1. Instructor Tavaris J. Thomas, Ph.D.
The Cooper Union Retraining Program at CAMBA Linux (Unix) Administration
Instructor
Tavaris J. Thomas, Ph.D.

2. Welcome! Do I need any previous Linux experience? Who am I?
Which Linux version is best for me?
Where is the closest help resource?
(puns intended )
whoami
which
whereis

3. Core Objectives
Getting started with windows environment edit text files with gedit/vi/vim
Understand Linux file system hierarchy and pathnames; manage files from the command line.
Understand Linux file access mechanisms; manage file access from the GUI and the command line.
Access documentation, both locally and online.
Configure the date and time.
Understand basic disk concepts and manage system disks.
Understand logical volume concepts and manage logical volumes.
Manage CPU, memory, and disk utilization.
Manage system software locally
Understand basic shell concepts, execute simple commands, and use basic job control techniques.
Use man and info pages and find documentation in /usr/share/doc.
Understand basic network concepts; configure, manage, and test network settings.
Manage users and groups.
Share and connect to a desktop; use SSH
Understand run-levels and manage GRUB.
Deploy an FTP server and a web server.

4. Course Objectives we will not learn
Hacking
BlackHat Techniques
Penetration Testing
Programming (beyond simple scripting)
Developing/building your own kernel or modifications.
However, I will try to introduce Linux concepts to you with a security minded approach.

5. Linux Admin Session 1 Outline
Brief History of Linux
Obtaining the Operating System
Assistance, Resources, and Information
Common Architectures
Shells and Scripting
Booting Procedures
Shutdown Procedures

6. (Brief) History of Linux
UNIX Developed by Dennis Ritchie and Ken Thompson at AT&T Bell Labs 1970s
Heavy license fees for UNIX spurred the development of the reimplementation of an open sourced version UNIX
In 1991 Linus Torvalds (Li) + UNIX (nux) = Linux

7. Downloading the distribution(s)
Fedora (RedHat)
CentOS
Debian (open)
Ubuntu
Virtual Machines are your friend
VMware, Parallels, Microsoft, Virtual Box, etc

8. Installing your distribution
Stand alone
Virtual Machine
Live CD
Dual/multiple boot

9. Assistance, Resources, and Information
me –
Online:
HOW TO guides - Google
Linux – Where to go for information????
$man topic
$info topic
$info emacs (an excellent tutorial for info)

10. Secure Installation
Security begins with the first time you put that CD or DVD into your disk drive (or .iso for VM) to install Linux.
Configuring your system securely from the beginning makes it easier to implement additional security settings later.
NIST recommends creating separate partitions for /boot, /, /home, /tmp, and /var/tmp.

11. Common Architectures Hardware Kernel Shell Applications/GUI
Keyboard, hard drives, processors, memory, optical drives, etc
Kernel
Device drivers, network stack, memory interface/mapping, etc
Shell
Command Line Interface
Applications/GUI
Desktop env, web browser, terminal, etc

12. What is the shell???
The shell acts as a buffer between the user and the machine, taking input from the user and interpreting it to the computer.
The shell has several associated environment variables that it uses to keep track of information, including the current directory and where to look for files and applications.
The shell can be used as a “mini-programming environment,” to execute a series of commands (i.e. a script)
The terminal application can be viewed as a program that provides an interface that can accept user input from the keyboard and display characters on-screen for the user.
The default shell is bash (the “Bourne-again” shell)
sh - (the original Bourne shell) It was developed by Stephen Bourne at Bell Labs in 1977 for Unix Version 7. – source: Wikipedia

13. Scripting
Scripts standardize and automate the performance of administrative duties.
Scripts vary in complexity from simple ones that encapsulate a few static commands to major software projects that manage host configurations and administrative data for an entire organization.
cron - the name for scripts that run on a regular basis

14. When NOT to use scripts
Resource-intensive tasks, especially where speed is a factor (sorting, hashing, recursion)
Procedures involving heavy-duty math operations, especially floating point arithmetic, arbitrary precision calculations, or complex numbers (use C++ or FORTRAN instead)
Mission-critical applications upon which you are betting the future of the company
Extensive file operations required (Bash is limited to serial file access, and that only in a particularly clumsy and inefficient line-by-line fashion.)
Need native support for multi-dimensional arrays
Need data structures, such as linked lists or trees
Need to generate / manipulate graphics or GUIs
Proprietary, closed-source applications (Shell scripts put the source code right out in the open for all the world to see.)

15. Shells and Scripting
Why?? - Most environments include a hefty complement of existing sh scripts, and those scripts frequently need to be read, understood, and tweaked by administrators.
Every process has at least three communication channels available to it: “standard input” (STDIN 0 ), “standard output” (STDOUT 1), and “standard error” (STDERR 2).
Source: Wikipedia

16. Shells and Scripting cont’
The shell interprets the symbols “<, >, and >>” as instructions to reroute a command’s input or output to or from a file.
“<“ symbol directs STDIN to the contents of an existing file.
“>” and “>>” symbols redirect STDOUT;
“>>” appends to file
Examples “find / -name core > test 2>&1”
echo test > junk 2>&1
$ echo "This is a test message." > /tmp/mymessage
$echo “this is another appended message” >> /temp/mymessage
$ grep test < /tmp/mymessage

17. Shells and Scripting cont’
To redirect both STDOUT and STDERR to the same place, use the “>&” symbol. To redirect STDERR only, use “2>”.
The “|” symbols takes the output of one command and redirects it to the input of another. (example)
“ &&” - executes a second command only if first command completes successfully
“||” symbol executes the following command only if the preceding command fails.
ping find / -name core
$ find / name core 2> /dev/null (sends error messages here permission denied)
$ find / -name core > /tmp/corefiles 2> /dev/null
$ ps –ef | grep httpd
cmd > log 2>&1 This redirects stdout to log and then redirects stderr to wherever stdout is now being redirected, which is log.
End result: both stdout and stderr are redirected to log.
ping -c1 abc.com && ssh
ping google.com, and display useful information to user if its pingable or not.
ping -c1 google.com && echo “Thats good, able to ping google.com” || echo “Thats bad unable to ping google.com”

18. Bootstrap Process “bootstrap” procedures:
Loading and initialization of the kernel
Device detection and configuration
Creation of kernel threads
(manual boot control - optional)
Execution of startup scripts
Multiuser operations

19. Booting the PC Startup your Linux distribution BOOT LOADERS
Power on & BIOS
Loading the boot loader
Master Boot Record (MBR) contains the location of the boot loader
BOOT LOADERS
GRUB – The GRand Unified Boot loader
LILO – the traditional Linux boot loader

20. GRUB Installed on most distributions
Very useful booting multiple operating systems, kernels, configurations, etc
Good for users that change configurations often
GRUB configuration (accessed at boot time) is located at:
/boot/grub2/grub.cfg

21. CentOS runlevel
Previous versions of Red Hat Enterprise Linux, which were distributed with SysV init or Upstart, used init scripts located in the /etc/rc.d/init.d/ directory.
In general, users operate Red Hat Enterprise Linux at runlevel 3 or runlevel 5 — both full multi-user modes.
These init scripts were typically written in Bash, and allowed the system administrator to control the state of services and daemons in their system. In Red Hat Enterprise Linux 7, these init scripts have been replaced with service units.

22. systemctl
Service units end with the .service file extension and serve a similar purpose as init scripts. To view, start, stop, restart, enable, or disable system services, use the systemctl command
The service and chkconfig commands are still available in the system and work as expected, but are only included for compatibility reasons and should be avoided.

25. systemd
Previous versions of Red Hat Enterprise Linux, implemented a predefined set of runlevels that represented specific modes of operation.
These runlevels were numbered from 0 to 6 and were defined by a selection of system services to be run when a particular runlevel was enabled by the system administrator.
In Red Hat Enterprise Linux 7, the concept of runlevels has been replaced with systemd targets.

26. systemd
Systemd targets are represented by target units. Target units end with the .target file extension and their only purpose is to group together other systemd units through a chain of dependencies.

27. Run Levels

28. Checking/changing run-levels
Try the following command:
This shows the current default run-level
Try another commands:
# systemctl get-default
# systemctl list-units --type=target
# systemctl set-default multi-user.target

29. How to reset root http://www.unixmen.com/reset-root-password-centos-7/
CentOS 7 –
Edit Grub (previous slide)
Go to the line of Linux 16 and change ro with rw init=/sysroot/bin/sh
chroot /sysroot
passwd root
touch /.autorelabel
exit
reboot

30. Rebooting and Shutting Down
halt instructs the hardware to stop all CPU functions.
poweroff sends an ACPI signal which instructs the system to power down.
reboot instructs the system to reboot.
Suspend does not turn off your computer. It puts the computer and all peripherals on a low power consumption mode. If the battery runs out or the computer turns off for some reason, the current session and unsaved changes will be lost.
Hibernate saves the state of your computer to the hard disk and completely powers off. When resuming, the saved state is restored to RAM.

31. Rebooting and Shutting Down
In Red Hat Enterprise Linux 7, the systemctl utility replaces a number of power management commands used in previous versions of the Red Hat Enterprise Linux system.

33. Assignment 1
Download and install a copy of CentOS 7 using one of the methods described in this chapter
Read chapters 1 and 2 of text.
Practice commands presented during class