Per man page, listen(fd, 0) is valid. A backlog argument of 0 may allow the socket to accept connections, in which case the length of the listen queue may be set to an implementation-defined minimum value.
http://pubs.opengroup.org/onlinepubs/009695399/functions/listen.html I just notice additional entries in dmesg. Which do not appear previously. [101304.240385] TCP: request_sock_TCP: Possible SYN flooding on port 32000. Sending cookies. Check SNMP counters. [178237.343790] TCP: request_sock_TCP: Possible SYN flooding on port 42000. Sending cookies. Check SNMP counters. #!/usr/bin/python import socket sock = socket.socket() sock.bind(('127.0.0.1',42000)) sock.listen(0) s, a= sock.accept() s.send('test') And telnet to it. On Sat, Jan 23, 2016 at 4:11 PM, Eric Dumazet <eric.duma...@gmail.com> wrote: > On Sat, 2016-01-23 at 15:54 -0800, Kui Zhang wrote: >> Hello, >> >> One of our java software would not start after this: >> >> # first bad commit: [ef547f2ac16bd9d77a780a0e7c70857e69e8f23f] tcp: >> remove max_qlen_log >> >> >> Log from software: >> >> STATUS | monitor | 2016/01/23 14:22:55 | Launching a Service... >> INFO | buserver | 2016/01/23 14:23:00 | WrapperManager class >> initialized by thread: main Using classloader: >> sun.misc.Launcher$AppClassLoader@2876b359 >> INFO | buserver | 2016/01/23 14:23:00 | >> INFO | buserver | 2016/01/23 14:23:00 | Wrapper Manager: JVM #1 >> INFO | buserver | 2016/01/23 14:23:00 | Running a 64-bit JVM. >> INFO | buserver | 2016/01/23 14:23:00 | Wrapper Manager: Registering >> shutdown hook >> INFO | buserver | 2016/01/23 14:23:00 | Wrapper Manager: Using wrapper >> INFO | buserver | 2016/01/23 14:23:00 | Load native library. One or >> more attempts may fail if platform specific libraries do not exist. >> INFO | buserver | 2016/01/23 14:23:00 | Loading native library >> failed: libwrapper-linux-x86-64.so Cause: >> java.lang.UnsatisfiedLinkError: no wrapper-linux-x86-64 in >> java.library.path >> INFO | buserver | 2016/01/23 14:23:00 | Loaded native library: >> libwrapper.so >> INFO | buserver | 2016/01/23 14:23:00 | Calling native initialization >> method. >> INFO | buserver | 2016/01/23 14:23:00 | Inside native WrapperManager >> initialization method >> INFO | buserver | 2016/01/23 14:23:00 | Java Version : >> 1.7.0_80-b15 Java HotSpot(TM) 64-Bit Server VM >> INFO | buserver | 2016/01/23 14:23:00 | Java VM Vendor : Oracle Corporation >> INFO | buserver | 2016/01/23 14:23:00 | >> INFO | buserver | 2016/01/23 14:23:00 | >> WrapperManager.start(com.r1soft.backup.server.BUServerWrapper@7e515f40, >> args["wait"]) called by thread: main >> INFO | buserver | 2016/01/23 14:23:00 | Open socket to >> wrapper...Wrapper-Connection >> ERROR | monitor | 2016/01/23 14:23:24 | Startup failed: Timed out >> waiting for a signal from the Service. >> >> >> ### normal output around this point >> ### INFO | buserver | 2016/01/23 14:30:57 | Opened Socket from 31000 to >> 32000 >> >> >> ADVICE | monitor | 2016/01/23 14:23:24 | >> ADVICE | monitor | 2016/01/23 14:23:24 | >> ------------------------------------------------------------------------ >> ADVICE | monitor | 2016/01/23 14:23:24 | Advice: >> ADVICE | monitor | 2016/01/23 14:23:24 | The Wrapper consists of a >> native component as well as a set of classes >> ADVICE | monitor | 2016/01/23 14:23:24 | which run within the Service >> that it launches. The Java component of the >> ADVICE | monitor | 2016/01/23 14:23:24 | Wrapper must be initialized >> promptly after the Service is launched or the >> ADVICE | monitor | 2016/01/23 14:23:24 | Wrapper will timeout, as >> just happened. Most likely the main class >> ADVICE | monitor | 2016/01/23 14:23:24 | specified in the Wrapper >> configuration file is not correctly initializing >> ADVICE | monitor | 2016/01/23 14:23:24 | the Wrapper classes: >> ADVICE | monitor | 2016/01/23 14:23:24 | Main >> ADVICE | monitor | 2016/01/23 14:23:24 | While it is possible to do >> so manually, the Wrapper ships with helper >> ADVICE | monitor | 2016/01/23 14:23:24 | classes to make this >> initialization processes automatic. >> ADVICE | monitor | 2016/01/23 14:23:24 | Please review the >> integration section of the Wrapper's documentation >> ADVICE | monitor | 2016/01/23 14:23:24 | for the various methods >> which can be employed to launch an application >> ADVICE | monitor | 2016/01/23 14:23:24 | within the Wrapper: >> ADVICE | monitor | 2016/01/23 14:23:24 | >> http://wrapper.tanukisoftware.org/doc/english/integrate.html >> ADVICE | monitor | 2016/01/23 14:23:24 | >> ------------------------------------------------------------------------ >> ADVICE | monitor | 2016/01/23 14:23:24 | >> ERROR | monitor | 2016/01/23 14:23:24 | JVM did not exit on request, >> terminated >> DEBUG | monitor | 2016/01/23 14:23:24 | Signal trapped. Details: >> DEBUG | monitor | 2016/01/23 14:23:24 | signal number=17 >> (SIGCHLD), source="unknown" >> DEBUG | monitor | 2016/01/23 14:23:24 | Received SIGCHLD, calling wait(). >> DEBUG | monitor | 2016/01/23 14:23:24 | wait() returned, child >> process should be gone. >> STATUS | monitor | 2016/01/23 14:23:24 | Service Restarts disabled. >> Shutting down. >> STATUS | monitor | 2016/01/23 14:23:24 | <-- Monitor Stopped >> >> >> >> strace snippet: >> >> 10685 nanosleep({0, 100000000}, <unfinished ...> >> 10684 <... nanosleep resumed> NULL) = 0 >> 10684 socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 4 >> 10684 fcntl(4, F_SETFL, O_RDONLY|O_NONBLOCK) = 0 >> 10684 bind(4, {sa_family=AF_INET, sin_port=htons(32000), >> sin_addr=inet_addr("127.0.0.1")}, 16) = 0 >> 10684 stat("/etc/localtime", {st_dev=makedev(9, 2), st_ino=1828322, >> st_mode=S_IFREG|0644, st_nlink=1, st_uid=0, st_gid=0, st_blksize=4096, >> st_blocks=8, st_size=2875, st_atime=2015/10/13-11:06:06, >> st_mtime=2015/10/13-11:06:06, st_ctime=2015/10/13-11:06:06}) = 0 >> 10684 listen(4, 0) = 0 > > > listen(fd, 0) ? > >> 10684 accept(4, 0x7ffcae409990, [16]) = -1 EAGAIN (Resource >> temporarily unavailable) > ... >> 10684 accept(4, 0x7ffcae409990, [16]) = -1 EAGAIN (Resource >> temporarily unavailable) > ... > > It seems the bug is in user space program. > > Use listen(fd, 10) or listen(fd, 1000) ? > > >
