echo 1 > /proc/sys/net/ipv4/conf/eth0/arp_ignore
echo 2 > /proc/sys/net/ipv4/conf/eth0/arp_announce

net.ipv4.conf.eth0.arp_ignore = 1
net.ipv4.conf.eth0.arp_announce = 2

Before this, you’d have to write :

cookies[:user_preference] = {
  :value => @current_user.preferences,
  :expires => 20.years.from_now.utc
}

Now just becomes :

cookies.permanent[:user_preference] = @current_user.preferences

In case you happen to have seen my Railssummit presentation I had talked about using ActiveSupport::MessageVerifier for implementing “Remember me” functionality. The above commit makes that a whole lot easier.

In your model User.rb :

# User.rb
def self.authenticated_with_token(id, stored_salt)
  u = find_by_id(user_id)
  u && u.salt == stored_salt ? u : nil
end

And when the user checks “Remember me” box, make sure the following gets run :

cookies.permanent.signed[:remember_me] = [current_user.id, current_user.salt]

This will set a permanent and signed cookie using the secret specified in ActionController::Base.cookie_verifier_secret. If you don’t have the cookie_verifier_secret defined, you might want to do that in one of the initializers.

Now when you want to login using the cookie :

user = User.authenticated_with_token(*cookies.signed[:remember_me])

In this specific case, it’s very important to use the salt in the cookie value. That makes sure the cookie gets invalidated if the user changes his password.

[root@iscsi sysconfig]# yum install ntp
[root@iscsi sysconfig]# chkconfig --level 2345 ntpd on
[root@iscsi sysconfig]# vim /etc/sysconfig/ntpd
OPTIONS="-u ntp:ntp -x -p /var/run/ntpd.pid"
[root@iscsi sysconfig]# service ntpd restart

　　先看iSCSI服务器的硬盘配置信息，/dev/sda给本机使用，将/dev/sdb和/dev/sdc作为共享存储提供给其他客户机。

二、安装相关服务

　　通过yum命令先把服务器需要的服务装上：yum install scsi-target-utils

三、配置相关服务

配置iptables防火墙，打开TCP 3260端口，并重新启动iptables：
-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 3260 -j ACCEPT

安装完成后，编辑其配置文件：vim /etc/tgt/targets.conf ，找个合适的位置加上要共享出去的存储的配置信息：

<target iqn.2008-09.cn.edu.neu.oracle.iscsi:storage>
    backing-store /dev/sdb
    backing-store /dev/sdc
</target>

重新启动tgtd服务：service tgtd restart

并保持tgtd服务随系统启动：chkconfig --level 2345 tgtd on

四、配置结果测试

查看共享情况：tgtadm --op show --mode target

yum install freetds freetds-devel

第二步：下载php源码及编译sybase扩展

wget http://cn.php.net/get/php-5.3.6.tar.bz2/from/this/mirror
tar jxvf php-5.3.6.tar.bz2
cd php-5.3.6/ext/sybase_ct/
phpize
./configure --with-sybase-ct=/usr
make
make install

第三步：载入PHP的sybase扩展

cd /etc/php.d
vim sybase_ct.ini
extension=sybase_ct.so

第四步：重新启动Apache完成

service httpd restart

　　esc+ctrl+]

　　使用这三个组合键即可，注意先后顺序，先按esc，然后ctrl，最后才是]

　　一种简单的解决办法是吧PassivePortRange的端口范围全部加到iptables的配置文件中：

　　-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 30000:50000 -j ACCEPT

　　不过这个方法有个缺点，如果在FTP Server里把端口范围改掉了，同时需要在iptables也把这个范围改掉，算是有点小缺憾吧。

　　另外一种办法是给iptables加上ftp模块，让他自动识别PassivePort，在/etc/sysconfig/iptables-config中加入：

　　IPTABLES_MODULES="ip_conntrack_netbios_ns ip_nat_ftp"

But the differences between "NoSQL" databases are much bigger than it ever was between one SQL database and another. This means that it is a bigger responsibility on software architects to choose the appropriate one for a project right at the beginning.

In this light, here is a comparison of Cassandra, Mongodb, CouchDB, Redis, Riak and HBase:

CouchDB

• Written in: Erlang
• Main point: DB consistency, ease of use
• License: Apache
• Protocol: HTTP/REST
• Bi-directional (!) replication,
• continuous or ad-hoc,
• with conflict detection,
• thus, master-master replication. (!)
• MVCC - write operations do not block reads
• Previous versions of documents are available
• Crash-only (reliable) design
• Needs compacting from time to time
• Views: embedded map/reduce
• Formatting views: lists & shows
• Server-side document validation possible
• Authentication possible
• Real-time updates via _changes (!)
• Attachment handling
• thus, CouchApps (standalone js apps)
• jQuery library included

Best used: For accumulating, occasionally changing data, on which pre-defined queries are to be run. Places where versioning is important.

For example: CRM, CMS systems. Master-master replication is an especially interesting feature, allowing easy multi-site deployments.

Redis

• Written in: C/C++
• Main point: Blazing fast
• License: BSD
• Protocol: Telnet-like
• Disk-backed in-memory database,
• but since 2.0, it can swap to disk.
• Master-slave replication
• Simple keys and values,
• but complex operations like ZREVRANGEBYSCORE
• INCR & co (good for rate limiting or statistics)
• Has sets (also union/diff/inter)
• Has lists (also a queue; blocking pop)
• Has hashes (objects of multiple fields)
• Of all these databases, only Redis does transactions (!)
• Values can be set to expire (as in a cache)
• Sorted sets (high score table, good for range queries)
• Pub/Sub and WATCH on data changes (!)

Best used: For rapidly changing data with a foreseeable database size (should fit mostly in memory).

For example: Stock prices. Analytics. Real-time data collection. Real-time communication.

MongoDB

• Written in: C++
• Main point: Retains some friendly properties of SQL. (Query, index)
• License: AGPL (Drivers: Apache)
• Protocol: Custom, binary (BSON)
• Master/slave replication
• Queries are javascript expressions
• Run arbitrary javascript functions server-side
• Better update-in-place than CouchDB
• Sharding built-in
• Uses memory mapped files for data storage
• Performance over features
• After crash, it needs to repair tables
• Better durablity coming in V1.8

Best used: If you need dynamic queries. If you prefer to define indexes, not map/reduce functions. If you need good performance on a big DB. If you wanted CouchDB, but your data changes too much, filling up disks.

For example: For all things that you would do with MySQL or PostgreSQL, but having predefined columns really holds you back.

Cassandra

• Written in: Java
• Main point: Best of BigTable and Dynamo
• License: Apache
• Protocol: Custom, binary (Thrift)
• Tunable trade-offs for distribution and replication (N, R, W)
• Querying by column, range of keys
• BigTable-like features: columns, column families
• Writes are much faster than reads (!)
• Map/reduce possible with Apache Hadoop
• I admit being a bit biased against it, because of the bloat and complexity it has partly because of Java (configuration, seeing exceptions, etc)

Best used: When you write more than you read (logging). If every component of the system must be in Java. ("No one gets fired for choosing Apache's stuff.")

For example: Banking, financial industry (though not necessarily for financial transactions, but these industries are much bigger than that.) Writes are faster than reads, so one natural niche is real time data analysis.

Riak

• Written in: Erlang & C, some Javascript
• Main point: Fault tolerance
• License: Apache
• Protocol: HTTP/REST
• Tunable trade-offs for distribution and replication (N, R, W)
• Pre- and post-commit hooks,
• for validation and security.
• Built-in full-text search
• Map/reduce in javascript or Erlang
• Comes in "open source" and "enterprise" editions

Best used: If you want something Cassandra-like (Dynamo-like), but no way you're gonna deal with the bloat and complexity. If you need very good single-site scalability, availability and fault-tolerance, but you're ready to pay for multi-site replication.

For example: Point-of-sales data collection. Factory control systems. Places where even seconds of downtime hurt.

HBase

(With the help of ghshephard)

• Written in: Java
• Main point: Billions of rows X millions of columns
• License: Apache
• Protocol: HTTP/REST (also Thrift)
• Modeled after BigTable
• Map/reduce with Hadoop
• Query predicate push down via server side scan and get filters
• Optimizations for real time queries
• A high performance Thrift gateway
• HTTP supports XML, Protobuf, and binary
• Cascading, hive, and pig source and sink modules
• Jruby-based (JIRB) shell
• No single point of failure
• Rolling restart for configuration changes and minor upgrades
• Random access performance is like MySQL

Best used: If you're in love with BigTable. And when you need random, realtime read/write access to your Big Data.

For example: Facebook Messaging Database (more general example coming soon)

Of course, all systems have much more features than what's listed here. I only wanted to list the key points that I base my decisions on. Also, development of all are very fast, so things are bound to change. I'll do my best to keep this list updated.

nameserver xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx

vim会有红色警告，不理会他就是了~