3.1 Save your workIndex

You will create some minimal file system structure in your HOME directory on the CLS.

Most work will involve changes in your own Linux Virtual Machine running Centos 6.6. You can use the Checking Program to check your work as you go. You can check your work with the Checking Program as often as you like before you submit your final mark.

When you are finished, leave the files and directories in place on both the CLS and your own CentOS Virtual Machine as part of your deliverables. Do not delete any assignment work until after the term is over! Assignments may be re-marked at any time on the CLS; you must have your term work available on the CLS right until term end.

3.2 The Source DirectoryIndex

All references to the “Source Directory” below are to the CLS directory ~idallen/cst8177/14f/assignment09/ and that name starts with a tilde character ~ followed by a user name with no intervening slash. The leading tilde indicates to the shell that the pathname starts with the HOME directory of the account idallen (seven letters).

You do not have permission to list the names of all the files in the Source Directory, but you can access any files whose names you already know.

3.3 Searching the course notes on the CLSIndex

The previous term’s course notes are available on the Internet here: CST8207 GNU/Linux Operating Systems I. All the notes files are also on the CLS. You can learn about how to read and search these files using the command line on the CLS under the heading Copies of the CST8207 course notes near the bottom of the page Course Linux Server.

3.4 Review of CST8207 account managementIndex

Review your work from CST8207 GNU/Linux Operating Systems I:

• In this assignment you will need to remember how to use: passwd, useradd, userdel, groupadd, gpasswd, usermod, chown, chgrp, chmod, chsh
• CST8207 Modes and Permissions
• CST8207 Modes and Permissions assignment
• CST8207 Users and Groups
• CST8207 Users and Groups assignment

3.5 Review of CST8207 partitioning and filesystemsIndex

Review your work from CST8207 GNU/Linux Operating Systems I:

• In this assignment you will need to remember how to use: fdisk, mkfs, mount, /etc/fstab
• CST8207 Partitions and File Systems – fdisk, mkfs, mount, swap
• CST8207 Booting and GRUB – how to boot into single user mode.

3.6 Backup and Recovery on CentOSIndex

1. Take a snapshot of your virtual machine before you begin each section of this lab so that you can recover back to the snapshot if needed.
   • You can delete the unused snapshots if everything works well.
   • CentOS snapshots are very small and fast compared to your Windows snapshots; you can save lots of them.
2. Are you keeping an external backup copy of all your coursework (including your virtual machines) somewhere? You should be!

3.7 Use a remote login, not the VMware consoleIndex

I recommend that once you have booted your CentOS VM, you connect to it and work using a remote login session (e.g. ssh or PuTTY) where copy-and-paste works and where you can have multiple simultaneous connections into the VM. The VMware console is not friendly.

If you can’t get an SSH (PuTTY or ssh) connection working into your Linux VM, see the [Network Diagnostics] page.

Note that SSH sessions (and whatever you are doing inside them) do not survive across a VMware suspend. Make sure you save your editor files and exit your SSH session before you pause or suspend your virtual machine. (Editor sessions that run inside the VMware console do survive across suspend and resume, since they don’t depend on a network connection.)

Advanced users may look into the various virtual terminal programs such as tmux and screen that do allow you to suspend and resume your sessions even from a remote login.

4.1 CentOS: SnapshotIndex

1. Complete your CentOS Install and Configure.

2. Before you begin this assignment, create a snapshot of your CentOS Virtual Machine.

   • Enter a comment explaining where and when you took this snapshot.
   • You can restore back to this snapshot if anything goes wrong.

4.2 Set Up – On The CLSIndex

1. Do a Remote Login to the Course Linux Server (CLS) from any existing computer, using the host name appropriate for whether you are on-campus or off-campus.

2. Make the CLS directory ~/CST8177-14F/Assignments/assignment09

4.3 CentOS: Set Up – The Base Directory on CentOSIndex

1. In your own sysadmin account in your CentOS Virtual Machine, also make the CentOS directory ~/CST8177-14F/Assignments/assignment09 (the same hierarchy as you have already made on the CLS).

This CentOS assignment09 directory in your sysadmin account is the Base Directory for all pathnames in this assignment. Store your CentOS files and answers below in this sysadmin Base Directory.

Run the Fetch and Checking Program to verify your work so far.

4.4 CentOS: Creating a few new users “by hand”Index

You will use the standard account management tools to create a few ordinary (non-admin) accounts, just as you did last term. You will force password expiry so that the users must change their passwords when they first log in.

1. Log in to your CentOS system administration account, if necessary, and obtain root shell privileges using the sudo command, if necessary.

   • Your shell prompt should change from $ to include the # character that indicates root privileges.
   • Make sure you have the full root PATH that includes /sbin

2. Type whoami or id to confirm that you are the root user.

3. Take a VMware snapshot that you can return to if things go wrong.

   • Enter a comment explaining where and when you took this snapshot.

4. Create three new users by running the appropriate command three times:

   1. Usernames: user001, user002, user003
   2. Full Names (GECOS comment field): User One, User Two, User Three
   3. Verify that the new accounts appear in the password file and that the HOME directories all exist.
   4. Note that the new accounts have been given default hidden files from the /etc/skel/ directory.

5. Set different, good initial passwords for the three users.

6. Force these users to change their password upon first login.

   • Search the lecture slides for how to force passwd change on login.

7. Set their HOME directory permissions to be as follows:

   • the owner can do everything
   • group can search and read but not write
   • other users can do nothing (no permissions)

Run the Fetch and Checking Program to verify your work so far.

4.5 CentOS: Create many more users in bulkIndex

Few organizations create users manually. The batch newusers command (RTFM) can read a text file and create user accounts in bulk. In this section, you will be creating a text file suitable for input to the newusers command, then using newusers to quickly create almost a hundred new accounts.

1. Log in to your CentOS system administration account, if necessary.

   • Exit from the root shell, if you are running as root.

2. Type whoami or id to confirm that you are not running as root.

3. Take a VMware snapshot that you can return to if things go wong.

   • Enter a comment explaining where and when you took this snapshot.

4. On CentOS, create your Base Directory in which you will create the files and scripts resulting from the following tasks. (You already did this on the CLS; now do it here on CentOS.)

5. Copy the file userlist.csv from the Source Directory on the CLS to your CentOS Base Directory.

   1. Read about using the scp command in Unix/Linux SCP Command.
   2. Use the “preserves modification times” option to the scp command.
   3. You may find it useful to create an alias in your accounts that always uses the “preserve” option when you type the scp command name.
      • You may already have a similar alias defined for the cp command.
      • Make sure you define and save the alias on both the CLS and CentOS.

Imagine that the userlist.csv file was given to you from the Human Resources department by someone who created it with a spreadsheet.

Examine this file, and notice that it is in Colon-Separated-Value format. It is 98 lines: a header line and a username and a real name for each of 97 new users that need an account on your system.

The file contains five fields, separated by colons (:). Read the header line to know what the five fields are. (A real spreadsheet export would be separated by commas, but we’re making it easier for you.)

We need to create a text file suitable for batch input to the newusers command. Every line in the file we give to newusers must have the correct format: it must have the userid at the start and the seven colon-separated fields described at the top of the newusers man page.

The file given to us only has five fields, and it has a poor password set for all the accounts. We need to fix this file before we can feed it to the newsers command.

Note: If you read all the words in this section before you start working, you will save yourself some file copying by using one command pipeline (no temporary files needed) instead.

6. Create a new file called userlist.newusers based on userlist.csv, but make the following changes.

   1. Copy the userlist.csv file into the new file userlist.newusers.

   2. The first line in userlist.csv is a header line, not a user to be created; the first line must be deleted. Use a command to read the file, remove the first (header) line, and write a temporary output file. The temporary output file should be only 97 lines long. (Hints: What command shows the last 97 lines of a file? That same command has a syntax to “print beginning with the Kth item from the start of each file” which allows you to skip the first line without knowing how many lines are in the file. Don’t use the number 97, since it might change in future.)

   3. Move the temporary output file to be the userlist.newusers file.

      • The file should now have only 97 lines in it.
      • Make sure the header line is gone.

   4. Use sed to read the new file and on every line insert the two colon characters that correspond to the location of the missing pw_uid and pw_gid fields needed by newusers, and write a temporary output file. For example, use sed to change this line:

      user066:password:User 066:/home/user066:/bin/bash

      to this line with two more colon characters in the right place:

      user066:password:::User 066:/home/user066:/bin/bash

      on all 97 lines. (This is a one-expression sed substitution.) (Hint: You can’t simply change a colon to three colons. Use some fixed context around your expression, to select the correct colon to change.)

   5. Move the temporary output file to be the userlist.newusers file.

      • Verify that every line now has seven colon-separated fields, with three colons right after the password field.
      • There should still be exactly 97 lines in the file.

   6. All the seven fields in the file are acceptable except the pw_passwd field that currently contains password, which is not a good default password for all these accounts. RTFM to see how the pw_passwd field is used by newusers.

      • Use sed to read the new file and on every line change the pw_passwd field from the dummy value password to a single, common password that all of these new users will get. You choose the new password. (This is not very secure, but it’s the best you can do without writing a more complex script.)
      • Do not choose any obvious password such as password.
      • To make this change, use an invocation of the sed command to read this file and change the word password to the password that you made up, redirecting the output of the sed command to a temporary output file.

   7. Move the temporary output file to be the userlist.newusers file.

   8. Verify that your output file is 97 lines (no header line) and the only field that has changed in each line is the new password field.

      • Every line should contain your new password in the pw_passwd field position.

7. Realize that the above three edits could be done as one pipeline that reads the original userlist.csv file, and makes each of the above three changes using filters. With a pipeline, no temporary files are needed.

   • Write this command pipeline and when it is working, remove all the file names and put the commands in a script named convert_userlist.sh. With file names removed, the script should act as a “filter” and read standard input and write standard output, so that you can type:

     $ ./convert_userlist.sh <userlist.csv >userlist.newusers

   Hints: The script file will contain two or three commands (which might inclue tail and sed and maybe another sed) separated by pipe characters. If you RTFM, you can combine the two sed commands into one sed command with two expressions, or perhaps even into one single expression that does both edits at the same time. Remove all file names from the script, so that the script reads standard input and writes to standard output, as shown above. Do not put file names in the script.

8. Verify that the userlist.newusers file created by your script contains 97 lines and 194 words, with seven fields per line, with good passwords.

9. Use sudo to run the newusers command with this file to create all of these 97 new users.

10. Make sure all the new users and HOME directories exist:

    • Should have account entries and HOME directories for user001 through user100
    • Use pipelines to select and count the accounts in the password, group, and shadow files. Do they all exist?
    • Use pipelines to select and count the account HOME directories. Do they all exist?
    • Note that these accounts do NOT have hidden files copied from /etc/skel/ in them. Only useradd copies these files.

4.6 CentOS: Management of the bulk usersIndex

This reviews the account management commands you learned above and in your previous term. Links to previous term notes and worksheets are given above under Review of CST8207 account management. None of the items below require you to text-edit any system files using a text editor. Actions can be performed using the correct account management commands. Most account management commands will require root permissions to run.

0. Make sure you have correctly followed all the above steps, including using the newusers command to create 97 accounts. Verify that you have created all the users and HOME directories for accounts user001 through user100 before continuing.

1. Use a system admin command to create a new group called common.

   • Do NOT edit the group file! Use the correct system admin command.
   • Do NOT make this a system group. It is a normal group.
   • Verify the change by looking in the group file.

2. Use a system admin command to add users User 004 and User 005 to the common group.

   • Do NOT edit the group file! Use the correct system admin command.
   • Verify the change by looking in the group file.

3. Create a directory called /home/common owned by your sysadmin user, and group-owned by the new common group.

4. Change the permissions on /home/common so that your sysadmin user can read/write/search, members of the common group can read/write/search, and it is not accessible in any way to other users.

5. Become User 004 without using a password (using your sysadmin powers)

   • As User 004 create a file /home/common/README containing the text:
     This common directory is for members of the common group.
   • Make the file group-writeable
   • Put the file in the common group you just created.
   • Note the permissions on the file when you create it.
   • Make sure you change only the group and group permissions of this file.
   • Do not remove any existing permissions on the file.
   • Exit from this user004 shell to revert back to your superuser-self.

6. Become User 005, and ensure that as user005 you can edit the file /home/common/README and change the text “for members” to “for all members”.

   • If you can’t edit and save this file, fix the group and group permissions.
   • Exit from this user005 shell to revert back to your superuser-self.

7. Become User 006 and ensure that as user006 you have no access to the /home/common/ directory.

   • Exit from this user006 shell to revert back to your superuser-self.

8. Use a sysadmin command to change the “real name” (GECOS/comment field) of User 005 to: CommonUser 005

   • Do NOT edit the file! Use the correct system admin command.
   • Verify the change by looking in the password file.

9. Lock the password for User 006 and User 007.

   • Do NOT edit the file! Use the correct system admin command.
   • Verify the change by looking in the shadow file.

10. Change the shell for User 008 and User 009 to /bin/sh.

    • Do NOT edit the group file! Use the correct system admin command.
    • Verify the change by looking in the password file.

11. Use the correct command to delete the accounts for User 010 and User 011 without deleting their HOME directories.

    • Verify the change by looking in the password file.
    • Make sure their HOME directories still exist in the file system. (Note what ls tells you about the file owner now!)
    • The group entries for these accounts may also continue to exist.

12. Use the correct command to delete the user010 and user011 groups, if they are still present on your machine.

    • Do not edit the group file! Use the correct system command.
    • You may see an error about removing the shadow group entry, because the newusers command did not create shadow group entries. Ignore the error – the groups don’t exist in the group shadow file.

13. Delete the accounts for User 012 and User 013 using the option that also deletes the HOME directory at the same time.

    • Verify the change by looking in the password file.
    • Make sure their HOME directories are gone from the file system.
    • The group entries for these accounts will also be deleted.

None of the items above require you to text-edit any system files using a text editor. Actions can be performed using the correct account management commands. Most account management commands will require root permissions to run. Do not text-edit the system files!

Run the Fetch and Checking Program to verify your work so far.

4.7 CentOS: Add a second disk to your VM: sdbIndex

You will add a second hard disk to your CentOS Virtual Machine, and partition it. The procedure for adding a hard disk to an actual physical computer is different only in the steps that take place while the machine is powered off. Any step carried out while the machine is running would be the same for physical machines as it is for virtual machines. The console of a physical machine is its actual keyboard and monitor, but in the case of a VM, the console is the VMware window of the machine.

Most of the system admin commands in this assignment access the raw disk and will require you to prefix the actual command name with sudo to gain root permissions (unless you are in single-user mode and therefore running everything as root). If you get “permission denied” errors, you forgot to use sudo.

1. If your CentOS Virtual Machine is not already powered off, login and use the correct command to power off the virtual machine.

   • Never user the VMware Power Off button to kill power!
   • Never unplug a running Linux machine!

2. With your CentOS machine still powered off, use the VMware Settings menu for your CentOS VM to add to your VM a virtual 10GB hard disk, accepting defaults for everything except the size. (You did similar work in CST8207 adding a VMware disk; review the notes.)

3. After adding the new disk, power on your VM, then login as your system administrator user.

4. Ensure the /proc/partitions file contains the second disk you added.

   • Verify that there is a second disk of the correct size:
     • The size of your second drive should be 10485760.
     • Divide: 10485760/1024/1024 to confirm the number of gigabytes.
   • Verify that no partitions are listed for the second disk.
   • If you have any sdb1 or sdb2 or other sdb partitions, this is not a new disk with no partition table. Get help.
   • Note the three-letter device name of the second disk.

5. When the second disk is correct, copy /proc/partitions to file partitions_before.txt in your CentOS sysadmin Base Directory (6 lines, 20 words).

   • Remember: all files should be kept under your sysadmin Base Directory on CentOS for marking.

6. Verify that the three-letter device name for the second disk also exists under the /dev directory. Put a long (ls -l) listing of all names under /dev that start with the first two letters of the new disk name into file sd_all.txt in your base directory.

   • Do not change your current directory.
   • Use the absolute pathnames for the device names.
   • No pipeline or other complex command is needed.
   • The output should show the absolute paths of two disks, and two partitions in the first disk: 4 lines, 40 words.
   • Hint: GLOB Patterns

4.8 CentOS: Viewing and Creating Partitions: fdiskIndex

1. First, you must have added a new 10GB hard drive in VMware and rebooted, as described above. Log in to the machine.

2. Run (always with root privileges) fdisk -cul /dev/sdb and make sure you see Disk /dev/sdb: 10.7 GB with no errors and no partitions listed under it.

   $ sudo fdisk -cul /dev/sdb
   Disk /dev/sdb: 10.7 GB, 10737418240 bytes

   If you don’t see 10.7 GB, then shut down, delete the disk, recreate the disk, and reboot until your 10GB disk install works.

Make sure you only change things on this new sdb disk in this section! The sda disk is your Linux ROOT disk; if you damage it you will need to recover back to your snapshot. Make sure you have a snapshot to go back to!

3. In the man page for the fdisk command, locate and make a note of two option letters:

   • The option to “Switch off DOS-compatible mode. (Recommended)”
   • The option to “give sizes in sectors instead of cylinders”

4. Run the command fdiskdevicename, where devicename is the absolute path of the device corresponding to the new disk under /dev. This will start the fdisk program, just as you did in CST8207 Fdisk Command.

   1. As fdisk starts, read the WARNING about DOS-compatible mode.
   2. This is a serious warning. Quit the fdisk program.
   3. Re-run fdisk command, this time inserting the two option letters you found in the man page. (Keep the same device name.)
   4. The WARNING about DOS-compatible mode should be gone when you start fdisk with those two options. Always use these two options on CentOS. (Other versions of fdisk use these options as defaults.)
   5. You may see another Warning about an invalid flag; ignore it.
   6. Inside fdisk, display the partition table and verify that the disk you are working on is the 10GiBi disk with no partition table.

5. Inside fdisk use the command to display the partition table and verify that the disk you are working on is the 10GiBi disk with no partition table. Use fdisk commands to partition the new disk as follows:

   1. First, make sure the new disk has no partitions configured. If you see partitions, you are using fdisk on the wrong disk. Make sure you use fdisk on the new disk device name!
   2. Create a 500M (not 500MB) primary partition as Partition 1.
      • Notice that one of the options for specifying the last cylinder of a partition is +sizeM where size is the number of megabytes.
      • Use suffix M and not MB so that you create power-of-two MeBi bytes instead of power-of-ten Mega Bytes.
   3. Create an extended partition as Partition 2, consuming the rest of the disk.
   4. Create a 400 MB logical partition
   5. Create another logical partition consuming the rest of Partition 2.
   6. Save your changes.
   7. Notice whether fdisk tells you as it quits whether you need to reboot for the new partition table to take effect. Do what it says.

6. Copy the new version of /proc/partitions (showing the new partitions you just created) to partitions_after.txt in your sysadmin Base Directory.

   • Also note that the new partitions now appear under the /dev directory.

7. Use the diff command to find the differences between the old and new partitions_{before,after}.txt and redirect the results to partitions_diff.txt in your sysadmin base directory.

8. Examine the differences file, and verify that your new partitions are the only differences. You should see four additional lines in the new partition file, corresponding to the four partitions you created:

   6a7,10
   >    8       17     512000 sdb1
   >    8       18          1 sdb2
   >    8       21     409600 sdb5
   >    8       22    9561088 sdb6

   If your numbers differ, perhaps you forgot to use the fdisk options that turn off DOS-compatibility mode and switch to using sectors instead of cylinders, or perhaps you used MB instead of M. Delete and start over.

4.9 CentOS: Migrate the /home directory to its own filesystemIndex

You will create an ext4 filesystem on the primary partition of the new hard disk. Then, in single user mode, you will migrate the contents of the /home directory to that new filesystem. You will configure the /etc/fstab so that the new filesystem will be automatically mounted on /home, with the option for giving the users disk space quotas.

4.10 CentOS: Practice with rsyncIndex

The rsync command is an intelligent form of copy command that only transfers data if the data isn’t already there. You will practice using rsync between your CentOS VM and its loop-back network adapter, which we will call the Backup machine (even though it’s really the same machine). A trivial change to the remote host name lets you transfer files to any machine on the Internet that lets you run rsync.

The modern rsync command uses an underlying SSH protocol to actually transfer the data, so any configuration you have done for SSH (such as private keys, host aliases, or SSH agents) applies to rsync as well.

$ date >foo
$ rsync -avH foo backup@localhost:
$ rsync -avH foo abcd0001@cst8177.idallen.ca:

4.11 CentOS: Boot into single user modeIndex

If you find yourself locked out of a Linux machine, and you have access to the console, booting into single user mode will will often not require a password, and in single-user mode you can change passwords or perform various other repair tasks. (Some systems do password-protect single-user mode, in which case you would need to boot a “live” or “rescue” CD to reset your root password.)

1. Use the correct command to reboot your CentOS VM, and when you see the GNU GRUB menu and the countdown timer, halt the GRUB countdown by pressing the space bar or an arrow key.

2. Use GRUB to edit your boot options so you boot into single user mode. (Refer to last term’s CST8207 Booting and GRUB.)

3. Verify that you are in single user mode: when you issue the command runlevel, the output should be either N S or unknown

4. Note that you are running as root and can change the password of any user in single-user mode, including the root password.

5. Put the output of the command ps auxww into a file named ps_auxww.txt in your sysadmin Base Directory, and change the ownership and group of this file to your ordinary sysadmin user. (Don’t leave root-owned files in ordinary user accounts!)

6. Exit this single-user shell, which will allow the system to boot into the default runlevel.

7. Log in (using SSH if possible) and verify you’re in the default runlevel by issuing the runlevel command.

   • You should see: S 3

Run the Fetch and Checking Program to verify your work so far.

4.12 CentOS: Boot into rescue modeIndex

If you find a Linux machine is unbootable, and you have console access, you may be able to rescue it by booting the machine from a “Live CD”. You will use the CentOS installation DVD to boot into “rescue” mode, which is a “Live CD” mode.

1. Shut down or power down your CentOS VM gracefully using the proper command.

2. Attach the CentOS Installation ISO image file to your VMware virtual DVD drive, connect it, and make sure it will be connected at Power On. (You did exactly this when you first installed CentOS.)

3. Access the VMware Settings for your Virtual Machine and increase the RAM to at least 1024MB. (The installer and Rescue mode needs more RAM for the graphics than the server-style CentOS machine.)

4. Boot into the VMware BIOS of your virtual machine, as follows:

   1. On VMware Workstation 7.x and later, to enter the BIOS setup for the guest operating system, click VM > Power > Power On to BIOS
   2. On VMware Fusion, or an earlier version of VMware Workstation:
      • Shut down the virtual machine.
      • Go to where the virtual machine is stored on your host O/S.
      • Make a backup of the VMware *.vmx file.
      • Add this line to the end of the *.vmx file to give a longer pause on the VMware BIOS screen: bios.bootDelay = "60000"
      • Reboot your virtual machine and you should have 60 seconds to use the correct key to enter the VMware BIOS menu.

5. In the VMware BIOS menu, use the keyboard to change the “Boot” settings so that the CD/DVD drive is before the hard disk in the boot order, if it isn’t already.

6. Save and Exit the VMware BIOS to boot from the virtual CD/DVD drive that contains the CentOS installation ISO image file.

   • If you boot into your regular CentOS, then you didn’t set up either the Boot menu or the CD/DVD device correctly. Wait until the machine has finished booting, log in, shut it down and try again.

7. If the ISO image boots, you will see the blue CentOS Welcome boot screen below with the large CentOS-6 banner on the screen. The Welcome menu includes the item Rescue installed system. Use the arrow keys to select the Rescue line and boot it by pressing Enter:

8. Follow the instructions on the screen, choosing the defaults, to finish booting into rescue mode, allowing it to search for and mount your Linux system when it asks you. Answer these questions:
   1. You do not need to enable networking – choose No
   2. Use Continue and not Read-Only for your Linux installation, since we need to write on the file system.
   3. If it says it can’t mount your disk under /mnt/sysimage, see the Rescue CD Appendix I.
   4. When it says Your system has been mounted under write down the directory under /mnt that will be used to mount and access your Linux installation.
   5. At the three-item menu that starts with shell Start shell, choose the first item (start a shell). It will give you a root shell prompt in a black console screen of the Rescue system.
9. When you finally have a bash root prompt, type hostname and then cat the password file to see that this is not your own CentOS system running. It is the Rescue system, with its own Rescue machine name and Rescue password file.
   • If you see your CentOS machine name or password file, you didn’t boot from the Rescue CD. Shut down and try again.
10. Running df in this Rescue CD will confirm that your CentOS ROOT partition /dev/sda1 is now mounted on directory /mnt/sysimage and your CentOS HOME partition /dev/sdb1 is mounted on directory /mnt/sysimage/home
    • You should see 9 lines, 5 of which are /mnt/sysimage file systems.
    • See [Rescue CD Appendix I to mount these file systems manually.
    • Get help if this is not true!
11. Redirect the output of df to the file livecd_df.txt in your sysadmin Base Directory in your mounted CentOS system.
    • Use the correct path to your sysadmin Base Directory on its current mount point. (The correct path to your sysadmin Base Directory is NOT under /home when mounted on the Rescue CD! Read all the words above.)
12. Run ls -l on all the HOME directories in the HOME partition (which is NOT currently mounted under /home) and note that all the accounts have numeric owners and groups.
    • Even your own sysadmin HOME directory shows a numeric owner and group in the output of ls -l.
    • Exam question: Why are all these HOME directories showing as numbers instead of userids when viewed from the Rescue CD?
13. Save a copy of the LiveCD’s password file, preserving timestamps, permissions, etc., to the file livecd_passwd.txt in your sysadmin Base Directory in your mounted CentOS system.
    • Use the correct path to your sysadmin Base Directory on its current mount point. (The correct path to your sysadmin Base Directory is NOT under /home when mounted on the Rescue CD! Read all the words above.)
    • Since this is the Rescue CD, none of your aliases are defined. Make sure you use the right option to the copy command.
    • The sum of your livecd_passwd.txt file should be 63933 2
14. The owner and group of the livecd_passwd.txt file you just copied into your sysadmin directory is currently root.
    • Try (and fail) to change the file to be owned by your CentOS system admin account user name.
    • The command will say your sysadmin userid doesn’t exist: chown: invalid user: 'abcd0001'
    • Exam question: Why did the chown fail when run from the Rescue CD?
    • Why is your sysadmin userid invalid (doesn’t exist) in the Rescue CD environment?
15. Run the command chroot /mnt/sysimage to obtain a root shell running with /mnt/sysimage (your CentOS ROOT) as its ROOT directory.
    • As long as you remain in the chroot shell, the /mnt/sysimage directory will used as be actual ROOT directory named /.
    • Now when you cat the password file, you will see the password file relative to the new chroot ROOT directory, which is your CentOS ROOT directory, so you see your CentOS password file, not the LiveCD password file.
    • If you don’t see your own CentOS password file, get help.
16. Run the df command now and note the familiar list of file systems, with sda1 mounted on the ROOT and sdb1 mounted on /home, etc.
    • The chroot command hides the /mnt/sysimage mount point and makes it look like the real ROOT directory as long as we stay in this chroot shell.

All programs you run from this chroot shell will behave as if they used your CentOS file system as the ROOT. The file name /etc/passwd now refers to your CentOS password file, not the Rescue CD password file.

You could fix a broken MBR with the command grub-install at this point, or do any other repairs to your CentOS Linux file system.

17. In the chroot shell you are running, pathnames work as if your CentOS machine were running. Everything works as expected.

    • Confirm that you can now see your two livecd_*.txt files in your usual CentOS sysadmin Base Directory using its usual path with respect to the usual CentOS ROOT directory:

      # cd /home/abcd0001/CST8177-14F/Assignments/assignment09
      # ls -l livecd_passwd.txt livecd_df.txt

    (Always use your own sysadmin userid, never abcd0001.) Note that the above files in your account are still owned by root.

18. Change the owner and group of the livecd_*.txt files to your system admin account user name. The command will succeed this time.

    • Exam question: Why did the chown succeed in the chroot shell but fail in the Rescue CD shell before using chroot?

19. Exit the chroot shell back to the Rescue CD shell prompt.

20. Run the df command again in this Rescue CD shell and note how everything again appears mounted under /mnt/sysimage

21. At the Rescue CD root shell prompt, try to use the usual command to shut down and halt the machine safely. Do not use VMware Power Off!

    1. The command will fail: shutdown: Unable to shutdown system
    2. Exit the Rescue CD root shell and return to the three-itme Rescue CD text menu.
    3. Use the arrow keys to select: reboot Reboot from the menu.
    4. When the machine reboots and you again see the blue Welcome to CentOS 6.6 screen, use the VM -> Power -> Power Off menu to power off the system without starting CentOS.
       • You can safely power off a machine before CentOS starts.
       • Never power off a running CentOS machine!

22. With the machine powered off:

    1. Go to the VMware VM Settings, Hardware CD/DVD tab, under Device Status, and un-check Connect at power on.
    2. On the same screen, take the ISO file out of the virtual CD/DVD drive by switching the Connection back to Use a physical drive.
    3. Save the settings so that you do NOT boot again from the Rescue ISO image file.
    4. Go to the Hardware Memory settings and reduce the memory back to 256MB to make live snapshots quick and small.
    5. Save the settings.

23. Power on your CentOS VM. You should see a familiar GNU GRUB menu.

    • If you end up booting the CD/DVD again, use the VMware menu to disconnect it. Reboot or choose Boot from local drive.

24. When your CentOS has rebooted, log back in as your system admin account (using SSH if possible, since it’s nicer than the console).

25. Change the ownership and group to you of any remaining root owner or group files anywhere in your CentOS system admin account. (If you’ve done your work carefully, there should be nothing owned by root.)

    • System administrators often scan home directories, looking for root-owned files as an indication that someone has broken into the system. Don’t leave root-owned files in your own CentOS sysadmin account.
    • NOTE: The Checking Program does create root files in your CLS assignment directories. This is intentional: don’t delete these!

Run the Fetch and Checking Program to verify your work so far.

4.13 When you are doneIndex

That is all the tasks you need to do.

Submit your mark from the CLS following the Checking Program instructions below.

Optional: Keeping your main configuration snapshots, remove any intermediate snapshots you no longer require, to free up disk space. - Be careful not to remove your current work!