解决open()failed (13: Permission denied) while reading upstream的问题

出现问题：
网站页面出现异常，无法下载大文件。

查看nginx的error.log日志

020/01/21 11:57:59 [crit] 6561#0: *539 open() "/usr/local/nginx/proxy_temp/4/10/0000000104" failed (13: Permission denied) while reading upstream, client: 112.96.135.188, server: zimg.suwenini.com, request: "GET /img/c7d995212035d846228dc76db50e5c1c HTTP/1.1", upstream: "http://172.31.203.135:4869/c7d995212035d846228dc76db50e5c1c", host: "zimg.suwenini.com"

2020/01/21 11:59:45 [emerg] 6699#0: invalid number of arguments in "client_max_body_size" directive in /usr/local/nginx/conf/vhost/sw.conf:142

2020/01/21 12:01:58 [crit] 6772#0: *6 open() "/usr/local/nginx/proxy_temp/1/00/0000000001" failed (13: Permission denied) while reading upstream, client: 112.96.135.188, server: zimg.suwenini.com, request: "GET /img/c7d995212035d846228dc76db50e5c1c HTTP/1.1", upstream: "http://172.31.203.135:4869/c7d995212035d846228dc76db50e5c1c", host: "zimg.suwenini.com"

2020/01/21 12:02:21 [crit] 6770#0: *21 open() "/usr/local/nginx/proxy_temp/2/00/0000000002" failed (13: Permission denied) while reading upstream, client: 112.96.135.188, server: zimg.suwenini.com, request: "GET /img/c7d995212035d846228dc76db50e5c1c HTTP/1.1", upstream: "http://172.31.203.135:4869/c7d995212035d846228dc76db50e5c1c", host: "zimg.suwenini.com"

2020/01/21 12:02:33 [crit] 6772#0: *32 open() "/usr/local/nginx/proxy_temp/3/00/0000000003" failed (13: Permission denied) while reading upstream, client: 112.96.135.188, server: zimg.suwenini.com, request: "GET /img/c7d995212035d846228dc76db50e5c1c HTTP/1.1", upstream: "http://172.31.203.135:4869/c7d995212035d846228dc76db50e5c1c", host: "zimg.suwenini.com"

分析问题及解决方法：
分析问题：
出错原因是work进程没有打开/usr/local/nginx/proxy_temp/4/10/0000000104 文件的权限。work进程属于www用户组，www用户名。因此只要把proxy_temp 目录权限赋给www用户组，www用户名就可以了。
解决问题：