Advance Database Technique Practicals MCa Idol | Practicals | Bhandup Shree Ram
Review Please turn in any homework/practicals you may have Folders Paths Services Processes.
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Transcript of Review Please turn in any homework/practicals you may have Folders Paths Services Processes.
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