10 recorded Centos Video Classes, exclusively for you.

10 recorded Centos Video Classes, exclusively for you.
1. Introduction about Centos 7

Introduction to the Linux – Centos 7

2. File System Hierarchy with fully animated graphics

File System Hierarchy – Centos 7

3. Build your Lab using Virtualization

Centos Build Your Lab on Virtual

4. Installation of VirtualBox

Centos Install Virtual Box on Windows

5. Create your First Virtual Machine

Centos Create your First Virtual Machine

6. Centos 7 Installation Process Part -1

Centos 7 Installation Part 1 in virtual Box

7. Centos 7 Installation Process Part -2

Centos 7 Installation Part 2 in Virtual Box

8. First Look of Centos 7

Centos 7 Start the Centos

9.Few Basic Commands

Centos 7 ls Command to List files and Directories

10. Change and Moving between Directories

Centos 7 cd Command to move in between directories

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systemctl command in rhel 7 and centos 7

use systemctl to start, restart and shutdown rhel 7 and centos 7

In this article we are going to learn how to restart, shutdown and change run Levels = Targets in RHEL 7. This article is useful for the guys who are preparing for the RHCSA and RHCE examination.

Using operating systems

Start, restart and shutdown a system normally
Start systems manually in different destinations
Interrupting the boot process in order to gain access to a system
Identify the processes that make heavy use of the CPU and memory, adjust the priority of processes renice and kill processes
Locate and interpret system log files and newspapers
Access the console of a virtual machine
Start and stop virtual machines
Transfer files between different systems securely

How to use systemctl command in redhat enterprise linux 7
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collect server information using shell script

Gather server information within a second

If we have lot many servers and we would like to collect the asset inventory of each and every server then it is very difficult to run various commands we have to run in order to collect / gather entire information about each server. If we manually run all the commands in each server it may require 5 minutes of time for each server where using below script which may reduce your time to 2 minutes for 100 Servers wow..!!.

Gather server information within a second

Lets see how we can achieve this task using shell script.

Note: We do not recommend to run this script in any production servers, we strictly suggest you to run this in test or home environment only. This script will come either no WARRANTY with NO support.

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Top 5 Open Source Monitoring Tools

Most of the organizations works an servers to develop code, generate productivity so on. If suddenly Server goes down OR Network device goes Down there is a big question mark for all System Administrators, Managers and Engineers. Get ride of unknown server down. No need ping the servers to see whether servers are running. Just install and configure any of these monitoring tools that’s it, they will monitor all servers, services and network devices whenever any device / service stopped they will send us an alert via Email OR SMS.

Troubleshooting Networking devices and testing using tools — Tech Tutorials

Tech tutorials by ARK http://www.arkit.co.in Troubleshooting Networking devices and testing using tools Troubleshooting Networking Data transmitted within a network travels through various physical devices and finally reaches the intended destination. If any device in the transmission path is not working, the data will not be transmitted. Various testing and troubleshooting tools are available to keep…

via Troubleshooting Networking devices and testing using tools — Tech Tutorials

Mastering the art of troubleshooting book download

Preface
Chapter 1: Best Practices and Initial Investigation
Chapter 2: strace and System Call Tracing Explained
Chapter 3: The /proc Filesystem
Chapter 4: Compiling
Chapter 5: The Stack
Chapter 6: The GNU Debugger (GDB)
Chapter 7: Linux System Crashes and Hangs
Chapter 8: Kernel Debugging with KDB
Chapter 9: ELF: Executable and Linking Format
A: The Toolbox
B: Data Collection Script
Index
Contents
Preface xvii
1 Best Practices and Initial Investigation 1
1.1 Introduction 1
1.2 Getting Your System(s) Ready for Effective Problem
Determination 2
1.3 The Four Phases of Investigation 3
1.3.1 Phase #1: Initial Investigation Using Your Own Skills 5
1.3.2 Phase #2: Searching the Internet Effectively 9
1.3.3 Phase #3: Begin Deeper Investigation (Good Problem
Investigation Practices) 12
1.3.4 Phase #4: Getting Help or New Ideas 21
1.4 Technical Investigation 28
1.4.1 Symptom Versus Cause 28
1.5 Troubleshooting Commercial Products 38
1.6 Conclusion 39
2 strace and System Call Tracing Explained 41
2.1 Introduction 41
2.2 What Is strace? 41
2.2.1 More Information from the Kernel Side 45
2.2.2 When to Use It 48
2.2.3 Simple Example 49
2.2.4 Same Program Built Statically 53
2.3 Important strace Options 54
2.3.1 Following Child Processes 54
2.3.2 Timing System Call Activity 55
2.3.3 Verbose Mode 57
2.3.4 Tracing a Running Process 59
2.4 Effects and Issues of Using strace 60
2.4.1 strace and EINTR 61
2.5 Real Debugging Examples 62
2.5.1 Reducing Start Up Time by Fixing
LD_LIBRARY_PATH 62
2.5.2 The PATH Environment Variable 65
2.5.3 stracing inetd or xinetd (the Super Server) 66
2.5.4 Communication Errors 68
2.5.5 Investigating a Hang Using strace 69
2.5.6 Reverse Engineering (How the strace Tool Itself Works) 71
2.6 System Call Tracing Examples 74
2.6.1 Sample Code 75
2.6.2 The System Call Tracing Code Explained 87
2.7 Conclusion 88
3 The /proc Filesystem 89
3.1 Introduction 89
3.2 Process Information 90
3.2.1 /proc/self 90
3.2.2 /proc/ in More Detail 91
3.2.3 /proc//cmdline 107
3.2.4 /proc//environ 107
3.2.5 /proc//mem 107
3.2.6 /proc//fd 108
3.2.7 /proc//mapped base 108
3.3 Kernel Information and Manipulation 109
3.3.1 /proc/cmdline 109
3.3.2 /proc/config.gz or /proc/sys/config.gz 109
3.3.3 /proc/cpufreq 109
3.3.4 /proc/cpuinfo 110
3.3.5 /proc/devices 110
3.3.6 /proc/kcore 111
3.3.7 /proc/locks 111
3.3.8 /proc/meminfo 111
3.3.9 /proc/mm 111
3.3.10 /proc/modules 112
3.3.11 /proc/net 112
3.3.12 /proc/partitions 112
3.3.13 /proc/pci 113
3.3.14 /proc/slabinfo 113
x Contents
3.4 System Information and Manipulation 113
3.4.1 /proc/sys/fs 113
3.4.2 /proc/sys/kernel 115
3.4.3 /proc/sys/vm 120
3.5 Conclusion 120
4 Compiling 121
4.1 Introduction 121
4.2 The GNU Compiler Collection 121
4.2.1 A Brief History of GCC 121
4.2.2 GCC Version Compatibility 122
4.3 Other Compilers 122
4.4 Compiling the Linux Kernel 123
4.4.1 Obtaining the Kernel Source 123
4.4.2 Architecture Specific Source 124
4.4.3 Working with Kernel Source Compile Errors 124
4.4.4 General Compilation Problems 128
4.5 Assembly Listings 133
4.5.1 Purpose of Assembly Listings 134
4.5.2 Generating Assembly Listings 135
4.5.3 Reading and Understanding an Assembly Listing 136
4.6 Compiler Optimizations 140
4.7 Conclusion 149
5 The Stack 151
5.1 Introduction 151
5.2 A Real-World Analogy 152
5.3 Stacks in x86 and x86-64 Architectures 153
5.4 What Is a Stack Frame? 157
5.5 How Does the Stack Work? 159
5.5.1 The BP and SP Registers 159
5.5.2 Function Calling Conventions 162
5.6 Referencing and Modifying Data on the Stack 171
5.7 Viewing the Raw Stack in a Debugger 173
5.8 Examining the Raw Stack in Detail 176
5.8.1 Homegrown Stack Traceback Function 180
5.9 Conclusion 191
6 The GNU Debugger (GDB) 193
6.1 Introduction 193
6.2 When to Use a Debugger 194
6.3 Command Line Editing 195
Contents xi
6.4 Controlling a Process with GDB 196
6.4.1 Running a Program Off the Command Line with GDB 197
6.4.2 Attaching to a Running Process 199
6.4.3 Use a Core File 200
6.5 Examining Data, Memory, and Registers 204
6.5.1 Memory Map 204
6.5.2 Stack 206
6.5.3 Examining Memory and Variables 210
6.5.4 Register Dump 217
6.6 Execution 220
6.6.1 The Basic Commands 221
6.6.2 Settings for Execution Control Commands 223
6.6.3 Breakpoints 228
6.6.4 Watchpoints 230
6.6.5 Display Expression on Stop 234
6.6.6 Working with Shared Libraries 235
6.7 Source Code 238
6.8 Assembly Language 240
6.9 Tips and Tricks 241
6.9.1 Attaching to a Process.Revisited 241
6.9.2 Finding the Address of Variables and Functions 244
6.9.3 Viewing Structures in Executables without Debug
Symbols 246
6.9.4 Understanding and Dealing with Endian-ness 250
6.10 Working with C++ 252
6.10.1 Global Constructors and Destructors 252
6.10.2 Inline Functions 256
6.10.3 Exceptions 257
6.11 Threads 260
6.11.1 Running Out of Stack Space 265
6.12 Data Display Debugger (DDD) 266
6.12.1 The Data Display Window 268
6.12.2 Source Code Window 272
6.12.3 Machine Language Window 273
6.12.4 GDB Console Window 274
6.13 Conclusion 274
7 Linux System Crashes and Hangs 275
7.1 Introduction 275
7.2 Gathering Information 275
7.2.1 Syslog Explained 276
7.2.2 Setting up a Serial Console 277
xii Contents
7.2.3 Connecting the Serial Null-Modem Cable 278
7.2.4 Enabling the Serial Console at Startup 279
7.2.5 Using SysRq Kernel Magic 281
7.2.6 Oops Reports 281
7.2.7 Adding a Manual Kernel Trap 281
7.2.8 Examining an Oops Report 284
7.2.9 Determining the Failing Line of Code 289
7.2.10 Kernel Oopses and Hardware 293
7.2.11 Setting up cscope to Index Kernel Sources 294
7.3 Conclusion 295
8 Kernel Debugging with KDB 297
8.1 Introduction 297
8.2 Enabling KDB 297
8.3 Using KDB 299
8.3.1 Activating KDB 299
8.3.2 Resuming Normal Execution 300
8.3.3 Basic Commands 300
8.4 Conclusion 305
9 ELF: Executable and Linking Format 307
9.1 Introduction 307
9.2 Concepts and Definitions 309
9.2.1 Symbol 309
9.2.2 Object Files, Shared Libraries, Executables, and Core
Files 311
9.2.3 Linking 314
9.2.4 Run Time Linking 318
9.2.5 Program Interpreter / Run Time Linker 318
9.3 ELF Header 318
9.4 Overview of Segments and Sections 324
9.5 Segments and the Program Header Table 325
9.5.1 Text and Data Segments 329
9.6 Sections and the Section Header Table 331
9.6.1 String Table Format 335
9.6.2 Symbol Table Format 335
9.6.3 Section Names and Types 338
9.7 Relocation and Position Independent Code (PIC) 362
9.7.1 PIC vs. non-PIC 363
9.7.2 Relocation and Position Independent Code 366
9.7.3 Relocation and Linking 367
9.8 Stripping an ELF Object 371
Contents xiii
9.9 Program Interpreter 372
9.9.1 Link Map 376
9.10 Symbol Resolution 377
9.11 Use of Weak Symbols for Problem Investigations 382
9.12 Advanced Interception Using Global Offset Table 386
9.13 Source Files 390
9.14 ELF APIs 392
9.15 Other Information 392
9.16 Conclusion 392
A The Toolbox 393
A.1 Introduction 393
A.2 Process Information and Debugging 393
A.2.1 Tool: GDB 393
A.2.2 Tool: ps 393
A.2.3 Tool: strace (system call tracer) 394
A.2.4 Tool: /proc filesystem 394
A.2.5 Tool: DDD (Data Display Debugger) 394
A.2.6 Tool: lsof (List Open Files) 394
A.2.7 Tool: ltrace (library call tracer) 395
A.2.8 Tool: time 395
A.2.9 Tool: top 395
A.2.10 Tool: pstree 396
A.3 Network 396
A.3.1 Tool: traceroute 396
A.3.2 File: /etc/hosts 396
A.3.3 File: /etc/services 396
A.3.4 Tool: netstat 397
A.3.5 Tool: ping 397
A.3.6 Tool: telnet 397
A.3.7 Tool: host/nslookup 397
A.3.8 Tool: ethtool 398
A.3.9 Tool: ethereal 398
A.3.10 File: /etc/nsswitch.conf 398
A.3.11 File: /etc/resolv.conf 398
A.4 System Information 399
A.4.1 Tool: vmstat 399
A.4.2 Tool: iostat 399
A.4.3 Tool: nfsstat 399
A.4.4 Tool: sar 400
A.4.5 Tool: syslogd 400
A.4.6 Tool: dmesg 400
xiv Contents
A.4.7 Tool: mpstat 400
A.4.8 Tool: procinfo 401
A.4.9 Tool: xosview 401
A.5 Files and Object Files 401
A.5.1 Tool: file 401
A.5.2 Tool: ldd 401
A.5.3 Tool: nm 402
A.5.4 Tool: objdump 402
A.5.5 Tool: od 402
A.5.6 Tool: stat 402
A.5.7 Tool: readelf 403
A.5.8 Tool: strings 403
A.6 Kernel 403
A.6.1 Tool: KDB 403
A.6.2 Tool: KGDB 403
A.6.3 Tool: ksymoops 404
A.7 Miscellaneous 404
A.7.1 Tool: VMWare Workstation 404
A.7.2 Tool: VNC Server 405
A.7.3 Tool: VNC Viewer 405
B Data Collection Script 407
B.1 Overview 407
B.1.1 -thorough 409
B.1.2 -perf, -hang , -trap, -error 409
B.2 Running the Script 410
B.3 The Script Source 410
B.4 Disclaimer 419

Cryptography involves encryption and decryption to safeguard data

Cryptography involves encryption and decryption to safeguard data

  • There are two types of threats internal and external
  • Cryptography involves encrypton and decryption to safeguard data
  • Digital signatures involve the use of private and public keys
  • Authentication involves verification before starting communication
  • Encryption refers to conversion of plain text into cipher text
  • Decryption means converting the cipher text back to plain text
  • Firewall blocks unwanted and unathorized access to system resources
  • Demilitarized zone is usally present between the firewall and internet
  • VLAN is a switched network logically segmented on an organizational basis
  • RAID uses different techniques of using multiple drives for data protection
  • Network Attached Storage is used to implement a file sharing server
  • SAN is used to transfer data between storage devices and computers
  • Tape backup is essential in case of hrdware or server crash
  • SSL is designed to provide security and compression services to data
  • IPSEC provides security to a packet at the network level
  • PPTP allows secure data transfer from a remote client to a private server
  • Point-to-Point Protocol (PPP) is used for point to access
  • SLIP is used to send IP datagrams between serially connected devices

An application layer solution. It is a connection-oriented service and thus uses TCP ONLY. SSH is primarily used for shell based solutions and ideally won’t be used to protect web browsing sessions and other application services (though it can via port forwarding)
Uses public key cryptography to prove the authenticity of the remote user. SSH can generate an RSA key pair (I believe Diffie-Hellman can also be used). It uses what’s known as a fingerprint which is a snapshot of an individual host’s actual public key (for instance the RSA public portion). The fingerprints are usually 128 bits in length. It is what the user can use to verify that a public key is that of an individual or host. SSH will maintain a list of trusted hosts. The actual data communication is secured using symmetric cryptography such as AES or 3DES, IDEA
The public portion of the key is transmitted to the remote endpoint/server via an out-of-band mechanism. Also a lack of key management
SSH does provide some extensible features. Two of these are port forwarding and secure tunneling. With port forwarding, you can tell the SSH daemon to listen to data communication on a particular port and forward this communication to the encrypted SSH session. This allows you to protect other services as well. In Linux, X11 forwarding takes advantage of this. X11 is used for graphical display of a remote system on your localhost. With port forwarding, SSH can be used to provide an encrypted session for X11