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Review

Review. Please hand in any homework and practicals Vim Scripting Inter-device communication. Today. Folders review Paths review Services Processes BE SAFE TOMORROW May Day, May 1 st Check your schedules, no class after 5pm. Directory Structure.

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Review

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  1. Review • Please hand in any homework and practicals • Vim • Scripting • Inter-device communication

  2. Today • Folders review • Paths review • Services • Processes • BE SAFE TOMORROW • May Day, May 1st • Check your schedules, no class after 5pm

  3. Directory Structure • Linux is a ‘tree’ or ‘hierarchical’ directory structure (so is Windows) • http://www.linux4windows.com/Articles/linux_directory_structure.png

  4. Paths Again • The relative path has to reflect our new position • Where We AreRelative Path • /home/tom/documents text • /home/tom (~) documents/text • /home tom/documents/text • Does ‘Where We Are’ look familiar? • It’s the Absolute path • Why?

  5. Full Linux Directory Structure

  6. Directories • This is why paths are important (abs vs relative) • You need to know where you are and where you need to go to • /bin, /sbin, /usr/bin, /usr/sbin • All contain commands (programs/executables) • /dev • Short for ‘devices’ – hard drives, usb, cd/dvd, etc… • /etc • Config files for the system – we’ve already seen sudo & passwd files, also has web browser, groups, logging, program config files, etc…

  7. Directories, pt 2 • /home • Holds user files (akin to the folder that holds ‘My Documents,’ ‘My Music,’ ‘My Pictures,’ etc… in Windows) • /tmp • Temp directory, used to store temporary files • Always the first directory to get deleted – don’t store files here and expect them to stay • /var • Directory that holds ‘variable’ files that change during the normal running of a system • Log files in /var/log/messages (logs get added, etc…); email (/var/spool/mail); webserver/ftp

  8. Misc Directories • Those are the directories you should get to know first • Others are for more advanced topics/functions: • /boot – holds the ‘live’ kernel • /lib – library files for kernel, updates, programming, etc… • /root – root user’s home dir • /opt – folder for 3rd party applications • /usr – files shared between users • And more

  9. Paths And Access • Useful administration tasks • Checking /tmp • Viewing configuration files/settings • Creating and running scripts • Moving around • Looking through processes

  10. Scenario 1 • We want to look for failures on a device • Login • Check log (permissions locked) • Escalate privileges • Check log again • <demo>

  11. For Those Viewing Later • Login: student • Password: • [student@it136centos65vm ~]# cat /var/log/messages • Error: permission denied • [student@it136centos65vm ~]# sundillon • Password: • [ndillon@it136centos65vm ~]# sudo cat /var/log/messages | grep error • Password:

  12. Scenario 2 • Setting/changing a static IP • Google • Log in • Escalate • Vi • …and the new thing for today… • Restart the ‘service’

  13. For Those Viewing Later • Google ‘linux set static ip’ • /etc/sysconfig/network-scripts/ifcfg-eth0 • Login: student • Password: • [student@it136centos65vm ~]# sundillon • Password: • [ndillon@it136centos65vm ~]# cp /etc/sysconfig/network-scripts/ifcfg-eth0 backups/ • [ndillon@it136centos65vm ~]# sudo vi /etc/sysconfig/network-scripts/ifcfg-eth0 • Inside vi, set IPADDR, BOOTPROTO, MASK, GATEWAY, and save and quit • [ndillon@it136centos65vm ~]# sudo /etc/init.d network restart • [ndillon@it136centos65mv ~]# ip eth0

  14. Summary • 1) Know what you’re doing • Modifying a config file? • Checking system resources? • 2) Know what resources you’re working with • And where they are • IP address? Files? /tmp? HDD (SAS/SATA or IDE)? • 3) Have a good tutorial • Different tutorials will explain it different ways • Figure out which ways work best for you (graphical, text, video, etc…)

  15. Questions on Paths? • When you log into a system you’ll be in /home/<username> • From there you can access things through the relative path or through the absolute path

  16. Processes and Users • A process is an action or job for the computer to do • Either persistent (goes on for a while – ‘run a shell’), or immediate (‘list the files in this directory’ = ls) • When the first is run, the shell is started, and stays there until we force it to exit • In the second, the ls is run and it’s done • The ps command shows the processes running on the system at that exact moment

  17. Most PS instances • ps –ef flags help show: • UID = user who started the job/process • PID = process id (this is used with other commands to specify a process to manipulate) • TTY – tons o'fun here – this is the ‘space’ in the system allotted to the specific user • Time – the time the command was entered • Command – the command (with options) that is currently running • LOT of info (will scroll off the screen)

  18. Output of ps • From liquidweb.com

  19. We can see what's running • And we can see it live! • The top command shows the 'top' running processes • Lots more useful info • And live, not just snapshot like ps • But also not to stdio (use q to quit) • This means its not useful in scripts

  20. Top Snapshot • (from: wikipedia article for top)

  21. Top Output • Type in top • Changes live, use the ‘q’ button to quit • Shows system information at the top – procs, memory, utilization, and more • Then shows live snapshot of system • PID = process ID, each process gets a number, numbers reset each boot, and increment (first process gets 1, second gets 2, third gets 3, etc) • Username = shows the user that started, and is running the command/utility • Nice = priority • Command = what was run to kick this off

  22. Processes Review • What is a limitation of the ‘top’ command? • What does ‘top’ show that ‘ps’ does not? • When is ‘ps’ more useful?

  23. Service • A service is a full application • So far we’ve done things that have used single processes • One running instance of the bash shell • One running instance of ps • Services are commonly used applications that usually encompass more than one process • Networking: IP address, ports, communication streams, etc…

  24. Manipulating Services • Services are controlled through the service command • [ndillon@it136centos65vm ~]# sudoservicessh start • If the SSH service is not running, it will start it • If it is running, nothing will happen • [ndillon@it136centos65vm ~]# sudoservice network stop • Will stop all network services (no internet connection of any kind) • [ndillon@it136centos65vm ~]# sudoservice apache restart • Will stop and then start the Apache web server • If Apache is off, it will just start it again

  25. Question on Services • Questions?

  26. Own Study • Folders review • SobellCh 4 – The Filesystem (81-89) • Paths review • SobellCh 4 – The Filesystem (81-89) • Processes • SobellCh 8 – The Bourne Again Shell (323)

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