$ uptime
11:12:26 up 3:44, 4 users, load average: 0.38, 0.31, 0.19

系统平均负载被定义为在特定时间间隔内运行队列中的平均进程树。如果一个进程满足以下条件则其就会位于运行队列中：

• 它没有在等待I/O操作的结果
• 它没有主动进入等待状态(也就是没有调用'wait')
• 没有被停止(例如：等待终止)

上面的输出，load average后面分别是1分钟、5分钟、15分钟的负载情况。数据是每隔5秒钟检查一次活跃的进程数，然后根据这个数值算出来的。如果这个数除以CPU 的数目，结果高于5的时候就表明系统在超负荷运转了。

Refer to: http://www.cnblogs.com/wangkangluo1/archive/2012/04/17/2453975.html

可以看作命令行浏览器

1、开启gzip请求
curl -I http://www.sina.com.cn/ -H Accept-Encoding:gzip,defalte

2、监控网页的响应时间
curl -o /dev/null -s -w "time_connect: %{time_connect}\ntime_starttransfer: %{time_starttransfer}\ntime_total: %{time_total}\n" "http://www.kklinux.com"

3. 监控站点可用性
curl -o /dev/null -s -w %{http_code} "http://www.kklinux.com"

4、以http1.0协议请求（默认为http1.1） 
curl -0 .............. 
      1）读取网页 
　　$ curl linuxidc.com">http://www.linuxidc.com 
　　2）保存网页 
　　$ curl http://www.linuxidc.com > page.html $ curl -o page.html http://www.linuxidc.com 
　　3）使用的proxy服务器及其端口：-x 
　　$ curl -x 123.45.67.89：1080 -o page.html http://www.linuxidc.com 
　　4）使用cookie来记录session信息 
　　$ curl -x 123.45.67.89：1080 -o page.html -D cookie0001.txt http://www.linuxidc.com 
option： -D 是把http的response里面的cookie信息存到一个特别的文件中去，这样，当页面被存到page.html的同时，cookie信息也被存到了cookie0001.txt里面了 
    5）那么，下一次访问的时候，如何继续使用上次留下的cookie信息呢？ 
　　使用option来把上次的cookie信息追加到http request里面去：-b 
　　$ curl -x 123.45.67.89：1080 -o page1.html -D cookie0002.txt -b cookie0001.txt http://www.linuxidc.com 

6）浏览器信息~~~~ 
随意指定自己这次访问所宣称的自己的浏览器信息： -A
curl -A "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0)" -x 123.45.67.89:1080 -o page.html -D cookie0001.txt http://www.yahoo.com 
这样，服务器端接到访问的要求，会认为你是一个运行在Windows 2000上的IE6.0，嘿嘿嘿，其实也许你用的是苹果机呢！ 
而"Mozilla/4.73 [en] (X11; U; Linux 2.2; 15 i686"则可以告诉对方你是一台PC上跑着的Linux，用的是Netscape 4.73，呵呵呵 

7）
另外一个服务器端常用的限制方法，就是检查http访问的referer。比如你先访问首页，再访问里面所指定的下载页，这第二次访问的referer地址就是第一次访问成功后的页面地 
址。这样，服务器端只要发现对下载页面某次访问的referer地址不 是首页的地址，就可以断定那是个盗连了~~~~~ 
讨厌讨厌~~~我就是要盗连~~~~~！！
幸好curl给我们提供了设定referer的option： -e
curl -A "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0)" -x 123.45.67.89:1080 -e "mail.yahoo.com" -o page.html -D cookie0001.txt http://www.yahoo.com 
这样，就可以骗对方的服务器，你是从mail.yahoo.com点击某个链接过来的了，呵呵呵 

8）curl 下载文件 
刚才讲过了，下载页面到一个文件里，可以使用 -o ，下载文件也是一样。
比如， curl -o 1.jpg http://cgi2.tky.3web.ne.jp/~zzh/screen1.JPG
这里教大家一个新的option： -O
大写的O，这么用： curl -O http://cgi2.tky.3web.ne.jp/~zzh/screen1.JPG
这样，就可以按照服务器上的文件名，自动存在本地了！ 
再来一个更好用的。
如果screen1.JPG以外还有screen2.JPG、screen3.JPG、....、screen10.JPG需要下载，难不成还要让我们写一个script来完成这些操作？
不干！
在curl里面，这么写就可以了：
curl -O http://cgi2.tky.3web.ne.jp/~zzh/screen[1-10].JPG 
呵呵呵，厉害吧？！~~~ 
9）
再来，我们继续讲解下载！
curl -O http://cgi2.tky.3web.ne.jp/~{zzh,nick}/[001-201].JPG 
这样产生的下载，就是
~zzh/001.JPG
~zzh/002.JPG
...
~zzh/201.JPG
~nick/001.JPG
~nick/002.JPG
...
~nick/201.JPG 
够方便的了吧？哈哈哈 
咦？高兴得太早了。
由于zzh/nick下的文件名都是001，002...，201，下载下来的文件重名，后面的把前面的文件都给覆盖掉了~~~ 
没关系，我们还有更狠的！
curl -o #2_#1.jpg http://cgi2.tky.3web.ne.jp/~{zzh,nick}/[001-201].JPG 
--这是.....自定义文件名的下载？
--对头，呵呵！ 
#1是变量，指的是{zzh,nick}这部分，第一次取值zzh，第二次取值nick
#2代表的变量，则是第二段可变部分---[001-201]，取值从001逐一加到201
这样，自定义出来下载下来的文件名，就变成了这样：
原来： ~zzh/001.JPG ---> 下载后： 001-zzh.JPG
原来： ~nick/001.JPG ---> 下载后： 001-nick.JPG 
这样一来，就不怕文件重名啦，呵呵 

9）
继续讲下载
我们平时在windows平台上，flashget这样的工具可以帮我们分块并行下载，还可以断线续传。
curl在这些方面也不输给谁，嘿嘿 
比如我们下载screen1.JPG中，突然掉线了，我们就可以这样开始续传
curl -c -O http://cgi2.tky.3wb.ne.jp/~zzh/screen1.JPG 
当然，你不要拿个flashget下载了一半的文件来糊弄我~~~~别的下载软件的半截文件可不一定能用哦~~~ 
分块下载，我们使用这个option就可以了： -r
举例说明
比如我们有一个http://cgi2.tky.3web.ne.jp/~zzh/zhao1.mp3 要下载（赵老师的电话朗诵 :D ）
我们就可以用这样的命令：
curl -r 0-10240 -o "zhao.part1" http:/cgi2.tky.3web.ne.jp/~zzh/zhao1.mp3 &\
curl -r 10241-20480 -o "zhao.part1" http:/cgi2.tky.3web.ne.jp/~zzh/zhao1.mp3 &\
curl -r 20481-40960 -o "zhao.part1" http:/cgi2.tky.3web.ne.jp/~zzh/zhao1.mp3 &\
curl -r 40961- -o "zhao.part1" http:/cgi2.tky.3web.ne.jp/~zzh/zhao1.mp3 
这样就可以分块下载啦。
不过你需要自己把这些破碎的文件合并起来
如果你用UNIX或苹果，用 cat zhao.part* > zhao.mp3就可以
如果用的是Windows，用copy /b 来解决吧，呵呵 
上面讲的都是http协议的下载，其实ftp也一样可以用。
用法嘛，
curl -u name:passwd ftp://ip:port/path/file
或者大家熟悉的
curl ftp://name:passwd@ip:port/path/file 
  
10)上传的option是 -T 
比如我们向ftp传一个文件： curl -T localfile -u name:passwd ftp://upload_site:port/path/ 
当然，向http服务器上传文件也可以
比如 curl -T localfile http://cgi2.tky.3web.ne.jp/~zzh/abc.cgi
注意，这时候，使用的协议是HTTP的PUT method 
刚才说到PUT，嘿嘿，自然让老服想起来了其他几种methos还没讲呢！
GET和POST都不能忘哦。 
http提交一个表单，比较常用的是POST模式和GET模式 
GET模式什么option都不用，只需要把变量写在url里面就可以了
比如：
curl http://www.yahoo.com/login.cgi?user=nickwolfe&password=12345 
而POST模式的option则是 -d 
比如，curl -d "user=nickwolfe&password=12345" http://www.yahoo.com/login.cgi
就相当于向这个站点发出一次登陆申请~~~~~ 
到底该用GET模式还是POST模式，要看对面服务器的程序设定。 
一点需要注意的是，POST模式下的文件上的文件上传，比如
<form method="POST" enctype="multipar/form-data" action="http://cgi2.tky.3web.ne.jp/~zzh/up_file.cgi">
<input type=file name=upload>
<input type=submit name=nick value="go">
</form>
这样一个HTTP表单，我们要用curl进行模拟，就该是这样的语法：
curl -F upload=@localfile -F nick=go http://cgi2.tky.3web.ne.jp/~zzh/up_file.cgi 
罗罗嗦嗦讲了这么多，其实curl还有很多很多技巧和用法
比如 https的时候使用本地证书，就可以这样
curl -E localcert.pem https://remote_server 
再比如，你还可以用curl通过dict协议去查字典~~~~~
curl dict://dict.org/d:computer 

今天为了检查所有刺猬主机上所有域名是否有备案．在使用wget不爽的情况下，找到了curl这个命令行流量器命令．发现其对post的调用还是蛮好的．特别有利于对提交信息及变 
更参数进行较验．对于我想将几十万域名到miibeian.gov.cn进行验证是否有备案信息非常有用．发现这篇文章很不错，特为转贴． 
我的目标：
curl -d "cxfs=1&ym=xieyy.cn" http://www.miibeian.gov.cn/baxx_cx_servlet 
在出来的信息中进行过滤，提取备案号信息，并设置一个标识位．将域名，备案号及标识位入库 

用curl命令，post提交带空格的数据 
今天偶然遇到一个情况，我想用curl登入一个网页，无意间发现要post的数据里带空格。比如用户名为"abcdef"，密码为"abc def"，其中有一个空格，按照我以前的方式提交： 
curl -D cookie -d "username=abcdef&password=abc def" http://login.xxx.com/提示登入失败。 

于是查看curl手册man curl。找到： 
d/--data (HTTP) Sends the speci?ed data in a POST request to the HTTP server, in a way that can emulate as if a user has ?lled in a HTML form and pressed the 
submit button. Note that the data is sent exactly as speci?ed with no extra processing (with all newlines cut off). The data is expected to be "url-encoded". 
This will cause curl to pass the data to the server using the content-type application/x-www-form-urlencoded. Compare to -F/--form. If this option is used 
more than once on the same command line, the data pieces speci?ed will be merged together with a separating &-letter. Thus, using ’-d name=daniel -d 
skill=lousy’ would generate a post chunk that looks like ’name=daniel&skill=lousy’. 
于是改用： 
curl -D cookie -d "username=abcdef" -d "password=abc efg" http://login.xxx.com/这样就能成功登入了。 

完

目录下，有三个脚本catalina.sh, startup.sh, 和 shutdown.sh。如果查看startup.sh和shutdown.sh，都是通过catalina.sh来启动的。脚本如下：

在Eclipse中远程调试Tomcat

首先将Tomcat 5.5.26的源代码分为container connectors jasper servletapi build五个项目，导入到Eclipse中。启动相关的代码主要在container中，就以它为当前项目，打开”Debug Configurations“对话框。

然后创建一个”Remote Java Application“，Connection Type选择”Standard (Socket Attach)“，Host填写localhost（Tomcat所在的主机地址），Port填写8000。最后点击”Apply“保存。

首先确保已经执行了jpda.bat，Tomcat正在等待调试器连接；然后执行上述的Debug Configuration，Eclipse就可以连上Tomcat。

Tomcat的启动是从Bootstrap的main方法开始，我在第一行代码处设置了断点，Tomcat的启动就停在了这一行：

接着，让Tomcat继续执行，我们可以看到，控制台输出了启动信息。

用wget指令直接下载这两个东西.下载回源文件后。
1.先安装libevent。这个东西在配置时需要指定一个安装路径，即./configure --prefix=/usr；然后make；然后make install；
2.再安装memcached，只是需要在配置时需要指定libevent的安装路径即./configure --with-libevent=/usr；然后make；然后make install；
这样就完成了Linux下Memcache服务器端的安装。详细的方法如下：

1.分别把memcached和libevent下载回来，放到 /tmp 目录下：
# cd /tmp
# wget http://www.danga.com/memcached/dist/memcached-1.2.0.tar.gz
# wget http://www.monkey.org/~provos/libevent-1.2.tar.gz

2.先安装libevent：
# tar zxvf libevent-1.2.tar.gz
# cd libevent-1.2
# ./configure --prefix=/usr
# make
# make install

3.测试libevent是否安装成功：
# ls -al /usr/lib | grep libevent
lrwxrwxrwx 1 root root 21 11?? 12 17:38 libevent-1.2.so.1 -> libevent-1.2.so.1.0.3
-rwxr-xr-x 1 root root 263546 11?? 12 17:38 libevent-1.2.so.1.0.3
-rw-r--r-- 1 root root 454156 11?? 12 17:38 libevent.a
-rwxr-xr-x 1 root root 811 11?? 12 17:38 libevent.la
lrwxrwxrwx 1 root root 21 11?? 12 17:38 libevent.so -> libevent-1.2.so.1.0.3
还不错，都安装上了。

4.安装memcached，同时需要安装中指定libevent的安装位置：
# cd /tmp
# tar zxvf memcached-1.2.0.tar.gz
# cd memcached-1.2.0
# ./configure --with-libevent=/usr
# make
# make install
如果中间出现报错，请仔细检查错误信息，按照错误信息来配置或者增加相应的库或者路径。
安装完成后会把memcached放到 /usr/local/bin/memcached ，

5.测试是否成功安装memcached：
# ls -al /usr/local/bin/mem*
-rwxr-xr-x 1 root root 137986 11?? 12 17:39 /usr/local/bin/memcached
-rwxr-xr-x 1 root root 140179 11?? 12 17:39 /usr/local/bin/memcached-debug

安装Memcache的PHP扩展
1.在http://pecl.php.net/package/memcache 选择相应想要下载的memcache版本。
2.安装PHP的memcache扩展

tar vxzf memcache-2.2.1.tgz
cd memcache-2.2.1
/usr/local/php/bin/phpize
./configure --enable-memcache --with-php-config=/usr/local/php/bin/php-config --with-zlib-dir
make
make install

Installing shared extensions: /usr/local/php/lib/php/extensions/no-debug-non-zts-2007xxxx/

extension_dir = "/usr/local/php/lib/php/extensions/no-debug-non-zts-2007xxxx/"

memcached的基本设置：
1.启动Memcache的服务器端：
# /usr/local/bin/memcached -d -m 10 -u root -l 192.168.0.200 -p 12000 -c 256 -P /tmp/memcached.pid

-d选项是启动一个守护进程，
-m是分配给Memcache使用的内存数量，单位是MB，我这里是10MB，
-u是运行Memcache的用户，我这里是root，
-l是监听的服务器IP地址，如果有多个地址的话，我这里指定了服务器的IP地址192.168.0.200，
-p是设置Memcache监听的端口，我这里设置了12000，最好是1024以上的端口，
-c选项是最大运行的并发连接数，默认是1024，我这里设置了256，按照你服务器的负载量来设定，
-P是设置保存Memcache的pid文件，我这里是保存在 /tmp/memcached.pid，

2.如果要结束Memcache进程，执行：

# kill `cat /tmp/memcached.pid`

3.重启apache，service httpd restart

Memcache环境测试：
运行下面的php文件，如果有输出This is a test!，就表示环境搭建成功。开始领略Memcache的魅力把！
< ?php
$mem = new Memcache;
$mem->connect("127.0.0.1", 11211);
$mem->set('key', 'This is a test!', 0, 60);
$val = $mem->get('key');
echo $val;
?>

File Transfer Protocol (FTP) is a TCP protocol for downloading files between computers. In the past, it has also been used for uploading but, as that method does not use encryption, user credentials as well as data transferred in the clear and are easily intercepted. So if you are here looking for a way to upload and download files securely, see the section on OpenSSH in Remote Administration instead.

FTP works on a client/server model. The server component is called an FTP daemon. It continuously listens for FTP requests from remote clients. When a request is received, it manages the login and sets up the connection. For the duration of the session it executes any of commands sent by the FTP client.

Access to an FTP server can be managed in two ways:

In the Anonymous mode, remote clients can access the FTP server by using the default user account called "anonymous" or "ftp" and sending an email address as the password. In the Authenticated mode a user must have an account and a password. This latter choice is very insecure and should not be used except in special circumstances. If you are looking to transfer files securely see SFTP in the section on OpenSSH-Server. User access to the FTP server directories and files is dependent on the permissions defined for the account used at login. As a general rule, the FTP daemon will hide the root directory of the FTP server and change it to the FTP Home directory. This hides the rest of the file system from remote sessions.

sudo apt-get install vsftpd 

anonymous_enable=Yes 

sudo mkdir /srv/files/ftp sudo usermod -d /srv/files/ftp ftp  

sudo restart vsftpd 

write_enable=YES 

sudo restart vsftpd 

anon_upload_enable=YES 

chroot_local_user=YES 

chroot_list_enable=YES chroot_list_file=/etc/vsftpd.chroot_list 

sudo restart vsftpd 

ssl_enable=Yes 

rsa_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem rsa_private_key_file=/etc/ssl/private/ssl-cert-snakeoil.key 

sudo restart vsftpd 

# /etc/shells: valid login shells /bin/csh /bin/sh /usr/bin/es /usr/bin/ksh /bin/ksh /usr/bin/rc /usr/bin/tcsh /bin/tcsh /usr/bin/esh /bin/dash /bin/bash /bin/rbash /usr/bin/screen /usr/sbin/nologin 

auth    required        pam_shells.so 

In this post, we’ll show you how to set up an SSH server on Ubuntu 12.04 Precise Pangolin.

The default SSH server package for Ubuntu 12.04 Precise Pangolin is OpenSSH Server, which we’ll use here.

First, you’ll need to install OpenSSH Server. To do so, open up a Terminal window and type the following command:

sudo apt-get install openssh-server

Enter your password to authenticate, and the apt utility will download and install OpenSSH Server for you. Depending on the speed of your Internet connection and your computer, the installation may take several minutes.

Once the installation has finished, return to the Terminal window. We’ll need to make a few changes to your /etc/ssh/sshd_config file in order to increase SSH’s security. First, as always, we’ll want to make a backup copy of your sshd_config file in case anything goes wrong. Type this command into the Terminal:

sudo cp /etc/ssh/sshd_config ~

This will make a backup copy of the sshd_config file in your home directory.

Next, we’ll need to edit the sshd_config file itself.

sudo vi /etc/ssh/sshd_config

(Note that you can use emacs or gedit or another text editor of your choice.)

Like almost every other server software package, SSH is controlled by a number of directives in its configuration file. The default installation of OpenSSH server is reasonably secure. However, you might want to make a few changes to tighten up its security to additional degree.

The “PermitRootLogin” directive is one you’ll want to change. Once you’re editing the /etc/ssh/sshd_config file, you’ll want to change the following directive as follows:

PermitRootLogin no

This will keep anyone from attempting to log into your server via SSH as root. It’s generally a good idea not to allow any to log into your SSH server as root. If an attacker manages to hack into your SSH server with the root login, he will have complete control over your machine, and that is definitely not a good thing.

Another directive you might want to change is the “AllowUsers.” When the AllowUsers directive is active, only users specifically specified in the directive can access the system through SSH. This adds an additional layer of protection to your SSH server by only allowing specific users to connect via SSH. For instance, if you wanted to limit SSH access to just the “camalas” user account, edit the AllowUsers directive like this:

AllowUsers camalas

To add multiple users to the AllowUsers directive, just add them one by one without commas or semicolons. An AllowUsers directive that permits the camalas user account and the lmaraeus user account to log in would look like this:

AllowUsers camalas lmaraeus

You may also want to consider changing the Port directive. By default SSH runs over TCP/IP port 22, which means that any malware bot autoscanning port 22 can target it. If you set up your user accounts with a weak password (always a bad idea), eventually an automated bot might break through and guess the password. Changing the Port directive to something different will make SSH run over a different port, blocking some of those automated cracking attempts. To set SSH to run over port 5699 instead, make sure your Port directive looks like this:

Port 5699

Note that if you change your SSH server’s default port, you’ll need to remember the new port number when using an SSH client, which we’ll cover in the next section.

After you’ve finished changing the directives in /etc/ssh/sshd_config, switch vi to command mode, and save and quit vi. After you return to the command line, restart the SSH daemon with this command:

sudo restart ssh

You should now be able to SSH into your Ubuntu 12.04 Precise Pangolin machine from another system with an SSH client.

Set Up

Step One—Install Apache

sudo apt-get update 
sudo apt-get install apache2

How to Find your Server’s IP address

ifconfig eth0 | grep inet | awk '{ print $2 }'

Step Two—Install MySQL

sudo apt-get install mysql-server libapache2-mod-auth-mysql php5-mysql

sudo mysql_install_db

sudo /usr/bin/mysql_secure_installation

Enter current password for root (enter for none):  
OK, successfully used password, moving on...

By default, a MySQL installation has an anonymous user, allowing anyone to log into MySQL 
without having to have a user account created for them.  This is intended only for testing, 
and to make the installation go a bit smoother.  You should remove them before moving into
 a production environment.  
Remove anonymous users? [Y/n] y                                              
... Success!  

Normally, root should only be allowed to connect from 'localhost'.  This ensures that someone
 cannot guess at the root password from the network.  
Disallow root login remotely? [Y/n] y 
... Success!  

By default, MySQL comes with a database named 'test' that anyone can access.  This is also 
intended only for testing, and should be removed before moving into a production environment.  
Remove test database and access to it? [Y/n] y  
- Dropping test database...  
... Success!  
- Removing privileges on test database...  
... Success!  

Reloading the privilege tables will ensure that all changes made so far will take effect 
immediately.  
Reload privilege tables now? [Y/n] y  
... Success!  
Cleaning up...

Step Three—Install PHP

sudo apt-get install php5 libapache2-mod-php5 php5-mcrypt

sudo nano /etc/apache2/mods-enabled/dir.conf

<IfModule mod_dir.c>            
    DirectoryIndex index.php index.html index.cgi index.pl index.php index.xhtml index.htm  
</IfModule>

PHP Modules

apt-cache search php5-

php5-cgi - server-side, HTML-embedded scripting language (CGI binary) 
php5-cli - command-line interpreter for the 
php5 scripting language 
php5-common - Common files for packages built from the 

sudo apt-get install name of the module

Step Four—RESULTS: See PHP on your Server

sudo nano /var/www/info.php

<?php phpinfo(); ?>

sudo service apache2 restart

See More

To split large file into several smaller files, you can use split command in Linux. Just follow the steps below and you will be able to split large file into smaller files. 

• Done. You just split your large file into several smaller files

* You can change the output file size by changing the –bytes=1m to your preference. You can use b, k, or m. b represent bytes, k represent kilobytes, m represent megabytes.

To restore the original file, you can use cat command.
To join all the smaller file to restore the original file type:-

Command To List Number Of Open File Descriptors

Use the following command command to display maximum number of open file descriptors:
cat /proc/sys/fs/file-max
Output:

75000

75000 files normal user can have open in single login session. To see the hard and soft values, issue the command as follows:
# ulimit -Hn
# ulimit -Sn
To see the hard and soft values for httpd or oracle user, issue the command as follows:
# su - username
In this example, su to oracle user, enter:
# su - oracle
$ ulimit -Hn
$ ulimit -Sn

System-wide File Descriptors (FD) Limits

The number of concurrently open file descriptors throughout the system can be changed via /etc/sysctl.conf file under Linux operating systems.

The Number Of Maximum Files Was Reached, How Do I Fix This Problem?

Many application such as Oracle database or Apache web server needs this range quite higher. So you can increase the maximum number of open files by setting a new value in kernel variable /proc/sys/fs/file-max as follows (login as the root):
# sysctl -w fs.file-max=100000
Above command forces the limit to 100000 files. You need to edit /etc/sysctl.conf file and put following line so that after reboot the setting will remain as it is:
# vi /etc/sysctl.conf
Append a config directive as follows:
fs.file-max = 100000
Save and close the file. Users need to log out and log back in again to changes take effect or just type the following command:
# sysctl -p
Verify your settings with command:
# cat /proc/sys/fs/file-max
OR
# sysctl fs.file-max

User Level FD Limits

The above procedure sets system-wide file descriptors (FD) limits. However, you can limit httpd (or any other users) user to specific limits by editing /etc/security/limits.conf file, enter:
# vi /etc/security/limits.conf
Set httpd user soft and hard limits as follows:
httpd soft nofile 4096
httpd hard nofile 10240
Save and close the file. To see limits, enter:
# su - httpd
$ ulimit -Hn
$ ulimit -Sn

xargs is more safer and easy to use

xargs functionality can be achived using the backquote feature of shell. But, it offers more options. It can deal with blanks or special characters in file names easily. It is often used with find, grep and other commands.

xargs examples

For example following example will print 1 2 3 4 using xargs (echo command is default)
$ echo 1 2 3 4 | xargs echo
OR
$ echo 1 2 3 4 | xargs
You can force xargs to use at most max-args arguments per command line. For example following will use first two argument per command:
$ echo 1 2 3 4 | xargs -n 2
Find all .bak files in or below the current directory and delete them.
$ find . -name "*.bak" -type f -print | xargs /bin/rm -f

{} as the argument list marker

{} is the default argument list marker. You need to use {} this with various command which take more than two arguments at a time. For example mv command need to know the file name. The following will find all .bak files in or below the current directory and move them to ~/.old.files directory:
$ find . -name "*.bak" -print0 | xargs -0 -I {} mv {} ~/old.files
You can rename {} to something else. In the following example {} is renamed as file. This is more readable as compare to previous example:
$ find . -name "*.bak" -print0 | xargs -0 -I file mv file ~/old.files
Where,

1. -0 If there are blank spaces or characters (including newlines) many commands will not work. This option take cares of file names with blank space.
2. -I Replace occurrences of replace-str in the initial-arguments with names read from standard input. Also, unquoted blanks do not terminate input items; instead the separator is the newline character.

Dealing file names with blank spaces and newline

The following will work incorrectly if there are any filenames containing newlines or spaces (it will find out all .mp3 file located in current directory and play them using mplayer):
$ find . -iname "*.mp3" -print | xargs mplayer
To get rid of this problem use -0 option:
$ find . -iname "*.mp3" -print0 | xargs -0 -I mp3file mplayer mp3file
To find out all *.c file located in 100s of subdirectories and move them to another directory called ~/old.src, use:
$ find /path/to/dir -iname "*.c" -print0 | xargs -0 -I file mv file ~/old.src

Avoiding errors and resource hungry problems with xargs and find combo

To copy all media files to another location called /bakup/iscsi, you can use cp as follows:
$ cp -r -v -p /share/media/mp3/ /backup/iscsi/mp3
However, cp command may fail if an error occurs such as if the number of files is too large for the cp command to handle. xargs in combination with find can handle such operation nicely. xargs is more resource efficient and will not halt with an error:

$ find /share/media/mp3/ -type f -name "*.mp3" -print0 | xargs -0 -r -I file cp -v -p file --target-directory=/bakup/iscsi/mp3

Please note that all of the above commands are tested with GNU/xargs version. BSD and UNIX xargs command may not have options such as -r. Please refer to your local xargs man page for further info:
man xargs

A. An inode is a data structure on a Unix / Linux file system. An inode stores basic information about a regular file, directory, or other file system object. You can use following two commands to display an inode:
[a] ls command : list directory contents

[b] stat command : display file or file system status

ls command

Type ls command with -i ( print the index number of each file ) option:
$ ls -i /etc/passwd
Output:

752010 /etc/passwd

752010 is index number (inode) for /etc/passwd file.

stat command

$ stat /etc/passwd
Output:

 File: `/etc/passwd' Size: 2026 

Blocks: 8 IO Block: 4096 regular file 

Device: 811h/2065d Inode: 752010 

Links: 1 Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root) 

Access: 2007-08-20 23:19:20.000000000 +0530 

Modify: 2007-07-07 00:06:56.000000000 +0530 

Change: 2007-07-07 00:06:56.000000000 +0530

You can use inode number to delete or search a file.

[b] stdout - Use to write information (screen)

[c] stderr - Use to write error message (screen)

Understanding I/O streams numbers

The Unix / Linux standard I/O streams with numbers:

Redirecting the standard error stream to a file

The following will redirect program error message to a file called error.log:
$ program-name 2> error.log
$ command1 2> error.log

Redirecting the standard error (stderr) and stdout to file

Use the following syntax:
$ command-name &>file
OR
$ command > file-name 2>&1
Another useful example:
# find /usr/home -name .profile 2>&1 | more

Redirect stderr to stdout

Use the command as follows:
$ command-name 2>&1

my %seen;
while ( <> ) { 
    print if $seen{$_}++;
}

As a "one-liner":

perl -ne 'print if $seen{$_}++'

More data? This prints <file name>:<line number>:<line>:

perl -ne 'print ( $ARGV eq "-" ? "" : "$ARGV:" ), "$.:$_" if $seen{$_}++'

Explanation on %seen:

• %seen declares a hash. For each unique line in the input $seen{$_} is a scalar slot in the hash named by the the text of the line.
• Using the postfix increment operator (x++) we take the value for our expression, remembering toincrement it after the expression. So, if we haven't "seen" the line $seen{$_} is undefined--but when forced into an numeric "context" like this, it's taken as 0--and false.
• Then it's incremented to 1.

So the first time we see a line, we take the undefined value which fails the if. It increments the count at the slot to 1. Thus, it is 1 for any future occurrences at which point it passes the if condition.

Now as I said above, %seen declares a hash, but with strict turned off, any variable expression can be created on the spot. So the first time perl sees $seen{$_} it knows that I'm looking for %seen, it doesn't have it, so it creates it.

An added neat thing about this is that at the end, if you care to use it, you have a count of how many times each line was repeated.

# dmesg | grep RAMDISK
RAMDISK driver initialized: 16 RAM disks of 16384K size 1024 blocksize

You should get above output on CentOS and RHEL.  Other linux flavors will have similar output as well.  If you would like to see how they are named and what you would need to refer to, do the following:

# ls -l /dev/ram*
lrwxrwxrwx 1 root root 4 Apr 24 12:05 /dev/ram -> ram1
brw-rw---- 1 root disk 1, 0 Apr 24 12:05 /dev/ram0
brw-rw---- 1 root disk 1, 1 Apr 24 12:05 /dev/ram1
brw-rw---- 1 root disk 1, 10 Apr 24 12:05 /dev/ram10
brw-rw---- 1 root disk 1, 11 Apr 24 12:05 /dev/ram11
brw-rw---- 1 root disk 1, 12 Apr 24 12:05 /dev/ram12
brw-rw---- 1 root disk 1, 13 Apr 24 12:05 /dev/ram13
brw-rw---- 1 root disk 1, 14 Apr 24 12:05 /dev/ram14
brw-rw---- 1 root disk 1, 15 Apr 24 12:05 /dev/ram15
brw-rw---- 1 root disk 1, 2 Apr 24 12:05 /dev/ram2
brw-rw---- 1 root disk 1, 3 Apr 24 12:05 /dev/ram3
brw-rw---- 1 root disk 1, 4 Apr 24 12:05 /dev/ram4
brw-rw---- 1 root disk 1, 5 Apr 24 12:05 /dev/ram5
brw-rw---- 1 root disk 1, 6 Apr 24 12:05 /dev/ram6
brw-rw---- 1 root disk 1, 7 Apr 24 12:05 /dev/ram7
brw-rw---- 1 root disk 1, 8 Apr 24 12:05 /dev/ram8
brw-rw---- 1 root disk 1, 9 Apr 24 12:05 /dev/ram9
lrwxrwxrwx 1 root root 4 Apr 24 12:05 /dev/ramdisk -> ram0

All those ramdisks listed have same size.  In above example, they are all 16MB.  Let us change that so we have more space allowed.  Note that I say allowed and not allocated.  We allocate space in one of the later steps by formatting one of the drives above.   Let us set it up so we have 128 MB.  Since this has to be in multiples of 1024, we will setup Ramdisk to have 131072K. 

vi /etc/grub.conf

Find first line which looks similar to following:

kernel /vmlinuz-2.6.9-42.0.10.EL ro root=/dev/VolGroup00/LogVol00

add ramdisk_size=131072 to the end of the line.  Now your line should look like:

kernel /vmlinuz-2.6.9-42.0.10.EL ro root=/dev/VolGroup00/LogVol00ramdisk_size=131072Save and exit grub.conf.  At this point you have it configured to have ramdisk with new size but it does not take effect until you reboot your system.  Once you have rebooted your system, we can start doing rest of configurations.

mke2fs -m 0 /dev/ram0

This will format the ram0 ramdrive for us to use. At this point, kernel will allocate space for you.  Let us setup Ramdisk mount point so we can use it.  We will also have it be owned by user “sunny” so that user can read/write to that mount.

mkdir /home/ramdisk
mount /dev/ram0 /home/ramdisk
chown sunny.sunny /home/ramdisk

At this point you should be able to type:  mount and see your new Ramdisk drive mounted on /home/ramdisk

Remember that everything you put on this drive will be gone if you reboot your server.  If you unmounted the Ramdisk drive and remounted it, your files will still be there.  It is because your system has that much ram set aside for your Ramdisk and will not use it for anything else.   If you would like to setup Ramdisk the same next time you boot up, add these lines to your /etc/rc.local files.

mke2fs -m 0 /dev/ram0
mount /dev/ram0 /home/ramdisk
chown sunny.sunny /home/ramdisk

————————————-
DISCLAIMER: Please be smart and use code found on internet carefully. Make backups often. And yeah.. last but not least.. I am not responsible for any damage caused by this posting. Use at your own risk.

Find is able to execute one or more commands for each file it has found with the -exec option. Unfortunately, one cannot simply enter the command. You need to remember two syntactic tricks:

1. The command that you want to execute need to contain a special macro argument {}, which will be replaced by the matched filename on each invocation of -exec predicate. 
   
2. You need to specify \; (or ';' ) at the end of the command. (If the \ is left out, the shell will interpret the ; as the end of the find command.) . For example, the following two commands are equivalent:

   find . -name "*rc.conf"  -exec chmod o+r {} \;

   find . -name "*rc.conf" -exec chmod o+r '{} ;'

If you spend a lot of time typing plain text, writing programs or HTML, you can save much of that time by using a good editor and using it effectively. This paper will present guidelines and hints for doing your work more quickly and with fewer mistakes.

The open source text editor Vim (Vi IMproved) will be used here to present the ideas about effective editing, but they apply to other editors just as well. Choosing the right editor is actually the first step towards effective editing. The discussion about which editor is the best for you would take too much room and is avoided. If you don't know which editor to use or are dissatisfied with what you are currently using, give Vim a try; you won't be disappointed.

[Vim commands and options are printed in this font]

1. Move around quickly

Most time is spent reading, checking for errors and looking for the right place to work on, rather than inserting new text or changing it. Navigating through the text is done very often, thus you should learn how to do that quickly.

Quite often you will want to search for some text you know is there. Or look at all lines where a certain word or phrase is used. You could simply use the search command /pattern to find the text, but there are smarter ways:

• If you see a specific word and want to search for other occurrences of the same word, use the * command. It will grab the word from under the cursor and search for the next one.
• If you set the 'incsearch' option, Vim will show the first match for the pattern, while you are still typing it. This quickly shows a typo in the pattern.
• If you set the 'hlsearch' option, Vim will highlight all matches for the pattern with a yellow background. This gives a quick overview of where the search command will take you. In program code it can show where a variable is used. You don't even have to move the cursor to see the matches.

In structured text there are even more possibilities to move around quickly. Vim has specific commands for programs in C (and similar languages like C++ and Java):

• Use % to jump from an open brace to its matching closing brace. Or from a "#if" to the matching "#endif". Actually, % can jump to many different matching items. It is very useful to check if () and {} constructs are balanced properly.
• Use [{ to jump back to the "{" at the start of the current code block.
• Use gd to jump from the use of a variable to its local declaration.

There are many more, of course. The point is that you need to get to know these commands. You might object that you can't possibly learn all these commands - there are hundreds of different movement commands, some simple, some very clever - and it would take weeks of training to learn them all. Well, you don't need to; instead realize what your specific way of editing is, and learn only those commands that make your editing more effective.

There are three basic steps:

1. While you are editing, keep an eye out for actions you repeat and/or spend quite a bit of time on.
2. Find out if there is an editor command that will do this action quicker. Read the documentation, ask a friend, or look at how others do this.
3. Train using the command. Do this until your fingers type it without thinking.

Let's use an example to show how it works:

1. You find that when you are editing C program files, you often spend time looking for where a function is defined. You currently use the * command to search for other places where the function name appears, but end up going through a lot of matches for where the function is used instead of defined. You get the idea that there must be a way to do this faster.
2. Looking through the quick reference you find a remark about jumping to tags. The documentation shows how this can be used to jump to a function definition, just what you were looking for!
3. You experiment a bit with generating a tags file, using the ctags program that comes with Vim. You learn to use the CTRL-] command, and find you save lots of time using it. To make it easier, you add a few lines to your Makefile to automatically generate the tags file.

A couple of things to watch out for when you are using these three steps:

• "I want to get the work done, I don't have time to look through the documentation to find some new command". If you think like this, you will get stuck in the stone age of computing. Some people use Notepad for everything, and then wonder why other people get their work done in half the time...
• Don't overdo it. If you always try to find the perfect command for every little thing you do, your mind will have no time left to think about the work you were actually doing. Just pick out those actions that take more time than necessary, and train the commands until you don't need to think about it when using them. Then you can concentrate on the text.

In the following sections there will be suggestions for actions that most people have to deal with. You can use these as inspiration for using the three basic steps for your own work.

2. Don't type it twice

There is a limited set of words we type. And even a limited number of phrases and sentences. Especially in computer programs.  Obviously, you don't want to type the same thing twice.

Very often you will want to change one word into another. If this is to be done in the whole file, you can use the :s (substitute) command. If only a few locations needs changing, a quick method is to use the * command to find the next occurrence of the word and use cw to change the word. Then type nto find the next word and . (dot) to repeat the cw command.

The . command repeats the last change. A change, in this context, is inserting, deleting or replacing text. Being able to repeat this is a very powerful mechanism. If you organise your editing around it, many changes will become a matter of hitting just that . key. Watch out for making other changes in between, because it will replace the change that you were repeating. Instead you might want to mark the location with the m command, continue your repeated change and come back there later.

Some function and variable names can be awkward to type. Can you quickly type "XpmCreatePixmapFromData" without a typo and without looking it up? Vim has a completion mechanism that makes this a whole lot easier. It looks up words in the file you are editing, and also in #include'd files. You can type "XpmCr", then hit CTRL-N and Vim will expand it to "XpmCreatePixmapFromData" for you. Not only does this save quite a bit of typing, it also avoids making a typo and having to fix it later when the compiler gives you an error message.

When you are typing a phrase or sentence multiple times, there is an even quicker approach. Vim has a mechanism to record a macro. You type qa to start recording into register 'a'. Then you type your commands as usual and finally hit q again to stop recording. When you want to repeat the recorded commands you type @a. There are 26 registers available for this.

With recording you can repeat many different actions, not just inserting text. Keep this is mind when you know you are going to repeat something.

One thing to watch out for when recording is that the commands will be played back exactly as you typed them. When moving around you must keep in mind that the text you move over might be different when the command is repeated. Moving four characters left might work for the text where you are recording, but it might need to be five characters where you repeat the commands. It's often necessary to use commands to move over text objects (words, sentences) or move to a specific character.

When the commands you need to repeat are getting more complicated, typing them right at once is getting more difficult. Instead of recording them, you should then write a script or macro. This is very useful to make templates for parts of your code; for example, a function header. You can make this as clever as you like.

3. Fix it when it's wrong

It's normal to make errors while typing. Nobody can avoid it. The trick is to quickly spot and correct them. The editor should be able to help you with this. But you need to tell it what's wrong and what's right.

Very often you will make the same mistake again and again. Your fingers just don't do what you intended. This can be corrected with abbreviations. A few examples:

:abbr Lunix Linux
:abbr accross across
:abbr hte the

The same mechanism can be used to type a long word with just a few characters. Especially useful for words that you find hard to type, and it avoids that you type them wrong. Examples:

:abbr pn penguin
:abbr MS Mandrake Software

However, these tend to expand to the full word when you don't want it, which makes it difficult when you really want to insert "MS" in your text. It is best to use short words that don't have a meaning of their own.

To find errors in your text Vim has a clever highlighting mechanism. This was actually meant to be used to do syntax highlighting of programs, but it can catch and highlight errors as well.

Syntax highlighting shows comments in colour. That doesn't sound like an important feature, but once you start using it you will find that it helps a lot. You can quickly spot text that should be a comment, but isn't highlighted as such (you probably forgot a comment marker).Or see a line of code highlighted as comment (you forgot to insert a "*/"). These are errors which are hard to spot in a B&W file and can waste a lot of time when trying to debug the code.

The syntax highlighting can also catch unbalanced braces. An unbalanced ")" is highlighted with a bright red background. You can use the % command to see how they match, and insert a "(" or ")" at the right position.

Other common mistakes are also quickly spotted, for example using "#included <stdio.h>" instead of "#include <stdio.h>". You easily miss the mistake in B&W, but quickly spot that "include" is highlighted while "included" isn't.

A more complex example: for English text there is a long list of all words that are used. Any word not in this list could be an error. With a syntax file you can highlight all words that are not in the list. With a few extra macros you can add words to the wordlist, so that they are no longer flagged as an error. This works just as you would expect in a word processor. In Vim it is implemented with scripts and you can further tune it for your own use: for example, to only check the comments in a program for spelling errors.

4. A file seldom comes alone

People don't work on just one file. Mostly there are many related files, and you edit several after each other, or even several at the same time. You should be able to take advantage of your editor to make working with several files more efficient.

The previously mentioned tag mechanism also works for jumping between files. The usual approach is to generate a tags file for the whole project you are working on. You can then quickly jump between all files in the project to find the definitions of functions, structures, typedefs, etc. The time you save compared with manually searching is tremendous; creating a tags file is the first thing I do when browsing a program.

Another powerful mechanism is to find all occurrences of a name in a group of files, using the :grep command. Vim makes a list of all matches, and jumps to the first one. The :cn command takes you to each next match. This is very useful if you need to change the number of arguments in a function call.

Include files contain useful information. But finding the one that contains the declaration you need to see can take a lot of time. Vim knows about include files, and can search them for a word you are looking for. The most common action is to lookup the prototype of a function. Position the cursor on the name of the function in your file and type [I: Vim will show a list of all matches for the function name in included files. If you need to see more context, you can directly jump to the declaration. A similar command can be used to check if you did include the right header files.

In Vim you can split the text area in several parts to edit different files. Then you can compare the contents of two or more files and copy/paste text between them. There are many commands to open and close windows, jump between them, temporarily hide files, etc. Again you will have to use the three basic steps to select the set of commands you want to learn to use.

There are more uses of multiple windows. The preview-tag mechanism is a very good example. This opens a special preview window, while keeping the cursor in the file you are working on. The text in the preview window shows, for example, the function declaration for the function name that is under the cursor. If you move the cursor to another name and leave it there for a second, the preview window will show the definition of that name. It could also be the name of a structure or a function which is declared in an include file of your project.

5. Let's work together

An editor is for editing text. An e-mail program is for sending and receiving messages. An Operating System is for running programs. Each program has its own task and should be good at it. The power comes from having the programs work together.

A simple example: Select some structured text in a list and sort it: !sort. The external "sort" command is used to filter the text. Easy, isn't it? The sorting functionality could be included in the editor. But have a look at "man sort", it has a lot of options. And it's probably a nifty algorithm that does the sorting. Do you want to include all that in an editor? Also for other filter commands? It would grow huge.

It has always been the spirit of Unix to have separate programs that do their job well, and work together to perform a bigger task. Unfortunately, most editors don't work too well together with other programs - you can't replace the e-mail editor in Netscape with another one, for example. You end up using a crippled editor. Another tendency is to include all kinds of functionality inside the editor; Emacs is a good example of where this can end up. (Some call it an operating system that can also be used to edit text.)

Vim tries to integrate with other programs, but this is still a struggle. Currently it's possible to use Vim as the editor in MS-Developer Studio and Sniff. Some e-mail programs that support an external editor, like Mutt, can use Vim. Integration with Sun Workshop is being worked on. Generally this is an area that has to be improved in the near future. Only then will we get a system that's better than the sum of its parts.

6. Text is structured

You will often work with text that has some kind of structure, but different from what is supported by the available commands. Then you will have to fall back to the "building blocks" of the editor and create your own macros and scripts to work with this text. We are getting to the more complicated stuff here.

One of the simpler things is to speed up the edit-compile-fix cycle. Vim has the :make command, which starts your compilation, catches the errors it produces and lets you jump to the error locations to fix the problems. If you use a different compiler, the error messages will not be recognised. Instead of going back to the old "write it down" system, you should adjust the 'errorformat' option. This tells Vim what your errors look like and how to get the file name and line number out of them. It works for the complicated gcc error messages, thus you should be able to make it work for almost any compiler.

Sometimes adjusting to a type of file is just a matter of setting a few options or writing a few macros. For example, to jump around manual pages, you can write a macro that grabs the word under the cursor, clears the buffer and then reads the manual page for that word into the buffer. That's a simple and efficient way to lookup cross-references.

Using the three basic steps, you can work more effectively with any sort of structured file. Just think about the actions you want to do with the file, find the editor commands that do it and start using them. It's really as simple as it sounds. You just have to do it.

7. Make it a habit

Learning to drive a car takes effort. Is that a reason to keep driving your bicycle? No, you realize you need to invest time to learn a skill. Text editing isn't different. You need to learn new commands and turn them into a habit.

On the other hand, you should not try to learn every command an editor offers. That would be a complete waste of time. Most people only need to learn 10 to 20 percent of the commands for their work. But it's a different set of commands for everybody. It requires that you lean back now and then, and wonder if there is some repetitive task that could be automated. If you do a task only once, and don't expect having to do it again, don't try to optimise it. But you probably realize you have been repeating something several times in the last hour. Then search the documentation for a command that can do it quicker. Or write a macro to do it.  When it's a larger task, like lining out a specific sort of text, you could look around in newsgroups or on the Internet to see if somebody already solved it for you.

The essential basic step is the last one. You can think of a repetitive task, find a nice solution for it and after the weekend you forgot how you did it. That doesn't work. You will have to repeat the solution until your fingers do it automatically. Only then will you reach the efficiency you need. Don't try to learn too many things at once. But doing a few at the same time will work well. For tricks you don't use often enough to get them in your fingers, you might want to write them down to be able to look them up later. Anyway, if you keep the goal in view, you will find ways to make your editing more and more effective.

One last remark to remind you of what happens when people ignore all the above: I still see people who spend half their day behind a VDU looking up at their screen, then down at two fingers, then up at the screen, etc. - and then wonder why they get so tired... Type with ten fingers! It's not just faster, it also is much less tiresome. Using a computer program for one hour each day, it only takes a couple of weeks to learn to touch-type.

Epilogue

The idea for the title comes from the successful book "The 7 habits of highly effective people" by Stephen R. Covey. I recommend it to everyone who wants to solve personal and professional problems (and who doesn't?). Although some of you will claim it came from the Dilbert book "Seven years of highly defective people" by Scott Adams (also recommended!). See http://iccf-holland.org/click1.html and go to "recommended books and CDs".

About the author

Bram Moolenaar is the main author of Vim. He writes the core Vim functionality and selects what code submitted by many others is included. He graduated at the technical university of Delft as a computer technician. Now he mainly works on software, but still knows how to handle a soldering iron. He is founder and treasurer of ICCF Holland, which helps orphans in Uganda. He does freelance work as a systems architect, but actually spends most time working on Vim. His e-mail address: Bram AT Moolenaar.net.