•md5sum获取有些软连接的MD5值存在问题
•不支持对空目录进行备份，因为md5sum无法获取空目录的md5值
•权限的修改md5sum无法判断

解决方案：

利用文件的mtime ctime

mtime（Modified time）是在写入文件时随文件内容的更改而更改的
ctime（Create time）是在写入文件、更改所有者、权限或链接设置时随Inode的内容更改而更改的
废话不多说直接上代码：

#!/usr/bin/env python
import time,os,sys,cPickle

fileInfo = {}

def logger(time,fileName,status,fileNum):
 f = open('backup.log','a')
 f.write("%s	%s	%s	%s
" % (time,fileName,status,fileNum))

def tar(sDir,dDir,fileNum):
 command = "tar zcf %s %s >/dev/null 2>&1" % (dDir + ".tar.gz",sDir)
 if os.system(command) == 0:
 logger(time.strftime('%F %X'),dDir + ".tar.gz",'success',fileNum)
 else:
 logger(time.strftime('%F %X'),dDir + ".tar.gz",'failed',fileNum)

def fullBak(path):
 fileNum = 0
 for root,dirs,files in os.walk(path):
 for name in files:
 file = os.path.join(root, name)
 mtime = os.path.getmtime(file)
 ctime = os.path.getctime(file)
 fileInfo[file] = (mtime,ctime)
 fileNum += 1
 f = open(P,'w')
 cPickle.dump(fileInfo,f)
 f.close()
 tar(S,D,fileNum)

def diffBak(path):
 for root,dirs,files in os.walk(path):
 for name in files:
 file = os.path.join(root,name)
 mtime = os.path.getmtime(file)
 ctime = os.path.getctime(file)
 fileInfo[file] = (mtime,ctime)

 if os.path.isfile(P) == 0:
 f = open(P,'w')
 f.close()

 if os.stat(P).st_size == 0:
 f = open(P,'w')
 cPickle.dump(fileInfo,f)
 fileNum = len(fileInfo.keys())
 f.close()
 print fileNum
 tar(S,D,fileNum)
 else:
 f = open(P)
 old_fileInfo = cPickle.load(f)
 f.close()
 difference = dict(set(fileInfo.items())^set(old_fileInfo.items()))
 fileNum = len(difference)
 print fileNum

 difference_file = ' '.join(difference.keys())
 print difference_file

 tar(difference_file,D,fileNum)
 f = open(P,'w')
 cPickle.dump(fileInfo,f)
 f.close()

def Usage():
 print '''
 Syntax: python file_bakcup.py pickle_file model source_dir filename_bk
 model: 1:Full backup 2:Differential backup

 example: python file_backup.py fileinfo.pk 2 /etc etc_$(date +%F)
 explain: Automatically add '.tar.gz' suffix
 '''
 sys.exit()

if len(sys.argv) != 5:
 Usage()

P = sys.argv[1]
M = int(sys.argv[2])
S = sys.argv[3]
D = sys.argv[4]

if M == 1:
 fullBak(S)
elif M == 2:
 diffBak(S)
else:
 print "