Freebsd jail 命令执行无故报错

我尝试执行命令：

# service jail start myjail

我调试 /etc/rc.d/jail 并转储真正的命令是：

/usr/sbin/jail -l -U root -i -f /var/run/jail.myjail.conf -c myjail

输出是：

usage: jail [-dhilqv] [-J jid_file] [-u username] [-U username]
            -[cmr] param=value ... [command=command ...]
       jail [-dqv] [-f file] -[cmr] [jail]
       jail [-qv] [-f file] -[rR] ['*' | jail ...]
       jail [-dhilqv] [-J jid_file] [-u username] [-U username]
            [-n jailname] [-s securelevel]
            path hostname [ip[,...]] command ...

文件 /var/run/jail.myjail.conf 由 rc jail 脚本根据 rc.conf 中先前工作的 jail 的变量自动生成

内容是：

myjail {
        host.hostname = "myjail.example.com";
        path = "/var/jail/myjail.root";
        ip4.addr += "192.168.0.150/32";
        allow.raw_sockets = 0;
        exec.clean;
        exec.system_user = "root";
        exec.jail_user = "root";
        exec.start += "/bin/sh /etc/rc";
        exec.stop = "/bin/sh /etc/rc.shutdown";
        exec.consolelog = "/var/log/jail_myjail_console.log";
        mount.devfs;
        allow.set_hostname = 0;
        allow.sysvipc = 0;
}

怎么了？