How to modify IP, default gateway in Linux

Use Ifconfig, specifiy the network card to be modify and the values, it should be effective after the command:
  
# ifconfig eth0 192.168.0.20 netmask 255.255.255.0

One can also modify it at the file which specifies the network setting, this method requires a restart of the :

#vi /etc/sysconfig/network-scripts/ifcfg-eth0
          
            DEVICE=eth0
            BOOTPROTO=static
            BROADCAST=192.168.202.255
            HWADDR=00:09:6B:09:0E:BE
            IPADDR=192.168.202.244
            NETMASK=255.255.255.0
            NETWORK=192.168.202.0
            ONBOOT=yes

 Change the default gateway that take in effect immediately:
 # route add default gw 192.168.0.254

or

#vi /etc/sysconfig/network

           NETWORKING=yes
           NETWORKING_IPV6=no
           HOSTNAME=x3451
          GATEWAY=192.168.202.254

Ti restart the network card, the command is:

#/etc/init.d/network restart

How to move 2Gb or bigger file in a script

#!/bin/sh

find /backup/include -printf '%s %p\n' | while read size name; do
    if [ "$size" -gt 2000000000 ]; then
        mv -i "$name" /backup/exclude
    fi
done

How to load user preference at user login

At Linux/Unix, user can set preference value(e.g. alias, folder and file default color). These values are loaded from a startup file every time when a user logs in or by excecuting the "source {filename}" command.

Startup file are different from one shell to and other. To confirm what the current shell is, simply do the command "echo $shell", and it will be shown on the screen. The startup file usually stored at the default root directory - usually this is the first location where a user hits after the login.

There are always some overly cautious administrator would assign the user to another directory other than the default root directory by executing a cd command at the startup file for the sake of safety. In this case, one must first guess what the the default root directory is by the username and have a search in the /usr/ directory.

Startup file are usually invisible(filenames with "." at the front) to the user, to make it visible, do "ls -a" and edit it with your default editor.

Startup file name by Shells:

.login      --      csh shell

.tcshrc    --     tcsh shell

A sample Startup script:

#set environment

#alias

alias lla 'ls -lrta'
alias ll 'ls -lrt'
alias ls 'ls -x --color'
alias pwd 'echo $cwd' # This is faster than executing the pwd command
alias rm '/bin/rm -i'
alias checkdate 'ls \\!^ | awk -F. {print $1 $7} | sort -u'

setenv LS_COLORS 'no=00:fi=00:di=01;34:ln=01;36:pi=40;33:so=01;35:bd=40;33;01:cd=40;33;01:or=01;05;37;41:mi=01;05;37;41:ex=01;32:*.cmd=01;32:*.exe=01;32:*.com=01;32:*.btm=01;32:*.bat=01;32:*.sh=01;32:*.csh=01;32:*.tar=01;31:*.tgz=01;31:*.arj=01;31:*.taz=01;31:*.lzh=01;31:*.zip=01;31:*.z=01;31:*.Z=01;31:*.gz=01;31:*.bz2=01;31:*.bz=01;31:*.tz=01;31:*.rpm=01;31:*.cpio=01;31:*.jpg=01;35:*.gif=01;35:*.bmp=01;35:*.xbm=01;35:*.xpm=01;35:*.png=01;35:*.tif=01;35:'

About chmod...

1. set it readable only for outsiders:

Before:	-rwxr-xr-x  archive.sh
Command:	chmod o=r archive.sh
After:	-rwxr-xr--  archive.sh

2. Take away all permissions for the group for topsecret.inf

Before:	-rw-r-----  topsecret.inf
Command:	chmod g= topsecret.inf
After:	-rw-------  topsecret.inf

3. Open up publicity.html for reading and writing by anyone.

Before:	-rw-r--r--  publicity.html
Command:	chmod og=rw publicity.html
After:	-rw-rw-rw-  publicity.html

Passwordless SSH connection

Spend the whole day to figure out how it works = ="

This is the scenario where server A wants to establish a connection to B without keying password:

a) Log in Server A with user Id 'userA' and corresponding passowrd.

b) Create the keys in server 'A' with the following command.
/user/local/bin/ssh-keygen –t rsa

c) Copy the public key in id_rsa.pub file under HOME_DIRECTOR/.ssh directory of server 'A'

d) Copy the 'id_rsa.pub' file of server A to 'authorized_keys' file of server B in B's HOME_DIRECTORY/.ssh directory

e) Grant both .ssh/ of server A & B 700 (chmod -R 700 .ssh/)

f) Log into server 'A' with 'userA' user ID

g) Execute the sftp command for server B, eg. sftp userB@Bserver

Get Date of Yesterday

----------------------------Ksh Shell Script--------------------------------

#! /usr/bin/ksh
# Get yesterday's date in YYYY-MM-DD format.
# With argument N in range 1..28 gets date N days before.
# Tapani Tarvainen January 2002
# This code is in the public domain.

OFFSET=${1:-1}

case $OFFSET in
  *[!0-9]* | ???* | 3? | 29) print -u2 "Invalid input" ; exit 1;;
esac

eval `date "+day=%d; month=%m; year=%Y`
typeset -Z2 day month
typeset -Z4 year

# Subtract offset from day, if it goes below one use 'cal'
# to determine the number of days in the previous month.
day=$((day - OFFSET))
if (( day <= 0 )) ;then
  month=$((month - 1))
  if (( month == 0 )) ;then
    year=$((year - 1))
    month=12
  fi
  set -A days `cal $month $year`
  xday=${days[$(( ${#days[*]}-1 ))]}
  day=$((xday + day))
fi

print $year-$month-$day
print $month/$day/${year#??}


------------------------Bash Shell Script------------------------------

#!/bin/bash

OFFSET=1;

eval `date "+day=%d; month=%m; year=%Y"`

# Subtract offset from day, if it goes below one use 'cal'

# to determine the number of days in the previous month.

day=`expr $day - $OFFSET`

if [ $day -le 0 ] ;then

month=`expr $month - 1`

if [ $month -eq 0 ] ;then

year=`expr $year - 1`

month=12

fi

set `cal $month $year`

xday=${$#}

day=`expr $xday + $day`

fi

echo $year-$month-$day


------------------------- Linux--------------------------

curdate=`date +%y%m%d -d "yesterday"`

Useful monitoring command of Unix/Linux Vol.2

Change ownership of a directory: chown -Rv username somedir
Change usergroup or a directory: chgrp -Rv usergroup somedir
To set environment variable: setenv
To load the control file: source <filename> (Shell csh only)
To enable sqlplus/Oracle at the first run:

setenv ORACLE_HOME /opt/app/oracle/product/10.2.0/Db_1
setenv ORACLE_SID ASMDB003
setenv ORACLE_TRACE T
setenv ORAENV_ASK NO
setenv NLS_LANG American_America.we8iso8859p1

setenv LD_LIBRARY_PATH /usr/lib:/usr/ucblib:/usr/local/lib:/opt/SUNWspro/lib:$OR
ACLE_HOME/lib:$ORACLE_HOME/precomp/lib:$ORACLE_HOME/rdbms/lib:$ORACLE_HOME/jdbc/
lib:$ORACLE_HOME/dbjava/lib:/user/sfw/lib

setenv PATH /bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:/usr/cc
s/bin:/opt/SUNWspro/bin:${ORACLE_HOME}/bin
setenv PATH ${PATH}:${HOME}/bin

Difference on Changing Java SDK version between Solaris and Linux

Change Java SDK version

1. go to bin folder
/bin/ -> ls -l
2. change the symbolic link to point to the new versionln -s /usr/jdk/jdk1.6.0_20/bin/ControlPanel ControlPanel
ln -s /usr/jdk/jdk1.6.0_20/bin/HtmlConverter HtmlConverter
ln -s /usr/jdk/jdk1.6.0_20/bin/appletviewer appletviewer
ln -s /usr/jdk/jdk1.6.0_20/bin/apt apt
ln -s /usr/jdk/jdk1.6.0_20/bin/extcheck extcheck
ln -s /usr/jdk/jdk1.6.0_20/bin/idlj idlj
ln -s /usr/jdk/jdk1.6.0_20/bin/jar jar
ln -s /usr/jdk/jdk1.6.0_20/bin/jarsigner jarsigner
ln -s /usr/jdk/jdk1.6.0_20/bin/java java
ln -s /usr/jdk/jdk1.6.0_20/bin/javac javac
ln -s /usr/jdk/jdk1.6.0_20/bin/javadoc javadoc
ln -s /usr/jdk/jdk1.6.0_20/bin/javah javah
ln -s /usr/jdk/jdk1.6.0_20/bin/javap javap
ln -s /usr/jdk/jdk1.6.0_20/bin/javaws javaws
ln -s /usr/jdk/jdk1.6.0_20/bin/jdb jdb
ln -s /usr/jdk/jdk1.6.0_20/bin/keytool keytool
ln -s /usr/jdk/jdk1.6.0_20/bin/native2ascii native2ascii
ln -s /usr/jdk/jdk1.6.0_20/bin/orbd orbd
ln -s /usr/jdk/jdk1.6.0_20/bin/policytool policytool
ln -s /usr/jdk/jdk1.6.0_20/bin/rmic rmic
ln -s /usr/jdk/jdk1.6.0_20/bin/rmid rmid
ln -s /usr/jdk/jdk1.6.0_20/bin/rmiregistry rmiregistry
ln -s /usr/jdk/jdk1.6.0_20/bin/serialver serialver
ln -s /usr/jdk/jdk1.6.0_20/bin/servertool servertool
ln -s /usr/jdk/jdk1.6.0_20/bin/tnameserv tnameserv

For Linux used only:
Change Java SDK version

1. backup old java file
2. change the symbolic link to point to new version

e.g. 

mv java java.bk
ln -s /usr/local/jdk1.6.0_20/bin/java java
mv javac javac.bk
ln -s /usr/local/jdk1.6.0_20/bin/javac javac
mv javadoc javadoc.bk
ln -s /usr/local/jdk1.6.0_20/bin/javadoc javadoc
mv javah javah.bk
ln -s /usr/local/jdk1.6.0_20/bin/javah javah

Useful monitoring command of Unix/Linux Vol.1

For Solaris Only:

check number of core: prtdiag -v 
create new user: useradd jsmith
get user information: finger jsmith
set password: passwd jsmith
set default home directory: usermod -d /path/to/new/homedir/ username
set default Shell: change permenently the SHELL at etc/passwd
check Solaris release: cat /etc/release
Check current shell: echo $SHELL
Check shell version: /bin/bash --version