Linux check memory usage

$ free -t -m
$ vmstat
$ vmstat

Squid proxy How to filter or block a particular port

First open /etc/squid/squid.conf file
# vi /etc/squid/squid.conf
Locate your ACL section and add configuration directive as follows:
acl block_port port 1234
http_access deny block_port
http_access allow all

If you just want to skip a particular IP (192.168.1.5) try as follows:
acl block_port port 1234
acl no_block_port_ip src 192.168.1.5
http_access deny block_port !no_block_port_ip
http_access allow all

Close and save the file.

Restart squid proxy server:
# /etc/init.d/squid restart
##########################################################################################


PROXY & YUM


1. open the .bashrc file

Add this line to bashrc file
vi .bashrc
export http_proxy=http://proxy.server.ip:port(3128)
ZZ
export http_proxy
yum update
yum search vlc




TAR-TIPS

tar -xvf file.tar	unzip tar file
tar -t file.tar	list contents of tar file
tar -xvfz file.tar.gz	unzip tar.gz file
tar -xvfj file.tar.bz2	unzip tar.bz2 file
gunzip file.gz	unzip gzip file
unzip file.zip	unzip zip file
bunzip2 file.bz2	unzip bzip2 fil

postmaster

$ postmaster -D /usr/pg_data
To start the postmaster in the    background, use the usual shell syntax:
$ postmaster -D /usr/pg_data >logfile 2>&1 & 
This shell syntax can get tedious quickly.  Therefore the shell
script wrapper    pg_ctl    is provided to simplify some tasks.
For example:
$ pg_ctl start -l logfile