MikeTieden: Created page with "=Introduction= =Lab Procedure= == Prerequisites == # Open an SSH console to your Linux system using the PuTTY software, login with your standard user account == Exploring /pr..."

2021-01-22T23:00:37Z

Created page with "=Introduction= =Lab Procedure= == Prerequisites == # Open an SSH console to your Linux system using the PuTTY software, login with your standard user account == Exploring /pr..."

New page

=Introduction=
=Lab Procedure=
== Prerequisites ==
# Open an SSH console to your Linux system using the PuTTY software, login with your standard user account

== Exploring /proc ==
# Enter the ''/proc'' directory on your VM. ''/proc'' is a very special folder is its a virtual filesystem. Its sometimes referred to as a process information pseudo-filesystem. The reason for calling it a pseudo-file system is that all of the "files" in ''/proc'' are not really files at all, but kernel runtime configuration and system information.
# For example, use '''cat cpuinfo''' to view the contents of the ''/proc/cpuinfo'' "file". Notice how the output tells your information about the CPU that is running the VM. This isn't actually a file at all you are essentially asking the kernel to provide information about the CPU it's running on which it gathers in realtime. ''/proc'' is used not only to get hardware and kernel information, but it can also be used to tweak kernel settings while the system is running in a way similar to some Windows Registry edits. Look back on Lab 10 and notice how we echoed a "1" to a "file" in ''/proc'' to enable packet forwarding without rebooting the system.
# There are a few files in ''/proc'' you should get to know:
#* '''/proc/cpuinfo''' = Shows you the CPU info for your machine.
#* '''/proc/modules''' = Shows you the currently enabled kernel modules that are active on your kernel.
#* '''/proc/cmdline''' = Shows you the boot arguments used to boot your kernel.
#* '''/proc/version''' = Shows you your kernel version.
# It is important to note that some of these files have commands tied to them that can give you similar information but often formatted in a different way, for example.
#* '''/proc/modules''' = '''lsmod'''
#* '''/proc/mounts''' = '''mount'''
#* '''/proc/version''' = '''uname -a'''
# Normally it is best to use the command version to lookup the information as it is normally formatted to be easier to read and understand.
# Explore all of these files and commands and find the differences between the command line and file output versions as well as what types of information are available.
== Exploring /dev ==
# Change directories to ''/dev'' and list the "files". Notice there are A LOT, but don't worry, there is organization in the mess. Each "file", like in ''/proc'', is actually a device or interface on the machine so ''/dev'' is actually another pseudo-filesystem. Here is a list of the most common interfaces you will see:
#* '''/dev/sd*''' = SATA Hard Drives
#* '''/dev/hd*''' = IDE Hard Drives
#* '''/dev/vd*''' = VirtIO (Virtualized) Hard Drives
#* '''/dev/ttyS*''' = Serial Interfaces on your PC.
#* '''/dev/tty*''' = Virtual Consoles, similar to the one you are using to enter commands. Mostly used by background programs or services.
# There are also some commands you should learn that will help you with detecting, and looking up devices:
#* '''lsusb''' = List USB Devices (Bus, Device, ID, and advertised vendor)
#** Note: Many virtual machines do not include a virtual USB controller which means the USB drivers and software including '''lsusb''' are not installed.
#* '''lspci''' = List PCI Devices (Bus, Type, Advertised Name, Revision)
#* '''dmesg''' = Display or Driver Message. This shows kernel messages that are normally linked to adding, or removing devices.

== Adding a 2nd disk ==
# As you may have noticed when exploring ''/dev'', our VM setup uses ''sd'' devices for hard drives. Drives are identified by a letter such as ''sda'', ''sdb'', ''sdc'', etc. for the first, second, and third SATA drives on a system (including HDDs, CD/DVDs, SSDs, etc.). Each partition on the drive is then given a number starting with 0 for the first partition. So the first partition on the first disk, the full identifier for the partition would be ''/dev/sda0''.
# You may also have noticed there is an ''sdb'' that currently has no partitions. We are going to format this drive into 2 partitions, format them, and then setup automatic mounting of the partitions.
# To start, run '''cfdisk /dev/sdb''' as root. ''cfdisk'' is a graphical version of ''fdisk'', which is a tool used to setup disk partitioning. Note that ''fdisk'' or any other partitioning software only sets up the MBR, and does not actually format the drive even though you can set a partition type identifier such as '''fat32''', '''Linux''', etc. Also notice how we tell ''cfdisk'' what drive we want to edit the partition on by appending the drive device "file" to the end of the command.
# Because our new drives contain no existing partitions we are asked what type of partition table to create. Choose to create a ''dos'' (aka ''MBR'') style partition table. Although this is an older style partition table it is well supported by many operating systems and BIOSes. The primary benefit of the newer ''GPT'' style tables is their ability to work with very large drives.
# Once in ''cfdisk'', Select the ''New'' option. Now select ''primary'' as we are making a primary MBR partition, then set the size close to ''5GB'' (it doesn't need to be exact).
# Using the arrow keys to go down to the remaining ''Free Space'' on the drive, and press enter to again select ''New''. Create another ''primary'' partition, and set the size to about ''2GB''.
# At this point we should have two partitions, one named ''sdb1'' with a size of about 5GB (the program will round down to the closest boundary), and ''sdb2'' which takes up the next 2GB or so of the drive. Use the arrow keys to select the ''Write'' option, and press ''enter''. You will be warned that this will write the table to the disk. enter ''yes'', and press ''enter'' again to confirm.
# If, on the bottom of the screen, you see "The partition table has been altered", you have successfully written the MBR to the drive. Now you can navigate to ''Quit'' to exit the program.
# From the command line run '''ls -al /dev/sd*'''. Notice how you can now see both of the new partitions, ''sdb1'' and ''sdb2'' in the listing. This means the partition device "files" have been created and you are ready to format the partitions with a filesystem.
# The first partition will be formatted as ''ext4'', and the second partition will be formatted as ''btrfs''. Both filesystems (as well as many others) are commonly used on Linux systems. For more information on the differences and similarities between ''btrfs'' and ''ext4'', refer to your book or Google.
# To create the ''ext4'' partition, we will use the ''mkfs.ext4'' command. So as root, run the command ''mkfs.ext4 /dev/sdb1''. This will partition the drive as ''ext4'' with no label. If you would like to label the partition, look into the options of ''mkfs.ext4'' using ''man mkfs.ext4''.
# Before formatting the other partition as ''btrfs'' we need to install some tools. The required tools are part of the ''btrfs-tools'' software package so install that package at this time.
#* Note if you have issues with installing packages, check your firewall rules you created in a previous lab and ensure your Internet access is working properly from the VM.
# To format the second partition as a ''btrfs'' filesystem partition we will run ''mkfs.btrfs /dev/sdb2''. Just like before, we need to tell the ''mkfs.btrfs'' package what partition to format by including that on the command line.
# There are many other options that can be set for specific filesystems during the formatting process. For example, many newer large drives use 4096 byte "Advanced Format" sectors instead of the traditional 512 byte hard drive sectors. Using these disks most efficiently requires adjusting the sector size during the format process to match the physical sector size on the disk. Other features and filesystems include the ability to take snapshots of the drive for backups. The full details of all the options, settings, and filesystems available in Linux is beyond the scope of this course. Suffice it to say that Linux systems with a need for high speed I/O from disks or other specialized features are finely tuned.
# As a Linux system administrator at a minimum you should be familiar with the basic formatting of drives in the most common ''ext3'', ''ext4'', ''btrfs'', and ''fat'' (32) filesystems. Even though the FAT filesystem is not native to Linux (it doesn't have important features like user and group ownership) it is important as it is a cross platform filesystem commonly used to share files on thumb drives, external hard drives, or dual boot systems with MacOS or Windows users.
# Once your two partitions are formatted they need to be ''mounted'' to the filesystem structure so that we can begin using them for file storage.

== Mounting Partitions ==
<ol>
<li> There are two main ways to mount disks in Linux. One is done manually, and the other is to setup mounting at boot. Manual mounting is typically done for either temporary access to drives such as CD/DVDs, thumb drives, external hard drives, or to access a newly created partition before rebooting the system. Automatic mounting is done during the boot process so that you have immediate access to he drive once the system is booted.</li>
<li> To start, we will learn how to manually mount a partition. change into the ''/mnt'' directory and then create a new directory named ''part1''. This will become the location where we will mount our ''/dev/sdb1'' partition and be able to save files to it.</li>
<li> Enter the ''part1'' directory and create a new empty file (remember the '''touch''' command?) named ''unmounted''. Because we have not yet mounted ''/dev/sdb1'' this file will be stored on our existing partition (''/dev/sda1'').</li>
<li> Go back to the ''/mnt'' parent directory. Run the ''mount /dev/sdb1 /mnt/part1'' command as root. This command will mount, or attach, ''/dev/sdb1'' to the filesystem location ''/mnt/part1'' and everything stored in that "directory" from this point on will actually be saved onto the first partition of the second SATA drive.</li>
<li> Go back into the ''part1'' directory and try listing the files. Notice how the ''unmounted ''file you made appears to no longer exist. This is because the ''part1'' "directory is now being used as the mount point for the first partition on ''sdb'' and we haven't yet saved any files onto ''sdb1''.</li>
<li> You can see a list of all storage devices currently mounted on the system by simply running the command '''mount''' without any options. Try doing this and verify that the newly mounted partition is showing in the list.</li>
<li> Change back to the ''/mnt'' directory and unmount the partition by running the command ''umount /mnt/part1''.</li>
<li> Again list the contents of the ''part1'' directory. Notice how the ''unmounted'' file is back. The file didn't every really go away but it was not accessible while the other partition was mounted on the ''part1'' directory. When a drive is mounted on a directory, it overlays on top of any files in the directory, but it does not delete or touch the files on the original disk.</li>
<li> Make a directory named ''btrfs'' in ''/mnt''. Once created, using the file editor of your choice, open the ''/etc/fstab'' file.</li>
<li> The ''fstab'' file is used to tell a Linux system what drives and partitions is should mount at boot, as well as any mount options and where to mount the partitions. On the bottom of the file, add the following:
<pre>/dev/sdb1 /mnt/part1 ext4 defaults 0 0
/dev/sdb2 /mnt/btrfs btrfs defaults 0 0</pre> </li>
<li> Adding these lines will indicate both partitions should be mounted at boot to the directories we created. To mount the partitions without rebooting or entering individual mount commands, we can just run '''mount -a''' which will load and mount all partitions in the ''fstab'' file. Run the '''mount -a''' command now and verify both partitions are mounted.</li>
</ol>

== Disk and File Usage ==
<ol>
<li> Another way to verify the partitions which are mounted and to see how much disk space is used on each is to use the ''df'' command. When you run ''df'', you should see something similar to this at the bottom of the output:
<pre>/dev/sdb1 14712416 167576 13797488 2% /mnt/part1
/dev/sdb2 26995912 120 24870016 1% /mnt/btrfs</pre></li>
<li> This indicates that the two partitions are mounted properly to the folders we created earlier. ''df'' is a powerful command as not only will it show you what is mounted where, but it also shows you how much disk space is used and how much space is left.</li>
<li> The '''df''' command doesn't give the most easily readable disk or usage sizes by default. Try adding the ''-h'' option to the command like '''df -h''' to change the output to a "human readable" format and see what it looks like.</li>
<li> Now, '''cd''' into ''/mnt/part1'' so you are on the ext4 partition you created. Then as root, run the command '''cp -r /var/log ./'''</li>
<li> '''cd''' into the ''log'' folder, and run '''du -h'''. '''du''' is a command that allows you to view file usage in a tree format. Just like with '''df''' the ''-h'' flag tells '''du''' to output the usage in a "human readable" format, while the ''-a'' flag tells it to show you the results for all files, and not just for folders.</li>
<li> Read the '''man du''' page and play around with using the '''du''' command across the file system. How much data is the /etc/ folder taking up on your Linux system? What directories are the biggest?</li>
</ol>

Jon Lab 11 - Revision history

MikeTieden: Created page with "=Introduction= =Lab Procedure= == Prerequisites == # Open an SSH console to your Linux system using the PuTTY software, login with your standard user account == Exploring /pr..."