PHP 在接收POST大数据（大数组或大字符串）时出现500错误

今天服务器突然出现接收不到数据 ，拿curl写了个测试脚本，发现只有小字符串可以，收发成功，字符串在300K就不行了，服务器直接报‘500 Internal Server Error。
服务器是centos6，nginx，php的环境
开始调试，打开了php的错误日志，并没有发现任何错误信息，检查了下php的post的相关配置，配得都挺高也没有任何问题。
继续往下找原因，查看nginx的错误日志，然并卵，也没有看到任何错误信息，降低nginx的错误信息级别为warn，这里了，出现如下错误信息：

2016/04/19 15:57:53 [crit] 23931#0: *143499 open() "/var/lib/nginx/tmp/client_body/0000000114" failed (13: Permission denied), client: 11.11.11.60, server: server4.dongdong.com, request: "POST /test1.php HTTP/1.1", host: "server4.dongdong.com"
2016/04/19 15:57:54 [crit] 23931#0: *143512 open() "/var/lib/nginx/tmp/client_body/0000000115" failed (13: Permission denied), client: 11.11.11.60, server: server4.dongdong.com, request: "POST /test1.php HTTP/1.1", host: "server4.dongdong.com"
2016/04/19 15:57:54 [crit] 23931#0: *143515 open() "/var/lib/nginx/tmp/client_body/0000000116" failed (13: Permission denied), client: 11.11.11.60, server: server4.dongdong.com, request: "POST /test1.php HTTP/1.1", host: "server4.dongdong.com"
2016/04/19 15:57:54 [crit] 23931#0: *143518 open() "/var/lib/nginx/tmp/client_body/0000000117" failed (13: Permission denied), client: 11.11.11.60, server: server4.dongdong.com, request: "POST /test1.php HTTP/1.1", host: "server4.dongdong.com"
2016/04/19 15:57:54 [crit] 23931#0: *143521 open() "/var/lib/nginx/tmp/client_body/0000000118" failed (13: Permission denied), client: 11.11.11.60, server: server4.dongdong.com, request: "POST /test1.php HTTP/1.1", host: "server4.dongdong.com"
2016/04/19 15:57:55 [crit] 23931#0: *143524 open() "/var/lib/nginx/tmp/client_body/0000000119" failed (13: Permission denied), client: 11.11.11.60, server: server4.dongdong.com, request: "POST /test1.php HTTP/1.1", host: "server4.dongdong.com"
2016/04/19 15:58:02 [crit] 23932#0: *143644 open() "/var/lib/nginx/tmp/client_body/0000000120" failed (13: Permission denied), client: 11.11.11.60, server: server4.dongdong.com, request: "POST /test1.php HTTP/1.1", host: "server4.dongdong.com"

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根据错误信息得出，nginx的buffer等文件目录没有写权限。

chmod -R 775 /var/lib/nginx

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问题解决！！！！