首先要在2台服务器建立SSH直连.
服务器A和B都要分别重复以下步骤.
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ssh-keygen -t dsa

You will be prompted for a file in which the key and a passphrase will be saved. You may press Enter through each of these prompts. If you do so, the key generation program will assume that you wish to use the default file name of id_dsa and your private key will not be protected by a password.
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scp ~/.ssh/id_rsa.pub remote_host:/

3. Login to the remote host and check if you already have authorized_keys file in .ssh dir. If this doesn’t exist, create it with the following commands.

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touch ~/.ssh/authorized_keys

4. On the remote host where you are in step 3, copy your public key to the authorized_keys file, with the following command.

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cat /id_dsa.pub >> ~/.ssh/authorized_keys

5. You are set to use SSH authentication without password now. If you want you can delete or move id_rsa.pub file.

Most of you may already know how to do this, so forgive if this is too simple, but this may be helpful for some dedicated server owners whose /var mount (some hosts use separate partitions for /usr, /var, /home etc) has become full, which is usually do to large databases in /var/lib/mysql. There is usually plenty of room in /the /home partition. This will work on cPanel servers as well.

This simple tutorial lays out the steps involved to copy contents of /var/lib/mysql to /home and then symlink /var/lib/mysql to /home/mysql. Of course adjust accordingly if moving/symlinking to a different mount or directory.

1) Go to webpage that uses mysql to verify working pre-copy

2) Stop mysql service (I will usually also stop cpanel & http service just to be safe).

/etc/init.d/mysql stop
/etc/init.d/httpd stop
/etc/init.d/cpanel stop

3) Do the copy:

rsync -av /var/lib/mysql /home/

4) Verify copied folder same size as source with du:

du -sh /var/lib/mysql
du -sh /home/mysql

5) Move /var/lib/mysql to /home/mysql-bak (essentially removing /var/lib/mysql because the folder must not exist when symlink is created)

mkdir /home/mysql-bak
mv /var/lib/mysql /home/mysql-bak/

6) Create symlink:

ln -s /home/mysql /var/lib/mysql

7) Verify the symlink is correct when listing the contents of new symlinked /var/lib/mysql (you can refer to the rsync copy to make sure the paths are the same – they should be)

Restart mysql, httpd, cpanel
/etc/init.d/mysql start
/etc/init.d/httpd start
/etc/init.d/cpanel start

9) Verify mysql-reliant webpage is loading without issue

10) You should now have freed up space on /var. Verify with ‘df -h’

du -k | sort -nr | more

The du command along with the -k switch lists all directories and their respective size in kilobytes.
The sort command sorts the output so that the largest directory is shown first in the list. The -nr switch reverses the list and uses only numbers when sorting.

Here’s an example of the output:

12939451 .
1814892 ./abcdef
1219582 ./abcde
839586 ./abcd
718330 ./abc
695610 ./ab
690380 ./a

For human-readable output use the following command:

du -sh /*

To install on a cPanel server, you need a reseller or VPS hosting account. You’ll also need a dedicated IP address, to separate the site from others on the shared hosting server. Here at WebHostingBuzz, reseller accounts include dedicated IP address, and you may use one of those for your certificate.

Create a self-signed SSL certificate

Login to WHM.
Click “Generate a SSL Certificate & Signing Request”.
Enter “Contact info” with a valid e-mail address.
Enter or generate a password, making sure it is sufficiently long with a mixture of letters, numbers and symbols.
Under “Host to make cert for”, enter the domain on which you want the SSL.
Click “Create”.
Copy the text displayed for the .key and .crt, and paste them into a text file on your computer. You may need that text in the next steps.

Install a self-signed SSL certificate

In WHM, click “Install an SSL Certificate and Setup the Domain”.
Enter the domain name, account user name, and IP address for the certificate in the Domain, User, and IP Address fields.
Click “Fetch” to paste the .key and .crt files for the domain into the available display spaces, if they are currently on your server. (The first time I did this, clicking Fetch automatically pasted the required data into the fields. When I created later certs, the I had to manually paste in the information.)
Don’t enter anything in CA bundle: there is no Certificate Authority because you are installing a self-signed cert.
Click “Submit”, then wait for all processes to complete. WHM will display various lines of information and finally display “Finished Install Process.. “
Point your web browser to https:// followed by the domain, to see your new SSL connection working.

If you don’t see the SSL commands in your WHM, it may be because you don’t have a dedicated IP on your account. Once you have a dedicated IP assigned to a domain, the SSL Certificate links/commands will appear in WHM.

Since I began using self-signed SSL certificates a few years ago, several free and public domain certificate authorities have appeared. They issue certificates similar to those from the large commercial certificate authorities. The drawback is that most of them are not yet automatically trusted by major web browsers, meaning that users would see the same warning as when using a self-signed certificate. If these free issuers eventually get approval from the major web browsers, they would be a good alternative

解决办法：
Commented out the SSLCACertificateFile line
最好的办法是在CABUNDLE那里也填写上信息

restart httpd in whm

Please check http://downloads.service.softlayer.com for the latest 32bit or 64bit version of the Adaptec Storage Manager. VPN access is required to download from that page.

Next you will need to download and install the rpm on your server if it isn’t already installed. (If you used SoftLayer’s install and are not running a custom install, chances are it is already installed, though we will run through it just for the ones that do not have it installed)

First download the rpm from the link above using wget

At the command prompt type

wget **Link to RPM**

Next install the rpm,at the command prompt type:

rpm –Uvf asm_linux_v4.30-16038.rpm

After the application has been installed and started correctly, from the command prompt you will want to run the arcconf program in order to view the health of your array.

/usr/StorMan/arcconf getconfig 1

Here you will noticed that Device #1 is Online, while Device #2 is Failed, thus meaning we have a degraded array and a hard disk will need to be replaced.

Just open up a SoftLayer support ticket to schedule a maintenance window for the drive replacement.


ServerSignature On

Keep alive on
The Keep-Alive extension to HTTP/1.0 and the persistent connection feature of HTTP/1.1 provide long-lived HTTP sessions which allow multiple requests to be sent over the same TCP connection. In some cases this has been shown to result in an almost 50% speedup in latency times for HTML documents with many images. To enable Keep-Alive connections, set KeepAlive On.

For HTTP/1.0 clients, Keep-Alive connections will only be used if they are specifically requested by a client. In addition, a Keep-Alive connection with an HTTP/1.0 client can only be used when the length of the content is known in advance. This implies that dynamic content such as CGI output, SSI pages, and server-generated directory listings will generally not use Keep-Alive connections to HTTP/1.0 clients. For HTTP/1.1 clients, persistent connections are the default unless otherwise specified. If the client requests it, chunked encoding will be used in order to send content of unknown length over persistent connections.

When a client uses a Keep-Alive connection it will be counted as a single “request” for the MaxRequestsPerChild directive, regardless of how many requests are sent using the connection.

根据PageSpeed的规则，我们可以从KeepAlive，浏览器缓存，Gzip等方面对Apache进行些调整，从而提高网站性能。

1. 开启Keep-Alive

开启Keep-Alive后，可以保证浏览器和服务器之间的连接持久存在，这样如果同一个域名请求很多资源的情况下可以省去建立连接的时间和资源消耗。所以对于静态服务器来说，由于一个域名会请求N多资源，比较宜开启Keep-Alive，但是对于动态服务器，不宜开启Keep-Alive，因为这样会造成很多的空闲进程，浪费内存空间。
配置：

KeepAlive On #开启KeepAlive
KeepAliveTimeout 5 #保持连接5秒

2. HTTP缓存设置

当直接在浏览器中输入一个URL，或者点击一个链接的时候，那么浏览器缓存就会起作用，如果缓存没有过期，那么浏览器会从本地读取资源，不会发起HTTP请求，如果缓存过期，那么浏览器会发起新的浏览器请求。按ctrl+F5，浏览器会情况本地缓存，重新请求资源。
Expires是HTTP/1.0的缓存头， Cache-Control: max-age 是HTTP/1.1是用来进行HTTP缓存的头。Expires指定了资源过期的绝对时间，GMT格式，Cache-Control: max-age指定了资源过期的相对时间，单位是秒。在支持HTTP/1.1的浏览器上，如果发送两个头，那么Cache-Control: max-age会覆盖掉Expires；在支持HTTP/1.0的浏览器上，即使发送了两个头，但是只有Expires会起作用，所以为了兼容老的浏览器，还是要同时发送这两个头。设置HTTP缓存，需要安装expires_module，其会发送Expires和Cache-Control: max-age两个HTTP头。
配置：

<IfModule expires_module>
ExpiresActive On
ExpiresByType application/x-javascript  "access plus 30 days"

ExpiresByType text/css  "access plus 30 days"
ExpiresByType image/gif  "access plus 30 days"
ExpiresByType image/jpeg  "access plus 30 days"
ExpiresByType image/png  "access plus 30 days"
</IfModule>

ExpiresByType application/x-javascript “access plus 30 days” 表示对js资源设置Expires和Cache-Control: max-age头，其中Expires的值是以客户端访问资源的时间为基准的后30天，Cache-Control: max-age的值是3600x24x30秒。

ExpiresByType application/x-javascript “modification plus 30 days”和上面效果一样，只是Expires的时间是以资源最后修改的时间作为计算的基准。

3. 开启Gzip压缩，并设置vary头

Gzip会对文本资源进行压缩，一般能节省40%的大小，二进制内容不需要开启Gzip压缩，因为这些文件是已经压缩过的，如果再进行Gzip压缩反而会增加其大小。静态资源一般都会在代理服务器上进行缓存，而有的浏览器支持Gzip，但是也有不支持Gzip的老旧浏览器，所以需要设置Vary: Accept-Encoding 头，这个头告诉代理缓存服务器要对资源缓存两份，一份压缩过的，一份没有压缩过，然后根据浏览器发送的Accept-Encoding头来返回压缩或者不压缩的内容。设置Gzip压缩，需要安装deflate_module。
配置：

<IfModule deflate_module>
#对js,html,xml,css,普通文本开启Gzip压缩
AddOutputFilterByType DEFLATE application/x-javascript text/html text/plain text/xml text/css
</IfModule>

4. 关掉ETag

Last-Modified与ETag是同样的功能，都是用来标识一个资源是否更改过，Last-Modified的值是资源的时间戳，如果按F5或者刷新按钮则If-Modified-Since头会带着时间戳发送到服务器，如果服务器上资源的最后修改时间<=这个时间，那么返回304 Not Modified，否则返回200 OK 以及新的资源；ETag的值是通过资源的信息（一般为inode，大小，时间戳）而计算出来的一个字符串，如果按F5或者刷新按钮则If-None-Match头会带着这个值发送到服务器，服务器用这个值来和当前资源的值进行比对，如果相等，则返回304 Not Modified，否则返回200 OK 以及新的资源。默认情况下Apache对静态资源会发送Last-Modified和ETage，但是由于ETage的计算会耗费服务器的CPU资源，所以选择关掉，只开启Last-Modified。

配置：

FileETag None
Header unset ETag

A. In Linux, as in most other Unix-like operating systems, it is common to use a whole partition of a hard disk for swapping. However, with the 2.6 Linux kernel, swap files are just as fast[7] as swap partitions, although Red Hat recommends using a swap partition. The administrative flexibility of swap files outweighs that of partitions; since modern high capacity hard drives can remap physical sectors, no partition is guaranteed to be contiguous. You can add swap file as a dedicated partition or use following instructions to create a swap file.

Procedure to add a swap file

You need to use dd command to create swapfile. Next you need to use mkswap command to set up a Linux swap area on a device or in a file.

a) Login as the root user SSH登录root 账户

b) Type following command to create 2G swap file (1024 * 2048MB = 2097152 block size):

# dd if=/dev/zero of=/swapfile1 bs=1024 count=2097152

c) Set up a Linux swap area:
# mkswap /swapfile1

d) Activate /swapfile1 swap space immediately:
# swapon /swapfile1

e) To activate /swapfile1 after Linux system reboot, add entry to /etc/fstab file. Open this file using text editor such as vi:
# vi /etc/fstab

Append following line:
/swapfile1 swap swap defaults 0 0

So next time Linux comes up after reboot, it enables the new swap file for you automatically.

g) How do I verify swap is activated or not?
Simply use free command:
$ free -m

如果想关闭虚拟内存或者向扩大， 要先disable
swapoff /swapfile1