在centos下启动nginx出现Failed to start nginx.service:unit not found

错误的原因就是没有添加nginx服务，所以启动失败。

解决方法：

1.    在/root/etc/init.d/目录下新建文件，文件名为nginx

　　或者用命令在根目录下执行:# vim /etc/init.d/nginx    (注意vim旁边有一个空格)

2.    插入以下代码 

#!/bin/sh
# nginx - this script starts and stops the nginx daemin
#
# chkconfig:   - 85 15

# description:  Nginx is an HTTP(S) server, HTTP(S) reverse \
#               proxy and IMAP/POP3 proxy server

# processname: nginx
# config:      /usr/local/nginx/conf/nginx.conf
# pidfile:     /usr/local/nginx/logs/nginx.pid

# Source function library.

. /etc/rc.d/init.d/functions

# Source networking configuration.

. /etc/sysconfig/network

# Check that networking is up.

[ "$NETWORKING" = "no" ] && exit 0

nginx="/usr/local/nginx/sbin/nginx"

prog=$(basename $nginx)

NGINX_CONF_FILE="/usr/local/nginx/conf/nginx.conf"

lockfile=/var/lock/subsys/nginx

start() {

    [ -x $nginx ] || exit 5

    [ -f $NGINX_CONF_FILE ] || exit 6

    echo -n $"Starting $prog: "

    daemon $nginx -c $NGINX_CONF_FILE

    retval=$?

    echo

    [ $retval -eq 0 ] && touch $lockfile

    return $retval

}

stop() {

    echo -n $"Stopping $prog: "

    killproc $prog -QUIT

    retval=$?

    echo

    [ $retval -eq 0 ] && rm -f $lockfile

    return $retval

}

restart() {

    configtest || return $?

    stop

    start

}

reload() {

    configtest || return $?

    echo -n $"Reloading $prog: "

    killproc $nginx -HUP

    RETVAL=$?

    echo

}

force_reload() {

    restart

}

configtest() {

  $nginx -t -c $NGINX_CONF_FILE

}

rh_status() {

    status $prog

}

rh_status_q() {

    rh_status >/dev/null 2>&1

}

case "$1" in

    start)

        rh_status_q && exit 0
        $1
        ;;

    stop)

        rh_status_q || exit 0
        $1
        ;;

    restart|configtest)
        $1
        ;;

    reload)
        rh_status_q || exit 7
        $1
        ;;

    force-reload)
        force_reload
        ;;
    status)
        rh_status
        ;;

    condrestart|try-restart)

        rh_status_q || exit 0
            ;;

    *)

        echo $"Usage: $0 {start|stop|status|restart|condrestart|try-restart|reload|force-reload|configtest}"
        exit 2

esac

3. 用命令进入此目录

　　# cd /etc/init.d

4. 依此执行以下命令

# chmod 755 /etc/init.d/nginx

# chkconfig --add nginx   (注意add前面是两个短横线-)

5. 开启nginx

# service nginx start