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OPS235 Lab 4 - CentOS7

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[[Category:OPS235]]

{{Admon/caution|THIS IS AN OLD VERSION OF THE LAB|'''This is an archived version. Do not use this in your OPS235 course.'''}}

=LAB PREPARATION=

=== Part 1: How do we Manage System Services? ===

We have seen that maintaining unneeded '''packages can be a security risk''' due to the unnecessary increase in the complexity of your system. Similarly, it is also unnecessarily hazardous, and even more so, to leave unneeded services running. In this investigation, we will learn how to '''control services, and turn off those services that we think are not necessary to help reduce security risks'''.}}

#Use your '''centos2''' VM for this part.

<li>Note the services that are currently running.</li>

<li>Use the command <code>service iptables stop</code> to stop the service named '''iptables'''</li>

<li>Run a command to verify that the '''iptables''' service has stopped. '''NOTE:''' Although the service command seems to work, it is '''deprecated''' (i.e. "out-dated:). It has been replaced by using the [http://zenit.senecac.on.ca/wiki/index.php/Init_vs_systemd#systemd_Command_Usage systemctl] command. This is a command based upon a newer method of starting and managing system services called [http://zenit.senecac.on.ca/wiki/index.php/Init_vs_systemd systemd ] (which replaces init - the "initialization table"). This method allows services to run more independently of each other, so that a service may be stopped without other dependent services to be stopped as well. The most ~~popular~~ common '''systemctl ''' commands are shown below (it is optional to include the filename extension '''.service''' after the service-name):<ul><li>'''systemctl list-units --all'''   (get a listing of all service names. Can pipe to grep to list service you are interested in)</li><li>'''systemctl status service-name'''   (Confirm status of a service - running or not-running)</li><li>'''systemctl stop service-name'''   (stop a service)</li><li>'''systemctl start service-name'''   (start a service)</li><li>'''systemctl restart service-name'''   (restart a service)</li><li>'''systemctl enable service-name'''   (enable service so service runs upon system startup)</li><li>'''systemctl disable service-name'''   (disable service so it does NOT run upon system startup) </li></ul></li>

<li>If you reboot now - the iptables service will be turned back on. We don't want it on though, it causes students headaches. To turn it off permanently we need to use the '''systemctl''' command:<code>systemctl disable iptables</code> (the '''chkconfig''' command used to be the way to enble/disable services, but is now deprecated).</li>

<li>Use the '''systemctl''' command to verify that the '''iptables''' service is no longer running ('''hint:''' issue command, and pipe to grep "'''iptables'''").

'''Answer Part 1 observations / questions in your lab log book.'''

===Part 2: How do we Manage Runlevels?===

|- valign="top"

|

{{Admon/tip|Bash Shell Scripting Tips:| <ul><li>'''The case statement:''' The case statement is a control-flow statement that works in a similar way as the if-elif-else statement (but is more concise). This statement presents scenerios or "cases" based on values or regular expressions (not ranges of values like if-elif-else statements). After action(s) are taken for a particular scenerio (or "case"), a break statement (''';;''') is used to "break-out" of the statement (and not perform other actions). A default case (*) is also used to catch exceptions. '''Examples (try in shell script):''' ''read -p "pick a door (1 or 2): " pick case $pick in   1) echo "You win a car!" ;;   2) echo "You win a bag of dirt!" ;;   *) echo "Not a valid entry"      exit 1 ;; esac'' ''read -p "enter a single digit: " digit case $digit in   [0-9]) echo "Your single digit is: $digit" ;;          *) echo "not a valid single digit"              exit 1 ;; esac'' </li><li>'''The getopts function:''' </li></ul>The getopts function allows the shell scripter to create scripts that accept options (like options for Linux commands). This provides the Linux administrator with scripts that provide more flexibility and versatility. A built-in function called '''getopts''' (i.e. get command options) is used in conjunction with a '''while''' loop and a '''case''' statement to carry out actions based on if certain options are present when the shell script is run. The variable '''$OPTARG''' can be used if an option accepts text (denoted in the getopts function with an option letter followed by a colon. Case statement exceptions use the ''':)''' and '''\?)''' cases for error handling. '''Example of getopts''' (try in script and run with options) ''while getopts abc: name do   case $name in     a) echo "Action for option \"a\"" ;;     b) echo "Action for option \"b\"" ;;     c) echo "Action for option \"c\""         echo Value is: $OPTARG" ;;     :) echo "Error: You need text after -c option"         exit 1 ;;     \?) echo "Error: Incorrect option"         exit 1 ;; esac'' done }}

|}

for x

do

mail -s "Server Account Information" $(echo $x | cut -d":" -f3) <<+

Here is your server account information:

servername: myserver.senecac.on.ca

username: $(echo $x | cut -d":" -f1)

password: $~~(date | md5sum | cut -d" " -f1)~~userPassWd

Regards,

IT Department

Chris.johnson

Bureaucrats, Administrators

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OPS235 Lab 4 - CentOS7

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