Damaged wakeboard pictures with shipping box.

kill signal의 종류

＃ kill의 시그널 종류

1. SIGHUP(HUP) : 연결 끊기. 프로세스의 설정파일을 다시 읽는데 사용된다.

2. SIGINT(INT) : 인터럽트

3. SIGQUIOT(QUIT) : 종료

4. SIGILL(ILL) : 잘못된 명령

5. SIGTRAP(TRAP) : 트렙 추적

6. SIGIOT(IOT) : IOT 명령

7. SIGBUS(BUS) : 버스 에러

8. SIGFPE(FPE) : 고정 소수점 예외

9. SIGKILL(KILL) : 죽이기. 이 시그널은 잡히지 않는다.

10. SIGUSR1(USR1) : 사용자 정의 시그널 1

11. SIGSEGV(SEGV) : 세그멘테이션 위반

12. SIGUSR2(USR2) : 사용자 정의 시그널 2

13. SIGPIPE(PIPE) : 읽을 것이 없는 파이프에 대한 시그널

14. SIGALRM(ALRM) : 경고 클럭

15. SIGTERM(TERM) : 소프트웨어 종료 시그널, 일반적으로 kill 시그널이 전송되기 전에 전송된다.

                            잡히는 시그널이기 때문에 종료되는 것을 트랙할 수 있다.

16. SIGKFLT : 코프로세서 스택 실패

17. SIGCHLD(CHLD) : 자식 프로세스의 상태변화

18. SIGCONT(CONT) : STOP 시그널 이후 계속 진행할 때 사용

19. SIGSTOP(STOP) : 정지. 이 시그널 역시 잡을 수 없다.

20. SIGTSTP(TSTP) : 키보드에 의해 발생하는 시그널로 Ctrl+Z로 생성된다.

SSD performance tips for RHEL6 and Fedora

SSD performance tips for RHEL6 and Fedora

Posted by Jim Perrin at 9:50 AM Monday, November 21, 2011 

    Solid State drives provide a pretty substantial performance boost over traditional hard drive technology, but they have some limitations that require some additional planning. There are basically two big things to do, enable discard/trim support in the filesystem, and limit write operations to the SSD. You want to enable discard to deal with underlying drive specific performance degradation that will happen over time. You want to limit writes to the disk to forestall the impending cell death that awaits any SSD device.  Without further ado, lets get to the tuning tips.

1. Enable discard: in /etc/fstab, append 'discard' as a mount option.

(NOTE: Make sure your disk supports trim. The following command should return a result telling you trim is supported: hdparm -I /dev/yourdisk | grep -i trim)

    sample fstab entry:  /dev/sda2        /      ext4     defaults,discard     1 1

 2. Move /tmp to ram.  This depends on how much ram you have and how much /tmp space you use, but it really helps to limit writes to the SSD

sample fstab entry:  none       /tmp      tmpfs        defaults      0 0

3. Change the mount options for your ext4 filesystem. Again, we're looking to limit writes here. These options are very helpful, but assume that you're using some form of battery backup (UPS, laptop usage, etc). Specifically we're looking at noatime, data, and commit options.

• change data from the default of ordered to writeback. This reduces the journal data to meta-data only, thus limiting writes.
• change the commit value from the default of 5 seconds to 10, or 15. This gets you a 2 to 3x write savings, though you risk losing a bit more data if you lose power.
• If you don't need access time records (mtime and ctime should be enough for most folks) disabling atime will also limit write operations. 

sample fstab entry:  /dev/sda2        /      ext4     defaults,discard,data=writeback,noatime,commit=15     1 1

 4. Lastly, you might want to consider changing the scheduler to noop, since SSD performance will change the system dynamic. You'll likely want to benchmark this to see if it makes a difference for you. To do this, simply add 'elevator=noop' as a kernel option in /etc/grub.conf

This setup will provide a decent base for a laptop or workstation using SSD storage drives. Enjoy!

Install MySQL 5.5.33 on Fedora 18/17, CentOS/Red Hat (RHEL) 6.4/5.9

MySQL is a relational database management system (RDBMS) that runs as a server providing multi-user access to a number of databases. This is guide, howto install or upgrade MySQL Community Server latest and greatest version 5.5.33 on Fedora 18/17/16/15/14/13/12, CentOS 6.4/6.3/6.2/6.1/6/5.9 and Red Hat (RHEL) 6.4/6.3/6.2/6.1/6/5.9.

Note: If you are upgrading MySQL (from earlier version), then make sure that you backup (dump and copy) your database and configs. And remember run mysql_upgrade command.

Install MySQL Database 5.5.33 on Fedora 18/17/16/15/14/13/12, CentOS 6.4/5.9, Red Hat (RHEL) 6.4/5.9

1. Change root user

su - ## OR ## sudo -i

2. Install Remi repository

Fedora

## Remi Dependency on Fedora 18, 17, 16 rpm -Uvh http://download1.rpmfusion.org/free/fedora/rpmfusion-free-release-stable.noarch.rpm rpm -Uvh http://download1.rpmfusion.org/nonfree/fedora/rpmfusion-nonfree-release-stable.noarch.rpm   ## Fedora 18 ## rpm -Uvh http://rpms.famillecollet.com/remi-release-18.rpm   ## Fedora 17 ## rpm -Uvh http://rpms.famillecollet.com/remi-release-17.rpm   ## Fedora 16 ## rpm -Uvh http://rpms.famillecollet.com/remi-release-16.rpm   ## Fedora 15 ## rpm -Uvh http://rpms.famillecollet.com/remi-release-15.rpm   ## Fedora 14 ## rpm -Uvh http://rpms.famillecollet.com/remi-release-14.rpm   ## Fedora 13 ## rpm -Uvh http://rpms.famillecollet.com/remi-release-13.rpm   ## Fedora 12 ## rpm -Uvh http://rpms.famillecollet.com/remi-release-12.rpm

CentOS and Red Hat (RHEL)

## Remi Dependency on CentOS 6 and Red Hat (RHEL) 6 ## rpm -Uvh http://download.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm   ## CentOS 6 and Red Hat (RHEL) 6 ## rpm -Uvh http://rpms.famillecollet.com/enterprise/remi-release-6.rpm     ## Remi Dependency on CentOS 5 and Red Hat (RHEL) 5 ## rpm -Uvh http://dl.fedoraproject.org/pub/epel/5/i386/epel-release-5-4.noarch.rpm   ## CentOS 5 and Red Hat (RHEL) 5 ## rpm -Uvh http://rpms.famillecollet.com/enterprise/remi-release-5.rpm

3. Check Available MySQL versions

Fedora 18, 17, 16, 15, 14, 13, 12

yum --enablerepo=remi list mysql mysql-server

CentOS 6.4/6.3/6.2/6.1/6/5.9 and Red Hat (RHEL) 6.4/6.3/6.2/6.1/6/5.9

yum --enablerepo=remi,remi-test list mysql mysql-server

Output:

Loaded plugins: changelog, fastestmirror, presto, refresh-packagekit ... remi | 3.0 kB 00:00 remi/primary_db | 106 kB 00:00 Available Packages mysql.i686 5.5.33-1.fc18.remi @remi mysql-server.i686 5.5.33-1.fc18.remi @remi

4. Update or Install MySQL 5.5.33

Fedora 18, 17, 16, 15, 14, 13, 12

yum --enablerepo=remi install mysql mysql-server

CentOS 6.4/6.3/6.2/6.1/6/5.9 and Red Hat (RHEL) 6.4/6.3/6.2/6.1/6/5.9

yum --enablerepo=remi,remi-test install mysql mysql-server

5. Start MySQL server and autostart MySQL on boot

Fedora 18/17/16

systemctl start mysqld.service ## use restart after update   systemctl enable mysqld.service

Fedora 15/14/13/12/11, CentOS 6.4/6.3/6.2/6.1/6/5.9 and Red Hat (RHEL) 6.4/6.3/6.2/6.1/6/5.9

/etc/init.d/mysqld start ## use restart after update ## OR ## service mysqld start ## use restart after update   chkconfig --levels 235 mysqld on

6. MySQL Secure Installation

• Set (Change) root password
• Remove anonymous users
• Disallow root login remotely
• Remove test database and access to it
• Reload privilege tables

Start MySQL Secure Installation with following command

/usr/bin/mysql_secure_installation

Output:

NOTE: RUNNING ALL PARTS OF THIS SCRIPT IS RECOMMENDED FOR ALL MySQL SERVERS IN PRODUCTION USE! PLEASE READ EACH STEP CAREFULLY!     In order to log into MySQL to secure it, we\'ll need the current password for the root user. If you\'ve just installed MySQL, and you haven\'t set the root password yet, the password will be blank, so you should just press enter here.   Enter current password for root (enter for none): OK, successfully used password, moving on...   Setting the root password ensures that nobody can log into the MySQL root user without the proper authorisation.   Set root password? [Y/n] Y New password: Re-enter new password: Password updated successfully! Reloading privilege tables.. ... Success!     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...       All done! If you\'ve completed all of the above steps, your MySQL installation should now be secure.   Thanks for using MySQL!

Note: If you don’t want some reason, do a “MySQL Secure Installation” then at least it’s very important to change the root user’s password

mysqladmin -u root password [your_password_here]   ## Example ## mysqladmin -u root password myownsecrectpass

7. Connect to MySQL database (localhost) with password

mysql -u root -p   ## OR ## mysql -h localhost -u root -p

8. Create Database, Create MySQL User and Enable Remote Connections to MySQL Database

This example uses following parameters:

• DB_NAME = webdb
• USER_NAME = webdb_user
• REMOTE_IP = 10.0.15.25
• PASSWORD = password123
• PERMISSIONS = ALL

## CREATE DATABASE ## mysql> CREATE DATABASE webdb;   ## CREATE USER ## mysql> CREATE USER 'webdb_user'@'10.0.15.25' IDENTIFIED BY 'password123';   ## GRANT PERMISSIONS ## mysql> GRANT ALL ON webdb.* TO 'webdb_user'@'10.0.15.25';   ## FLUSH PRIVILEGES, Tell the server TO reload the GRANT TABLES ## mysql> FLUSH PRIVILEGES;

Enable Remote Connection to MySQL Server –> Open MySQL Port (3306) on Iptables Firewall (as root user again)

1. Edit /etc/sysconfig/iptables file:

nano -w /etc/sysconfig/iptables

2. Add following INPUT rule:

-A INPUT -m state --state NEW -m tcp -p tcp --dport 3306 -j ACCEPT

3. Restart Iptables Firewall:

service iptables restart ## OR ## /etc/init.d/iptables restart

4. Test remote connection:

mysql -h dbserver_name_or_ip_address -u webdb_user -p webdb

SysBench on CentOS – HowTo

If you want to test server performance, you can think about SysBench. SysBench is a modular, cross-platform and multi-threaded benchmark tool for evaluating OS parameters that are important for a system running a database under intensive load. The idea of this benchmark suite is to quickly get an impression about system performance without setting up complex database benchmarks or even without installing a database at all.

Current features allow to test the following system parameters:

* file I/O performance
* scheduler performance
* memory allocation and transfer speed
* POSIX threads implementation performance
* database server performance (OLTP benchmark)
(Primarily written for MySQL server benchmarking, SysBench will be further extended to support multiple database backends, distributed benchmarks and third-party plug-in modules)

I couldn’t find CentOS RPM so here are few tips how to install it manually.

Download Sysbench (current version is 0.4.12)

# wget http://garr.dl.sourceforge.net/sourceforge/sysbench/sysbench-0.4.12.tar.gz

Then unpack it and install with

# tar -xvzf sysbench-0.4.12.tar.gz # cd sysbench-0.4.12 # libtoolize --force --copy # ./autogen.sh # ./configure # make # make install

To test CPU performance you can try

# sysbench --test=cpu --cpu-max-prime=20000 run

For MySQL test, you’ll need to prepare database for testing with

# sysbench --test=oltp --mysql-table-engine=innodb --oltp-table-size=500000 --mysql-user=test_database --mysql-password=test_database_password --mysql-socket=/var/lib/mysql/mysql.sock prepare

(replace test_database with valid username and test_database_password with valid password)

This command will create sample table inside test_database and it will have 500 000 rows (InnoDB engine).

sysbench 0.4.12: multi-threaded system evaluation benchmark   No DB drivers specified, using mysql Creating table 'test-database'... Creating 500000 records in table 'test-database'...

Now to start read test

# sysbench --num-threads=16 --max-requests=100000 --test=oltp --oltp-table-size=500000 --mysql-socket=/var/lib/mysql/mysql.sock --oltp-read-only --mysql-user=test_database --mysql-password=test_database_password run

For read-write test you can try

# sysbench --num-threads=16 --max-requests=10000 --test=oltp --oltp-table-size=500000 --mysql-socket=/var/lib/mysql/mysql.sock --oltp-test-mode=complex --mysql-user=test_database --mysql-password=test_database_password run

More info about specific parameters can be found in official docs (http://sysbench.sourceforge.net/docs/)