CSE 265: System and Network Administration

Lab #5

Lots to do today: we practice using sudo and creating new users and groups, look at logging, and explore a new scripting language (Perl).

1. Sudo instead of su

   In lab #4, you learned how to resize a filesystem, resize a logical volume, create volumes, etc. Let's configure sudo to allow your regular account to have the ability to perform commands with root priviledges.

   Modify the sudo configuration file to include an entry for your account and to permit it to run commands as root. Verify that it works by executing sudo /sbin/fdisk -l /dev/sda to see the partitions defined on your hard drive.

   Now use sudo and lvrename to change the name of your lv_home logical volume to be named lv_swap2, so that the next person who looks at your logical volumes is not confused. Note that this means you'll also need to change /etc/fstab so that your system finds your new swap volume at next boot.

2. Managing accounts

   In this task, we explore how to manage user accounts.

   Create an account for a friend using useradd and passwd. Notice that it automatically created a home directory and a personal group in /etc/group. Look at the password you created in /etc/shadow to see whether it is md5 or not. How can you tell?

   Establish an account for me, called prof, with the specific password: $6$9lAKxQZj$1Agt39ynQJRY28OsnwM/Kh8omTqhix0CpdBg8gLIPnV7qL39gWftM6DqmM4duDfMgfCamD0Kt8EvRrbmTIV0n0 so that I can log in with a password that I know. Create a new entry in /etc/group for a new group, and add your personal account and the prof account to it. Verify that your account is now in two groups using the groups command.

3. Try out signals

   Start the firefox browser. From a shell, use ps aux to find the PID for firefox. Now use the kill command to stop the firefox process; what happens when you move the firefox window around or click on its menus? Now send it the continue signal, and notice that it recovers. This is essentially the same situation if you were to press ctrl-z at a shell that is currently running some program (like emacs) which then stops functioning (because it has been suspended).

4. Schedule a periodic job with cron

   Log in as root. Use crontab -e to create and edit a crontab file for root. Add a crontab entry that will run the uptime command every minute for today only, and capture the output by appending to a file in /var/log. For example,

   uptime >> /var/log/uptime.log

   Then save and quit your editor. Later in the lab, take a look to see the results in this log file.

   Look in /var/log/cron to see what cron has been doing. What scripts are run daily?

5. The tool /sbin/ifconfig can be used to configure or show the status of the network interfaces. The machines in the Sandbox lab are configured with two ethernet interfaces.

   One is typically attached to the departmental network. We usually leave the second empty, for use in the future for networking-specific exercises.

   Running ifconfig with no arguments generates a list of all network devices and their configurations. Note the list includes another device we have not mentioned -- the network loopback device, which is defined to be 127.0.0.1 for all systems, and is usually defined with the DNS name of "localhost". You can, for example, ping localhost with the same effect as pinging with the current name of your machine.

   Revise the local boot script from lab #3 to incorporate the output of ifconfig on every boot. (No, it doesn't need to be all on one line this time.)

6. Perl

   In this exercise, we will use the Perl scripting language to replace the logger(1) command. To start, try out the logger command by typing "logger hello" and then use tail on /var/log/messages to see your log entry.

   If you are unfamiliar with Perl, start by skimming through the section on Perl in chapter 2 of ULSAH. If you are uncertain of your programming skills, I suggest: Picking Up Perl. If you are more confident, try Perl in 20 pages.

   There is lots of Perl documentation online and there are multiple books on Perl in the Lehigh Safari e-book library.

   Now write a very simple Perl script that prints out the parameters given to it, like the echo(1) command. It should work like this:

   % ./echo.pl hello world
   hello world
   

   The following script will write the words 'hello world' to syslog, along with the PID of the logger.pl process. Modify it to write the contents of all parameters of the script instead (like the echo script above).

   #!/usr/bin/perl
   
   use strict;                              # compile-time checks
   use warnings;                            # enable run-time warnings
   
   use Sys::Syslog qw(:DEFAULT setlogsock); # library for syslog functions
   
   setlogsock('unix');                      # use a unix domain socket
   openlog("logger.pl", 'pid', 'user');     # register ourselves
   syslog('info', 'hello world');           # the syslog call
   closelog();                              # close the socket
   

   Verify that it works by running it and checking /var/log/messages.

   Challenge task (optional): modify your local boot script so that it extracts the IP address from ipconfig and adds it to the single line output (and ignores the rest of the ipconfig data). Then write a perl script that replicates the functionality of your improved local boot script.

7. Wrapping Up

   In order to sign the lab completion sheet when I get back, you will need to:
   1. demonstrate the use of sudo with lvs
   2. show me the output of groups prof
   3. tell me how you continued your stopped Firefox
   4. show me your /var/log/uptime.log file, and tell me what scripts are run daily by cron
   5. demonstrate your perl script by running it with a multi-word message and seeing the effect on /var/log/messages
   6. Show /var/log/network-startup.log containing ifconfig data

If you have time, you might start looking at Project #1 (due in two weeks).