How to configure DRBD On CentOS 6.5 IntroductionThe Distributed Replicated Block Device (DRBD) is a distributed replicated storage system for the Linux platform. It is implemented as several userspace management applications and some shell scripts and is normally used on high availability (HA) computer clusters. DRBD refers as well to the logical block devices provided by the scheme and to software that implements it. The DRBD software is free software released under the terms of the GNU General Public License version 2. DRBD is part of the Lisog open source stack initiative. Distributed Replicated Block Device is actually a network based RAID 1. If you need to secure data on certain disk and are therefore mirroring your data to another disk via network, you have to configure DRBD on your system.In this tutorial, let us see how to install and configure DRBD on CentOS 6.5.Requirements– Two disks  (preferably same size)– Networking b...

How To Configure A High Available Load-balancer With HAProxy And Keepalived This tutorial explains how to set up a two-node load balancer with HAProxy and keepalived on CentOS 7. The load balancer sits between the user and two (or more) backend Apache web servers that hold the same content.  If one of them is down, all requests will automatically be redirected to the remaining backend server. which means the users will not notice any disruption of the service.For configuring HA-Load balanceer, You need 2 virtual/physical servers for the load-balancers and 2 virtual/physical servers to load-balance. In addition to the 4 IP addresses needed by the servers themselves, a fifth virtual IP address (VIP) is necessary. The two load-balanc...

Install Oracle Database 12c On CentOS7 In this tutorial, we will show you how to Install Oracle Database 12c On CentOS 7OS information:[root@ora-c7 ~]# cat   /etc/centos-release CentOS Linux release 7.0.1406 (Core) Network:[root@ora-c7 ~]# ip a   | grep inet    inet 127.0.0.1/8 scope host lo     inet6 ::1/128 scope host     inet 192.168.119.139/24 brd 192.168.119.255 scope global dynamic eno16777736     inet6 fe80::20c:29ff:fe41:1494/64 scope link Login as root and add required groups: /usr/sbin/groupadd -g 501 oinstall /usr/sbin/groupadd -g 502 dba /usr/sbin/groupadd -g 503 operAdd user Oracle:/usr/sbin/useradd -u 502 -g oinstall -G dba,oper oracleChange password for user:passwd oracleAdd kernel parameters to /etc/sysctl.conf. kernel.shmmni = 4096 kernel.shmmax = 4398046511104 kernel.shmall = 1073741824 kernel.sem = 250 32000 100 128 fs.aio...

本文 centos 6.5 优化 的项有18处:1、centos6.5最小化安装后启动网卡2、ifconfig查询IP进行SSH链接3、更新系统源并且升级系统4、系统时间更新和设定定时任5、修改ip地址、网关、主机名、DNS6、关闭selinux，清空iptables7、创建普通用户并进行sudo授权管理8、修改SSH端口号和屏蔽root账号远程登陆9、锁定关键文件系统（禁止非授权用户获得权限）10、精简开机自启动服务11、调整系统文件描述符大小12、设置系统字符集13、清理登陆的时候显示的系统及内核版本14、内核参数优化15、定时清理/var/spool/clientmqueue16、删除不必要的系统用户和群组17、关闭重启ctl-alt-delete组合键18、设置一些全局变量1、启动网卡#centos6.x最小化安装后，网卡默认不是启动状态 ifup eth02、SSH链接 ifconfig 查看IP后SSH终端连接。3、更新源 最小化安装是没有wget工具的，必须先安装在修改源)yum install wget备份原系统更新源mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup进入yum.repos.d目录cd /etc/yum.repos.d下载网易镜像源或者搜狐镜像源#下载网易镜像源： wget http://mirrors.163.com/.help/CentOS6-Base-163.repo #或者 #下载搜狐镜像源： w...

Configuring A High Availability Apache Cluster With Pacemaker On CentOS 7 Hello everyone.Today we will learn how we can setup & configure Pacemaker on two CentOS 7 Linux servers for high availability purposes. I will stuck with the very basic fundamental and I will not dive deep on it over here for this tutorial.Let’s begin then.First, we need to know what is CentOS, Pacemaker and High Availability and why we need them.Why CentOS?CentOS Linux is a community-supported distribution derived from sources freely provided to the public by Red Hat for Red Hat Enterprise Linux (RHEL). As such, CentOS Linux aims to be functionally compatible with RHEL. The CentOS Project mainly changes packages to remove upstream vendor branding and artwork. CentOS Linux is no-cost and free to redistribute. Each CentOS version is maintained for up to 10 years (by means of security updates — the duration of the support interval by Red Hat has varied...

How to upgrade or update kernel of the CentOS to Latest stable KernelThe kernel is the core of the operating system, and runs the CPU, manages system memory, controls access to disk drives, and contains device drivers that enable you to interact with the system and use the hardware and peripherals attached to the  computer.Naturally, kernel update  appeals most system administrators who are responsible for wringing the most performance and benefit out of their existing hardware and software. In some cases, rebuilding the kernel(kernel upgrade or kernel update) is required in order to support new hardware that is not supported, or that is poorly supported, by your system’s existing kernel.Check the current kernel of the system by using uname –r option.[root@localhost ~]# uname -r 3.10.0-327.el7.x86_64 After you have determined the version of the kernel you are currently running, the next step is to obtain the latest version of the k...

Install GFS2 In CentOS 6.5 In computing, the Global File System 2 or GFS2 is a shared disk file system for Linux computer clusters. GFS2 differs from distributed file systems (such as AFS, Coda, InterMezzo, or GlusterFS) because GFS2 allows all nodes to have direct concurrent access to the same shared block storage. In addition, GFS or GFS2 can also be used as a local filesystem. GFS  has no disconnected operating-mode, and no client or server roles. All nodes in a GFS cluster function as peers. Using GFS in a cluster requires hardware to allow access to the shared storage, and a lock manager to control access to the storage. The lock manager operates as a separate module: thus GFS and GFS2 can use the Distributed Lock Manager (DLM) for cluster configurations and the “nolock” lock manager for local filesystems. Older versions of GFS also support GULM, a server based lock manager which implements redundancy via failover.Here is my t...

Active Session History (ASH) performed an emergency flush 告警日志信息 Tue Sep 15 14:29:27 2015 Active Session History (ASH) performed an emergency flush. This may mean that ASH is undersized. If emergency flushes are a recurring issue, you may consider increasing ASH size by setting the value of _ASH_SIZE to a sufficiently large value. Currently, ASH size is 67108864 bytes. Both ASH size and the total number of emergency flushes since instance startup can be monitored by running the following query: select total_size,awr_flush_emergency_count from v$ash_info; 执行告警日志中查询语句 SYS@hkprdbuat> select total_size/1024/1024 MB,awr_flush_emergency_count from v$ash_info; MB AWR_FLUSH_EMERGENCY_COUNT ---------- ------------------------- 64   3 查询当前大小 select x.ksppinm name,y.ksppstvl value,y.ksppstdf isdefault,decode(bitand(y.ksppstvf,7),1,'MODIFIED',4,'SYSTEM_MOD','FALSE') ismod,       decode(bitand(y.ksppstvf,2),2,'TRUE','FALSE') isadj from sys.x$ksp...

大家都知道Linux平台上，可以通过history命令查看最近所执行过的命令，但history命令默认所显示的只有编号和命令的，只知道命令是最近所执行的，但不知具体执行的日期、时、分、秒，有时给寻找证据带来不便，例如如下显示情况：352  exit353  history354  vi /etc/profile355  history下面就来讲一下，如何让history命令显示最近所执行过的命令的具体执行时间与修改命令保存行数为10000。步骤如下：1、以ROOT用户编辑/etc/profile文件，在里面加入下面内容（我一般习惯在最末尾加）：sed -i 's/HISTSIZE=1000/HISTSIZE=10000/g' /etc/profileecho 'export HISTTIMEFORMAT="%Y%m%d-%H%M%S: “’ >> /etc/profile注意：在末尾的“引号”与“S”之间，加入一位空格，将日期时间和历史命令用空格相隔开来。2、退出系统重新登陆注意：在第2步以前所执行的历史命令，在重新登陆后，执行时间全部分显示为第二步执行时的时间，后面所执行的命令，才会显示正确的实际执行时间。

安装CentOS 6.6出现Disk sda contains BIOS RAID metadata 今天在安装CentOS 6.6的时候，当进到检测硬盘步骤的时候，总是过不去，报错如下：Disk sda contains BIOS RAID metadata, but is not part of any recognized BIOS RAID sets. Ignoring disk sda服务器有两块硬盘sda、sdb，都有这样的提示；这种情况在安装Ubuntu，SUSE都有类似的情况，只是提示不太一样而已。          故障原因：因为服务器上有两块盘，之前做过Raid1，且安装过Windows操作系统，现在直接改装CentOS不认磁盘，肿么办？          插入安装光盘，进入CetnOS 6.6安装选择菜单时，按“TAB”键，会进入到Linux的命令行模式，然后在启动命令行的后面添加 nodmraid（注意前面有个空格）并按“回车”键。加nodmraid命令是为了关掉阵列；接下来进入安装过程中检测硬盘时就会发现硬盘找到了；