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How Does a Raid 10 Array Work

If you need to implement a storage solution that supports I/O-intensive operations (such as database, email, and web servers), RAID 10 is the way to go. Let me show you why. Let’s refer to the below image. Imagine a file that is composed of blocks A, B, C, D, E, and F in the above  Full Article…

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create a software RAID-1 array with mdadm

Redundant Array of Independent Disks (RAID) is a storage technology that combines multiple hard disks into a single logical unit to provide fault-tolerance and/or improve disk I/O performance. Depending on how data is stored in an array of disks (e.g., with striping, mirroring, parity, or any combination thereof), different RAID levels are defined (e.g., RAID-0,  Full Article…

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Overview of Public Key Cryptography

Everyone has public key & a private key messages encrypted with Joe’s private key can only be decrypted with Joe’s public key.   /etc/ssh # /etc/ssh/sshd_config HostKey /etc/ssh/ssh_host_key /etc/ssh/ssh_host_rsa_key   for protocol version 1 /etc/ssh/ssh_host_dsa_key for protocol version 2   IgnoreRhosts .rhosts .shosts   LogLevel MaxAuthTries PermitRootLogin   ssh obtains configuration data from the following sources  Full Article…

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SSH Secure Shell

Allows you to create a secure connections between two computers Client transmits auth info in encrypted form Data send & rcvd also encrypted After first connection client can verify its connected to same server on later sessions Client can use X11 apps lunched from shell   SSH Software Open SSH Open SSL From those other  Full Article…

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NIS Network Information Service

Network Information Service. The Network Information Service (NIS) provides a simple network lookup service consisting of databases and processes. It was formerly known as Sun Yellow Pages (YP). The functionality of the two remains the same; only the name has changed. Its purpose is to provide information, that has to be known throughout the network,  Full Article…

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Network News

Types of News Servers Full Newsfeed – it’s like a large Leaf Node Server – only select group Local News Server  – for a particular company   Configuring Local news Server inn  package conf files in /etc/news inn.conf %s – your user name use like a sender of the email status / timer – how  Full Article…

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Mail procmail

Send mail /etc # less aliases Send mail uses aliases file to read direct mail The program “newaliases” will need to be run after this file updated for any changes to show through to sendmail. /etc # less majordom.cf vi .forward  (file)   -f  flag to update || exit 75 code $HOME/mail.backup     proc  Full Article…

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DNS Domain Name System

DNS Domain Name System Like a phone book for the internet  name <—> numbers   Domain namespace similar to filesystem structure   A  Address NS name server SOA authority PTR pointer MX mail efer   Name Server holds info about structure of tree& resource records every domain has authority name server can cache info so  Full Article…

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Apache Web Server

cd /etc/apache2 file name main configurations files : httpd.conf or /etc/http/ include /etc/apache2/uid.cof   # run under this user/group id less default-server.conf    –set of the document root UserDir:   User directory directive Server Tuning /etc/apache2 #  less server-tuning.conf  – performance of the web server, StartServers  2 MinSpareServers    #for a fast server experience MaxSpareServers  # ServerLimit MaxClients    Full Article…

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Linux home network

/etc #   more resolv.conf # more hosts # more host.conf /etc/sysconfig/network # Diagnostic error /etc # ping dig route ifconfig tcpdump – dump traffic on a network netstat -r   #print router table netstat –inet -a    – examine the various service are listening at your system, what port it’s  opening ps – show process not show  Full Article…

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proc file system

/proc ls for each proces for the system sow a number in that directory find information about that particular process   more cmdline information about process memory used each process have a directory top command cpufreq cpuinfo filesystem interrupts kmsg loadavg – what going on to the system meminfo /proc lsdev | more lsmod |  Full Article…

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Troubleshooting

Keep track of: – system hardware – installation of O.S – HW and SW additions – anomalies Kernel Panics What? a problem occurs that is so serious that kernel stops systems When? typically during boot – with boot message -what the message say  – dmesg command How to diagnose? Start with boot messages , LKCD  Full Article…

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Structure of PERL Scripting

demo.pl   #!/usr/bin/perl -W #enable all warring messages print “What is your first name?\n”;  # \n is a special character represent a new line character $name=<STDIN>;  #variable always variable with sign $ chomp($name); #a new line character $len=lenght($name); # create a variable $len an assigned print”\nHello $name. Your name has $len characters.\n”; #start with a  Full Article…

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backupscript

bash shell script > more backupscript.sh #!/bin/bash backup_log=/usr/local/backups.log backup_err=/usr/local/backups.err mv $backup_log $backup_log.old mv $backup_err $backup_err.old echo “Starting backup on /mnt/data” ‘date’ .” >> $backup_log echo “Errors reported for backup/verify:” ‘date’ .” >> $backup_err  #information appended cd /mnt/data   # change directory tar -cvf /dev/st0 . 2 >>$backup_err   # st0 it’s scsi drv tar saving all in  Full Article…

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Sections of .spec file

Header summary, name, version, copyright,. Prep Steps to prepare source (e.g. apply patch) Build commands to compile source Install installs relative to build root  (/tmp ) Clean cleans build root Files must list all files for binary pkg.

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Hardware RAID vs Software RAID

HW RAID has controller that handles all aspects of RAID level (with a RAID controller / controller take care of all control aspects) HW RAID makes the RAID array appear as a single disk to O.S.     SW RAID is implemented in kernel SW RAID does not require expensive controllers or hot swap chassis  Full Article…

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RAID levels

Level 0  – disk striping  – break in peaces ant put in every disk fast transfer – by loosing 1 disk we loose all date Level 1  – disk mirroring – every hdd have a backup, data integrity Level 5  – disk striping with distributed parity –   Level 4 – data recovery activity –  Full Article…

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RAID

Redundant Array of Inexpensive Disks Large capacity, high performance yet cheap Can also provide data security

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Linux NFS-HOWTO

Table of Contents 1. Preamble 1.1. Latest Version 1.2. Disclaimer 1.3. Contributors 1.4. Feedback 1.5. Translation 1.6. Dedication 2. Introduction 2.1. What is NFS? 2.2. The Purpose of this Document 2.3. Knowledge Pre-Requisites 2.4. Software Pre-Requisites: Kernel Version and nfs-utils 2.5. Where to get help and further information 3. Setting Up an NFS Server 3.1.  Full Article…

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NFS Network File System

Allows Linux machines to share files Typical uses: share home directories between hosts in a network share binaries   NFS overview  NFS configurations   /etc/hosts.allow /etc/hosts.deny /etc/exports  (configure a directory properties)     :/etc > more exports /usr/local    192.168.1.0/255.255.255.0 (ro,root_squas, sync)   mount user local machine mounted in this directory :/mnt # 192.168.1.101:/usr/local /mnt/nugger1usrlocal/ :/mnt/nugger1usrlocal/  Full Article…

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Configuring Samba

edit smb.conf hand (use testparm smb.conf to check syntax of the configuration) Yast system tools utilities on SUSE SWAT – Samba Web Admin Tool Webmin

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smb.conf layout

3 special sections   [global]   global config settings [homes] Share users home directories [printers] defines shared printer access   User define sections [programs] path=/usr/local/programs writable=true valid users=joe browsable=yes create mode =0700   A zillion parameters require passwords limit by host limit by time of day    

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Samba overview

uses session message block protocol allows Windows & Linux to interact Simple to complex configurations /etc/samba/smb.conf  

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Creating a loopback filesystem

Creating a loopback filesystem   allow to have a filesystem contain in a single files   losetup /dev/loop0   /tm/fstest.img mke2fs /dev/loop0 mkdir /mnt/fstestimage munt /dev/look0 /mnt/fstestimage/ df -h /mnt/fstestimage umount /mnt/fstestimage/ mount -o loop /tmp/fstest.img /mnt/fstestimage/ cd fstestimage/ ls dumpe2fs /tm/fstest.img     (look at the dump of the filesystem,inodes in use, ecc)

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Relocating a filesystem

Relocating a filesystem /dev/hdb partition & format it move file to it /home Associate /home with it permanently 1. Install new drive double check jumpers large drivers & old BIOS sometimes incompatible 2. Create partition table and mount it mke2fs  -c  -j  /dev/hdb1 (-c   -j) mkdir /mnt/driverb (temporary month point ) mount -t ext3 /dev/hdb1    Full Article…

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Runlevels, shutdown, and reboot

Runlevels Runlevels define what tasks can be accomplished in the current state (or runlevel) of a Linux system. Every Linux system supports three basic runlevels, plus one or more runlevels for normal operation. The basic runlevels are shown in Table 1. Table 1. Linux basic runlevels Level Purpose 0 Shut down (or halt) the system  Full Article…

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Run levels

A run level is a state of init and the whole system that defines what system services are operating. Run levels are identified by numbers. Some system administrators use run levels to define which subsystems are working, e.g., whether X is running, whether the network is operational, and so on. Others have all subsystems always  Full Article…

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Naming Conventions for Hard Disks and Partitions

The naming conventions GRUB uses for hard disks and partitions differ from those used for normal Linux devices. It more closely resembles the simple disk enumeration the BIOS does and the syntax is similar to that used in some BSD derivatives. In GRUB, the numbering of the partitions starts with zero. This means that (hd0,0)  Full Article…

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GRUB

/boot/grub   /boot/grub/ menu.lst /boot/grub/device.map /etc/grub.conf   Installation Installation of GRUB is a two-step process. The first step is to install or build GRUB in a host OS environment, and for this we will, of course, use Linux. The second step is to install and configure GRUB as the boot loader for your system. The  Full Article…

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LILO errors

When LILO loads itself it displays the word “LILO”. Each letter is printed before or after some specific action. If LILO fails at some point, the letters printed so far can be used to identify the problem. (nothing) No part of LILO has been loaded. LILO either isn’t installed or the partition on which its  Full Article…

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LILO

lilo.conf This file, by default /etc/lilo.conf, is read by the boot loader installer ‘lilo’  The /etc/lilo.conf  File As with many Linux utilities, LILO can be customized with a configuration file in the /etc directory. The lilo.conf file has its own man page which is quite thorough. In fact, it may be a little too thorough  Full Article…

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Boot Loaders

2 way to set it up BIOS loads IPL from MBR BIOS loades another boot loader which load TPL from /boot   IPL= initial program loader a.k.a first stage boot loader MBR = master boot loader

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