ngx_add_inherited_sockets开始通过getenv获取"NGINX"环境变量，如果是NULL，直接return，通过增加log发现，正常这个值确实是NULL。
NGINX_VAR环境变量的设置是在平滑升级的时候才设置，nginx所采用的平滑升级能够保证在不中止服务的状况下更新nginx版本，具体需要看下ngx_exec_new_binary函数的实现。
所以ngx_add_inherited_sockets一般情况下用处不大，除非是需要升级nginx。
static ngx_int_t
ngx_add_inherited_sockets(ngx_cycle_t *cycle) {
u_char *p, *v, *inherited;
ngx_int_t s;
ngx_listening_t *ls;
inherited = (u_char *)getenv(NGINX_VAR);
if (inherited == NULL) {
return NGX_OK;
}
ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0,
"using inherited sockets from "%s"", inherited);
if (ngx_array_init(&cycle->listening, cycle->pool, 10,
sizeof(ngx_listening_t)) != NGX_OK) {
return NGX_ERROR;
}
for (p = inherited, v = p; *p; p++) {
if (*p == ':' || *p == ';') {
s = ngx_atoi(v, p - v);
if (s == NGX_ERROR) {
ngx_log_error(NGX_LOG_EMERG, cycle->log, 0,
"invalid socket number "%s" in " NGINX_VAR
" environment variable, ignoring the rest"
" of the variable",
v);
break;
}
v = p + 1;
ls = ngx_array_push(&cycle->listening);
if (ls == NULL) {
return NGX_ERROR;
}
ngx_memzero(ls, sizeof(ngx_listening_t));
ls->fd = (ngx_socket_t)s;
}
}
if (v != p) {
ngx_log_error(NGX_LOG_EMERG, cycle->log, 0,
"invalid socket number "%s" in " NGINX_VAR
" environment variable, ignoring",
v);
}
ngx_inherited = 1;
return ngx_set_inherited_sockets(cycle);
}
ps找到nginx的进程，然后看nginx的environ也没有什么信息
$ ps -ef | grep nginx root 4993 2764 0 12:01 ? 00:00:00 nginx: master process ./sbin/nginx hui 5007 4993 0 12:01 ? 00:00:00 nginx: worker process $ sudo cat /proc/4993/environ process ./sbin/nginx $ cat /proc/5007/environ process附：nginx中输出log的办法
在nginx的main函数中，每个函数调用前增加log后，在logs/error.log文件中，只能输出到ngx_log_redirect_stderr，因为在这之后的log都被redirect了。
$ sudo cat logs/error.log 2021/09/28 11:23:27 [notice] 24632#0: ungx_save_argv 2021/09/28 11:23:27 [notice] 24632#0: ngx_process_options 2021/09/28 11:23:27 [notice] 24632#0: ngx_os_init 2021/09/28 11:23:27 [notice] 24632#0: ngx_crc32_table_init 2021/09/28 11:23:27 [notice] 24632#0: ngx_slab_sizes_init 2021/09/28 11:23:27 [notice] 24632#0: ngx_add_inherited_sockets 2021/09/28 11:23:27 [notice] 24632#0: ngx_preinit_modules 2021/09/28 11:23:27 [notice] 24632#0: ngx_init_cycle 2021/09/28 11:23:27 [notice] 24633#0: ngx_log_redirect_stderr
所以要输出全部log，需要在nginx.conf文件中配置log输出路径到/home/hui/disk4t/media-test/samples/log.txt，后面的debug是对应的log level。
worker_processes 1; error_log /home/hui/disk4t/media-test/samples/log.txt debug;
nginx中的log level有8级
#define NGX_LOG_STDERR 0 #define NGX_LOG_EMERG 1 #define NGX_LOG_alert 2 #define NGX_LOG_CRIT 3 #define NGX_LOG_ERR 4 #define NGX_LOG_WARN 5 #define NGX_LOG_NOTICE 6 #define NGX_LOG_INFO 7 #define NGX_LOG_DEBUG 8
如果没有在configure的时候带上debug选项，输出的log是很少的，比如启动nginx，就只有下面这几行log
2021/09/28 11:28:32 [notice] 29022#0: using the "epoll" event method 2021/09/28 11:28:32 [notice] 29022#0: nginx/1.18.0 2021/09/28 11:28:32 [notice] 29022#0: built by gcc 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04) 2021/09/28 11:28:32 [notice] 29022#0: OS: Linux 5.4.0-81-generic 2021/09/28 11:28:32 [notice] 29022#0: getrlimit(RLIMIT_NOFILE): 1024:4096 2021/09/28 11:28:32 [notice] 29023#0: start worker processes 2021/09/28 11:28:32 [notice] 29023#0: start worker process 29024
加上--with-debug选项后，输出log就很多了：
./configure --prefix=/usr/local/nginx --with-debug --with-http_ssl_module --add-module=../nginx-rtmp-module --with-http_flv_module --with-http_mp4_module
$ tail /home/hui/disk4t/media-test/samples/log.txt 2021/09/28 12:38:53 [debug] 5007#0: *4 free: 000056092AC69560, unused: 0 2021/09/28 12:38:53 [debug] 5007#0: *4 free: 000056092ACADD60, unused: 2772 2021/09/28 12:38:53 [debug] 5007#0: *4 free: 000056092AC3B320 2021/09/28 12:38:53 [debug] 5007#0: *4 hc free: 0000000000000000 2021/09/28 12:38:53 [debug] 5007#0: *4 hc busy: 0000000000000000 0 2021/09/28 12:38:53 [debug] 5007#0: *4 reusable connection: 1 2021/09/28 12:38:53 [debug] 5007#0: *4 event timer add: 3: 65000:962096260 2021/09/28 12:38:53 [debug] 5007#0: timer delta: 15016 2021/09/28 12:38:53 [debug] 5007#0: worker cycle 2021/09/28 12:38:53 [debug] 5007#0: epoll timer: 65000
参考
-Nginx启动流程之ngx_add_inherited_sockets
