Review Please turn in any homework/practicals you

may have Folders Paths Services Processes

Today

Jobs IDs Backgrounding

Runlevels Partitions HDDs

Process Actions (commands) executed on a server are

processes A process is a specific task to be completed Simple as ‘run ls’ or complicated as ‘listen for

TCP connection on port 80’ From the time the server/computer is booted,

each task is given a number This is the ‘process ID’ Starts counting at 1 and increments as soon as

a PID is assigned

System These all build to run our system

One process runs the clock One process runs authentication One process runs logging One process runs a shell One process runs …

Similarly grouped processes are ‘services’ Network: IP, port, protocol Web: data, specific port, specific protocol

Slow Processes We can run a process “in the background” Most of our commands have been quick

Our scripts too But what about when they’re not quick?

Timed Performance Testing ‘Burn-in’ SQL

Background Services run “behind” our shell, we can still type [root@it136introtolinux ~]# service network start Bringing up loopback interface [ OK ] [root@it136introtolinux ~]# Processes do not give shell back until they end If we know (or find out) something is going to

take a while, we can run it ‘in the background’ while we do other stuff

Example Setup Setup: A script that has one major command

line – sleep 100 This will take 100 seconds to execute, during

which we will not have the shell Finally, it prints to STDOUT “done” 1) We can stop a script (or command) and run it

in the background 2) We can start a script, pause it, and move it to

the background

sleep_script.sh So what does it look like?

Move it to the Background So if I’ve run my sleep_script.sh, and I see it’s

taking forever, I can move it to the background Press ctrl+z – this will stop the job and give me

a shell back It will also tell me the ‘job number’ This is NOT process ID – this is job number Process ID (PID) is a unique number given by

the system Job number (job) is relative to the shell and the

number of jobs running in your user’s shell

Moving Pt 2 Job number is in [1] – this is job number 1 Also, it’s stopped/paused right now So we can use that to move it to the

‘background’ and restart it We use the bg command bg <job> bg 1 Then we can use the fg command to get it back

if we need to fg 1

Example [student@it136centos58vm ~]$ ./sleep_script.sh ^z [1]+ Stopped ./sleep_script.sh # The above is ‘paused’ – still taking up

resources, but not running/consuming more [student@it136centos58vm ~]$ bg 1 [1]+ ./sleep_script.sh & # Now it’s running again [student@it136centos58vm ~]$ fg 1 ./sleep_script.sh

Finishing If the job completes while in the background we

get a nice message: [student@it136centos58vm ~]$ cd ~ [1]+ Done ./sleep_script.sh (wd: ~) (wd now: ~) It told us it finished elsewhere Or, if we’ve pulled it back to the fg, our shell

comes back [student@it136centos58vm ~]$ fg 1 ./sleep_script.sh [student@it136centos58vm ~]$

Starting in Bg [student@it136centos58vm ~]$ ./sleep_script.sh & [1] 21251 What is 21251?

How do I check to see if we’re right on what 21251 is?

Starting in Bg 2 [student@it136centos58vm ~]$ ps -ef | grep -i

sleep_script.sh student 21251 21017 0 12:59 tty1 /bin/bash ./sleep_script.sh student 21258 21017 0 13:00 tty1 grep -i sleep_script.sh

It’s the PID Now we can call it in bf/fg or kill/nice

Questions on Background?

Runlevels

Control how many and which processes start on boot

A way to reference the system state once the ‘default’ scripts have run

7 total Numbering starts at 0

Runlevels Listed

0 – Off 1 – Single User Mode 2 – Multi-User Mode (Limited) 3 – Multi-User Mode w/Networking 4 – Reserved 5 – GUI 6 – Reboot

0-1 Explained 0 – Off

service network stop There are ‘stop’ scripts that tell them how to stop

‘gracefully’ Turn EVERYTHING off Runlevel 0 runs these ‘off’ scripts for the whole

system 1 – Single User Mode

‘Recovery’ mode Only the ‘base’ for what is needed to boot You have to load other things yourself

Why I Hate Ubuntu (Pt 1)

• Runlevel 2 – Multi-user Mode

• Does not configure network (and other stuff)

• Oh, right, except for Ubuntu

• Runlevel 3 – Multi-user w/Networking

• Wikipedia: “Starts the system normally”

• We boot into runlevel 3

• Runlevel 4 – Reserved

• Runlevel 5 – Runlevel 3 w/GUI

• Runlevel 6 – Reboot

What’s Going On?

• Switch levels through the ‘init’ command

• This will go through a reboot

• “Init” or initialization scripts set up how the system is configured

• Configured…config…

• Where do you think these scripts are located?

/etc/init.d• The scripts in /etc/init.d are linked to the folders

• /etc/rc0.d

• /etc/rc1.d

• /etc/rc2.d

• /etc/rc3.d

• /etc/rc4.d

• /etc/rc5.d

• /etc/rc6.d

• Look familiar?

• The system calls each script in each folder a certain way

/etc/rc3.d (for example)

• Holds scripts starting with S and K

• S is ‘start’ script

• /etc/rc3.d/S08iptables

• K is ‘kill’ script

• /etc/rc3.d/K74ipsec

• Numbered 00-99

• S01sysstat-S99local

• Lower numbers are run first & case sensitive

Questions On Runlevels?

• Runlevels

• Set what automatically starts (or stops)

• 0-7 (8 total)

• Scripts are called in a certain way (shutdown vs kill)

One Last Note

• Partitions

• A ‘partition’ is a physical divider

• A Linux partition is a section of a physical hard drive (hdd)

• You set it for a physical maximum size, and the system can’t exceed that maximum

• What happens if all data is in one cup (say it’s dyed blue), and this firehose just blasts neon green at the cup

• What happens to the blue?

Record Player

• “I’m too old for this” – Danny Glover, Lethal Weapon

• This may be an ancient reference, but it holds up the best

• A record player

• Needle running across it (head)

• Data is song

• Tracks are sectors

Reference

Partitions 3

So we can think of partitions as the colored areas

Yellow is our / partition, red is our /swap, blue is our /var, black is our /home, and white is our application (/opt or /var/www or….)

Keep in mind that they all take up 2 circles, but the outside circles are bigger

Partitions

The df command shows free space on our system

To create a partition on a new hdd use

fdisk –l <drive> #that’s a lowercase L

File Systems Table

• Use the mount command to set a drive for use

• mount /dev/<drive> /<location>

• mount /dev/sdc /nfsshare1

Why Best Practice Rocks• Went to ‘DefCon’ with old IDS admins

• They missed over half the trip because they had to continuously deal with these failures

• I took over the IDS systems

• I demanded the vendor partition the system w/best practice (among other things)

• /var filled, system still ran

• I stopped waking up at 2am

• My last 6 months I had one device failure

• It was a hardware failure, not a system failure

Questions on Partitions• df

• Show ‘disk file’ usage – how much room on which partitions

• fdisk -l /dev/sda

• Use fdisk tool to list partitions on that hard drive

• mount /dev/sda /mnt

• Make /dev/sda usable via the /mnt folder

• /etc/fstab

• File systems table – file that holds system partition info

Own Study

• Jobs

• Job IDs – Sobell, Intro (p60), more (p130), p323

• Backgrounding – Sobell, Chapter 5 (p146)• Job Control P294

• Runlevels – Sobell, Startup Files (p278)

• Partitions & HDDs

• http://www.yolinux.com/TUTORIALS/LinuxTutorialAdditionalHardDrive.html