===> Creating groups.
Creating group 'mysql' with gid '88'.
===> Creating users
Creating user 'mysql' with uid '88'.
pw: user 'mysql' disappeared during update
===> Creating homedir(s)
install: unknown user mysql
pkg: PRE-INSTALL script failed
出现该原因，是因为数据未同步，不止pkg安装，包括自己创建用户时，也可能会出现
解决方案:/usr/sbin/pwd_mkdb -p /etc/master.passwd
