memcached是一套分布式的高速缓存系统，由LiveJournal的Brad Fitzpatrick开发，但被许多网站使用。这是一套开放源代码软件，以BSD license授权发布。

memcached缺乏认证以及安全管制，这代表应该将memcached服务器放置在防火墙后。

memcached的API使用三十二比特的循环冗余校验（CRC-32）计算键值后，将数据分散在不同的机器上。当表格满了以后，接下来新增的数据会以LRU机制替换掉。由于memcached通常只是当作缓存系统使用，所以使用memcached的应用程序在写回较慢的系统时（像是后端的数据库）需要额外的代码更新memcached内的数据。

memcached作为缓存文件服务，默认是操作系统里面是可以直接yum -y install memcached进行安装的。

/etc/init.d/memcached 是属于系统shell编写的管理脚本，下面这个脚本是python脚本编写出来的memcached管理脚本，和shell编写的脚本实现的效果一样。

代码如下

#!/usr/bin/python

import sys
import os
from subprocess import Popen,PIPE

class Process(object):
  '''memached rc script'''
  args = {'USER':'memcached',
      'PORT':11211,
      'MAXCONN':1024,
      'CACHESIZE':64,
      'OPTION':''}

  def __init__(self,name,program,workdir):
    self.name = name
    self.program = program
    self.workdir = workdir

  def _init(self):
    '''/var/tmp/memcached'''
    if not os.path.exists(self.workdir):
      os.mkdir(self.workdir)
      os.chdir(self.workdir)

  def _pidFile(self):
    '''/var/tmp/memcached/memcached.pid'''
    return os.path.join(self.workdir, "%s.pid" % self.name)

  def _writePid(self):
    if self.pid:
      with open(self._pidFile(),'w') as fd:
        fd.write(str(self.pid))


  def _readConf(self,f):
    with open(f) as fd:
      lines = fd.readlines()
      return dict([ i.strip().replace('"','').split('=') for i in lines])

  def _parseArgs(self):
    conf = self._readConf('/etc/sysconfig/memcached')       
    if 'USER' in conf:
      self.args['USER'] = conf['USER']
    if 'PORT' in conf:
      self.args['PORT'] = conf['PORT']
    if 'MAXCONN' in conf:
      self.args['MAXCONN'] = conf['MAXCONN']
    if 'CACHESIZE' in conf:
      self.args['CACHESIZE'] = conf['CACHESIZE']
    options = ['-u',self.args['USER'],
          '-p',self.args['PORT'],
          '-m',self.args['CACHESIZE'],
          '-c',self.args['MAXCONN']]
    os.system("chown %s %s" % (self.args['USER'],self.workdir))
    return options

  def start(self):
    pid = self._getPid()
    if pid:
      print "%s is running..." % self.name
      sys.exit()
    self._init()
    cmd = [self.program] + self._parseArgs() + ['-d','-P',self._pidFile()]
    p = Popen(cmd,stdout=PIPE)
    #self.pid = p.pid
    #self._writePid()
    print "%s start Sucessful \t\t [OK]" % self.name

  def _getPid(self):
    p = Popen(['pidof',self.name],stdout=PIPE)
    pid = p.stdout.read().strip()
    return pid

  def stop(self):
    pid = self._getPid()
    if pid:
      os.kill(int(pid),15)
      if os.path.exists(self._pidFile()):
        os.remove(self._pidFile())
      print "%s is stopped \t\t\t [OK]" % self.name

  def restart(self):
    self.stop()
    self.start()


  def status(self):
    pid = self._getPid()
    if pid:
      print "%s is already running" % self.name
    else:
      print "%s is not running" % self.name

  def help(self):
    print "Usage:%s {start|stop|status|restart|} " % __file__


def main():
  name = 'memcached'
  prog = '/usr/bin/memcached'
  args = '-u nobody -p 11211 -c 1024 -m 64' 
  wd = '/var/tmp/memcached'
  pm = Process(name = name,
         program = prog,
         workdir = wd)
  try:
    cmd = sys.argv[1]
  except IndexError,e:
    print "Option error"
    sys.exit()
  if cmd == 'start':
    pm.start()
  elif cmd == 'stop':
    pm.stop()
  elif cmd == 'restart':
    pm.restart()
  elif cmd == 'status':
    pm.status()
  else:
    pm.help()

if __name__ == '__main__':
  main()

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