汶川地震期间，四川某地某教室，某北大出来的教授正在给学生上课。发现地震时，没管他的学生，自己先从教师楼跑出来。

最近媒体在谈论此事，众人给他起了个“范跑跑“的绰号。哈，更有人在电视节目上，当着全国人的面，骂他无耻。那个人，也被大家起了个绰号--郭道德。

大家都有家室，大家都是人，逃跑是人的本能. 他身为老师，就必须当圣人？

在8级地震时，仅因为他没选择做英雄，就要批评他吗？ 他影响学生逃跑了吗?

某些标榜“道德“的卫士们，你们不要太愚昧，太自欺欺人了。

某些媒体们，你们不要找一个百姓揪住不放了。中国有多少反面教材？那么多贪官，那么多腐败的事，你们不敢访问，怕丢了饭碗，怕砸了公司，就骚扰百姓吗？

事后，当媒体问“范跑跑“，你是否为你的行为后悔呢？ 他依然回答，不后悔。

这是真正的人，一个不愿自欺欺人的人，一个坦然的君子！

英雄毕竟是少数，比起某些愚昧的英雄，我们更需要这些君子。一个敢当着全国人的面，坦然地回答自己的想法，不屈服所谓“郭道德“们的压力的“范跑跑“， 其实是英雄！

媒体应该做出正确的导向. 去表扬那些在困难面前舍我就人的英雄,但不要再如此批评不愿做英雄的正常人了.

补：

“跑跑“最终丢了饭碗, 还给全国人民道了歉。

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Usage: ./httpd [-D name] [-d directory] [-f file]
               [-C "directive"] [-c "directive"]
               [-k start|restart|graceful|stop]
               [-v] [-V] [-h] [-l] [-L] [-t] [-S]
Options:
  -D name           : define a name for use in <IfDefine name> directives
  -d directory      : specify an alternate initial ServerRoot
  -f file           : specify an alternate ServerConfigFile
  -C "directive"    : process directive before reading config files
  -c "directive"    : process directive after reading config files
  -e level          : show startup errors of level (see LogLevel)
  -E file           : log startup errors to file
  -v                : show version number
  -V                : show compile settings
  -h                : list available command line options (this page)
  -l                : list compiled in modules
  -L                : list available configuration directives
  -t -D DUMP_VHOSTS : show parsed settings (currently only vhost settings)
  -S                : a synonym for -t -D DUMP_VHOSTS
  -t                : run syntax check for config files

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The MySQL server receives queries in the SQL format. Once a query is received, it first needs to be parsed, which involves translating it from what is essentially a textual format into a combination of internal binary structures that can be easily manipulated by the optimizer.

MySQL's optimizer has several important tasks:
. Determine which keys can be used to retrieve the records from tables, and choose the best one for each table.
. For each table, decide whether a table scan is better than reading on a key. If there are a lot of records that match the key value, the advantages of the key are reduced and the table scan becomes faster.
. Determine the order in which tables should be joined when more than one table is present in the query.
. Rewrite the WHERE clause to eliminate dead code, reducing the unnecessary computations and changing the constraints whenever possible to open the way for using keys.
. Eliminate unused tables from the join.
. Determine whether keys can be  used for ORDER BY and GROUP BY.
. Attempt to replace an outer join with an inner join.
. Attempt to simplify subqueries, as well as determine to what extent their results can be cached.
. Merge views.

Using EXPLAIN to Understand the Optimizer
The MySQL EXPLAIN command tells the optimizer to show its query plan.
E.g,
EXPLAIN SELECT ... \G
Understanding the output of EXPLAIN

EXPLAIN FIELD	DESCRIPTION
id	QueryID. Meaningful only when subqueries are used.
select_type	Indicates what happens with the result set retrieved from the table. A join not involving subqueries or UNION will have this value set to simple. See the upcoming section "Select types" for details.
table	The alias the table is referenced by in the query. If no alias is used, the real name of this table.
type	The method used for retrieving the records from the table. See the upcoming section "Record access types" for details.
possible_keys	A list of keys that can be used in conjunction with the WHERE clause to retrieve the records from this table.
key	The name of the key used for retrieving the records. When index_merge optimization is used, contains a list of keys.
key_len	The length of the key used in a query. This does not have to be the full length of the key - it is possible to use only a key prefix.
ref	A list of fields from other tables whose values are involved in an index lookup in this table.
rows	Average estimated number of records in this table to be retrieved on each join iteration.
Extra	Additional comments on the optimization strategy. See the section "Extra field" for details.

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High-level view of MySQL modules

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1. A proper locking mechanism is necessary to ensure data consistency when there is a possibility of multiple clients accessing and possibly modifying the same data at the same time.
2. table-level locks, page-level locks, and row-level locks
3. MyISAM and MEMORY storage engines can only work with table-level locks. InnoDB supports row-level locks, and Berkeley DB supports page-level locks.
4. MyISAM - If the insert operation results in writing the record at the end of the datafile, reading can be done without a lock.
5. InnoDB Locking
There are two types of row-level locks: shared and exclusive.
InnoDB also uses so-called intension locks on a table. There are also two types of intension table locks, shared and exclusive.
Rocord locking
What InnoDB actually locks is the index entry, the space before it, and the space after the last record. This method is called next-key locking.
The next-key locking is necessary to avoid the phantom row problem in transactions. If we did not lock the space before the record, it would be possible for another transaction to insert another record in between. Thus, if we were to run the same query again, we would see the record that was not there the first time we ran the query. This would make it impossible to meet the requirement of the serializable read transaction isolation level.
InnoDB has an automatic deadlock detection lagorithm. It will usually roll back the last transaction involed in a deadlock.  Additionally, some transactions may be considered to be in a virtual deadlock. For example, if a query is written is such a way that it examines several billion records, it may not release its locks for weeks, although from a theoretical point of view it eventually will. For such situations InnoDB uses a lock timeout, which is controlled by the configuration variable innodb_lock_wait_timeout.

 Accessing records always in the same index order, writing properly optimized queries, and commiting transactions frequently are some of techniques that help prevent potential deadlocks.

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> dfisk -l
> df -T -h
> mount
> cat /etc/fstab

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mkfifo
    > mkfifo my_pipe
    > cat a.txt > my_pipe
    > cat my_pipe

ldd
    > ldd /usr/java/jre1.5.0_11/bin/java

xmlwf
    > curl -s 'http://bashcurescancer.com' > bcc.html
    > xmlwf bcc.html

删除文件的恢复

lsof
    > cp ~/code/demo.cpp /tmp/workspace/test.cpp
    > cd /tmp/workspace
    > less test.cpp
    > rm -f test.cpp
    > lsof | grep test.cpp
    less      6173  dirkxu    4r      REG      253,0     2876     669315 /tmp/workspace/test.cpp (deleted)
    > cat /proc/6173/fd/4 > recover.cpp
    > cmp ~/code/demo.cpp recover.cpp

文件的分割、合并、校验

split [OPTION] [INPUT [PREFIX]]
       -b, --bytes=SIZE
              put SIZE bytes per output file

       -C, --line-bytes=SIZE
              put at most SIZE bytes of lines per output file

       -d, --numeric-suffixes
              use numeric suffixes instead of alphabetic

       -l, --lines=NUMBER
              put NUMBER lines per output file
    > split -b 3k larger.txt small
    > ls -lh /etc | split -l 40 - small_line

    #combine multi files into one file
    > cat smalla smallb smallc > new_larger
    > cat small_linea small_lineb >> history

    #validate whether the new file equals the old file
    > md5sum larger new_larger

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http://www.linuxsir.org/main/?q=node/210 作者：北南南北 来自：LinuxSir.Org

统计Apache进程数的时候，一般使用命令：
ps aux | grep httpd | grep -v grep | wc -l  等价于 pgrep httpd |wc -l

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# Install apache

> groupadd apache

> useradd -g apache apache

> ./configure --prefix=/usr/local/apache2 --enable-mods-shared=most --enable-ssl --enable-so

> make && make install

> cd /usr/local/apache2/bin

> cp apachectl /etc/rc.d/init.d/httpd

> vi /etc/rc.d.init.d/httpd

# chkconfig: 2345 70 30
# description: Apache is a World Wide Web server.  It is used to serve \
#              HTML files and CGI.
# processname: httpd 

...

case $ARGV in
start|stop|restart|graceful)
    $HTTPD -k $ARGV -DSSL
    ERROR=$?
    ;;

> /sbin/chkconfig --add httpd

> chown -R root .

> chgrp -R apache .

> chown -R apache error logs

> vi conf/httpd.conf

<DocumentRoot "" ...

User apache

Group apache

...

# Customize the ssl

> cd /tmp
> mkdir ssl
> cd /tmp
> mkdir ssl
> openssl req -new -out ssl/server.csr

Enter PEM pass phrase: abc123
Verifying - Enter PEM pass phrase: abc123
Country Name (2 letter code) [GB]: ALL PRESS ENTER TO SKIP FROM HERE

> openssl rsa -in privkey.pem -out ssl/server.key

Enter pass phrase for privkey.pem: abc123

> openssl x509 -in ssl/server.csr -out ssl/server.crt -req -signkey ssl/server.key -days 365
> mkdir /usr/local/apache2/conf/ssl.crt
> mkdir /usr/local/apache2/conf/ssl.key
> cp ssl/server.crt /usr/local/apache2/conf/ssl.crt
> cp ssl/server.key /usr/local/apache2/conf/ssl.key
> rm -rf privkey.pem ssl

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ActiveMQ CPP Library 2.1.3

# Install dependencies

1. libuuid

  > sudo yum install e2fsprogs-devel

2. CppUnit

  > sudo yum install cppunit cppunit-devel

3. GNU Build System

Tool        Recommended Version
autoconf    >= 2.60
automake    >= 1.10
libtool     >= 1.5.24

# Building on Unix/Linux

  > ./autogen.sh

  > ./configure

  > make

  > make install

# To generate the doxygen documentation for the project

  > make doxygen-run

Troubleshooting:

The above offical instruction is just woks on paper. Actually, I cannot install activemq cpp well base on it. I got the following error messages:

Error:

> ./autogen.sh
configure.ac:173: error: AC_SUBST: `DX_FLAG_[]DX_CURRENT_FEATURE' is not a valid
m4/ac_doxygen.m4:95: DX_REQUIRE_PROG is expanded from...
m4/ac_doxygen.m4:167: DX_ARG_ABLE is expanded from...
m4/ac_doxygen.m4:324: DX_INIT_DOXYGEN is expanded from...
configure.ac:173: the top level
autom4te: /usr/bin/m4 failed with exit status: 1
aclocal: autom4te failed with exit status: 1
autoreconf: aclocal failed with exit status: 1

The error is related to Doxygen.

Currently, I have no other ways except to disable all configurations about Doxygen.  Actually, it does not affect the main activemq work.

Solution:

1. > vi configure.ac

Comment on the following lines:

## Execute Doxygen macros
# DX_HTML_FEATURE(ON)
# DX_CHM_FEATURE(OFF)
# DX_CHI_FEATURE(OFF)
# DX_MAN_FEATURE(OFF)
# DX_RTF_FEATURE(OFF)
# DX_XML_FEATURE(OFF)
# DX_PDF_FEATURE(OFF)
# DX_PS_FEATURE(OFF)
# DX_INIT_DOXYGEN(activemq-cpp, doxygen.cfg, doc)

2. > vi Mikefile.am

Comment on the following lines:

# include doxygen-include.am

# EXTRA_DIST=autogen.sh $(DX_CONFIG) doc/html

OK. Please do autogen.sh, ./configure, make, and make install. It works fine now.

Start/Stop ActiveMQ

1. startup.sh

 if [ -e /tmp/smlog ]; then
         mv /tmp/smlog /tmp/smlog.bak;
 fi
 nohup bin/activemq > /tmp/smlog 2>&1 &
 echo "[INFO] ActiveMQ is running..."

2. shutdown.sh

 pid=`sudo ps -ef | grep "activemq" | awk ' { print $2 } '`
 kill $pid;
 echo "[INFO] ActiveMQ is stopped..."

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表2-6                                                            Bash配置文件

添加环境变量

PATH=.:$PATH ; export PATH

M=/work/time/files/info/memos ; export M

添加别名

alias p='pwd ; ls –CF'

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Downloads install package: mysql-5.1.24-rc.tar.tar

# Add user/group for MySQL

> groupadd mysql

> useradd -g mysql mysql

>  tar zxf mysql-5.1.24-rc.tar.tar

> cd mysql-5.1.24-rc

# check, compile, and install

> ./configure --prefix=/usr/local/mysql5.1.24 --with-embedded-server 

> make

> make install

# configure modifier, db info

> cp support-files/my-medium.cnf /etc/my.cnf

> cd /usr/local/mysql5.1.24

> chown -R mysql .

> chgrp -R mysql .

> bin/mysql_install_db --user=mysql

> chown -R root .

> chown -R mysql var

> bin/mysqld_safe --user=mysql &

# as service

> rm -f /etc/rc.d/init.d/mysqld

> cp support-files/mysql.server /etc/rc.d/init.d/mysqld

> chmod +755 /etc/rc.d/init.d/mysqld

> /sbin/chkconfig --add mysqld

> /sbin/chkconfig --level 345 mysqld on

# as lib

> vi /etc/ld.so.conf

/usr/local/mysql5.1.24/lib/mysql

> ldconfig /etc/ld.so.conf

> ldconfig　－v | grep mysql  (Optional)

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使用yum之前，请切换为root用户。

添加/删除/更新软件

1.仅安装指定的软件
命令：yum install <package_name>

yum会查询数据库，有无这一软件包，如果有，则检查其依赖冲突关系，如果没有依赖冲突，那么最好，下载安装;如果有，则会给出提示，询问是否要同时安装依赖，或删除冲突的包，你可以自己作出判断。

2.用YUM删除软件包
命令：yum remove <package_name>

同安装一样，yum也会查询数据库，给出解决依赖关系的提示。

3.列出所有可更新的软件清单
命令：yum check-update

4.更新所有已安装软件
命令：yum update

5.仅更新指定的软件
命令：yum update <package_name>

用YUM查询软件信息
1.使用YUM查找软件包
命令：yum search <keyword>

比如我们要安装一个Instant Messenger，但又不知到底有哪些，这时不妨用 yum search messenger这样的指令进行搜索，yum会搜索所有可用rpm的描述，列出所有描述中和messeger有关的rpm包，于 是我们可能得到gaim，kopete等等，并从中选择。
有时我们还会碰到安装了一个包，但又不知道其用途，我们可以用yum info packagename这个指令来获取信息。

2.列出所有可安裝的软件清单
命令：yum list

3.列出所有可更新的软件包
命令：yum list updates

4.列出所有已安装的软件包
命令：yum list installed

5.列出所有已安装但不在 Yum Repository 內的软件包
命令：yum list extras

6.列出所指定的软件包
命令：yum list <package_name>

7.使用YUM获取软件包信息
命令：yum info <package_name>

8.列出所有软件包的信息
命令：yum info

9.列出所有可更新的软件包信息
命令：yum info updates

10.列出所有已安裝的软件包信息
命令：yum info installed

11.列出所有已安裝但不在 Yum Repository 內的软件包信息
命令：yum info extras

12.列出软件包提供哪些文件
命令：yum provides <package_name>

清除YUM缓存
yum 会把下载的软件包和header存储在cache中，而不会自动删除。如果我们觉得它们占用了磁盘空间，可以使用yum clean指令进行清除。

1.清除缓存目录(/var/cache/yum)下的软件包
命令：yum clean packages

2.清除缓存目录(/var/cache/yum)下的 headers
命令：yum clean headers

3.清除缓存目录(/var/cache/yum)下旧的 headers
命令：yum clean oldheaders

4.清除缓存目录(/var/cache/yum)下的软件包及旧的headers
命令：yum clean, yum clean all (= yum clean packages; yum clean oldheaders)

举例：

yum groupinstall "GNOME Desktop Environment"

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