What is a cluster?

Cluster is a group of the computer that work as one.

Storage cluster, as we work with RAIDS but over a network.

服务由多个服务器来实现。解释为什么资源可能被转移

在它们之间。难道是满意，为客户多播的所有请求组

服务器作为实现流动性的透明度，为客户的一种方式？

Kernel en ubuntu

3down voteaccepted

To install the latest kernel you can always visit kernel.ubuntu.com to see what's going on. To install the latest 3.16 kernel all you need to do is: cd /tmp for 32bit: wget \ http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.16-utopic/linux-headers-3.16.0-031600-generic_3.16.0-031600.201408031935_i386.deb \ http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.16-utopic/linux-headers-3.16.0-031600_3.16.0-031600.201408031935_all.deb \ http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.16-utopic/linux-image-3.16.0-031600-generic_3.16.0-031600.201408031935_i386.deb for 64bit: wget \ http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.16-utopic/linux-headers-3.16.0-031600-generic_3.16.0-031600.201408031935_amd64.deb \ http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.16-utopic/linux-headers-3.16.0-031600_3.16.0-031600.201408031935_all.deb \ http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.16-utopic/linux-image-3.16.0-031600-lowlatency_3.16.0-031600.201408031935_amd64.deb then, making sure you have no other .debs in /tmp sudo dpkg -i *.deb then sudo reboot Todo el texto es una copia de  http://askubuntu.com/questions/506956/how-can-i-install-3-16-kernel-on-ubuntu-14-04

Replication NFS

Multiple location support in the automounter implements a simple network load-balancing scheme for replicated filesystems. At first glance, this seems to be a bit of overkill; after all, you don't need or want replication for read-write filesystems. However, serving large, read-only filesystems such as the manpages may add to an NFS server's request load. Having multiple servers share this load improves performance by reducing the total load placed on the most heavily used servers. Ideally, you want clients that are "close" to each server to mount its filesystems, reducing the amount of traffic that must go through bridges or routers.



For example, if you have four NFS servers that each export the manpages, the best client mounting scheme is probably not to have one-quarter of the clients mount/usr/man from each server. Instead, clients should mount the manpages from the server that is closest to them. Replicated filesystems are included in automounter maps simply by listing all possible servers in the map:


/usr/man -ro wahoo:/usr/man mahimahi:/usr/man \ thud:/usr/man onaga:/usr/man

The backslash at the end of the first line continues this indirect map entry onto the next line. If more than one server:directory pair is listed in an automounter map, the automounter pings all servers by sending a request to the null procedure of all NFS servers. From the set that responds, the automounter picks one that is "closest" by comparing the address of the servers with that of the clients. Ties are broken by using the server that responded to the ping first. The selected server is used by the automounter to serve the mount point.

Postfix SPAM BUG

Postfix Bug

Sometimes you think that 2+3 =5 and 3+2 you will get also 5. But on point of  view of programmer, you will get differents answers.


One of my servers was under attack, i realize  because  i have a lot of traffic. I got some calls, the system is broken,  slow.....

I got into the server   and nothing wrong. But the calls were up. The second time, when i was in the server, i find something wrong. What i see, a new user lol....  i mean, the email xyz@mydomain.com  was sending a bulk emails to comcast.

The xyz@mydomian.com doesn't  exist, but postfix dont realize about it. if you are using sender controller over postfix, you have to know this bug.


My old main.cf was

smtpd_recipient_restrictions =
 permit_mynetworks,
 permit_sasl_authenticated,
 reject_sender_login_mismatch,
 reject_unauth_destination,
 reject_unlisted_recipient,
 reject_invalid_hostname,
 reject_unauth_pipelining,
         reject_invalid_hostname,
         reject_unknown_recipient_domain,
         reject_unauth_pipelining,
 reject_unknown_sender_domain,
 reject_non_fqdn_recipient,
 reject_non_fqdn_sender,


I spend all day and i see that it was a bug, very simple to fix only change the lines. Now only pepelupe can send email by pepelupe@mydomian( no more xyz@mydomain)

smtpd_recipient_restrictions =
 permit_mynetworks,
 reject_sender_login_mismatch,
 permit_sasl_authenticated,
 reject_unauth_destination,
 reject_unlisted_recipient,
 reject_invalid_hostname,
 reject_unauth_pipelining,
         reject_invalid_hostname,
         reject_unknown_recipient_domain,
         reject_unauth_pipelining,
 reject_unknown_sender_domain,
 reject_non_fqdn_recipient,
 reject_non_fqdn_sender,


i hope that no  one have to waste time with it.

Lets talk about Interprocess Communication

An Overview of RMI Applications

RMI applications often comprise two separate programs, a server and a client. A typical server program creates some remote objects, makes references to these objects accessible, and waits for clients to invoke methods on these objects. A typical client program obtains a remote reference to one or more remote objects on a server and then invokes methods on them. RMI provides the mechanism by which the server and the client communicate and pass information back and forth. Such an application is sometimes referred to as a distributed object application.

Distributed object applications need to do the following:

• Locate remote objects. Applications can use various mechanisms to obtain references to remote objects. For example, an application can register its remote objects with RMI's simple naming facility, the RMI registry. Alternatively, an application can pass and return remote object references as part of other remote invocations.
• Communicate with remote objects. Details of communication between remote objects are handled by RMI. To the programmer, remote communication looks similar to regular Java method invocations.
• Load class definitions for objects that are passed around. Because RMI enables objects to be passed back and forth, it provides mechanisms for loading an object's class definitions as well as for transmitting an object's data.

[ref]

Broadcast on RPC

According to Peters broadcasting is the audio or video distribution  to a dispersed client via any electronic mass communications medium, it usually use spectrum (radio waves), in a "one to many" model.[1]