CS & IT Solutions

Open
vi filename

Close/Quit/Quit without save
:q = close the file, if you didnt modified anything
:q! = close the file even u modified and dont want to save it
:

Save/ Save quit
:wq = save and exit
= save and stay

Add

i = from cursor before start append
I = begin of line allow appending

a = after cursor append
A =end of line append

o = new line
O =before cursor new line

Edit
r = from cursor character edit
R = replace from cursor anything on type, until esc pressed

cw = word replace

Del

dd = entire line delete

x = single character

dw = single word

D = remaining of the line starting with current cursor position

Cut/Past

yy = copy the current line into the buffer

Nyy or yNy = copy the next N lines, including the current line, into the buffer

p = paste the line in the buffer into the text after the current line

Searching

/string  = search forward for occurrence of string in text

?string = search backward for occurrence of string in text

n = move to next occurrence of search string

N = move to occurrence of search string in opposite direction

Line numbers:

: .=    returns line number of current line at bottom of screen

:= returns the total number of lines at bottom of screen

^g  provides the current line number, along with the total number of lines, in the file at the bottom of the screen

KernelTo successfully run enterprise applications, such as a database server, on your Linux distribution, you may be required to update some of the default kernel parameter settings. For example, the 2.4.x series kernel message queue parameter msgmni has a default value (for example, shared memory, or shmmax is only 33,554,432 bytes on Red Hat Linux by default) that allows only a limited number of simultaneous connections to a database. Here are some recommended values (by the IBM DB2 Support Web site) for database servers to run optimally:

Shared Memory

Semaphores

ulimits

Message queues Read the rest of this entry »

rm -f /backup/mysql*
### System Setup ###
BACKUP=/backup
NOW=$(date +”%d-%m-%Y”)

### MySQL Setup ###
MUSER=”mysqluser”
MPASS=”password”
MHOST=”localhost”
MYSQL=”$(which mysql)”
MYSQLDUMP=”$(which mysqldump)”
GZIP=”$(which gzip)”

### Start MySQL Backup ###
# Get all databases name
DBS=”$($MYSQL -u $MUSER -h $MHOST -p$MPASS -Bse ‘show databases’)”
for db in $DBS
do
FILE=$BACKUP/mysql-$db.$NOW-$(date +”%T”).gz
$MYSQLDUMP -u $MUSER -h $MHOST -p$MPASS $db | $GZIP -9 > $FILE
done

source here

What is iptable? Iptables is a generic table structure that defines rules and commands as part of the netfilter framework that facilitates Network Address Translation (NAT), packet filtering, and packet mangling in the Linux 2.4 and later operating systems. NAT is the process of converting an Internet Protocol address (IP address) into another IP address. Packet filtering is the process of passing or blocking packets at a network interface based on source and destination addresses, ports, or protocols. Packet mangling is the ability to alter or modify packets before and/or after routing.

Iptables and netfilter are the successor to ipchains and ipfwadm in earlier versions of Linux. Netfilter and iptables are often combined into the single expression netfilter /iptables, which refers to the Linux 2.4 and later subsystems for NAT, firewall, and advanced packet processing.

How do I block an IP address or subnet under Linux operating system?

In order to block an IP on your Linux server you need to use iptables tools (administration tool for IPv4 packet filtering and NAT) and netfilter firewall. First you need to log into shell as root user. To block IP address you need to type iptables command as follows:
Syntax to block an IP address under Linux

Replace IP-ADDRESS with actual IP address. For example if you wish to block ip address 65.55.44.100 for whatever reason then type command as follows:

If you have IP tables firewall script, add above rule to your script.

If you just want to block access to one port from an ip 65.55.44.100 to port 25 then type command:
# iptables -A INPUT -s 65.55.44.100 -p tcp –destination-port 25 -j DROP
The above rule will drop all packets coming from IP 65.55.44.100 to port mail server port 25.

You can also create Security Shell Script to block the ips: Create /root/iptables/blocked.ips file as follows with list of ips and subnets to block entering your dedicated server.