[ubuntu 14.04]请教一个运维脚本,不知道错误在哪,用于监 memcached 进程

#!/bin/sh
PATH=$PATH:/usr/local/memcached/bin/memcached
DATE=`date -d "today" +"%Y-%m-%d-%H:%M"`
MM=`ps aux |grep "memcached" |grep "11211" |grep -v "grep" |wc -l`
if [ "$MM" == "0" ]; then
echo "$DATE The memcached is problem and restart" >> /home/testlogs/memcached.log
/etc/init.d/memcached restart
else
echo "$DATE The memcached is ok" >> /home/testlogs/memcached.log
fi

返回./mem.sh: 5: [: 1: unexpected operator

但是log有生成