1. install the xcode command line tools
   

   sudo xcode-select --install

2. Verify the installation of gcc
   

   gcc --version

3. Change the ownership of /usr/local to your login identity (not root)
   

   sudo chown -R `whoami` /usr/local

   Note: You may have to do this again someday for whatever reason

Apache 2.4

<VirtualHost *:80>
    ServerName www.example.com
    ServerAlias example.com

    DocumentRoot /var/www/www.example.com/docroot
    <Directory /var/www/www.example.com/docroot>
        Options Indexes FollowSymLinks
        AllowOverride All
        Require all granted
    </Directory>

    CustomLog /var/log/apache2/www.example.com_access.log combined
    ErrorLog /var/log/apache2/www.example.com_error.log

    # Force redirect to www.example.com
    RewriteEngine on
    RewriteCond %{HTTP_HOST} !^www\.example\.com$ [NC]

This bash script makes it easy to quickly ping an existing list of IPs:

#!/bin/bash
set -m 

forkme() {
RECIEVED=`ping -c 1 $1 | grep '1 received' &`
        if [ -z "$RECIEVED" ]
        then
                echo "$1 reports down"
        else
                echo "$1 reports up"
                unset RECIEVED
        fi
}

while read line
do
        forkme $line &
done

while [ 1 ]; do fg 2> /dev/null; [ $? == 1 ] && break; done

To run it, use the following command:

./scanip.sh < IP.List.txt | grep -v forkme > Results.txt

Connect to a vcenter server

1. Connect your vsphere client
2. Open PowerCLI

3. Connect-VIServer -Server [servername] -Protocol https -User [username] -Password [password]

Retrieve all the IPs of all the VMs

There were some homebrew packages installed as dependencies, which I didn't note at the time, but they should be pretty apparent as the build fails. The configure flags below is the part that took a while to get right. Switching between versions is as easy as doing a "make install", and reloading apache.

Yeah, I know this is old hat for some of us, but a good note in any case.

1. Edit the Grub boot command
2. On the kernel line, append the following into the end of the line:
   

    single init=/bin/bash

3. once booted in, run the following command:
   

   mount -n -o remount,rw / 

• Active Directory defaults to MaxPageSize == 1000, and it is not recommended to change it. (http://support.microsoft.com/kb/315071)
• To force a client-specified result size, or paging, which matches AD behavior as closely as possible, in olcDatabase={1}hdb.ldif:
  

  olcLimits: * size.soft=1000 size.hard=unlimited

  This will return the size-exceeded error if there are more than 1000 results, unless the client specified a higher sizelimit. It also allows paged results of up to 1000 results per page.

Use gdb to find the umask of a running process.

gdb program-name pid

For example:

~ # gdb nginx 21155
[...]
(gdb) call umask(0)
$1 = 18
(gdb) call umask(18)
$2 = 0
(gdb) quit

The first call sets the umask to 0000, and outputs the previous umask value in decimal. The second call restores the original umask.

Convert the decimal 18 to octal 0022, and there you have it.

Using CDP (Cisco Discovery Protocol) to identify which switch and port you are plugged into:

#tcpdump -nn -v -i eth0 -s 1500 -c 1 'ether[20:2] == 0x2000'

Apache Requests in real time:

#tcpdump -i eth0 -s 1024 -l -A port 80|grep "Host:"

Create pcap file compatible with wireshark

tcpdump -nn -w tcpdump.pcap -s0 *rules*

Pipe remote tcpdump into local wireshark

tcpdump -nn -w - -s0 *rules* | nc -l 9999

nc remote.server.address 9999 | wireshark -k -S -i -

Filtering Packets based up TCP Flags

Install pptpd

aptitude install pptpd

edit /etc/pptpd.conf, and set localip and remoteip (at the bottom)

localip 10.108.98.1
remoteip 10.108.98.2-254

Add the VPN users to /etc/ppp/chap-secrets

# Secrets for authentication using CHAP
# client    server  secret          IP addresses
user1       pptpd   password        *

Enable IP forwarding in /etc/sysctl.conf

net.ipv4.ip_forward=1

Make that setting live

sysctl -p

Configure iptables masquerading