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Umask is the number subtracted from the standard permissions when creating a file. Example: each new folder is by default created with 777, so when umask is set to 022, the result is that the permissions will be 777 – 022 = 755.

Most of the time umask will already be set by your distro to 022 but you can change it if you like. You can see what umask value is set with:


0022

If you want to change umask for temporally,


Note: These value will stay until you log out and then return to its default value.
To make it permanent, edit /etc/bashrc or to your ~/.bash_profile.

DEVICE=eth0
BOOTPROTO=static
HWADDR=00:04:75:D4:C8:F9
IPADDR_START=192.168.0.6
IPADDR_END=192.168.0.10
CLONENUM_START=1
NETMASK=255.255.255.0
ONBOOT=yes
TYPE=Ethernet  

Which would start at eth0:1

Sure Squid server is a popular open source GPLd proxy and web cache. It has a variety of uses, from speeding up a web server by caching repeated requests, to caching web, name server query , and other network lookups for a group of people sharing network resources. It is primarily designed to run on Linux / Unix-like systems. Squid is a high-performance proxy caching server for Web clients, supporting FTP, gopher, and HTTP data objects. Unlike traditional caching software, Squid handles all requests in a single, non-blocking, I/O-driven process. Squid keeps meta data and especially hot objects cached in RAM, caches DNS lookups, supports non-blocking DNS lookups, and implements negative caching of failed requests. Squid consists of a main server program squid, a Domain Name System lookup program (dnsserver), a program for retrieving FTP data (ftpget), and some management and client tools.

1. Check the necessary RPM
#rpm –q squid

if it's not installed first install it


2. Set the default gateway and the DNS on the proxy server, so it has a direct connection as an internet.
#system-config-network-tui

3. Give the information about your local network on the proxy server.
#nano /etc/squid/squid.conf
Press CTRL + W
Search – our_networks

4. Uncomment this lines
#acl our_networks src 192.168.1.0/24 192.168.2.0/24 //Remove # mark
#http_access allow our_networks //Remove # mark
5. Save (CTRL + O) and Exit (CTRL + X) file

6. Start the proxy service
#service squid start
#chkconfig squid on

Settings up proxy clients

The proxy client is an application that required internet through the proxy server
EX – Internet Explorer, Mozilla Firefox

Fire Fox
Edit --> Preferences --> Advanced --> Network --> Settings --> manually proxy configuration
http proxy : 192.168.2.101 port : 3128 // proxy server IP and port number

Now clients have to access internet through proxy………

Controlling web access through proxy

1. Open the following file
#nano /ect/squid/squid.conf
Press CTRL + W
Search – # http_access deny all

Put all the rules that you want to control web access through proxy under the above comment. All the block rules must come before the allow rules

• To block unwanted website
acl blockweb dstdomain .facebook.com .yahoo.com .google.com
http_access deny blockweb

• To block unwanted file download
acl blockfile urlpath_regex –i exe$ mp3$ avi$ rar$
http_access deny blockfile

• To allow POP3/ SMTP to access mail through proxy server
acl allowmail proto POP3 SMTP
http_access allow allowmail

2. Save (CTRL + O) and exit (CTRL +X) the file

3. Reload squid service
#service squid reload
---------------------------------------------------------
List of acl tags and examples
http://wiki.squid-cache.org
--------------------------------------------------------- 

. 1 Bit = Binary Digit
· 8 Bits = 1 Byte
· 1024 Bytes = 1 Kilobyte
· 1024 Kilobytes = 1 Megabyte
· 1024 Megabytes = 1 Gigabyte
· 1024 Gigabytes = 1 Terabyte
· 1024 Terabytes = 1 Petabyte
· 1024 Petabytes = 1 Exabyte
· 1024 Exabytes = 1 Zettabyte
· 1024 Zettabytes = 1 Yottabyte
· 1024 Yottabytes = 1 Brontobyte
· 1024 Brontobytes = 1 Geopbyte

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