9 97

Intercepting Signals

•

The shell can respond to signals using the

trap

command trap 'echo Interrupt ignored' INT QUIT

when signal 2(INT)or signal 3 (QUIT) are received they will be ignored; instead the command in quotes, in this example the echo command, will be executed

trap 'echo Terminating shell; exit 1' TERM

the action to be performed can include more that one command, program or indeed shell script

trap '' 2 3 15

if no action is required when intercepting signals, leave the quotes empy, but do include them; otherwise you will reset trapped signals (as below)

trap INT QUIT TERM

reset the three trapped signals (from now on, when received will be acted upon again)

•

Traps are used mostly within programs and scripts

The at Command

• • • •

Execute commands at a specified time or run the commands on a batch queue Syntax:

at

time

[

date

] [

increment

]

batch

Commands are read from

stdin

When the job is run

– stdout

and

stderr

mailed to user

– stdin

is redirected to

/dev/null – –

the job inherits current environment commands are run using the Bourne shell

$

at 8:00 tomorrow echo "Meeting at 9:30 today" ^D

Listing and Deleting at Jobs

•

Use options to

at at -l [

job...

] at -r [

job...

]

list jobs remove jobs

•

Newer SVR4 commands

atq [

user

]

list at queue

atrm -a

user

atrm -i

user

remove all jobs for named user interactive query on removal

$

at -l

78653200.a at Thu Jul 27 08:00:00 1995 $

at -r 78653200.a

The crontab Command

• • • •

Use crontab to run jobs at periodic intervals List cron table with

crontab -l [

user

]

•

Edit current cron table with

crontab -e [

user

] – EDITOR

or

VISUAL

variable must be defined Commands specified in crontab include information to determine when to run the command

– –

Space/tab separated columns specify comma separated list or range of values Fields in a cron table specify: minute hour day month weekday command

Exercise - Using cron

• •

What programs are run on Thursday and what on Sunday?

Which programs generate mail messages?

# "@(#) root 1.6 89/05/29 " 17 5 * * 0 /etc/cleanup > /dev/null 0 2 * * 0,4 /usr/lib/cron/logchecker 0 3 * * * /usr/lib/cleantmp > /dev/null 20 1 * * * /usr/bin/calendar 0 8 * * 5 echo "Fill in timesheet today" 0 8 29 2 * echo "Happy Birthday" 11 1 * * 0 /home/system/bin/full.backup

11 1,13 * * 1-5 /home/system/bin/inc.backup

Administering at & crontab

• • •

Control files kept in

at.allow

at.deny

cron.allow

cron.deny

(queuedefs

/etc/

users allowed to use at users denied use of at (only used if no at.allow) users allowed to use cron users denied use of cron (only used if no cron.allow)

limits jobs in at & batch queues)

SuSE / RedHat standard cron jobs

/etc/ Add jobs to be executed hourly..monthly at will in: cron.d

cron.daily

cron.hourly

cron.monthly

cron.weekly

Yast update intervals

Daily cron jobs Hourly cron jobs monthly cron jobs weekly cron jobs crontab crontab maintanese

Awaiting jobs are kept in

/var/spool/ at*/ cron/

storage directory for at jobs storage directory for crontab files

Summary

• • • • • • •

The Unix kernel is responsible for the hardware interface and multi-tasking All other functionality is performed by processes Look at processes using

ps

Daemon processes provide standard functionality such as scheduling using

cron

Processes react to signals which can be sent with the

kill

command Administrators use

crontab

to schedule regular jobs such as backups Unix systems should be left running all the time to enable cron jobs to run overnight