---
layout: post
title: Tar on Linux
category : Linux
tags : [Linux, Utilities]
---

在Linux下，文件以及文件系统的压缩与打包工具十分丰富，如compress,gzip,bzip2,tar,dump,restore,dd,cpio等等。这里仅针对文件的增量备份做一个简单的测试，主要使用tar。

命令组合：tar,bzip2,split。其中tar负责打包文件，bzip2负责压缩，split负责文件分割。

其他工具：rsync,inotify,sha1sum。rsync负责文件镜像，inotify负责文件实时监控，sha1sum负责文件校验。

## 测试

边打包、压缩，边分割

	[dylan@server ~]# tar -g snapshot/snapshot.snar -cjpvf - source | split -a 3 -b 1K - backup/backup_201303121100.tar.bz2.

tar 选项

	-c  创建新的归档文件
	-j  使用bzip2压缩归档文件
	-g  即--listed-incremental 指定增量备份
	-p  归档时保留文件权限
	-f  指定归档文件
	-   stdout
	
split 选项

	-a  指定后缀名的长度。根据数字或字母，确定分割后的最大文件数
		如果后缀为数字[0-9]，则分割后最多有 10 ** ${suffix_length};
		如果后缀为字母[a-z]，则分割后最多有 26 ** ${suffix_length}；
	-b  指定分割大小，以字节为单位
	-   stdin

查看目录结构

	[dylan@server ~]# tree .
	.
	├── backup
	│   ├── backup_201303121100.tar.bz2.aaa
	│   ├── backup_201303121100.tar.bz2.aab
	│   └── backup_201303121100.tar.bz2.aac
	├── snapshot
	│   └── snapshot.snar
	└── source
	     ... ...

测试分割后的文件	

	[dylan@server backup]# tar -tf backup_201303121100.tar.bz2.aaa 

	bzip2: Compressed file ends unexpectedly;
		perhaps it is corrupted?  *Possible* reason follows.
	bzip2: Inappropriate ioctl for device
		Input file = (stdin), output file = (stdout)
	
	It is possible that the compressed file(s) have become corrupted.
	You can use the -tvv option to test integrity of such files.
	
	You can use the `bzip2recover' program to attempt to recover
	data from undamaged sections of corrupted files.
	
	tar: Child returned status 2
	tar: Error is not recoverable: exiting now

合并分割后的文件

	[dylan@server backup]# cat * > backup_201303121100.tar.bz2

查看要恢复的文件

	[dylan@server backup]# tar -tf backup_201303121100.tar.bz2
	source/
	source/foo/
	source/foo/bar/
	source/foo/bar/fooo/
	source/0
	source/1

	[dylan@server backup]# tar -tf backup_201303121100.tar.bz2 | grep 50
	source/50

解压指定的文件

	[dylan@server backup]# tar -xjvf backup_201303121100.tar.bz2 source/50
	source/50

查看文件

	[dylan@server backup]# tree source/
	source/
	└── 50
	
	0 directories, 1 file


## 脚本

backup.sh

	#!/bin/sh
	#abstract:
	#backup files using tar, bzip2
	#history:
	#2013-3-12    dylanninin@gmail.com    first release
	
	source=/fs
	#backup settings
	dist=/backup
	prefix=''
	suffix='.tar.bz2.'
	timestamp=$(date +%Y%m%d%H%M%S)
	current=$(date +%Y/%m)
	size=500M
	recipients=dba
	base=${dist}/${current}
	pieces=${base}/${prefix}${timestamp}${suffix}
	snapshot=${base}/snapshot.snar
	log=${base}/${timestamp}.log    
	
	start=$(date +%s)
	checksum="sha1sum started:"
	ls ${source} ${dist} && mkdir -p ${base} && tar -g ${snapshot} -cjpvf - ${source} | split -b ${size} - ${pieces} && echo -e ${checksum} > ${log} && sha1sum ${pieces}* >> ${log}
	end=$(date +%s)
	elapsed=$(expr ${end} - ${start})
	summary="sha1sum ended.\nsummary:\n\tstarted: ${start}\tended: ${end}\n\telapsed: ${elapsed} seconds."
	echo -e ${summary}  >> ${log}
	
	#mail log 
	cat ${log} | mail -a ${log} -s "$(date +%Y-%m-%d\ %H:%M:%S):$(hostname) dba daily check of fs backup" ${recipients}

以上脚本每个月都会产生新的快照文件（snapshot每个月会重新创建）；增量备份的频率，即脚本运行的频率。若以月为周期太长，则可以更改`current=$(date +%Y/%m)`，（如`current=$(date +%Y/%M)`，周期为一个星期）自行定义。

log

	sha1sum started:
	24c00b3eff967fec250ac7663ac03cbd35cbe40e  /backup/2013/03/20130312163458.tar.bz2.aa
	c2ccb143c514d1afcebfb7a84b4642e168bdd93d  /backup/2013/03/20130312163458.tar.bz2.ab
	7313889f5057365b168980c8f1765f97016fe913  /backup/2013/03/20130312163458.tar.bz2.ac
	a186a9aee90606d53755719a63bed1f407ce6d88  /backup/2013/03/20130312163458.tar.bz2.ad
	945979757291b2f1ac588cbf5c82637f20e37eb3  /backup/2013/03/20130312163458.tar.bz2.ae
	642732865fcc1d43b620b255bf9f32d504f02079  /backup/2013/03/20130312163458.tar.bz2.af
	9cf6a651d4d084d5fe3dc595aa57dc4d61484e3c  /backup/2013/03/20130312163458.tar.bz2.ag
	9eae089684016860aec91b50913d451c5a8689ce  /backup/2013/03/20130312163458.tar.bz2.ah
	dce088dcdd7e3f6e8d7a58007e590cfdc9047b9e  /backup/2013/03/20130312163458.tar.bz2.ai
	5db4a8f6196e1c11cc9dcf29422f56248111dc6e  /backup/2013/03/20130312163458.tar.bz2.aj
	sha1sum ended.
	summary:
		started:1363077298	ended at:1363077466
		elapsed: 168 seconds.

## 参考

* [鸟哥的私房菜 文件与文件系统的压缩与打包](http://vbird.dic.ksu.edu.tw/linux_basic/0240tarcompress.php)
* [rsync wikipedia](http://en.wikipedia.org/wiki/Rsync)
* [inotify wikipedia](http://en.wikipedia.org/wiki/Inotify)