Linux : Boot Kernel to Single User Mode or Emergency Mode

http://www.linuxsv.org/training/l1_linux_boot.html

The way that uses GRUB to load the Linux Kernel can be customized directly at the console typing "e" following the instructions of the GRUB graphical menu showed at startup or directly modifying the file /etc/grub.conf: 

kernel /vmlinuz-2.6.18-53.el5 ro root=/dev/VolGroup01/LogVol00 rhgb quiet s
Single user mode "s" that provides a root shell without root password check. Very useful for root password recovery. 

kernel /vmlinuz-2.6.18-53.el5 ro root=/dev/VolGroup01/LogVol00 rhgb quiet emergency
Emergency mode provides a maintenance root shell after root password check. 

kernel /vmlinuz-2.6.18-53.el5 ro root=/dev/VolGroup01/LogVol00 rhgb quiet init=/bin/sh
With this configuration you can startup the system skipping the init process. It provides a root shell after root password check. 

kernel /vmlinuz-2.6.18-53.el5 ro root=/dev/VolGroup01/LogVol00 rhgb quiet 5
Graphical mode startup, the default behaviour. 

kernel /vmlinuz-2.6.18-53.el5 ro root=/dev/VolGroup01/LogVol00 rhgb quiet selinux=0
SElinux can be disabled at kernel boot time with this configuration.

Linux : NFS : Some NFS file systems are not mounted after reboot

Problem : Some NFS file systems are not mounted after reboot

Solution : Add options to /etc/fstab

Original fstab :

10.11.200.101:/test /test           nfs     rw      0 0

After :
10.11.200.101:/test /test           nfs     rw,bg,hard,rsize=32768,wsize=32768,vers=3      0 0

Also the following services need to be turned on

chkconfig nfs on
chkconfig portmap on
chkconfig netfs on

Oracle VM Manager : VMPinfo3

https://support.oracle.com/epmos/faces/DocumentDisplay?_afrLoop=393004587073657&id=1521931.1

Login as root
/u01/app/oracle/ovm-manager-3/ovm_tools/support/vmpinfo3.sh --username=admin
Enter OVM Manager Password:

Gathering files from all servers. This process may take some time.
Gathering OVM Model Dump files
:
:
:

SDN NFV readling list

http://www.nec-labs.com/~lume/sdn-reading-list.html

http://portal.etsi.org/Portals/0/TBpages/NFV/Docs/NFV_White_Paper3.pdf

VMWare : Virtual Networking Concepts

http://www.vmware.com/files/pdf/virtual_networking_concepts.pdf

VLANs in VMware Infrastructure
VLANs provide for logical groupings of stations or switch ports, allowing communications as if all stations or ports were on the same physical LAN segment. Confining broadcast traffic to a subset of the switch ports or end users saves significant amounts of network bandwidth and processor time.
In order to support VLANs for VMware Infrastructure users, one of the elements on the virtual or physical network has to tag the Ethernet frames with 802.1Q tag, as shown in Figure 3. There are three different configuration modes to tag (and untag) the packets for virtual machine frames.
• Virtual switch tagging (VST mode) — This is the most common configuration. In this mode, you provision one port group on a virtual switch for each VLAN, then attach the virtual machine’s virtual adapter to the port group instead of the virtual switch directly. The virtual switch port group tags all outbound frames and removes tags for all inbound frames. It also ensures that frames on one VLAN do not leak into a different VLAN.
Use of this mode requires that the physical switch provide a trunk.

Virtual machine guest tagging (VGT mode) — You may install an 802.1Q VLAN trunking driver inside the virtual machine, and tags will be preserved between the virtual machine networking stack and external switch when frames are passed from or to virtual switches. The format for the header of a packet tagged in this way is shown in Figure 3.
Use of this mode requires that the physical switch provide a trunk.
• External switch tagging (EST mode) — You may use external switches for VLAN tagging. This is similar to a physical network, and VLAN configuration is normally transparent to each individual physical server.
There is no need to provide a trunk in these environments.
For details on using VLANs with VMware Infrastructure, see the white paper titled VMware ESX Server 3 802.1Q VLAN Solutions, available from the VMTN Web site (http://www.vmware.com/vmtn/).

netcat cheat sheet

http://alexandreborgesbrazil.files.wordpress.com/2013/10/netcat_cheat_sheet_v1.pdf

Oracle VM Manager document

http://www.biztech.com/collateral/CollaborateSessions/ConfiguringMultipleVLAN%27s.pdf

http://mokumsolutions.com/chapter-7-oracle-vm-networking-8021q

http://alexandreborges.org/2013/12/09/fundamental-concepts-for-vlan-networkswith-oracle-vm-server-for-x86/

http://www.oracle.com/technetwork/articles/servers-storage-admin/vlan-networking-2047178.html

http://oraclevmsig.wordpress.com/2013/05/26/oracle-vm-useful-mos-ids/

http://linuxtechres.blogspot.com/2012/08/how-to-build-oracle-vm-manager-311.html

Linux : brctl

# brctl show
bridge name     bridge id               STP enabled     interfaces
104dcfa38e              8000.a0d3c1f34980       no              eth0
                                                        vif19.0
                                                        vif19.0-emu
                                                        vif21.0
108b829071              8000.a0d3c1f34983       no              eth3
                                                        vif19.1
                                                        vif19.1-emu
                                                        vif21.1
# brctl showstp 108b829071
108b829071
 bridge id              8000.a0d3c1f34983
 designated root        8000.a0d3c1f34983
 root port                 0                    path cost                  0
 max age                  20.00                 bridge max age            20.00
 hello time                2.00                 bridge hello time          2.00
 forward delay             0.00                 bridge forward delay       0.00
 ageing time             300.00
 hello timer               0.27                 tcn timer                  0.00
 topology change timer     0.00                 gc timer                   8.36
 hash elasticity           4                    hash max                 512
 mc last member count      2                    mc init query count        2
 mc router                 1                    mc snooping                0
 mc last member timer      1.00                 mc membership timer      260.00
 mc querier timer        255.00                 mc query interval        125.00
 mc response interval     10.00                 mc init query interval    31.25
 flags


eth3 (0)
 port id                0000                    state                forwarding
 designated root        8000.a0d3c1f34983       path cost                  4
 designated bridge      8000.a0d3c1f34983       message age timer          0.00
 designated port        8001                    forward delay timer        0.00
 designated cost           0                    hold timer                 0.00
 mc router                 1
 flags

vif19.1 (0)
 port id                0000                    state                forwarding
 designated root        8000.a0d3c1f34983       path cost                100
 designated bridge      8000.a0d3c1f34983       message age timer          0.00
 designated port        8003                    forward delay timer        0.00
 designated cost           0                    hold timer                 0.00
 mc router                 1
 flags

vif19.1-emu (0)
 port id                0000                    state                forwarding
 designated root        8000.a0d3c1f34983       path cost                100
 designated bridge      8000.a0d3c1f34983       message age timer          0.00
 designated port        8004                    forward delay timer        0.00
 designated cost           0                    hold timer                 0.00
 mc router                 1
 flags

vif21.1 (0)
 port id                0000                    state                forwarding
 designated root        8000.a0d3c1f34983       path cost                100
 designated bridge      8000.a0d3c1f34983       message age timer          0.00
 designated port        8002                    forward delay timer        0.00
 designated cost           0                    hold timer                 0.00
 mc router                 1
 flags

# brctl showmacs 108b829071

Linux : tcpdump

# tcpdump -D
1.eth0
2.nflog (Linux netfilter log (NFLOG) interface)
3.nfqueue (Linux netfilter queue (NFQUEUE) interface)
4.usbmon1 (USB bus number 1)
5.eth2
6.usbmon2 (USB bus number 2)
7.usbmon3 (USB bus number 3)
8.usbmon4 (USB bus number 4)
9.usbmon5 (USB bus number 5)
10.usbmon6 (USB bus number 6)
11.any (Pseudo-device that captures on all interfaces)
12.lo

Now we ping from server A to server B
On Server A :

# ping (IP of server B)

On Server A :

# tcpdump -i 5 host (IP of server A) and (IP of server B)
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth2, link-type EN10MB (Ethernet), capture size 65535 bytes
17:18:34.267810 (IP ServerA) > (IP of server B) : ICMP echo request, id 29773, seq 86, length 64
17:18:34.268159 IP (IP of server B) > (Server A): ICMP echo reply, id 29773, seq 86, length 64

Cassandra

https://www.youtube.com/watch?v=B-bTPSwhsDY

http://www.slideshare.net/planetcassandra/cassandra-20-introduction-use-cases-29122759

https://www.youtube.com/watch?v=N9QllqXI1sE