Network & SystemAdministrationClass 1

Introduction to Linux

Agenda

§ Introductions and expectations§ Introduction to Linux

§ Lab – Installing CentOS 7 locally

§ System navigation and administration§ Lab – command line usage, user management and system commands

§ Common Linux tools§ Lab – Working with Linux tools

Introductions and expectations

> This week I want everyone in the class to upload a recent picture of themselves to Canvas (if not already done) and post a brief introduction about themselves covering:

1. Linux experience2. Primary goal for this course3. Optional: something about yourself you want to share, kids, pets, sports

whatever.

> Course expectations– Speak up in class, participate in discussions and breakouts, attempt to

complete all assignments.

Class 1 Unit 1

What we are going to cover:§ CentOS/RHEL basics§ System admin basics

Takeaways from this session:§ Understand relationship between Red Hat and CentOS.§ Install requirements§ Major system changes and updates§ How to elevate your rights with su or sudo

Class details

The primary OS this quarter is CentOS 7. > In class work = “development” instances.>Homework = “production” instancesDevelopment instance = local build installed by you.Production instance = remote build provided to you.

Copy the CentOS 7 ISO to your desktop NOW. http://www.ulcert.uw.edu/iso/CentOS-7-x86_64-Minimal-1804.iso

About Linux

> Roots from Unix and Multics

> Ken Thompson and Dennis Ritchie

> Free and Open-source

> Linux released 1991 by Linus Torvalds

Community enterprise Operating System

> Free, based on Red Hat Enterprise Linux (RHEL)> Red Hat releases all source code> A core group of CentOS developers compile that code> Commercial support available> Support provided for at least 7 years.

– https://access.redhat.com/documentation/en-us/

> New public key with each major version> ABI and API stability> Single base install vs RHEL

What’s new in RHEL 7

> GRUB2> firewalld> Systemd> Gnome3> Filesystem defaults to XFS vs ext4> Kernel update to 3.10.0> Support for Linux Containers> and more.

A peak at the shell

We will be working from the command line this quarter.

We will be usingstandard user accounts

We will have access toroot or admin rights

System requirements

> 64bit architecture..– No 32bit support

> 512 MB.– 1GB recommended.

> 4 GB hard drive required.– 20 GB hard drive recommended.

> Network access to install updates.

Updated tools on CentOS/RHEL 7

What might be new for you:/usr/sbin/ip/usr/sbin/ss/bin/systemctlWhat has been replaced:/usr/bin/arp/usr/bin/ifconfig/usr/bin/netstat/usr/bin/route/sbin/service

Iptables or firewalld

> By default iptables is not running.# systemctl status iptables

> However by default firewalld IS running.# systemctl status firewalld# firewall-cmd –state

> Firewalld replaces the iptables utility> iptables net filtering still in effect

User and Group management

> /etc/passwd == maintains user accounts> /etc/group == maintains all groups> user management tools

– useradd– groupadd– usermod

> /usr/sbin/{useradd|groupadd|usermod}

Switch User SU

> Best practice – don’t login as “ROOT”.> When required SU to ”ROOT”

user@localhost $) su root*user@localhost $) su – root

> Run explicit commands as another user

user@localhost $) su root -c “cmd”user@localhost $) su root -c “cat /etc/shadow”

*Note the addition of the “-”, spawn new shell.

sudo – “su” do

Grant rights to run commands as root or another user without sharing passwords.

Sudo creates an audit trail

Best practice:edit the sudoers with visudo

/usr/sbin/visudo

*image source http://xkcd.com/149/

sudo configuration

The sudo configuration file is found here: /etc/sudoers

The best utility for editing this file is visudo/usr/sbin/visudo

The sudo binary is found here: /usr/local/bin/sudo

sudo configuration cont.

Grant local group “wheel” full access to system.## Grant all wheel users ALL commands%wheel ALL=(ALL) ALL

sudo actions are logged to /var/log/secure

Review

Support available for both CentOS and Red Hat.Documentation provided by Red Hat.Red Hat == multiple installations distributionsCentOS == one installation distribution.User management useradd, usermod, groupadd, Elevated user rights with su and sudo.No 32bit install supportifconfig replaced by ip, netstat replaced by sssbin/service replaced by systemctl and systemd.iptables replaced by firewalld

Lab 1

Lab notes for this session can be found in canvas.

Class 1, Unit 2

>What we are going to cover:– The FHS design.– Terminal navigation.

>Takeaways from this session:– standard files and directories structure.– Terminal navigation

Filesystem Hierarchy Standard

> Red Hat adheres to the FHS structure*. https://refspecs.linuxfoundation.org/FHS_3.0/fhs-3.0.pdf

> Maintained by the Linux Foundation > Supported by: IBM, Dell, Red Hat, and HP…

It all starts at slash, root, /

> Consider “/” to be the root or base.> Everything else hangs from this point.> Some of the common directories under /

/bin, /boot, dev, /etc, /home, /lib, /proc, /usr, and /var.

/

/bin /usr

/usr/bin/usr/local

/home

Linux file system details

> /boot = static files required to boot (kernel)> /dev = device nodes, represent attached physical or

virtual devices to the system> /etc = local host configuration files> /lib = files needed to execute binaries (/bin /sbin)> /media = used for removable media (dvd, usb…)> /mnt = mounted file systems (nfs, dvd, cdrom)

Linux file system details cont.

§ /proc = virtual filesystem, exposing kernel details.§ /sbin = executables used by root§ /sys = virtual filesystem, similar to /proc.§ /usr = sharable executables, often read-only.§ /usr/local used for software that is local to the host.

should be safe during upgrades.§ /var = stores variable data files§ /opt = most 3rd party app software packages

3 Basic Linux file types

> Ordinary (regular) files– Base file type, can contain data, text, compiled code,

etc.> Directory files– Contains other files and directories

> Special files– Special meaning, often some form of I/O – consider /proc/meminfo

The Shell

The primary program for interacting with the host system.

Use your shell to run other commands and programs.

The shell can also be a programming environment.

What is a shell?

Linux based on two broad categories:kernel and utilities.> The kernel is at the core of the system. It is loaded

into memory at boot and remains there until the system is halted

>Utilities exist on disk and are brought into memory as required.

> The shell is just another utility that is loaded into memory as needed.

/bin/sh The Bourne Shell

> A common Linux shell is the Bourne Shell.

> Replaced by Bourne Again SHell /bin/bash.

> Other example shells include the Korn Shell /bin/ksh and the C shell /bin/csh.

> Each shell includes slightly different commands, options and features.

Basic command whoami and ”who am i”

Once you find yourself at the shell maybe you want to know, who am i?

Another common option is to use whoami which will show you the effective userid.

Basic command echo.

The echo command prints to the terminal whatever is passed in next. echo will drop or ignore extraneous white space.

Basic commands cat, ls and wc

> /bin/cat print the contents of the file or file.

> /bin/ls list the files in a given directory.

> /bin/wc count the number of lines, words and characters contained in a file.

Basic commands cp and mv

/bin/cp used to copy a file.

/bin/mv. Move or rename a file. This commands involves a move and a delete.

Basic command rm

> /bin/rm to remove or delete a file.No warnings about deleting files.

Remember you use “ls” to list the files

Basic commands cd and pwd

> /bin/cd used to Change Directories. Defaults to home.> A successful login redirects to home by default.> Home location maintained in /etc/passwd >Moving from home to /usr/local requires cd

/bin/cd /usr/local

> Confirm current directory using /bin/pwd– Print Working Directory (pwd)

Basic commands mkdir, rmdir and rm -r

Make a directory using /bin/mkdir. /bin/mkdir /tmp/TEST

Creates a directory under /tmp called TEST.

Remove this directory with /bin/rmdir/bin/rmdir /tmp/TEST

Will not remove directories with files.

Remove directory and any files with rm -r/bin/rm –r /tmp/TEST

Basic commands options and man pages

>All commands have additional options. >Invoke an option using a “-” dash>Force rm to confirm a delete using -i/bin/rm –i /bin/TEST

>Use the /bin/man <cmd> > /bin/man rm >/bin/rm --help>To review options and help available.

Review

> FHS File System Hierarchy standard– Everything starts at /– Common directories /usr /bin /etc /home /lib /var– User space programs are found under /usr

>Shell is a utility. Shell interacts with the kernel>The System is divided between kernel and utilities.>Linux file types: Ordinary, Directory, Special files>Common commands, who, echo, cat, ls, wc, cp, mv, rm, cd, pwd, mkdir, rmdir.>Learn about options and help using /bin/man

Lab 2

Lab notes for this session can be found in canvas.

Class 1, Unit 3

>What we are going to cover:– Common Linux utilities.

>Takeaways from this session:– Regular expression basics– Common tools and combinations

Common tools in review…

>cut>paste>sed>tr>grep>sort

> uniq> awk> xargs> find

Common tools in review…

But first … Regular Expressions - regex. Regular expressions are sets of symbols and syntactic elements used to match patterns of text.

Many common Linux tools support regex.

Regular Expressions

* means zero or more, very greedy…? Means zero or one of the preceding character[…] means any characters in the brackets

[0123] or [A-Z] [4-9] [a-zA-Z]. Means single character except line break.^ beginning of line$ end of line\ means escape the special meaning.

Now back to tools with cut

■ Used to extract fields of data.cut –c<chars> file or datacut –c 4-8 /etc/passwd

■ Cut can be used with files and can interpret delimiters for the data.-d = delimiter (default is tab) use ‘ ‘ for space.-f = fieldscut -d: -f4 /etc/passwd

paste

■ Paste is just the opposite of cut, put lines togetherpaste file1 file2paste /etc/services /etc/passwd

■ Files are pasted side by side■ To insert delimiters between the files use -d ‘<value>’

paste –d ‘#’ /etc/passwd /etc/services

To paste files in serial, one at a time use -spaste –s /etc/passwd /etc/services

sed: Stream editor

sed cannot be used interactively. sed syntax is: sed <cmd> filesed –n 5,10p /etc/passwd

sed applies to each line of input.If no file is defined standard input is assumed.No changes to source file, all changes to standard out

To change nologin to upper case in /etc/passwdsed ‘s/nologin/NOLOGIN/’ /etc/passwd

Default changes first matchuse /g for global updates

Sed cont.

sed display characters used for delimiterssed –n ‘l’ /path/to/file = list out tabs notationsdelete lines in a file with –d #

sed ‘1d’ /etc/passwdsed '3,6d' /etc/passwd

Delete first line with “root”sed ‘/root/d’ /etc/passwd

tr – translate or transliterate

tr is used to translate characters from stdin.tr always expects input from standard inThe basic format is "tr from-char to-char"tr takes two sets of characters and replaces the second set with those from the first set.tr matches in order between character groups.

tr cont.

Use -s option to remove repeat characterstr -s ' ' ' ' < /etc/services

Use -d option to delete a charactertr -d '\11' </etc/services

\11 represents the octal value for tab.

switch case using either '[a-z]' '[A-Z]' or '[:lower:]' '[:upper:]'

tr '[:lower:]' '[:upper:]' </etc/passwd

grep – search for patterns

Search file or files for patterns.grep <pattern> file

-i = means case insensitive or ignore case-v = not matching

grep root -v -i /etc/passwd

-n = line numberingYou can use regular expressions also

grep 'dbd*' /etc/services

sort

Sorts each line of input in ACSIIbetically.ps –ef | sort

-u = remove duplicates from output-r = reverse the sort order-o = output to file-t = sort by defined delimiter, colon, #, etc.-k2 = sort based on the second column+2n = older syntax for column sort

uniq

Finds duplicates in a file.-d write out only the duplicates from a file-c provides numbers of duplicate lines

awk

Named after the creators; Alfred Aho, Peter Weinberger and Brian Kernighan

A pattern scanning and processing language.awk is similar to C and can be complexprint a column

who | awk '{print $2}‘print the entire line

who | awk ‘{print $0}’

number of fieldswho | awk ‘{print NF $0}’

awk can do math, create formatted output, and more

xargs

Accepts arguments from other commandsSome utilities have limited input. xargs works on

streams and has no limit.ls 4*txt | xargs echofind /tm/ -name [1-999].txt | xargs rm

Recursive text searchfind /tmp/*txt | xargs grep -i test

find

A powerful Linux commandCommon syntax isfind <path> -name <argument> -print

find /var –name “*log*” –printOther options include-mtime (modified time) –atime (access time), -

size ( -size +500k, -size +10M), etc.

Tool review

■ uniq -c ■ awk print columns■ xargs pass args■ find -mtime

■ regex . * ?■ cut -d -f■ paste ■ sed -s'/old/new/g'■ tr '[a-z]' '[A-Z]'■ grep -i■ sort -u -r

Lab 3

Lab notes for this session can be found in canvas.

Class 1, Unit 4

>What we are going to cover:– Vi or Vim.

>Takeaways from this session:– Ability to edit files at the command line

Introduction to Vi or Vim

> Vi is one of many editors found on Linux,> There are many utilities capable of processing files> common alternatives include nano and emacs. > In this course we will officially use Vi or Vim. > Labs and homework only include tips on using Vi > Vi is short for visual editor. > Vi is widely available and often installed by default.

Common tools in review…

> Command mode vs insert mode> “Command mode”, managing the file> ”Insert mode”, editing the file > Typically Vi commands are:– Case-sensitive– Are not echoed on the screen.– Do not require an <ENTER> after the command.

The 3 modes of Vi

> Command mode– Default mode when opening a file

>Enter commands to initiate a function such as find a pattern, move to end of file etc.

> Insert or Entry mode– Used to enter text into a file.

> Visual mode– Allows for the visual selection

of an area of text to edit.

Edit a file with vi

Creating or editing a file:/usr/bin/vim [filename]

If the file exists you will load the contents in to memory. Vi displays the contents from memory to the user for editing.Only when you save your edits is the original file overwritten. Vi works with a copy of the source file.It is possible to open a read only file with vi; however,attempts to save your changes to the source may fail.In most cases this can be remedied.

Vim command mode to insert mode

The default initial mode is “command” mode.The <ESC> used to switch between modesEnter <i> to switch to insert mode. inserts content just before the character.Enter <a> inserts content just

after the character

The capitol I and A take you to the first and last character on a line respectively.

Vi movement in command mode

Keep your fingers on the keyboard with Viprimary navigation keys are:

h move leftl move rightj move upk move down

**avoid using the arrow keys **

VIM save and edit

To save a file enter <ESC> colon and <w>.:<w>

To save a file and exit the file end with <q> for quit:<wq>

To force a save use <!>:<wq!>

The Vim Tutor

The vimtutor is a Vi tutorial To start logon to your server and type vimtutor

/usr/bin/vimtutor <enter>

Next follow the prompts.

If the command is not found, install the package/usr/bin/yum install vim-enhanced

Vim Review

> There are many editor options, in this course we will assume you are using vi or vim but you can use another editor if you choose.

> Do not use the arrow keys to navigate in Vim> The three primary modes for vi are:

Command mode, Insert mode, and visual mode.> Files are read into a buffer (memory) any changes you

make do not effect the source file until you save them.> Use vimtutor to learn Vim

Lab 4

Lab notes for this session can be found in canvas.

Homework

> All assignments must be attempted.> You must successfully complete 8 out of 10 assignments to

pass the course. > This week’s assignment will be posted on Canvas.