详解php+nginx 服务发生500 502错误排查思路

概述

当线上的服务中访问中出现500或者502错误时，需要紧急处理，排查问题，该怎么做？可以通过分析一些错误日志或者跟踪php-fpm进程来进行问题定位。

nginx error_log

nginx的error_log在nginx的配置文件中定义的

  server {   listen  80;   server_name localhost;   root   /var/www;     access_log /Users/jiao/logs/default.access.log;   error_log /Users/jiao/logs/default.error.log;   location / {    index index.html index.htm index.php;    autoindex on;   }   location = /info {    allow 127.0.0.1;    deny all;    rewrite (.*) /.info.php;   }   location ~ .php$ {    root /var/www;    fastcgi_pass 127.0.0.1:9000;    fastcgi_index index.php;    fastcgi_param SCRIPT_FILENAME /var/www$fastcgi_script_name;    include /usr/local/etc/nginx/fastcgi_params;   }  }

查看error_log

➜  tail /Users/jiao/logs/default.error.log
2019/07/17 11:08:18 [error] 77416#0: *76 kevent() reported about an closed connection (54: Connection reset by peer) while reading response header from upstream, client: 127.0.0.1, server: localhost, request: “GET / HTTP/1.1″, upstream: “fastcgi://127.0.0.1:9000”, host: “localhost”

发现出现了Connection reset by peer，连接被重置了，此时可以再查看php-fpm的error_log进一步分析问题

php-fpm error_log

php-fpm的error_log在php-fpm.conf文件中配置中定义的

  ; Error log file  ; If it's set to "syslog", log is sent to syslogd instead of being written  ; in a local file.  ; Note: the default prefix is /usr/local/var  ; Default Value: log/php-fpm.log  error_log = log/php-fpm.log

error_log里面的内容是这样的

  ➜ tail /usr/local/var/log/php-fpm.log  [17-Jul-2019 10:49:54] NOTICE: [pool www] child 81948 started  [17-Jul-2019 11:08:18] WARNING: [pool www] child 77537, script '/var/www/index.php' (request: "GET /index.php") execution timed out (3.801267 sec), terminating  [17-Jul-2019 11:08:18] WARNING: [pool www] child 77537 exited on signal 15 (SIGTERM) after 1503.113967 seconds from start  [17-Jul-2019 11:08:18] NOTICE: [pool www] child 94339 started

可以看到是请求/var/www/index.php文件出现了超时

dtruss

dtruss是动态跟踪命令，可以根据PID，name跟踪进程

mac环境下使用dtruss，linux环境可以使用strace，pstack

  ➜ dtruss   USAGE: dtruss [-acdefholLs] [-t syscall] { -p PID | -n name | command | -W name }

    -p PID   # examine this PID    -n name   # examine this process name    -t syscall  # examine this syscall only    -W name   # wait for a process matching this name    -a    # print all details    -c    # print syscall counts    -d    # print relative times (us)    -e    # print elapsed times (us)    -f    # follow children    -l    # force printing pid/lwpid    -o    # print on cpu times    -s    # print stack backtraces    -L    # don't print pid/lwpid    -b bufsize  # dynamic variable buf size

eg,

   dtruss df -h  # run and examine "df -h"   dtruss -p 1871  # examine PID 1871   dtruss -n tar  # examine all processes called "tar"   dtruss -f test.sh # run test.sh and follow children

跟踪php-fpm：sudo dtruss -a -n php-fpm 

此时访问web页面，就可以看到跟踪内容

  21416/0x3479b6:  1559  63  3 getrusage(0x0, 0x7FFEE1EC0760, 0x0)   = 0 0  21416/0x3479b6:  1561  4  0 getrusage(0xFFFFFFFFFFFFFFFF, 0x7FFEE1EC0760, 0x0)   = 0 0  21416/0x3479b6:  1627  77  17 poll(0x7FFEE1EC08C0, 0x1, 0x1388)   = 1 0  dtrace: error on enabled probe ID 2174 (ID 159: syscall::read:return): invalid kernel access in action #13 at DIF offset 68  dtrace: error on enabled probe ID 2174 (ID 159: syscall::read:return): invalid kernel access in action #13 at DIF offset 68  dtrace: error on enabled probe ID 2174 (ID 159: syscall::read:return): invalid kernel access in action #13 at DIF offset 68  dtrace: error on enabled probe ID 2174 (ID 159: syscall::read:return): invalid kernel access in action #13 at DIF offset 68  dtrace: error on enabled probe ID 2174 (ID 159: syscall::read:return): invalid kernel access in action #13 at DIF offset 68  21416/0x3479b6:  1872  29  24 lstat64("/var/www/index.php", 0x7FFEE1ECFF38, 0x0)   = 0 0  21416/0x3479b6:  1884  9  6 lstat64("/var/www", 0x7FFEE1ECFDF8, 0x0)   = 0 0  21416/0x3479b6:  1889  6  3 lstat64("/var", 0x7FFEE1ECFCB8, 0x0)   = 0 0  21416/0x3479b6:  1899  12  8 readlink("/var", 0x7FFEE1ED0090, 0x400)   = 11 0  21416/0x3479b6:  1905  6  4 lstat64("/private/var", 0x7FFEE1ECFB78, 0x0)   = 0 0  21416/0x3479b6:  1917  6  3 lstat64("/private", 0x7FFEE1ECFA38, 0x0)   = 0 0  21416/0x3479b6:  2178  18  14 stat64("/var/www/.user.ini", 0x7FFEE1ED0240, 0x0)   = -1 Err#2  21416/0x3479b6:  2217  5  1 setitimer(0x2, 0x7FFEE1ED07E0, 0x0)   = 0 0  21416/0x3479b6:  2225  4  0 sigaction(0x1B, 0x7FFEE1ED0788, 0x7FFEE1ED07B0)   = 0 0  21416/0x3479b6:  2237  5  1 sigprocmask(0x2, 0x7FFEE1ED0804, 0x0)   = 0x0 0  21416/0x3479b6:  3643  48  40 open_nocancel(".", 0x0, 0x1)   = 5 0  21416/0x3479b6:  3648  7  3 fstat64(0x5, 0x7FFEE1ED0110, 0x0)   = 0 0  21416/0x3479b6:  3653  7  2 fcntl_nocancel(0x5, 0x32, 0x10F252158)   = 0 0  21416/0x3479b6:  3661  12  7 close_nocancel(0x5)   = 0 0  21416/0x3479b6:  3670  10  7 stat64("/usr/local/var", 0x7FFEE1ED0080, 0x0)   = 0 0  21416/0x3479b6:  3681  11  8 chdir("/var/www", 0x0, 0x0)   = 0 0  21416/0x3479b6:  3698  4  0 setitimer(0x2, 0x7FFEE1ED02D0, 0x0)   = 0 0  21416/0x3479b6:  3710  6  3 fcntl(0x3, 0x8, 0x10F3FD858)   = 0 0  21416/0x3479b6:  3733  9  6 stat64("/private/var/www/index.php", 0x7FFEE1ECFF10, 0x0)   = 0 0  74904/0x332630: 723125 1073381  19 kevent(0x9, 0x0, 0x0)   = 0 0  74902/0x332629: 770666 1073387  17 kevent(0x8, 0x0, 0x0)   = 0 0  74904/0x332630: 723165 1061954  20 kevent(0x9, 0x0, 0x0)   = 0 0  74902/0x332629: 770709 1061954  20 kevent(0x8, 0x0, 0x0)   = 0 0  74904/0x332630: 723201 1074786  16 kevent(0x9, 0x0, 0x0)   = 0 0  74902/0x332629: 770747 1074783  16 kevent(0x8, 0x0, 0x0)   = 0 0  74904/0x332630: 723229 1069141  13 kevent(0x9, 0x0, 0x0)   = 0 0  74902/0x332629: 770777 1069145  11 kevent(0x8, 0x0, 0x0)   = 0 0  21416/0x3479b6:  3942 3902233  7 __semwait_signal(0x703, 0x0, 0x1)   = -1 Err#4  74902/0x332629: 770814  103  25 kill(21416, 15)   = 0 0  dtrace: error on enabled probe ID 2172 (ID 161: syscall::write:return): invalid kernel access in action #13 at DIF offset 68  dtrace: error on enabled probe ID 2172 (ID 161: syscall::write:return): invalid kernel access in action #13 at DIF offset 68  74902/0x332629: 771325  7  2 sigreturn(0x7FFEE1ECFC40, 0x1E, 0xC1A4B78E0404663A)   = 0 Err#-2  74902/0x332629: 771336  7  3 kevent(0x8, 0x0, 0x0)   = 1 0  dtrace: error on enabled probe ID 2174 (ID 159: syscall::read:return): invalid kernel access in action #13 at DIF offset 68  74902/0x332629: 771352  11  7 wait4(0xFFFFFFFFFFFFFFFF, 0x7FFEE1ED0748, 0x3)   = 21416 0  dtrace: error on enabled probe ID 2172 (ID 161: syscall::write:return): invalid kernel access in action #13 at DIF offset 68  74902/0x332629: 773511 1957 1899 fork()   = 28060 0  28060/0x3754c5:  125:  0:  0 fork()   = 0 0  28060/0x3754c5:  128  9  2 bsdthread_register(0x7FFF6774C418, 0x7FFF6774C408, 0x2000)   = -1 Err#22  dtrace: error on enabled probe ID 2172 (ID 161: syscall::write:return): invalid kernel access in action #13 at DIF offset 68  74902/0x332629: 773737  4  1 wait4(0xFFFFFFFFFFFFFFFF, 0x7FFEE1ED0748, 0x3)   = 0 0  74902/0x332629: 773742  6  3 read(0x5, "", 0x1)   = -1 Err#35  28060/0x3754c5:  320  4  0 getpid(0x0, 0x0, 0x0)   = 28060 0  28060/0x3754c5:  328  7  2 __mac_syscall(0x7FFF67758A17, 0x4, 0x7FFEE1ED0208)   = -1 Err#45  28060/0x3754c5:  332  5  2 csops(0x6D9C, 0xB, 0x7FFEE1ED0248)   = -1 Err#22  28060/0x3754c5:  755  14  11 dup2(0x1, 0x2, 0x0)   = 2 0  28060/0x3754c5:  797  89  22 close(0x4)   = 0 0  28060/0x3754c5:  806  11  6 dup2(0x7, 0x0, 0x0)   = 0 0  28060/0x3754c5:  817  4  0 geteuid(0x0, 0x0, 0x0)   = 501 0  28060/0x3754c5:  820  3  0 close(0x5)   = 0 0  28060/0x3754c5:  821  3  0 close(0x6)   = 0 0  28060/0x3754c5:  824  5  1 sigaction(0xF, 0x7FFEE1ED0688, 0x0)   = 0 0  28060/0x3754c5:  825  3  0 sigaction(0x2, 0x7FFEE1ED0688, 0x0)   = 0 0  28060/0x3754c5:  827  3  0 sigaction(0x1E, 0x7FFEE1ED0688, 0x0)   = 0 0  28060/0x3754c5:  828  3  0 sigaction(0x1F, 0x7FFEE1ED0688, 0x0)   = 0 0  28060/0x3754c5:  829  3  0 sigaction(0x14, 0x7FFEE1ED0688, 0x0)   = 0 0  28060/0x3754c5:  830  3  0 sigaction(0x3, 0x7FFEE1ED0688, 0x0)   = 0 0  28060/0x3754c5:  1043  3  0 close(0x7)   = 0 0

可以看到系统底层执行的函数，如lstat64获取文件内容信息，kill(21416, 15)kill掉php-fpm进程，fork()出新的php-fpm进程，有兴趣可以深入研究每个指令的作用