Check that tcp-backlog is matched by /proc/sys/net/core/somaxconn.

src/config.h

@@ -48,6 +48,7 @@
 #define HAVE_PROC_STAT 1
 #define HAVE_PROC_MAPS 1
 #define HAVE_PROC_SMAPS 1
+#define HAVE_PROC_SOMAXCONN 1
 #endif
 
 /* Test for task_info() */

src/redis.c

@@ -1621,6 +1621,23 @@ void adjustOpenFilesLimit(void) {
     }
 }
 
+/* Check that server.tcp_backlog can be actually enforced in Linux according
+ * to the value of /proc/sys/net/core/somaxconn, or warn about it. */
+void checkTcpBacklogSettings(void) {
+#ifdef HAVE_PROC_SOMAXCONN
+    FILE *fp = fopen("/proc/sys/net/core/somaxconn","r");
+    char buf[1024];
+    if (!fp) return;
+    if (fgets(buf,sizeof(buf),fp) != NULL) {
+        int somaxconn = atoi(buf);
+        if (somaxconn > 0 && somaxconn < server.tcp_backlog) {
+            redisLog(REDIS_WARNING,"WARNING: The TCP backlog setting of %d cannot be enforced because /proc/sys/net/core/somaxconn is set to the lower value of %d.", server.tcp_backlog, somaxconn);
+        }
+    }
+    fclose(fp);
+#endif
+}
+
 /* Initialize a set of file descriptors to listen to the specified 'port'
  * binding the addresses specified in the Redis server configuration.
  *
@@ -3648,6 +3665,7 @@ int main(int argc, char **argv) {
     #ifdef __linux__
         linuxMemoryWarnings();
     #endif
+        checkTcpBacklogSettings();
         loadDataFromDisk();
         if (server.cluster_enabled) {
             if (verifyClusterConfigWithData() == REDIS_ERR) {