Linux

In the name of god LINUX

red hat(centos)

Abolfazl Hashemi

Title

• What’s Linux?

• working with directories, files

• Using text editors like vi, vim

• Control on mount & un-mounting process

• File permissions & ownerships

• Linux installation & package management (yum, rpm, wget )

• process & threads

• Configure disk partitions

• Manage disk quota & create quota report

• Symbolic links, FHS

• Writing shell script

• Working with archive files

• System resource management

• Working with debuggers in Linux

• gpg command

• Introduction to network

• Security in linux

• Do automate tasks in Linux, cron job

• Configure & working with OpenSSH

• Working with tcpdump

• Configure web server

• Network configuration

Summary of Linux

• Linux clone of unix os

• Linux can run on small computer

• Open source os

• Distributed of Linux – Debian GNU/Linux

– Fedora Linux

– Gentoo Linux

– Libranet GNU/Linux

– Red Hat Linux

– Yellow Dog Linux

– …….

Kernel

Shell

User

bash tsh zsh

Graphic User Interface(GUI)

x86_64 i386

Installation

• Requirements

• Customize installation

• X configuration

• GUI: graphical user interface

• Install

• What is shell, terminal, virtual terminal, super terminal, konsole, tty.

• man, --help

working with directories, files, …

• Command line for directories

pwd: current working directory-> /root

cd: change working directory -> cd /etc/init.d

ls: list of directory, files, ... .

• ls –a: list of all directory,… .

• ls –l : list of all directory,... With details

mkdir: make directories -> mkdir test

working with directories, files, …(cont’d)

rm: remove file, directory, … .

rm –r: remove recursive ->rm –r file

mv: move file, directory, … .

mv /etc/test /var

cp: copy file, directory, … .

cp /etc/test /var


echo: display a line of text

date: print or set the system date and time date –s: set time and date

more: filter and show text less: opposite of more head: output the first part of file

Head –n 5 /etc/init.d/netfs

tail: output the last part of file tail–n 5 /etc/init.d/netfs

alias: summary of commands that you now it alias ll=“ls –l”

: -> arg out to arg in


Important files:

/

/etc

/var

/sbin

/bin

/dev

/usr

/home

/root

/proc

Exercise1

What is . ?

What is .. ?

Using text editors like vi, vim

vi & vim -> vi test.txt

vim: vi improved

command for vi: i -> insert

:w -> save

:q ->quit

:! ->force

:wq! ->save and quit with force

Using text editors like vi, vim(cont’d)

u بٍ حالت قبل بش می گشدد معادلCtrl+z

Ctrl+r بٍ حالت بعذ می سيد معادلCtrl+y

:r ٍتمام مته سا کپی ي بعذ بٍ مکان دلخًاٌ اضاف .می کىذ

xپاک کشدن کاساکتش. dwٍپاک کشدن کلم. ZZرخیشٌ کشدن ي خشيج. e:باصکشدن فایل جذیذ. :nسفته بٍ فایل بعذی کٍ دس حال تغییش است..

Ctrl+u باال بشدن مته يCtrl+e باال بشدن .صفحٍ

Ctrl+d پاییه بشدن مته يCtrl+y پاییه بشدن .صفحٍ

:e filename يیشایش فایل مًسد وظش. Ctrl+g اطالعاتی دس مًسد فایلی کٍ داخل آن

.َستیذ می دَذCtrl+} يCtrl+{ بٍ ابتذا ي اوتُای پاساگشاف

.می سيدJ باال بشدن خط َای پاییه محل مًسد وظش. H بٍ ايلیه خط می سيدL بٍ آخشیه خط می سيد. R بٍ مذ جایگزاسی می سيد. :s/search-text/replace-text/g فقط دس

می پشسذ gci/.خط مًسد وظش جایگزاسی می کىذبشای کل s%:.کٍ می خًاَی تغییش دَی یا خیش

g/start/s/text/rep:.خط َا اوجام می شًدقشاس می دَذ بٍ ششط repَستtextَشجایی کٍ

-start .:5,10s/searchششيع خط با text/replace-text/g جایگزاصی می کىذ اص

.12تا 5خط :3,9d سا پاک می کىذ 9تا خط 3اص خط .

:# سفته بٍ خط#

:5,10w filename سا دس فایل 10تا 5اص خط .مًسد وظش کپی می کىذ

v: سفته بٍ محیط يیژيیال


• :set remap Accept macros within macros

• :set report Indicates largest size of changes reported on status line

• :set ro Changes file type to "read only"

• :set scroll=n set n lines for CTRL-d and z

• :set sh=shell_path set shell escape (default is /bin/sh) to shell_path

• :set showmode Indicates input or replace mode at bottom

• :set slow Postpone display updates during inserts

• :set sm Show matching { or ( as ) or } is typed

• :set sw=n Sets shift width to n characters

• :set tags=x Path for files checked for tags (current directory included in default)

• :set term Prints terminal type

• :set terse Shorten messages with terse

• :set timeout Eliminates one-second time limit for macros

• :set tl=n Sets significance of tags beyond n characters (0 means all)

• :set ts=n Sets tab stops to n for text input

• :set wa Inhibits normal checks before write commands

• :set warn

• warn

• :set window=n Sets number of lines in a text window to n

• :set wm=n Sets automatic wraparound n spaces from right margin.

• :set ws Sets automatic wraparound n spaces from right margin.


• :set ai Turns on auto indentation

• :set all Prints all options to the screen

• :set ap Prints line after d c J m :s t u commands

• :set aw Automatic write on :n ! e# ^^ :rew ^} :tag

• :set bf Discards control characters from input

• :set dir=tmp Sets tmp to directory or buffer file

• :set eb Precedes error messages with a bell

• :set ed Precedes error messages with a bell

• :set ht= Sets terminal hardware tabs

• :set ic Ignores case when searching

• :set lisp Modifies brackets for Lisp

compatibility.

• :set list Shows tabs (^l) and end of line ($)

• :set magic Allows pattern matching with special characters

• :set mesg Allows others to send messages

• :set nooption Turns off option

• :set nu Shows line numbers

• :set opt Speeds output; eliminates automatic RETURN

• :set para= macro names that start paragraphs for { and } operators

• :set prompt Prompts for command input with :

• :set re Simulates smart terminal on dumb terminal


Exercise2

How to search word in text?

How to save output command in text?

What are grep and find command?


od: octal and other format

export: show variables

env: environments variable

wc: show word, char, … .

sort: sort text

uniq: delete repeated lines

pr: print text

touch: change file timestamps

cpio: copy files to and from archives

dd: convert and copy a file

Control on mount & un-mounting process

• mount: verify hardware(device) to Linux

• umount: unmount

• command for mount: mount -> show devices mounted

mount /dev/cdrom /mnt->mount cd rom

mount /dev/sda1 /mnt ->mount sda(storage device type a number1

mount –l –t <type> -> list and type of devices

/etc/udev/rules.d -> verify devices

Control on mount & un-mounting process(cont’d)

Important file:

/etc/fstab

/etc/mtab

/proc/mounts

Exercise3

What is mount point?

What is journaling?

File permissions & ownerships

d r-- r-- r-- = d 4 4 4 -> directory & permission is 444

- --- --- ---

- rwx rwx rwx -> read, write, execute

ll -> - --- --- ---

types are directory, link, … .

File permissions & ownerships(cont’d)

- Normal data file; may be text, an

executable program, graphics, compressed data, or just about any other type of data.

d Directory; disk directories are files

just like any others, but they contain filenames and pointers to disk in odes. Controlling Access to Files 195

l Symbolic link; the file contains the

name of another file or directory. When Linux accesses the symbolic link, it tries to read the linked-to file.

p Named pipe; a pipe enables two

running Linux programs to communicate with each other. One opens the pipe for reading, and the other opens it for writing, enabling data to be transferred between the

programs.

s Socket; a socket is similar to a

named pipe, but it permits network and bidirectional links.

b Block device; a file that

corresponds to a hardware device to and from which data is transferred in blocks of more than one byte. Disk devices (hard disks, floppies, CD-ROMs, and so on) are common block devices.

c Character device; a file that

corresponds to a hardware device to and from which data is transferred in units of one byte. Examples include parallel port, RS-232 serial port, and audio devices.


command for permission

chmod: change file mode -> chmod 777 filename

chown: change file owner and group-> chown user1 filename -> chown –R

Set User ID (SUID)

Set Group ID (SGID)





Command line:

groupadd: create new group -> groupadd test -p test

groupadd –r: create system group

groupdel: delete group

groupmems: add members to group ->groupmems –g test [-l] [-a] [-d]

groupmod: groupmod test –g 777


find / [-group name] [-user name]

newgrp: login to new group

useradd: create new user

Userdell: delete user

passwd: change password


Important directory: /etc/shadow

/etc/group

/etc/gshadow

/etc/login.defs

/etc/passwd

Exercise4 What is umask ?

What is file attributes?

What is sudoedit ?

symbol

• > Creates a new file containing standard output. If the specified file exists, it’s overwritten.

• >> Appends standard output to the existing file. If the specified file doesn’t exist, it’s created.

• 2> Creates a new file containing standard error. If the specified file exists, it’s overwritten.

• 2>> Appends standard error to the existing file. If the specified file doesn’t exist, it’s created.

• &> Creates a new file containing both standard output and standard error. If the specified file exists, it’s overwritten.

• < Sends the contents of the specified file to be used as standard input. • << Accepts text on the following lines as standard input. • <> Causes the specified file to be used for both standard input and

standard output.

Linux installation & package management

Install: some time you should install packages(program) for example MySQL packages. Type of packages are URL, .rpm, name, … . yum install package1 [package2] …

Upgrade: some time you should upgrade program for example change MySQL 4 to 5. yum upgrade [package1] [package2]

Update: some time you should update program for example MySQL 5 to 5.1. yum update [package1] [package2] …

Uninstall: some time you should uninstall program for example erase MySQL. remove | erase [package1] [package2] ….

Linux installation & package management(cont’d)

Another command for package management:

rpm just manage .rpm packages

rpm –i -> install

rpm –U -> upgrade

rpm –v -> print verbose information

rpm –h -> print 50 hash marks as the package archive is unpacked. Use with –v

rpm –e -> erase or uninstall

rpm –Uvh package.rpm


Another command for package management:

wget: download from network and support http, https and ftp.

wget –c -> continue

wget –d ->debug

For install all packages you need make file that and compile and copy configure. For example ./configure -> make -> make install


Important file:

/etc/yum

/etc/yum.conf

/etc/yum.repos.d

Exercise5

install mc packages from local use yum

go to /usr/share/doc and find mc files

Work by mc command

Configure disk partitions

sda1 sda2

LVM

Sda(n)

active Primary[4] Extended[5->]

LVM(Logical Volume Manager) partition

Standard partition

Extended : same as primary but don’t have file system and create logical partition on it and their have fs

Configure disk partitions(cont’d)


A partition can be primary, extended and active Just 1 active, 4 primary Name of hard: sda or hda Name of partition: sda1, sda2, … . Name of device: cdrw, cdrom, sdb, … . fdisk: partition table in linux

fdisk –l : list of all partition->fdisk –l name: details for name

fdisk [name of disk] -> fdisk /dev/sda : manage sda Interactive area m for help


a : bootable flag

n : new partition

q : exit with out save

w : write and exit

d : delete a partition

parted : same as fdisk

partx : show number of partition for sda


Create file system on partition

mke2fs : create ext2,ext3,ext4 fs

resize2fs : resize ext2,ext3,ext4 fs

mkfs: build a linux fs

mkswap : set up a linux swap area


Logical Volume Manager, or LVM, is a storage management solution that allows administrators to divide hard drive space into physical volumes (PV), which can then be combined into logical volume groups (VG), which are then divided into logical volumes (LV) on which the file system and mount point are created.



Example: lvm>

pvcreate pv1

vgcreate vg1

lvcraete –L 10g -n lv1 vg1

Mkfs.ext4 /dev/vg1/lv1

Important files:

/dev/*

/sbin/vg*

/etc/fstab

Exercise6

Create lvm disk and vg and pv

Create ext4 file system on lvm

Manage disk quota & create quota report

File system base disk quota allocation User or group based disk quota allocation

Hard limit – For example, if you specify 2GB as hard limit, user will not be able to create new files after 2GB

Soft limit – For example, if you specify 1GB as soft limit, user will get a warning message “disk quota exceeded”, once they reach 1GB limit. But, they’ll still be able to create new files until they reach the hard limit

Grace Period – For example, if you specify 10 days as a grace period, after user reach their hard limit, they would be allowed additional 10 days to create new files. In that time period, they should try to get back to the quota limit.

Manage disk quota & create quota report(cont’d)

Create user and group for disk quota

Enable disk quota check : ->go fstab

LABEL=/home /home ext2 defaults,usrquota,grpquota 1 2

mount -n -o remount /

Reboot server

Show disk quota: quotacheck –avug

a: Check all quota-enabled file system

v: Verbose mode

u: Check for user disk quota

g: Check for group disk quota

Assigned disk quota: edquota username

Manage disk quota & create quota report(cont’d)

Report disk quota:

Repquota /home

Add quota check daily:

Create cron -> next session

Example: go fastab

/dev/VolGroup1/LogVol1 /home ext3 defaults,usrquota 1 2

Symbolic links, FHS

Link : connection between 2 files. For example /var/spool/mail -> /var/mail

Soft link (symbolic link) : point to file

Hard link : pointer of file in directory so if delete file link is exist

ln : make links between files ln –s : create soft link

ln –p : hard link to soft link

FHS(Filesystem Hierarchy System)

Writing shell script

What is shell script : Shell scripts are plain-text files, so you create them in text editors. A shell script begins with a line that identifies the shell that’s used to run it.

The execute text file begin with #!/bin and if you want use bash commands you insert #!/bin/bash ->sharp bang

For execute that you should set execute permission and enter ./filename.

Writing shell script(cont’d)


Commands for shell script: set: for see system variables

BASH= Our shell name BASH_VERSION= Our shell version name COLUMNS= No. of columns for our screen HOME= Our home directory LINES= No. of columns for our screen LOGNAME= Our logging name OSTYPE= Our OS type PATH= Our path settings PS1= Our prompt settings PWD= Our current working directory SHELL= Our shell name USERNAME= User name who is currently login to this PC


export: definition variable -> export var=10 echo: show quantity of variable -> echo $var

-n Do not output the trailing new line. -e Enable interpretation of the following backslash escaped

characters in the strings: \a alert (bell) \b backspace \c suppress trailing new line \n new line \r carriage return \t horizontal tab \\ backslash

if [ -n "$var" ]; then echo "not empty"

else echo "empty"


How to use and create function:

What is function?

Example: function today {

echo “today is”

date +”%A,%B,%D,%Y”

}

Run today

type: show type of command


Conditions and loops: what is condition and loop? if: what is .bashrc->directory of store information of user bash and

variable and etc. if [ condition]; then commands elif commands else commands fi while: for like while while [condition ]

do commands done


• Example: #!/bin/bash x=“welcome” y=“welcome to linux” z=15 if [ $z –gt 10]; then echo “z=“$z; else if [ $x –eq $y ]; then echo “x=y”; fi echo “var=\n” $x ”\n” $y “\n” $z fi


for: for { variable name } in { list } Condition:

Exercise7 Input 2 number and compare their. so calculate a*b,

a+b, a/b, a10.

Working with archive files

tar: extract, archive, … .

tar –cvf filename.tar filetoarchive

tar –xzf filename –C directory->extract & zip

gzip: compress a file -> gunzip: expand a file

zip & unzip: similar to gzip

System resource management

Run level: 0 – 6 -> /etc/grub.conf

0: turn on

6: turn off

pstree: Shows the Parent-Child Relation Between Processes

gstack: print a stack trace of a running process -> gstack [PID]

more /proc/cpuinfo

top: display Linux task

s -> change delay

z -> change color

h -> help

b -> bold

q -> exit

System resource management(cont’d)

ps: report a snapshot of current process -> ps aux USER: The name of the user who started the process.

PID: The PID of the process. The command ps aux sorts the processes by their PID.

%CPU: The percentage of CPU time the process has used since startup.

%MEM: The percentage of memory the process is currently using.

VSZ: The virtual memory size, which is the total amount of memory claimed by this process.

RSS: The resident memory size, which is the amount of memory the process currently has in use.

TTY: The terminal (TTY) from which the process was started. A question mark indicates a daemon process that is not associated to any TTY.


STAT: The current status of the process.

START: The time at which the process was started.

TIME: The total amount of system time this process has been using since it started.

COMMAND: The command that was used to start this process. If the name of this command is between square brackets (you can see quite a few examples of this in (Listing 9-5), the process is not started with a command at the command line, but is a kernel thread.


Use limited system resource use ulimit command: Core File Limits The -c option limits the size of core dumps, which are

fi les created for

debugging purposes in certain types of program crashes.

File Limits The -f option limits the size of fi les that may be created by the shell, and –n limits the number of open fi le descriptors. (Most systems don’t honor the -n limits, though.)

Process Limits The -u option limits the number of processes a user may run, and -t limits the total CPU time in seconds.

Memory Limits The -v option sets the total amount of virtual memory available to the shell, -s sets the maximum stack size, -m sets the maximum resident set size, -d limits programs’ data set size, and -l sets the maximum size that may be locked into memory.


Hard and Soft Limits The -H and -S options modify other options, causing them to be set as hard or soft limits, respectively. Hard limits may not be subsequently increased, but soft limits may be. If neither option is provided, ulimit sets both the hard and soft limits for the feature specified.

Current Settings Passing -a causes ulimit to report its current settings.

Important directories: /proc/*

/boot/System.map –

Exercise8 Read command : pgrep, pkill, free, kill,

Working with debuggers in Linux

After you write shell script you need debug it and some time you need debug software for this problem we use gdb command.

gdb: GNU debugger

In shell script use (gdb) commands……(gdb)

For software use gdb (option) [ pid or name of software]

Some option of gdb

Working with debuggers in Linux(cont’d)

h: for help q: quit run: run [program name] bt: print call stack = where

up: move up one stack frame down: != up frame: frame n ->go to frame n info: info frame ->information current frame

Exercise9 If you need Debugger command see Debugging with gdb

Tenth Edition, for gdb version 7.6.1.2013, Richard Stallman, Roland Pesch, Stan Shebs, 658paper

gpg command

Checksum: when we transfer or storage data between computers maybe information destroyed and we don’t understand or understand not solve their so we use a method to solve it problem. For example CRC checksum. You Consider, checksum different with encrypt. In data encryption goal is encrypt and in checksum goal is solve and understand mistake. For best data transfer we encrypt and checksum methods.

gpg command(cont’d)

MD5: is a hashing method. First get checksum of data then get hash their.

gpg command(cont’d)

Encryption (gpg GNU Privacy Guard) : 2 way for encryption signature file: just who make file can access it

gpg --output file.sig --detach-sign file

Primary and public key: just who Possessing primary key can access it and other just encrypt file with public key. gpg --gen-key->generate private and public key

gpg --list-key->list of key

gpg --edit-key keyID->edit key

gpg --output [fileforsendkey.gpg] --export->create export key

gpg --armor --output [fileforsendkey.gpg] --export-> Creates ASCII armored output

Security in linux

Physical Access Problems Set bios password

Set grub password

[grub-crypt --sha-256] or [grub-crypt --md5]

Copy to /etc/grub.conf -> password –md5 ………………….

Stolen Passwords

Local Program Bugs Set SUID and SGID bit for program

find / -perm +6000 -type f

Server Bugs

Denial-of-Service Attacks

Encryption Issues

Security in linux(cont’d)

Creating Firewall Rules: iptable

/etc/services: see the services run on linux and more details about them.

netstat -> netstat –ap : see active internet connection



The iptables program is the utility that manages firewall.

First you should know about packet and packet filtering.

iptables -L -t filter Chain INPUT (policy ACCEPT) target prot opt source destination Chain FORWARD (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination



#!/bin/bash iptables -F INPUT iptables -F FORWARD iptables -F OUTPUT iptables -P INPUT DROP iptables -P FORWARD DROP iptables -P OUTPUT DROP # Let traffic on the loopback interface pass iptables -A OUTPUT -d 127.0.0.1 -o lo -j ACCEPT iptables -A INPUT -s 127.0.0.1 -i lo -j ACCEPT # Let DNS traffic pass iptables -A OUTPUT -p udp --dport 53 -j ACCEPT iptables -A INPUT -p udp --sport 53 -j ACCEPT

# Let clients' TCP traffic pass iptables -A OUTPUT -p tcp --sport 1024:65535 -m state \ --state NEW,ESTABLISHED,RELATED -j ACCEPT iptables -A INPUT -p tcp --dport 1024:65535 -m state \ --state ESTABLISHED,RELATED -j ACCEPT # Let local connections to local SSH server pass iptables -A OUTPUT -p tcp --sport 22 -d 172.24.1.0/24 -m state \ --state ESTABLISHED,RELATED -j ACCEPT iptables -A INPUT -p tcp --dport 22 -s 172.24.1.0/24 -m state \ --state NEW,ESTABLISHED,RELATED -j ACCEPT

Do automate tasks in Linux, cron job

What is automate task ?

When use automate task? Some system maintenance tasks should be

performed at regular intervals and are highly automated

Automate task in linux? at

cron: cron is a daemon

at & cron: at just run once and cron run ongoing

Command for cron job:


crontab: execute program to configuration cron crontab –l : see cron job crontab [-u user] [-l | -e | -r] [file]

/etc/cron.d: configuration directory -> sysstat /var/spool/cron: cron job Create cron job:

02 4 * * * root run-parts /etc/cron.daily This line begins with five fields that specify the time. The fields

are, in order, the minute (0–59), the hour (0–23), the day of the month (1–31), the month

(1–12), and the day of the week (0–7; both 0 and 7 correspond to Sunday)


In all cases, you can specify multiple values in several ways: An asterisk (*) matches all possible values.

A list separated by commas (such as 0,6,12,18) matches any of the specified values.

Two values separated by a dash (-) indicate a range, inclusive of the end points. For instance, 9-17 in the hour field specifies a time of from 9:00 a.m. to 5:00 p.m.

A slash, when used in conjunction with some other multi value option, specifies stepped values /a range in which some members are skipped. For instance, */10 in the minute field indicates a job that’s run every 10 minutes

at: at -f commands.txt noon

Working with tcpdump

Capture packets from a particular Ethernet interface using tcpdump -i

Capture only N number of packets using tcpdump -c

Display Captured Packets in ASCII using tcpdump -A


Display Captured Packets in HEX and ASCII using tcpdump -XX

Capture the packets and write into a file using tcpdump -w

Reading the packets from a saved file using tcpdump -r Capture packets with IP address using tcpdump -n Capture packets with proper readable timestamp

using tcpdump -tttt Read packets longer than N bytes

tcpdump -w g_1024.pcap greater 1024

Receive only the packets of a specific protocol type tcpdump -i eth0 arp


Receive packets flows on a particular port using tcpdump port tcpdump -i eth0 port 22

Capture packets for particular destination IP and Port tcpdump -w comm.pcap -i eth0 dst 16.181.170.246

and port 22

tcpdump Filter Packets – Capture all the packets other than arp and rarp tcpdump -i eth0 not arp and not rarp

Introduction to network

tcp/ip and osi model: physical layer data link layer network layer transport layer session layer presentation layer application layer

Topology of network Ring Star bus

protocol

Introduction to network (cont’d)

IP DNS DHCP Port telnet and ssh ftp http and https Arp and rarp icmp

Network configuration

Ifconfig

Setup

DNS Forward

Primary

Secondary

Stub

Reverse

/etc/resolv.conf

/etc/hosts

Network configuration(cont’d)

DHCP How to work dhcp ? /etc/dhcp/dhcpd.conf

Telnet & SSH how to work telnet or ssh? ssh 192.168.1.100 telnet 192.168.1.100

Network configuration(cont’d)

icmp

Ping

tracepath

ftp

How to work ftp?

scp

Education

Linux