说明：
nginx日志主要有两种：访问日志、错误日志。其中访问日志记录客户端访问nginx的每一个请求，包含用户地域来源、跳转来源、使用终端、某个URL访问量等信息，访问日志格式可以自定义；错误日志则记录客户端访问nginx出错时的日志，格式不支持自定义，通过错误日志，你可以得到系统某个服务或server的性能瓶颈等。两种日志都可以选择性关闭。
访问日志[Access.log]
log_format main ‘$remote_addr $remote_user [$time_local] “$request” $http_host ‘
‘$status $upstream_status $body_bytes_sent “$http_referer” ‘
‘”$http_user_agent” $ssl_protocol $ssl_cipher $upstream_addr ‘
‘$request_time $upstream_response_time’;
| 变量名称 | 变量描述 | 举例说明 |
| $remote_addr | 客户端地址 | 113.140.15.90 |
| $remote_user | 客户端用户名称 | – |
| $time_local | 访问时间和时区 | 18/Jul/2012:17:00:01 +0800 |
| $request | 请求的URI和HTTP协议 | “GET /pa/img/home/logo-alipay-t.png HTTP/1.1” |
| $http_host | 请求地址，即浏览器中你输入的地址（IP或域名） | img.alipay.com 10.253.70.103 |
| $status | HTTP请求状态 | 200 |
| $upstream_status | upstream状态 | 200 |
| $body_bytes_sent | 发送给客户端文件内容大小 | 547 |
| $http_referer | 跳转来源 | “https://cashier.alipay.com…/” |
| $http_user_agent | 用户终端代理 | “Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; SV1; GTB7.0; .NET4.0C; |
| $ssl_protocol | SSL协议版本 | TLSv1 |
| $ssl_cipher | 交换数据中的算法 | RC4-SHA |
| $upstream_addr | 后台upstream的地址，即真正提供服务的主机地址 | 10.228.35.247:80 |
| $request_time | 整个请求的总时间 | 0.205 |
| $upstream_response_time | 请求过程中，upstream响应时间 | 0.002 |
线上实例：
116.9.137.90 – [02/Aug/2012:14:47:12 +0800] “GET /images/XX/20100324752729.png HTTP/1.1″img.alipay.com 200 200 2038 https://cashier.alipay.com/XX/PaymentResult.htm?payNo=XX&outBizNo=2012XX “Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; Tablet PC 2.0; 360SE)” TLSv1 AES128-SHA 10.228.21.237:80 0.198 0.001
线下测试（$http_referer）：
10.14.21.197 – – [14/Aug/2012:17:28:22 +0800] “GET /spanner/watch/v1?–db=ztg-1&–mode=compare&–index=status&–option=&–cluster=whole&-F=2012%2F8%2F12-00%3A00%3A00&-T=%2B2880&-i=1&-n=0&_=1344936501292 HTTP/1.1” 200 94193 “http://spanner.alipay.net/optionFrame/history.html” “Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.1 (KHTML, like Gecko) Chrome/21.0.1180.60 Safari/537.1”
备注：$http_referer和重定向有关。
错误日志[Error.log]
| 错误信息 | 错误说明 |
| “upstream prematurely（过早的） closed connection” | 请求uri的时候出现的异常，是由于upstream还未返回应答给用户时用户断掉连接造成的，对系统没有影响，可以忽略 |
| “recv() failed (104: Connection reset by peer)” | （1）服务器的并发连接数超过了其承载量，服务器会将其中一些连接Down掉； （2）客户关掉了浏览器，而服务器还在给客户端发送数据； （3）浏览器端按了Stop |
| “(111: Connection refused) while connecting to upstream” | 用户在连接时，若遇到后端upstream挂掉或者不通，会收到该错误 |
| “(111: Connection refused) while reading response header from upstream” | 用户在连接成功后读取数据时，若遇到后端upstream挂掉或者不通，会收到该错误 |
| “(111: Connection refused) while sending request to upstream” | Nginx和upstream连接成功后发送数据时，若遇到后端upstream挂掉或者不通，会收到该错误 |
| “(110: Connection timed out) while connecting to upstream” | nginx连接后面的upstream时超时 |
| “(110: Connection timed out) while reading upstream” | nginx读取来自upstream的响应时超时
|
| “(110: Connection timed out) while reading response header from upstream” | nginx读取来自upstream的响应头时超时 |
| “(110: Connection timed out) while reading upstream” | nginx读取来自upstream的响应时超时 |
| “(104: Connection reset by peer) while connecting to upstream” | upstream发送了RST，将连接重置 |
| “upstream sent invalid header while reading response header from upstream” | upstream发送的响应头无效 |
| “upstream sent no valid HTTP/1.0 header while reading response header from upstream” | upstream发送的响应头无效 |
| “client intended to send too large body” | 用于设置允许接受的客户端请求内容的最大值，默认值是1M，client发送的body超过了设置值 |
| “reopening logs” | 用户发送kill -USR1命令 |
| “gracefully shutting down”, | 用户发送kill -WINCH命令 |
| “no servers are inside upstream” | upstream下未配置server |
| “no live upstreams while connecting to upstream” | upstream下的server全都挂了 |
| “SSL_do_handshake() failed” | SSL握手失败 |
| “SSL_write() failed (SSL:) while sending to client” | |
| “(13: Permission denied) while reading upstream” | |
| “(98: Address already in use) while connecting to upstream” | |
| “(99: Cannot assign requested address) while connecting to upstream” | |
| “ngx_slab_alloc() failed: no memory in SSL session shared cache” | ssl_session_cache大小不够等原因造成 |
| “could not add new SSL session to the session cache while SSL handshaking” | ssl_session_cache大小不够等原因造成 |
| “send() failed (111: Connection refused)” |