Java服务总在半夜挂，背后的真相竟然是...
一、写在前面
一、写在前面
最近有用户反馈测试环境Java服务总在凌晨00:00左右挂掉，用户反馈Java服务没有定时任务，也没有流量突增的情况，Jvm配置也合理，莫名其妙就挂了
【 问题复现 】
为了复现该问题，写了个springboot的demo部署在测试环境，其中demo里只做了hello world功能，应用类型为web_tomcat （war包部署），基础镜像是base_tomcat/java-centos6-jdk18-60-tom8050-ngx197，镜像使用的Java版本是1.8.0_60，有了上次MySQL被kill的经验，盲猜是linux limit惹的祸，因此将打好的镜像分别部署了两批不同的机器，果不其然，新机器当晚挂掉了，老机器服务正常
看一下挂掉的limit设置
【 排查过程 】
Java进程会受到limits影响？
按理说Java进程是不会受到系统limit open files（系统最大句柄数）影响的，但是为了验证这个问题，我们将他修改为正常机器的值，由于demo是web_tomcat应用，没法修改启动脚本，因此我们通过prlimit修改java进程的limit
prlimit -p 32672 --nofile=1048576 结果当晚00:00左右还是挂了，看来open files和java进程挂掉没关系，看dmesg也没发现什么问题
Java版本过低导致内存分配不合理？
通过寻求jdos研发组的帮助，jdos研发组的同学认为是java版本的问题，低版本可能没有限制住申请的内存大小，具体原因如下
https://blog.softwaremill.com/docker-support-in-new-java-8-finally-fd595df0ca54?gi=a0cc6736ed14
异常机器java内存情况
正常机器java内存情况
按照这个文档描述，使用docker cgroups限制内存可能会导致JVM进程被终止，原因是Java读取的还是宿主机的CPU，而不是docker cgroups限制的CPU，高版本的Java解决了这个问题，文档解决方案截图如下：
对此我们表示怀疑，因为我们的程序里设置了JVM参数
保持着试一试的心态，我们增加了一个实验组，实验组使用的Java版本是11.0.8
结果当晚实验组的Java进程还是死了，看来和Java版本也没关系
容器上存在定时任务导致的？
由于基础镜像是jdos官方提供的镜像，所以之前从来没有怀疑过是定时任务的问题，但是现在别无他法了，检查下容器的定时任务
虽然有定时任务，但是这个执行的时间点和Java挂掉的时间对不上，为此我们决定删除定时任务试试
结果当晚Java进程还是挂了，并且这次有dmesg的日志，发现Java被kill的同时crond也被kill了，被kill的原因是crond内存过高导致oom
难道还有系统级cron任务？于是查了一下/etc/crontab，发现果然还有cron任务（这是谁打的镜像！！！）
这个时间点和Java进程挂掉的时间点吻合，但是问题来了，执行的任务并没有logrotate.sh这个脚本，应该不会出现问题才对
到底是不是定时任务的问题，我们修改下cron的时间验证下，调整时间为中午11:00，验证下Java进程是否会挂，同时使用strace打印进程trace log
果然Java进程在中午11.00挂了，看来真的是cron任务导致的，让我们一起看一下strace
19:59:01 close(3) = 019:59:01 stat("/etc/pam.d", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 019:59:01 open("/etc/pam.d/crond", O_RDONLY) = 319:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=293, ...}) = 019:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd77080400019:59:01 read(3, "#\n# The PAM configuration file f"..., 4096) = 29319:59:01 open("/lib64/security/pam_access.so", O_RDONLY) = 519:59:01 read(5, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0000\17\0\0\0\0\0\0"..., 832) = 83219:59:01 fstat(5, {st_mode=S_IFREG|0755, st_size=18552, ...}) = 019:59:01 mmap(NULL, 2113800, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 5, 0) = 0x7fd76932200019:59:01 mprotect(0x7fd769325000, 2097152, PROT_NONE) = 019:59:01 mmap(0x7fd769525000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 5, 0x3000) = 0x7fd76952500019:59:01 close(5) = 019:59:01 open("/etc/ld.so.cache", O_RDONLY) = 519:59:01 fstat(5, {st_mode=S_IFREG|0644, st_size=16203, ...}) = 019:59:01 mmap(NULL, 16203, PROT_READ, MAP_PRIVATE, 5, 0) = 0x7fd7707f800019:59:01 close(5) = 019:59:01 open("/lib64/libnsl.so.1", O_RDONLY) = 519:59:01 read(5, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0p@\0\0\0\0\0\0"..., 832) = 83219:59:01 fstat(5, {st_mode=S_IFREG|0755, st_size=113432, ...}) = 019:59:01 mmap(NULL, 2198192, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 5, 0) = 0x7fd76910900019:59:01 mprotect(0x7fd76911f000, 2093056, PROT_NONE) = 019:59:01 mmap(0x7fd76931e000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 5, 0x15000) = 0x7fd76931e00019:59:01 mmap(0x7fd769320000, 6832, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fd76932000019:59:01 close(5) = 019:59:01 mprotect(0x7fd76931e000, 4096, PROT_READ) = 019:59:01 mprotect(0x7fd769525000, 4096, PROT_READ) = 019:59:01 munmap(0x7fd7707f8000, 16203) = 019:59:01 open("/etc/pam.d/password-auth", O_RDONLY) = 519:59:01 fstat(5, {st_mode=S_IFREG|0644, st_size=692, ...}) = 019:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd77080300019:59:01 read(5, "#%PAM-1.0\n# This file is auto-ge"..., 4096) = 69219:59:01 open("/lib64/security/pam_unix.so", O_RDONLY) = 619:59:01 read(6, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\240&\0\0\0\0\0\0"..., 832) = 83219:59:01 fstat(6, {st_mode=S_IFREG|0755, st_size=51960, ...}) = 019:59:01 mmap(NULL, 2196352, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 6, 0) = 0x7fd768ef000019:59:01 mprotect(0x7fd768efc000, 2093056, PROT_NONE) = 019:59:01 mmap(0x7fd7690fb000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 6, 0xb000) = 0x7fd7690fb00019:59:01 mmap(0x7fd7690fd000, 45952, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fd7690fd00019:59:01 close(6) = 019:59:01 mprotect(0x7fd7690fb000, 4096, PROT_READ) = 019:59:01 read(5, "", 4096) = 019:59:01 close(5) = 019:59:01 munmap(0x7fd770803000, 4096) = 019:59:01 open("/lib64/security/pam_loginuid.so", O_RDONLY) = 519:59:01 read(5, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\220\t\0\0\0\0\0\0"..., 832) = 83219:59:01 fstat(5, {st_mode=S_IFREG|0755, st_size=10240, ...}) = 019:59:01 mmap(NULL, 2105480, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 5, 0) = 0x7fd768ced00019:59:01 mprotect(0x7fd768cef000, 2093056, PROT_NONE) = 019:59:01 mmap(0x7fd768eee000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 5, 0x1000) = 0x7fd768eee00019:59:01 close(5) = 019:59:01 mprotect(0x7fd768eee000, 4096, PROT_READ) = 019:59:01 open("/etc/pam.d/password-auth", O_RDONLY) = 519:59:01 fstat(5, {st_mode=S_IFREG|0644, st_size=692, ...}) = 019:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd77080300019:59:01 read(5, "#%PAM-1.0\n# This file is auto-ge"..., 4096) = 69219:59:01 open("/lib64/security/pam_keyinit.so", O_RDONLY) = 619:59:01 read(6, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0`\10\0\0\0\0\0\0"..., 832) = 83219:59:01 fstat(6, {st_mode=S_IFREG|0755, st_size=10224, ...}) = 019:59:01 mmap(NULL, 2105488, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 6, 0) = 0x7fd768aea00019:59:01 mprotect(0x7fd768aec000, 2093056, PROT_NONE) = 019:59:01 mmap(0x7fd768ceb000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 6, 0x1000) = 0x7fd768ceb00019:59:01 close(6) = 019:59:01 mprotect(0x7fd768ceb000, 4096, PROT_READ) = 019:59:01 open("/lib64/security/pam_limits.so", O_RDONLY) = 619:59:01 read(6, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\320\20\0\0\0\0\0\0"..., 832) = 83219:59:01 fstat(6, {st_mode=S_IFREG|0755, st_size=18600, ...}) = 019:59:01 mmap(NULL, 2113848, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 6, 0) = 0x7fd7688e500019:59:01 mprotect(0x7fd7688e9000, 2093056, PROT_NONE) = 019:59:01 mmap(0x7fd768ae8000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 6, 0x3000) = 0x7fd768ae800019:59:01 close(6) = 019:59:01 mprotect(0x7fd768ae8000, 4096, PROT_READ) = 019:59:01 open("/lib64/security/pam_succeed_if.so", O_RDONLY) = 619:59:01 read(6, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\340\v\0\0\0\0\0\0"..., 832) = 83219:59:01 fstat(6, {st_mode=S_IFREG|0755, st_size=14384, ...}) = 019:59:01 mmap(NULL, 2109624, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 6, 0) = 0x7fd7686e100019:59:01 mprotect(0x7fd7686e4000, 2093056, PROT_NONE) = 019:59:01 mmap(0x7fd7688e3000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 6, 0x2000) = 0x7fd7688e300019:59:01 close(6) = 019:59:01 mprotect(0x7fd7688e3000, 4096, PROT_READ) = 019:59:01 read(5, "", 4096) = 019:59:01 close(5) = 019:59:01 munmap(0x7fd770803000, 4096) = 019:59:01 open("/etc/pam.d/password-auth", O_RDONLY) = 519:59:01 fstat(5, {st_mode=S_IFREG|0644, st_size=692, ...}) = 019:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd77080300019:59:01 read(5, "#%PAM-1.0\n# This file is auto-ge"..., 4096) = 69219:59:01 open("/lib64/security/pam_env.so", O_RDONLY) = 619:59:01 read(6, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\300\r\0\0\0\0\0\0"..., 832) = 83219:59:01 fstat(6, {st_mode=S_IFREG|0755, st_size=18592, ...}) = 019:59:01 mmap(NULL, 2113776, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 6, 0) = 0x7fd7684dc00019:59:01 mprotect(0x7fd7684e0000, 2093056, PROT_NONE) = 019:59:01 mmap(0x7fd7686df000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 6, 0x3000) = 0x7fd7686df00019:59:01 close(6) = 019:59:01 mprotect(0x7fd7686df000, 4096, PROT_READ) = 019:59:01 open("/lib64/security/pam_deny.so", O_RDONLY) = 619:59:01 read(6, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0000\5\0\0\0\0\0\0"..., 832) = 83219:59:01 fstat(6, {st_mode=S_IFREG|0755, st_size=5952, ...}) = 019:59:01 mmap(NULL, 2101272, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 6, 0) = 0x7fd7682da00019:59:01 mprotect(0x7fd7682db000, 2093056, PROT_NONE) = 019:59:01 mmap(0x7fd7684da000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 6, 0) = 0x7fd7684da00019:59:01 close(6) = 019:59:01 mprotect(0x7fd7684da000, 4096, PROT_READ) = 019:59:01 read(5, "", 4096) = 019:59:01 close(5) = 019:59:01 munmap(0x7fd770803000, 4096) = 019:59:01 read(3, "", 4096) = 019:59:01 close(3) = 019:59:01 munmap(0x7fd770804000, 4096) = 019:59:01 open("/etc/pam.d/other", O_RDONLY) = 319:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=154, ...}) = 019:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd77080400019:59:01 read(3, "#%PAM-1.0\nauth required "..., 4096) = 15419:59:01 read(3, "", 4096) = 019:59:01 close(3) = 019:59:01 munmap(0x7fd770804000, 4096) = 019:59:01 open("/etc/passwd", O_RDONLY|O_CLOEXEC) = 319:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=1057, ...}) = 019:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd77080400019:59:01 read(3, "root:x:0:0:root:/root:/bin/bash\n"..., 4096) = 105719:59:01 close(3) = 019:59:01 munmap(0x7fd770804000, 4096) = 019:59:01 uname({sys="Linux", node="host-11-159-73-176", ...}) = 019:59:01 open("/etc/security/access.conf", O_RDONLY) = 319:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=4620, ...}) = 019:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd77080400019:59:01 read(3, "# Login access control table.\n#\n"..., 4096) = 409619:59:01 read(3, " should get access from ipv4 net"..., 4096) = 52419:59:01 read(3, "", 4096) = 019:59:01 close(3) = 019:59:01 munmap(0x7fd770804000, 4096) = 019:59:01 getuid() = 019:59:01 open("/etc/passwd", O_RDONLY|O_CLOEXEC) = 319:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=1057, ...}) = 019:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd77080400019:59:01 read(3, "root:x:0:0:root:/root:/bin/bash\n"..., 4096) = 105719:59:01 close(3) = 019:59:01 munmap(0x7fd770804000, 4096) = 019:59:01 geteuid() = 019:59:01 open("/etc/shadow", O_RDONLY|O_CLOEXEC) = 319:59:01 fstat(3, {st_mode=S_IFREG, st_size=901, ...}) = 019:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd77080400019:59:01 read(3, "root:$6$4.53VPrJ$1wxMpbsWYp4VKea"..., 4096) = 90119:59:01 close(3) = 019:59:01 munmap(0x7fd770804000, 4096) = 019:59:01 socket(PF_NETLINK, SOCK_RAW, 9) = 319:59:01 fcntl(3, F_SETFD, FD_CLOEXEC) = 019:59:01 readlink("/proc/self/exe", "/usr/sbin/crond", 4096) = 1519:59:01 sendto(3, "p\0\0\0M\4\5\0\1\0\0\0\0\0\0\0op=PAM:accountin"..., 112, 0, {sa_family=AF_NETLINK, pid=0, groups=00000000}, 12) = 11219:59:01 poll([{fd=3, events=POLLIN}], 1, 500) = 1 ([{fd=3, revents=POLLIN}])19:59:01 recvfrom(3, "$\0\0\0\2\0\0\1\1\0\0\0\227\7\0\0\0\0\0\0p\0\0\0M\4\5\0\1\0\0\0"..., 8988, MSG_PEEK|MSG_DONTWAIT, {sa_family=AF_NETLINK, pid=0, groups=00000000}, [12]) = 3619:59:01 recvfrom(3, "$\0\0\0\2\0\0\1\1\0\0\0\227\7\0\0\0\0\0\0p\0\0\0M\4\5\0\1\0\0\0"..., 8988, MSG_DONTWAIT, {sa_family=AF_NETLINK, pid=0, groups=00000000}, [12]) = 3619:59:01 close(3) = 019:59:01 open("/etc/security/pam_env.conf", O_RDONLY) = 319:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=2980, ...}) = 019:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd77080400019:59:01 read(3, "#\n# This is the configuration fi"..., 4096) = 298019:59:01 read(3, "", 4096) = 019:59:01 close(3) = 019:59:01 munmap(0x7fd770804000, 4096) = 019:59:01 open("/etc/environment", O_RDONLY) = 319:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=0, ...}) = 019:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd77080400019:59:01 read(3, "", 4096) = 019:59:01 close(3) = 019:59:01 munmap(0x7fd770804000, 4096) = 019:59:01 socket(PF_NETLINK, SOCK_RAW, 9) = 319:59:01 fcntl(3, F_SETFD, FD_CLOEXEC) = 019:59:01 sendto(3, "p\0\0\0O\4\5\0\2\0\0\0\0\0\0\0op=PAM:setcred a"..., 112, 0, {sa_family=AF_NETLINK, pid=0, groups=00000000}, 12) = 11219:59:01 poll([{fd=3, events=POLLIN}], 1, 500) = 1 ([{fd=3, revents=POLLIN}])19:59:01 recvfrom(3, "$\0\0\0\2\0\0\1\2\0\0\0\227\7\0\0\0\0\0\0p\0\0\0O\4\5\0\2\0\0\0"..., 8988, MSG_PEEK|MSG_DONTWAIT, {sa_family=AF_NETLINK, pid=0, groups=00000000}, [12]) = 3619:59:01 recvfrom(3, "$\0\0\0\2\0\0\1\2\0\0\0\227\7\0\0\0\0\0\0p\0\0\0O\4\5\0\2\0\0\0"..., 8988, MSG_DONTWAIT, {sa_family=AF_NETLINK, pid=0, groups=00000000}, [12]) = 3619:59:01 close(3) = 019:59:01 open("/etc/passwd", O_RDONLY|O_CLOEXEC) = 319:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=1057, ...}) = 019:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd77080400019:59:01 read(3, "root:x:0:0:root:/root:/bin/bash\n"..., 4096) = 105719:59:01 close(3) = 019:59:01 munmap(0x7fd770804000, 4096) = 019:59:01 open("/proc/self/loginuid", O_WRONLY|O_TRUNC|O_NOFOLLOW) = 319:59:01 write(3, "0", 1) = 119:59:01 close(3) = 019:59:01 open("/etc/passwd", O_RDONLY|O_CLOEXEC) = 319:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=1057, ...}) = 019:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd77080400019:59:01 read(3, "root:x:0:0:root:/root:/bin/bash\n"..., 4096) = 105719:59:01 close(3) = 019:59:01 munmap(0x7fd770804000, 4096) = 019:59:01 getuid() = 019:59:01 getgid() = 019:59:01 keyctl(0, 0xfffffffd, 0, 0, 0) = 49646638519:59:01 keyctl(0, 0xfffffffb, 0, 0, 0x30) = 78570213219:59:01 open("/etc/passwd", O_RDONLY|O_CLOEXEC) = 319:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=1057, ...}) = 019:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd77080400019:59:01 read(3, "root:x:0:0:root:/root:/bin/bash\n"..., 4096) = 105719:59:01 close(3) = 019:59:01 munmap(0x7fd770804000, 4096) = 019:59:01 getrlimit(RLIMIT_CPU, {rlim_cur=RLIM_INFINITY, rlim_max=RLIM_INFINITY}) = 019:59:01 getrlimit(RLIMIT_FSIZE, {rlim_cur=RLIM_INFINITY, rlim_max=RLIM_INFINITY}) = 019:59:01 getrlimit(RLIMIT_DATA, {rlim_cur=RLIM_INFINITY, rlim_max=RLIM_INFINITY}) = 019:59:01 getrlimit(RLIMIT_STACK, {rlim_cur=8192*1024, rlim_max=RLIM_INFINITY}) = 019:59:01 getrlimit(RLIMIT_CORE, {rlim_cur=RLIM_INFINITY, rlim_max=RLIM_INFINITY}) = 019:59:01 getrlimit(RLIMIT_RSS, {rlim_cur=RLIM_INFINITY, rlim_max=RLIM_INFINITY}) = 019:59:01 getrlimit(RLIMIT_NPROC, {rlim_cur=RLIM_INFINITY, rlim_max=RLIM_INFINITY}) = 019:59:01 getrlimit(RLIMIT_NOFILE, {rlim_cur=1073741816, rlim_max=1073741816}) = 019:59:01 getrlimit(RLIMIT_MEMLOCK, {rlim_cur=64*1024, rlim_max=64*1024}) = 019:59:01 getrlimit(RLIMIT_AS, {rlim_cur=RLIM_INFINITY, rlim_max=RLIM_INFINITY}) = 019:59:01 getrlimit(RLIMIT_LOCKS, {rlim_cur=RLIM_INFINITY, rlim_max=RLIM_INFINITY}) = 019:59:01 getrlimit(RLIMIT_SIGPENDING, {rlim_cur=883632, rlim_max=883632}) = 019:59:01 getrlimit(RLIMIT_MSGQUEUE, {rlim_cur=800*1024, rlim_max=800*1024}) = 019:59:01 getrlimit(RLIMIT_NICE, {rlim_cur=0, rlim_max=0}) = 019:59:01 getrlimit(RLIMIT_RTPRIO, {rlim_cur=0, rlim_max=0}) = 019:59:01 getpriority(PRIO_PROCESS, 0) = 2019:59:01 open("/etc/security/limits.conf", O_RDONLY) = 319:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=1835, ...}) = 019:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd77080400019:59:01 read(3, "# /etc/security/limits.conf\n#\n#E"..., 4096) = 183519:59:01 read(3, "", 4096) = 019:59:01 close(3) = 019:59:01 munmap(0x7fd770804000, 4096) = 019:59:01 open("/etc/security/limits.d", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 319:59:01 getdents(3, /* 3 entries */, 32768) = 8819:59:01 open("/usr/lib64/gconv/gconv-modules.cache", O_RDONLY) = 519:59:01 fstat(5, {st_mode=S_IFREG|0644, st_size=26060, ...}) = 019:59:01 mmap(NULL, 26060, PROT_READ, MAP_SHARED, 5, 0) = 0x7fd7707f500019:59:01 close(5) = 019:59:01 getdents(3, /* 0 entries */, 32768) = 019:59:01 close(3) = 019:59:01 open("/etc/security/limits.d/90-nproc.conf", O_RDONLY) = 319:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=193, ...}) = 019:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd77080400019:59:01 read(3, "# Default limit for number of us"..., 4096) = 19319:59:01 read(3, "", 4096) = 019:59:01 close(3) = 019:59:01 munmap(0x7fd770804000, 4096) = 019:59:01 setrlimit(RLIMIT_NPROC, {rlim_cur=RLIM_INFINITY, rlim_max=RLIM_INFINITY}) = 019:59:01 setpriority(PRIO_PROCESS, 0, 0) = 019:59:01 getuid() = 019:59:01 open("/etc/passwd", O_RDONLY|O_CLOEXEC) = 319:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=1057, ...}) = 019:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd77080400019:59:01 read(3, "root:x:0:0:root:/root:/bin/bash\n"..., 4096) = 105719:59:01 close(3) = 019:59:01 munmap(0x7fd770804000, 4096) = 019:59:01 socket(PF_NETLINK, SOCK_RAW, 9) = 319:59:01 fcntl(3, F_SETFD, FD_CLOEXEC) = 019:59:01 sendto(3, "t\0\0\0Q\4\5\0\3\0\0\0\0\0\0\0op=PAM:session_o"..., 116, 0, {sa_family=AF_NETLINK, pid=0, groups=00000000}, 12) = 11619:59:01 poll([{fd=3, events=POLLIN}], 1, 500) = 1 ([{fd=3, revents=POLLIN}])19:59:01 recvfrom(3, "$\0\0\0\2\0\0\1\3\0\0\0\227\7\0\0\0\0\0\0t\0\0\0Q\4\5\0\3\0\0\0"..., 8988, MSG_PEEK|MSG_DONTWAIT, {sa_family=AF_NETLINK, pid=0, groups=00000000}, [12]) = 3619:59:01 recvfrom(3, "$\0\0\0\2\0\0\1\3\0\0\0\227\7\0\0\0\0\0\0t\0\0\0Q\4\5\0\3\0\0\0"..., 8988, MSG_DONTWAIT, {sa_family=AF_NETLINK, pid=0, groups=00000000}, [12]) = 3619:59:01 close(3) = 019:59:01 setgid(0) = 019:59:01 open("/proc/sys/kernel/ngroups_max", O_RDONLY) = 319:59:01 read(3, "65536\n", 31) = 619:59:01 close(3) = 019:59:01 socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 319:59:01 connect(3, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)19:59:01 close(3) = 019:59:01 socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 319:59:01 connect(3, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)19:59:01 close(3) = 019:59:01 open("/etc/group", O_RDONLY|O_CLOEXEC) = 319:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=497, ...}) = 019:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd77080400019:59:01 lseek(3, 0, SEEK_CUR) = 019:59:01 read(3, "root:x:0:\nbin:x:1:bin,daemon\ndae"..., 4096) = 49719:59:01 read(3, "", 4096) = 019:59:01 close(3) = 019:59:01 munmap(0x7fd770804000, 4096) = 019:59:01 setgroups(1, [0]) = 019:59:01 setreuid(0, 4294967295) = 019:59:01 rt_sigaction(SIGCHLD, {SIG_DFL, [CHLD], SA_RESTORER|SA_RESTART, 0x7fd76fa316a0}, {0x558826e03b80, [], SA_RESTORER|SA_RESTART, 0x7fd76fa316a0}, 8) = 019:59:01 pipe([3, 5]) = 019:59:01 pipe([6, 7]) = 019:59:01 clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fd7707fca70) = 194619:59:01 gettid() = 194319:59:01 open("/proc/self/task/1943/attr/exec", O_RDWR) = 819:59:01 write(8, NULL, 0) = -1 EINVAL (Invalid argument)19:59:01 close(8) = 019:59:01 close(3) = 019:59:01 close(7) = 019:59:01 close(5) = 019:59:01 fcntl(6, F_GETFL) = 0 (flags O_RDONLY)19:59:01 fstat(6, {st_mode=S_IFIFO|0600, st_size=0, ...}) = 019:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd77080400019:59:01 lseek(6, 0, SEEK_CUR) = -1 ESPIPE (Illegal seek)19:59:01 read(6, "/bin/bash: ./logrotate.sh: \346\262\241\346\234"..., 4096) = 5519:59:01 uname({sys="Linux", node="host-11-159-73-176", ...}) = 019:59:01 getrlimit(RLIMIT_NOFILE, {rlim_cur=1073741816, rlim_max=1073741816}) = 019:59:01 mmap(NULL, 4294967296, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd6682da00019:59:01 --- SIGCHLD (Child exited) @ 0 (0) ---19:59:06 +++ killed by SIGKILL +++
可以看到最后用 mmap 一次分配了 4G 内存，然后就被kill了。
mmap前调用了getrlimit，和上次MySQL的问题一样，都是根据系统资源限制来分配内存
为了确定就是cron导致java挂掉的元凶，我们把cron进程手动kill掉，这样就不会执行定时任务了，这次我们在验证下Java进程是否会挂掉
果不其然，Java进程并没有挂掉，看来真的是cron任务导致的
高版本CentOS是否也会出现类似问题？
按理说oom killer应该只kill掉占用内存最高的才对，Java进程占用内存又不是最高的，高版本的CentOS系统oom killer策略会不会有升级？
让我们来一起验证下高版本的CentOS系统是否有这个问题
当前镜像的CentOS版本是CentOS release 6.6 (Final)，为了验证高版本的CentOS是否也有类似的问题，我们将增加两个实验组，分别升级基础镜像至CentOS release 6.10 (Final)和CentOS Linux release 7.9.2009 (Core)，也添加相同的cron任务
结果发现CentOS release 6.10 (Final)和CentOS Linux release 7.9.2009 (Core)都没有kill掉Java进程，只kill掉了cron的子进程
【 结论 】
由于容器limit open files(系统最大句柄数)设置不合理导致cron执行任务时使容器内存飙升，存在内存溢出的风险，linux由于保护机制会kill掉占用内存高的进程，导致cron子任务进程和Java进程一起被kill（但是问题来了，这个jdos基础镜像为什么会执行一个完全不存在的shell脚本，而且还是执行两次？？？），高版本的CentOS系统不会kill java进程，猜测不同版本的CentOS的kill选择策略略有不同
【 问题分析 】
Cron任务执行逻辑
在Linux中，crontab工具是由croine软件包提供的，让我们一起看下cron的执行过程
其中child_process（）执行了cron子进程，cron执行子进程时会有发送mail的动作
cron_popen在执行时会按照open files(系统最大句柄数)清除内存
综上，cron oom的原因找到了，是由于open files设置过大且cron任务没有标准输出，导致执行了发送mail逻辑，而清除的内存大小超出了容器本身内存的大小，导致oom。
croine 1.5.4 版本之后修复了该问题，如果想查看当前容器croine版本可执行如下命令：
rpm -q cronieLinux内核OOM killer机制
Linux 内核有个机制叫OOM killer(Out Of Memory killer)，该机制会监控那些占用内存过大，尤其是瞬间占用内存很快的进程，然后防止内存耗尽而自动把该进程杀掉。内核检测到系统内存不足、挑选并杀掉某个进程的过程可以参考内核源代码linux/mm/oom_kill.c，当系统内存不足的时候，out_of_memory()被触发，然后调用select_bad_process()选择一个”bad”进程杀掉。
以下是一些主要的进程选择策略：
1.内存使用情况：OOM Killer首先倾向于选择占用内存最多的进程，因为终止这些进程可以释放最多的内存。
2.OOM分数：每个进程都有一个OOM分数，该分数是基于其内存使用情况和其他因素计算出来的。OOM Killer倾向于终止OOM分数最高的进程。
3.进程优先级：在选择要终止的进程时，OOM Killer通常会避免终止对系统至关重要的系统进程。这些进程通常具有较高的优先级，因此它们更不容易成为终止目标。
4.进程资源需求：OOM Killer还会考虑进程的资源需求。它倾向于终止那些请求较少资源的进程，以最小化影响其他进程的运行。
5.进程属性：某些进程可能被标记为不可终止，例如通过设置/proc/[PID]/oom_score_adj的值来调整OOM分数。这些进程通常不容易被OOM Killer终止。
注：不同版本的Linux oom killer机制可能会存在一些差异
【 解决方案 】
使用高版本稳定的CentOS系统，如果业务无法升级CentOS，则需要设置合理的limit open files数量，application_worker类型应用可以在启动脚本中手动修改limit，web_tomcat类型应用没法修改启动脚本，可以选择kill掉cron进程或删除系统cron任务，也可以手动升级cronie的版本至1.5.7-5
三、写在后面open files这个坑很大，栽这个坑两次了，大家一定要检查自己服务对应容器的CentOS版本和limit设置是否合理，本次案例发生在测试环境，尚不会引起事故，如果在生产出现类似情况，后果不堪设想
由于测试环境新增的这批机器都存在这个问题，我们团队已经联系机器提供方上报了该问题，后续这批机器会由提供方统一修改系统最大句柄数，如果当前问题影响到了业务的正常使用，可以临时删除容器中/etc/crontab中的任务
参考文献
https://cloud.tencent.com/developer/article/1183262
https://github.com/cronie-crond/cronie
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