flyinweb's blog

简介： 使用 Sockets API，我们可以开发客户机和服务器应用程序，它们可以在本地网络上进行通信，也可以通过 Internet 在全球范围内进行通信。与其他 API 一样，您可以通过一些方法使用 Sockets API，从而提高 Socket 的性能，或者限制 Socket 的性能。本文探索了 4 种使用 Sockets API 来获取应用程序的最大性能并对 GNU/Linux® 环境进行优化从而达到最好结果的方法。

1.查看系统Swap空间使用

[root@~ usr]# free
total used free shared buffers cached
Mem: 513980 493640 20340 0 143808 271780
-/+ buffers/cache: 78052 435928
Swap: 1052248 21256 1030992

2.在空间合适处创建swap文件

[root@~ usr]# mkdir swap
[root@~ usr]# cd swap
[root@~ swap]# dd if=/dev/zero of=swapfile bs=1024 count=10000
10000+0 records in
10000+0 records out
[root@~ swap]# ls -al
total 10024
drwxr-xr-x 2 root root 4096 7月 28 14:58 .
drwxr-xr-x 19 root root 4096 7月 28 14:57 ..
-rw-r--r-- 1 root root 10240000 7月 28 14:58 swapfile
[root@~ swap]# mkswap swapfile
Setting up swapspace version 1, size = 9996 KiB

NFSv4, network file system version 4, is the new version of NFS (for setting up the older NFSv3, see Nfs) with new features like strong authentication and integrity via Kerberos and SPKM-3, improved performance, safe file caching, lock migration, UTF-8, ACLs and better support for Windows file sharing semantics.

This article covers installing and configuring NFSv4.

CentOS and RHEL both supports network installation using the NFS, FTP, or HTTP protocols. A network installation can be started from a boot media or a bootable flash memory drive. Alternatively, if the system to be installed contains a network interface card (NIC) with Pre-Execution Environment (PXE) support, Pre-Execution Environment (PXE) can also be used to install CentOS and RHEL.

How PXE works

1、启动系统，我是用iso镜像挂载，挂载到/media/cdrom
mkdir /media/cdrom
mount -a -t iso9660 -o loop /home/user1/CentOS-5.6-i386-bin-DVD.iso /media/cdrom
2、安装FTP服务（如果系统已带则在桌面 管理－服务器设置－服务 可以很方便的启动vsftpd服务）
cd /media/cdrom/CentOS
rpm -ivh vsftpd*
chkconfig vsftpd on
service vsftpd start
3、安装createrepo的软件包
cd /media/cdrom/CentOS
rpm -ivh createrepo*
4、拷贝系统盘里的文件到本机
cp -R /media/cdrom/CentOS /var/ftp/pub
cp -R /media/cdrom/repodata /var/ftp/pub
5、生成yum源
（1）生成依赖关系
[root@flyinweb repodata]# createrepo -g /var/ftp/pub/repodata/comps.xml /var/ftp/pub/CentOS/
2682/2682 - nfs-utils-lib-devel-1.0.8-7.6.el5.i386.rpm                         
Saving Primary metadata
Saving file lists metadata
Saving other metadata

这几天格式化硬盘，记录一下用到的命令：

[root@db ~]# fdisk /dev/sdb

The number of cylinders for this disk is set to 253981.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
(e.g., DOS FDISK, OS/2 FDISK)

Command (m for help): p

Disk /dev/sdb: 2089.0 GB, 2089072092672 bytes
255 heads, 63 sectors/track, 253981 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/sdb1 1 124495 1000006056 83 Linux

Command (m for help): n
Command action
e extended
p primary partition (1-4)
p
Partition number (1-4): 2
First cylinder (124496-253981, default 124496):
Using default value 124496
Last cylinder or +size or +sizeM or +sizeK (124496-253981, default 253981):
Using default value 253981

Command (m for help): p

Disk /dev/sdb: 2089.0 GB, 2089072092672 bytes
255 heads, 63 sectors/track, 253981 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/sdb1 1 124495 1000006056 83 Linux
/dev/sdb2 124496 253981 1040096295 83 Linux

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.

WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table.
The new table will be used at the next reboot.
Syncing disks.

此时，分区里看不到新建的磁盘分区，提示通过重启才可以重用分区表，此时可以通过partprobe探测硬盘：

背景：6块硬盘，每个1TB，用一块硬盘做raid0,安装系统，剩余5块做raid5。由于ext3文件系统不支持大于2TB的分区，所以考虑使用GPT首先以root身份登录系统，查看硬盘信息：fdisk -l
[root@libftp ~]# fdisk -l

Disk /dev/cciss/c0d0: 1000.1 GB, 1000171331584 bytes
255 heads, 63 sectors/track, 121597 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/cciss/c0d0p1 * 1 33 265041 83 Linux
/dev/cciss/c0d0p2 34 116105 932348340 83 Linux
/dev/cciss/c0d0p3 116106 118655 20482875 83 Linux
/dev/cciss/c0d0p4 118656 121597 23631615 5 Extended
/dev/cciss/c0d0p5 118656 120567 15358108+ 83 Linux
/dev/cciss/c0d0p6 120568 121587 8193118+ 82 Linux swap / Solaris

WARNING: GPT (GUID Partition Table) detected on '/dev/cciss/c0d1'! The util fdisk doesn't support GPT. Use GNU Parted.

Disk /dev/cciss/c0d1: 4000.6 GB, 4000684662784 bytes
255 heads, 63 sectors/track, 486388 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/cciss/c0d1p1 1 267350 2147483647+ ee EFI GPT