Oracle Net: TNS and EasyConnect

1. sqlplus id/pwd@
2. sqlplus id/pwd@server:port/service (service is schema that is given by DBA)

cx_Oracle

Follow http://mostperfect.net/blog/2010/07/28/installing-cx_oracle-on-windows/,

A looking at cx_Oracle.pyd with dependency walker (from MS) will show it depends on OCI.dll.
As a result, we need to install Oracle Instant Client from here

http://www.oracle.com/technetwork/database/features/instant-client/index-097480.html

strace

stats: strace -c -p

look for system call: strace -f -p -e epoll_wait

Customize the Nginx Server:Apache

1. vi src/http/ngx_http_header_filter_module.c
2. static char ngx_http_server_string[] = "Server: Apache" CRLF;
3. static char ngx_http_server_full_string[] = "Server: Apache" CRLF;
4. configure, make, make install.

how to change user-agent for chrome

C:\Users\vyang\AppData\Local\Google\Chrome\Application\chrome.exe -user-agent="Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1)"

a smtp proxy server

http://code.activestate.com/recipes/577260-multi-threaded-smtp-proxy/

is useful for helping me to test my html email via outlook. This is due to the real MTA that can deliver to outlook is IP based, and my workstation is not allowed but as long as I run the server on the allowed IP, it works.

ldapsearch usage

For example,

In order to find the home directory for a certain user id.

ldapsearch -H "ldap://ldapserver/" -D -W -vvv -L -x -b 'OU=Users,DC=mycomp,DC=com' -z 0 uid=$1 Home

range(a..z): python generator expression for

In order to generate a..z with generator expression.

import string

for filter in ('uid='+x+'*' for x in string.lowercase):

print(filter)

Play with TTL value with ping

Router will decrement TTL value within IP packet.

"ping" can be used to simulate how ICMP works in more complex tool such as "mtr", "traceroute". 

Please try increasing ttl-value against any target machine is ICMP is enabled along the route.
  

on unix/linux: ping -t target-ip

on windows: ping -i target-ip

mtr

mtr -n www.microsoft.com

ping test with incremental TTL

Similar like Traceroute (and mtr),

We can conduct an incremental testing with one ICMP packet each time:
ping -t 1  -c 1 www.yahoo.com
ping -t 2  -c 1 www.yahoo.com

...

how to find default IP TTL value of the remote system

TTL value is 1 byte within IP header.

1. "ping " will show ttl returned by the remote machine.
2. Find out how many hops between src and remote ip. traceroute/mtr
3. Add the value from Step 1 and 2 will get the default TTL value of remote system
4. For the curious, can look up http://www.binbert.com/blog/2009/12/default-time-to-live-ttl-values/ to take a guess what the remote system might be.

Mythical 5% programmer

http://www.artima.com/weblogs/viewpost.jsp?thread=221622

Generator Expression and List Comprehension

Generator http://en.wikipedia.org/wiki/Generator_(computer_science)

Generator Expression and List Comprehension

http://python-history.blogspot.com/2010/06/from-list-comprehensions-to-generator.html

winpcap 's dlls

There are two dlls with winpcap installation.

• wpcap.dll implements the libpcap API (plus some extensions) for Win32 systems.
• packet.dll, and the drivers for various Win32 operating systems, provide a Win32-specific raw link-layer packet

set up rsync daemon

start_rsyncd.sh

/usr/bin/rsync --daemon --config=rsyncd.conf


rsyncd.conf (server runs on port 9873)

pid file=/home/vic/opt/rsync/pid
log file=/home/vic/opt/rsync/log
lock file=/home/vic/rsync/lock
port=9873
address=192.168.1.100
timeout=600

[data]
path=/home/vic/tmp
use chroot=false
read only=no
transfer logging=yes
max connections=1


rsync client test
rsync -v foo rsync://192.168.1.100:9873/data

How to build mod_wsgi,web.py with httpd and python from source code

It is best to compile everything from source code.

Version usedPython: 2.7 (with shared library)httpd 2.2.17 (with shared DSO support)WSGI (integrating with httpd): mod_wsgi 3.3
Web framework: web.py 0.34

Compile Python for shared lib

./configure --prefix= --enable-shared

Set up LD_LIBRARY_PATH so that running "python" would find its shared lib
export LD_LIBRARY_PATH=${python-lib}:$LD_LIBRARY_PATH

Compile (apache) httpd Add DSO support
./configure --prefix= --enable--module=module_so



Compile mod_wsgi
./configure --with-apxs=$APACHE_HOME/bin/apxs --with-python=$PYTHON_BIN/python

Configure httpd.conf for mod_wsgi

LoadModule wsgi_module modules/mod_wsgi.so

WSGIScriptAlias /wsgi/ /u/local/www/wsgi-scripts/

WSGIApplicationGroup admin-scripts

Order allow,deny

Allow from all

WSGIProcessGroup example1.com

WSGIDaemonProcess example1.com processes=2 threads=15 display-name=example1.com

Install a sample python code under /u/local/www/wsgi-scripts/sniff

import sys

def application(environ, start_response):

status = '200 OK'

output = 'sys.version= %s\nsys.prefix=%s\n' % (sys.version, sys.prefix)

output += 'sys.path= %s\n' % (sys.path)

response_headers = [('Content-type', 'text/plain'),

('Content-Length', str(len(output)))]

start_response(status, response_headers)

return [output]

To install Nginx from source

./configure --prefix=/u/pandev/opt/nginx --without-http_rewrite_module

netstat + lsof = my friend

linux

1. "netstat -anpt | grep -i listen | grep 8888" will find out the process id is running on that port.
2. "/usr/sbin/lsof -p " find out what file and sockets it opens.
3. "lsof -P -n -i TCP" will list all the TCP sockets with unresolved (numeric) IP and port

Database connection pooling with firewall troubleshooting tip: Use Netcat

Database connection pooling is useful and common feature for performance. However there are some cavets.
Sometimes your sql query just got timed out, and you wonder why.
If you suspect the TCP connection between your application hosted in DMZ to the database (which is usually sits behind a firewall) got dropped by the firewall. It is very likely firewall has a policy to terminate any idle connection.

Let's go back to the basics to use Netcat.

Server(internal machine):
nc -v -l 9999

Client (DMZ machine):
nc 9999

Assuming port 9999 is allowd on the firewall.

Let's assume the firewall drops the connection after 30 minutes idle time, then the nc will be broken after 30 minutes.

Remote disk space monitor

The following is a poor man's disk space monitor script.
"ssh id@host df -h " is the core of the script. It relies on SSH RSA authentication so that the remote "df" can work like local.


#!/bin/ksh
homedir=`dirname $0`
RUN_DATE_LONG=$(date +'%Y%m%d')
LOGFILE=${homedir}/diskmon_log.$RUN_DATE_LONG

HOSTS="192.168.1.1 192.168.1.2 192.168.1.3 192.168.1.4 "

alert=90
alert_email="admin@foo.com"
typeset -i email=0

function rdf
{
echo "$1 is sshing into $2 doing a df......." >> $LOGFILE
ssh $1@$2 df -hP | grep -vE '^Filesystem' | awk '{print $4 " " $5 " " $1 " " $2}' | while read line;
do
typeset -i used=$(echo $line | awk '{print $1}' | cut -d "%" -f 1)
if [[ $used -ge $alert ]]; then
email=1
echo $line >> $LOGFILE
fi
done
echo "ssh done......." >> $LOGFILE
}



for h in $HOSTS
do
rdf sshid $h
done


if [[ ${email} -eq 1 ]]; then
echo "alert email will be setnt" >> $LOGFILE
# put whatever mailer you use here
fi

Dtrace could be the secret weapon

I had this vision of setting up a high end consulting firm which only serves some hard problem such as performance. One of secret weapon is Dtrace.

DTrace for linux: http://www.crisp.demon.co.uk/tools.html

DTrace with Python: http://blogs.sun.com/levon/entry/python_and_dtrace_in_build