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最近有用戶反饋測試環(huán)境Java服務(wù)總在凌晨00:00左右掛掉，用戶反饋Java服務(wù)沒有定時任務(wù)，也沒有流量突增的情況，Jvm配置也合理，莫名其妙就掛了

寫在前面

問題排查

問題復現(xiàn)

為了復現(xiàn)該問題，寫了個springboot的demo部署在測試環(huán)境，其中demo里只做了hello world功能，應(yīng)用類型為web_tomcat （war包部署），基礎(chǔ)鏡像是base_tomcat/java-centos6-jdk18-60-tom8050-ngx197，鏡像使用的Java版本是1.8.0_60，有了上次MySQL被kill的經(jīng)驗，盲猜是linux limit惹的禍，因此將打好的鏡像分別部署了兩批不同的機器，果不其然，新機器當晚掛掉了，老機器服務(wù)正常

Java服務(wù)總在半夜掛，背后的真相竟然是...

看一下掛掉的limit設(shè)置

Java服務(wù)總在半夜掛，背后的真相竟然是...

排查過程

Java進程會受到limits影響？

按理說Java進程是不會受到系統(tǒng)limit open files（系統(tǒng)最大句柄數(shù)）影響的，但是為了驗證這個問題，我們將他修改為正常機器的值，由于demo是web_tomcat應(yīng)用，沒法修改啟動腳本，因此我們通過prlimit修改java進程的limit

prlimit -p 32672 --nofile=1048576

Java服務(wù)總在半夜掛，背后的真相竟然是...

結(jié)果當晚00:00左右還是掛了，看來open files和java進程掛掉沒關(guān)系，看dmesg也沒發(fā)現(xiàn)什么問題

Java服務(wù)總在半夜掛，背后的真相竟然是...

Java版本過低導致內(nèi)存分配不合理？

通過尋求jdos研發(fā)組的幫助，jdos研發(fā)組的同學認為是java版本的問題，低版本可能沒有限制住申請的內(nèi)存大小，具體原因如下

https://blog.softwaremill.com/docker-support-in-new-java-8-finally-fd595df0ca54?gi=a0cc6736ed14

異常機器java內(nèi)存情況

Java服務(wù)總在半夜掛，背后的真相竟然是...

正常機器java內(nèi)存情況

Java服務(wù)總在半夜掛，背后的真相竟然是...

按照這個文檔描述，使用docker cgroups限制內(nèi)存可能會導致JVM進程被終止，原因是Java讀取的還是宿主機的CPU，而不是docker cgroups限制的CPU，高版本的Java解決了這個問題，文檔解決方案截圖如下：

Java服務(wù)總在半夜掛，背后的真相竟然是...

對此我們表示懷疑，因為我們的程序里設(shè)置了JVM參數(shù)

Java服務(wù)總在半夜掛，背后的真相竟然是...

保持著試一試的心態(tài)，我們增加了一個實驗組，實驗組使用的Java版本是11.0.8

結(jié)果當晚實驗組的Java進程還是死了，看來和Java版本也沒關(guān)系

Java服務(wù)總在半夜掛，背后的真相竟然是...

容器上存在定時任務(wù)導致的？

由于基礎(chǔ)鏡像是jdos官方提供的鏡像，所以之前從來沒有懷疑過是定時任務(wù)的問題，但是現(xiàn)在別無他法了，檢查下容器的定時任務(wù)

雖然有定時任務(wù)，但是這個執(zhí)行的時間點和Java掛掉的時間對不上，為此我們決定刪除定時任務(wù)試試

結(jié)果當晚Java進程還是掛了，并且這次有dmesg的日志，發(fā)現(xiàn)Java被kill的同時crond也被kill了，被kill的原因是crond內(nèi)存過高導致oom

Java服務(wù)總在半夜掛，背后的真相竟然是...

難道還有系統(tǒng)級cron任務(wù)？于是查了一下/etc/crontab，發(fā)現(xiàn)果然還有cron任務(wù)（這是誰打的鏡像?。。。?/p>

Java服務(wù)總在半夜掛，背后的真相竟然是...

這個時間點和Java進程掛掉的時間點吻合，但是問題來了，執(zhí)行的任務(wù)并沒有logrotate.sh這個腳本，應(yīng)該不會出現(xiàn)問題才對

Java服務(wù)總在半夜掛，背后的真相竟然是...

到底是不是定時任務(wù)的問題，我們修改下cron的時間驗證下，調(diào)整時間為中午11:00，驗證下Java進程是否會掛，同時使用strace打印進程trace log

Java服務(wù)總在半夜掛，背后的真相竟然是...

果然Java進程在中午11.00掛了，看來真的是cron任務(wù)導致的，讓我們一起看一下strace

19:59:01 close(3)                        = 0
19:59:01 stat("/etc/pam.d", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
19:59:01 open("/etc/pam.d/crond", O_RDONLY) = 3
19:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=293, ...}) = 0
19:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd770804000
19:59:01 read(3, "#\n# The PAM configuration file f"..., 4096) = 293
19:59:01 open("/lib64/security/pam_access.so", O_RDONLY) = 5
19:59:01 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) = 832
19:59:01 fstat(5, {st_mode=S_IFREG|0755, st_size=18552, ...}) = 0
19:59:01 mmap(NULL, 2113800, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 5, 0) = 0x7fd769322000
19:59:01 mprotect(0x7fd769325000, 2097152, PROT_NONE) = 0
19:59:01 mmap(0x7fd769525000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 5, 0x3000) = 0x7fd769525000
19:59:01 close(5) = 0
19:59:01 open("/etc/ld.so.cache", O_RDONLY) = 5
19:59:01 fstat(5, {st_mode=S_IFREG|0644, st_size=16203, ...}) = 0
19:59:01 mmap(NULL, 16203, PROT_READ, MAP_PRIVATE, 5, 0) = 0x7fd7707f8000
19:59:01 close(5) = 0
19:59:01 open("/lib64/libnsl.so.1", O_RDONLY) = 5
19:59:01 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) = 832
19:59:01 fstat(5, {st_mode=S_IFREG|0755, st_size=113432, ...}) = 0
19:59:01 mmap(NULL, 2198192, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 5, 0) = 0x7fd769109000
19:59:01 mprotect(0x7fd76911f000, 2093056, PROT_NONE) = 0
19:59:01 mmap(0x7fd76931e000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 5, 0x15000) = 0x7fd76931e000
19:59:01 mmap(0x7fd769320000, 6832, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fd769320000
19:59:01 close(5) = 0
19:59:01 mprotect(0x7fd76931e000, 4096, PROT_READ) = 0
19:59:01 mprotect(0x7fd769525000, 4096, PROT_READ) = 0
19:59:01 munmap(0x7fd7707f8000, 16203) = 0
19:59:01 open("/etc/pam.d/password-auth", O_RDONLY) = 5
19:59:01 fstat(5, {st_mode=S_IFREG|0644, st_size=692, ...}) = 0
19:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0)                     = 0x7fd770803000
19:59:01 read(5, "#%PAM-1.0\n# This file is auto-ge"..., 4096) = 692
19:59:01 open("/lib64/security/pam_unix.so", O_RDONLY) = 6
19:59:01 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) = 832
19:59:01 fstat(6, {st_mode=S_IFREG|0755, st_size=51960, ...}) = 0
19:59:01 mmap(NULL, 2196352, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 6, 0) = 0x7fd768ef0000
19:59:01 mprotect(0x7fd768efc000, 2093056, PROT_NONE) = 0
19:59:01 mmap(0x7fd7690fb000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 6, 0xb000) = 0x7fd7690fb000
19:59:01 mmap(0x7fd7690fd000, 45952, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fd7690fd000
19:59:01 close(6)                       = 0
19:59:01 mprotect(0x7fd7690fb000, 4096, PROT_READ) = 0
19:59:01 read(5, "", 4096)              = 0
19:59:01 close(5) = 0
19:59:01 munmap(0x7fd770803000, 4096) = 0
19:59:01 open("/lib64/security/pam_loginuid.so", O_RDONLY) = 5
19:59:01 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) = 832
19:59:01 fstat(5, {st_mode=S_IFREG|0755, st_size=10240, ...}) = 0
19:59:01 mmap(NULL, 2105480, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 5, 0) = 0x7fd768ced000
19:59:01 mprotect(0x7fd768cef000, 2093056, PROT_NONE) = 0
19:59:01 mmap(0x7fd768eee000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 5, 0x1000) = 0x7fd768eee000
19:59:01 close(5) = 0
19:59:01 mprotect(0x7fd768eee000, 4096, PROT_READ) = 0
19:59:01 open("/etc/pam.d/password-auth", O_RDONLY) = 5
19:59:01 fstat(5, {st_mode=S_IFREG|0644, st_size=692, ...}) = 0
19:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd770803000
19:59:01 read(5, "#%PAM-1.0\n# This file is auto-ge"..., 4096) = 692
19:59:01 open("/lib64/security/pam_keyinit.so", O_RDONLY) = 6
19:59:01 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) = 832
19:59:01 fstat(6, {st_mode=S_IFREG|0755, st_size=10224, ...}) = 0
19:59:01 mmap(NULL, 2105488, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 6, 0)                      = 0x7fd768aea000
19:59:01 mprotect(0x7fd768aec000, 2093056, PROT_NONE)                     = 0
19:59:01 mmap(0x7fd768ceb000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 6, 0x1000) = 0x7fd768ceb000
19:59:01 close(6) = 0
19:59:01 mprotect(0x7fd768ceb000, 4096, PROT_READ) = 0
19:59:01 open("/lib64/security/pam_limits.so", O_RDONLY) = 6
19:59:01 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) = 832
19:59:01 fstat(6, {st_mode=S_IFREG|0755, st_size=18600, ...}) = 0
19:59:01 mmap(NULL, 2113848, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 6, 0) = 0x7fd7688e5000
19:59:01 mprotect(0x7fd7688e9000, 2093056, PROT_NONE) = 0
19:59:01 mmap(0x7fd768ae8000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 6, 0x3000) = 0x7fd768ae8000
19:59:01 close(6) = 0
19:59:01 mprotect(0x7fd768ae8000, 4096, PROT_READ) = 0
19:59:01 open("/lib64/security/pam_succeed_if.so", O_RDONLY) = 6
19:59:01 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) = 832
19:59:01 fstat(6, {st_mode=S_IFREG|0755, st_size=14384, ...}) = 0
19:59:01 mmap(NULL, 2109624, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 6, 0) = 0x7fd7686e1000
19:59:01 mprotect(0x7fd7686e4000, 2093056, PROT_NONE) = 0
19:59:01 mmap(0x7fd7688e3000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 6, 0x2000) = 0x7fd7688e3000
19:59:01 close(6) = 0
19:59:01 mprotect(0x7fd7688e3000, 4096, PROT_READ)                       = 0
19:59:01 read(5, "", 4096) = 0
19:59:01 close(5)                     = 0
19:59:01 munmap(0x7fd770803000, 4096) = 0
19:59:01 open("/etc/pam.d/password-auth", O_RDONLY)                      = 5
19:59:01 fstat(5, {st_mode=S_IFREG|0644, st_size=692, ...}) = 0
19:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0)                      = 0x7fd770803000
19:59:01 read(5, "#%PAM-1.0\n# This file is auto-ge"..., 4096) = 692
19:59:01 open("/lib64/security/pam_env.so", O_RDONLY) = 6
19:59:01 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) = 832
19:59:01 fstat(6, {st_mode=S_IFREG|0755, st_size=18592, ...}) = 0
19:59:01 mmap(NULL, 2113776, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 6, 0)                       = 0x7fd7684dc000
19:59:01 mprotect(0x7fd7684e0000, 2093056, PROT_NONE) = 0
19:59:01 mmap(0x7fd7686df000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 6, 0x3000) = 0x7fd7686df000
19:59:01 close(6) = 0
19:59:01 mprotect(0x7fd7686df000, 4096, PROT_READ)                     = 0
19:59:01 open("/lib64/security/pam_deny.so", O_RDONLY) = 6
19:59:01 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) = 832
19:59:01 fstat(6, {st_mode=S_IFREG|0755, st_size=5952, ...}) = 0
19:59:01 mmap(NULL, 2101272, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 6, 0)                       = 0x7fd7682da000
19:59:01 mprotect(0x7fd7682db000, 2093056, PROT_NONE) = 0
19:59:01 mmap(0x7fd7684da000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 6, 0)                      = 0x7fd7684da000
19:59:01 close(6) = 0
19:59:01 mprotect(0x7fd7684da000, 4096, PROT_READ) = 0
19:59:01 read(5, "", 4096) = 0
19:59:01 close(5) = 0
19:59:01 munmap(0x7fd770803000, 4096) = 0
19:59:01 read(3, "", 4096)             = 0
19:59:01 close(3) = 0
19:59:01 munmap(0x7fd770804000, 4096)                      = 0
19:59:01 open("/etc/pam.d/other", O_RDONLY)                      = 3
19:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=154, ...}) = 0
19:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0)   = 0x7fd770804000
19:59:01 read(3, "#%PAM-1.0\nauth     required     "..., 4096) = 154
19:59:01 read(3, "", 4096) = 0
19:59:01 close(3) = 0
19:59:01 munmap(0x7fd770804000, 4096) = 0
19:59:01 open("/etc/passwd", O_RDONLY|O_CLOEXEC)   = 3
19:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=1057, ...}) = 0
19:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd770804000
19:59:01 read(3, "root:x:0:0:root:/root:/bin/bash\n"..., 4096) = 1057
19:59:01 close(3) = 0
19:59:01 munmap(0x7fd770804000, 4096) = 0
19:59:01 uname({sys="Linux", node="host-11-159-73-176", ...}) = 0
19:59:01 open("/etc/security/access.conf", O_RDONLY) = 3
19:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=4620, ...}) = 0
19:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd770804000
19:59:01 read(3, "# Login access control table.\n#\n"..., 4096) = 4096
19:59:01 read(3, " should get access from ipv4 net"..., 4096) = 524
19:59:01 read(3, "", 4096) = 0
19:59:01 close(3) = 0
19:59:01 munmap(0x7fd770804000, 4096) = 0
19:59:01 getuid() = 0
19:59:01 open("/etc/passwd", O_RDONLY|O_CLOEXEC) = 3
19:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=1057, ...}) = 0
19:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0)  = 0x7fd770804000
19:59:01 read(3, "root:x:0:0:root:/root:/bin/bash\n"..., 4096) = 1057
19:59:01 close(3)                       = 0
19:59:01 munmap(0x7fd770804000, 4096) = 0
19:59:01 geteuid() = 0
19:59:01 open("/etc/shadow", O_RDONLY|O_CLOEXEC) = 3
19:59:01 fstat(3, {st_mode=S_IFREG, st_size=901, ...}) = 0
19:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd770804000
19:59:01 read(3, "root:$6$4.53VPrJ$1wxMpbsWYp4VKea"..., 4096) = 901
19:59:01 close(3) = 0
19:59:01 munmap(0x7fd770804000, 4096)                      = 0
19:59:01 socket(PF_NETLINK, SOCK_RAW, 9)                       = 3
19:59:01 fcntl(3, F_SETFD, FD_CLOEXEC)   = 0
19:59:01 readlink("/proc/self/exe", "/usr/sbin/crond", 4096) = 15
19:59:01 sendto(3, "p\0\0\0M\4\5\0\1\0\0\0\0\0\0\0op=PAM:accountin"..., 112, 0, {sa_family=AF_NETLINK, pid=0, groups=00000000}, 12)                      = 112
19:59:01 poll([{fd=3, events=POLLIN}], 1, 500)   = 1 ([{fd=3, revents=POLLIN}])
19:59:01 recvfrom(3, "$\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]) = 36
19:59:01 recvfrom(3, "$\0\0\0\2\0\0\1\1\0\0\0\227\7\0\0\0\0\0\0p\0\0\0M\4\5\0\1\0\0\0"..., 8988, MSG_DONTWAIT, {sa_family=AF_NETLINK, pid=0, groups=00000000}, [12]) = 36
19:59:01 close(3) = 0
19:59:01 open("/etc/security/pam_env.conf", O_RDONLY) = 3
19:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=2980, ...}) = 0
19:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd770804000
19:59:01 read(3, "#\n# This is the configuration fi"..., 4096) = 2980
19:59:01 read(3, "", 4096) = 0
19:59:01 close(3)                      = 0
19:59:01 munmap(0x7fd770804000, 4096)                       = 0
19:59:01 open("/etc/environment", O_RDONLY)   = 3
19:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=0, ...}) = 0
19:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0)               = 0x7fd770804000
19:59:01 read(3, "", 4096) = 0
19:59:01 close(3) = 0
19:59:01 munmap(0x7fd770804000, 4096) = 0
19:59:01 socket(PF_NETLINK, SOCK_RAW, 9) = 3
19:59:01 fcntl(3, F_SETFD, FD_CLOEXEC) = 0
19:59:01 sendto(3, "p\0\0\0O\4\5\0\2\0\0\0\0\0\0\0op=PAM:setcred a"..., 112, 0, {sa_family=AF_NETLINK, pid=0, groups=00000000}, 12)                       = 112
19:59:01 poll([{fd=3, events=POLLIN}], 1, 500)   = 1 ([{fd=3, revents=POLLIN}])
19:59:01 recvfrom(3, "$\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]) = 36
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_DONTWAIT, {sa_family=AF_NETLINK, pid=0, groups=00000000}, [12]) = 36
19:59:01 close(3) = 0
19:59:01 open("/etc/passwd", O_RDONLY|O_CLOEXEC) = 3
19:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=1057, ...}) = 0
19:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd770804000
19:59:01 read(3, "root:x:0:0:root:/root:/bin/bash\n"..., 4096) = 1057
19:59:01 close(3) = 0
19:59:01 munmap(0x7fd770804000, 4096) = 0
19:59:01 open("/proc/self/loginuid", O_WRONLY|O_TRUNC|O_NOFOLLOW)        = 3
19:59:01 write(3, "0", 1) = 1
19:59:01 close(3) = 0
19:59:01 open("/etc/passwd", O_RDONLY|O_CLOEXEC) = 3
19:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=1057, ...}) = 0
19:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd770804000
19:59:01 read(3, "root:x:0:0:root:/root:/bin/bash\n"..., 4096) = 1057
19:59:01 close(3) = 0
19:59:01 munmap(0x7fd770804000, 4096) = 0
19:59:01 getuid() = 0
19:59:01 getgid() = 0
19:59:01 keyctl(0, 0xfffffffd, 0, 0, 0) = 496466385
19:59:01 keyctl(0, 0xfffffffb, 0, 0, 0x30) = 785702132
19:59:01 open("/etc/passwd", O_RDONLY|O_CLOEXEC) = 3
19:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=1057, ...}) = 0
19:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd770804000
19:59:01 read(3, "root:x:0:0:root:/root:/bin/bash\n"..., 4096) = 1057
19:59:01 close(3) = 0
19:59:01 munmap(0x7fd770804000, 4096) = 0
19:59:01 getrlimit(RLIMIT_CPU, {rlim_cur=RLIM_INFINITY, rlim_max=RLIM_INFINITY}) = 0
19:59:01 getrlimit(RLIMIT_FSIZE, {rlim_cur=RLIM_INFINITY, rlim_max=RLIM_INFINITY}) = 0
19:59:01 getrlimit(RLIMIT_DATA, {rlim_cur=RLIM_INFINITY, rlim_max=RLIM_INFINITY}) = 0
19:59:01 getrlimit(RLIMIT_STACK, {rlim_cur=8192*1024, rlim_max=RLIM_INFINITY}) = 0
19:59:01 getrlimit(RLIMIT_CORE, {rlim_cur=RLIM_INFINITY, rlim_max=RLIM_INFINITY}) = 0
19:59:01 getrlimit(RLIMIT_RSS, {rlim_cur=RLIM_INFINITY, rlim_max=RLIM_INFINITY}) = 0
19:59:01 getrlimit(RLIMIT_NPROC, {rlim_cur=RLIM_INFINITY, rlim_max=RLIM_INFINITY}) = 0
19:59:01 getrlimit(RLIMIT_NOFILE, {rlim_cur=1073741816, rlim_max=1073741816}) = 0
19:59:01 getrlimit(RLIMIT_MEMLOCK, {rlim_cur=64*1024, rlim_max=64*1024}) = 0
19:59:01 getrlimit(RLIMIT_AS, {rlim_cur=RLIM_INFINITY, rlim_max=RLIM_INFINITY}) = 0
19:59:01 getrlimit(RLIMIT_LOCKS, {rlim_cur=RLIM_INFINITY, rlim_max=RLIM_INFINITY}) = 0
19:59:01 getrlimit(RLIMIT_SIGPENDING, {rlim_cur=883632, rlim_max=883632}) = 0
19:59:01 getrlimit(RLIMIT_MSGQUEUE, {rlim_cur=800*1024, rlim_max=800*1024}) = 0
19:59:01 getrlimit(RLIMIT_NICE, {rlim_cur=0, rlim_max=0}) = 0
19:59:01 getrlimit(RLIMIT_RTPRIO, {rlim_cur=0, rlim_max=0}) = 0
19:59:01 getpriority(PRIO_PROCESS, 0) = 20
19:59:01 open("/etc/security/limits.conf", O_RDONLY) = 3
19:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=1835, ...}) = 0
19:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd770804000
19:59:01 read(3, "# /etc/security/limits.conf\n#\n#E"..., 4096) = 1835
19:59:01 read(3, "", 4096) = 0
19:59:01 close(3) = 0
19:59:01 munmap(0x7fd770804000, 4096) = 0
19:59:01 open("/etc/security/limits.d", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
19:59:01 getdents(3, /* 3 entries */, 32768) = 88
19:59:01 open("/usr/lib64/gconv/gconv-modules.cache", O_RDONLY)                       = 5
19:59:01 fstat(5, {st_mode=S_IFREG|0644, st_size=26060, ...}) = 0
19:59:01 mmap(NULL, 26060, PROT_READ, MAP_SHARED, 5, 0) = 0x7fd7707f5000
19:59:01 close(5)  = 0
19:59:01 getdents(3, /* 0 entries */, 32768) = 0
19:59:01 close(3) = 0
19:59:01 open("/etc/security/limits.d/90-nproc.conf", O_RDONLY) = 3
19:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=193, ...}) = 0
19:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd770804000
19:59:01 read(3, "# Default limit for number of us"..., 4096) = 193
19:59:01 read(3, "", 4096)              = 0
19:59:01 close(3)                       = 0
19:59:01 munmap(0x7fd770804000, 4096)   = 0
19:59:01 setrlimit(RLIMIT_NPROC, {rlim_cur=RLIM_INFINITY, rlim_max=RLIM_INFINITY}) = 0
19:59:01 setpriority(PRIO_PROCESS, 0, 0) = 0
19:59:01 getuid() = 0
19:59:01 open("/etc/passwd", O_RDONLY|O_CLOEXEC) = 3
19:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=1057, ...}) = 0
19:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd770804000
19:59:01 read(3, "root:x:0:0:root:/root:/bin/bash\n"..., 4096) = 1057
19:59:01 close(3) = 0
19:59:01 munmap(0x7fd770804000, 4096)                     = 0
19:59:01 socket(PF_NETLINK, SOCK_RAW, 9)                      = 3
19:59:01 fcntl(3, F_SETFD, FD_CLOEXEC)                      = 0
19:59:01 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) = 116
19:59:01 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]) = 36
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_DONTWAIT, {sa_family=AF_NETLINK, pid=0, groups=00000000}, [12]) = 36
19:59:01 close(3) = 0
19:59:01 setgid(0) = 0
19:59:01 open("/proc/sys/kernel/ngroups_max", O_RDONLY) = 3
19:59:01 read(3, "65536\n", 31)         = 6
19:59:01 close(3)                       = 0
19:59:01 socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
19:59:01 connect(3, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
19:59:01 close(3) = 0
19:59:01 socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
19:59:01 connect(3, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110)                       = -1 ENOENT (No such file or directory)
19:59:01 close(3) = 0
19:59:01 open("/etc/group", O_RDONLY|O_CLOEXEC) = 3
19:59:01 fstat(3, {st_mode=S_IFREG|0644, st_size=497, ...}) = 0
19:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd770804000
19:59:01 lseek(3, 0, SEEK_CUR) = 0
19:59:01 read(3, "root:x:0:\nbin:x:1:bin,daemon\ndae"..., 4096) = 497
19:59:01 read(3, "", 4096)              = 0
19:59:01 close(3)                       = 0
19:59:01 munmap(0x7fd770804000, 4096)                     = 0
19:59:01 setgroups(1, [0]) = 0
19:59:01 setreuid(0, 4294967295) = 0
19:59:01 rt_sigaction(SIGCHLD, {SIG_DFL, [CHLD], SA_RESTORER|SA_RESTART, 0x7fd76fa316a0}, {0x558826e03b80, [], SA_RESTORER|SA_RESTART, 0x7fd76fa316a0}, 8) = 0
19:59:01 pipe([3, 5])                   = 0
19:59:01 pipe([6, 7])                   = 0
19:59:01 clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fd7707fca70) = 1946
19:59:01 gettid()                     = 1943
19:59:01 open("/proc/self/task/1943/attr/exec", O_RDWR) = 8
19:59:01 write(8, NULL, 0) = -1 EINVAL (Invalid argument)
19:59:01 close(8) = 0
19:59:01 close(3) = 0
19:59:01 close(7) = 0
19:59:01 close(5) = 0
19:59:01 fcntl(6, F_GETFL)                       = 0 (flags O_RDONLY)
19:59:01 fstat(6, {st_mode=S_IFIFO|0600, st_size=0, ...}) = 0
19:59:01 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0)                     = 0x7fd770804000
19:59:01 lseek(6, 0, SEEK_CUR)                     = -1 ESPIPE (Illegal seek)
19:59:01 read(6, "/bin/bash: ./logrotate.sh: \346\262\241\346\234"..., 4096) = 55
19:59:01 uname({sys="Linux", node="host-11-159-73-176", ...}) = 0
19:59:01 getrlimit(RLIMIT_NOFILE, {rlim_cur=1073741816, rlim_max=1073741816}) = 0
19:59:01 mmap(NULL, 4294967296, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd6682da000
19:59:01 --- 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 內(nèi)存，然后就被kill了。

mmap前調(diào)用了getrlimit，和上次MySQL的問題一樣，都是根據(jù)系統(tǒng)資源限制來分配內(nèi)存

為了確定就是cron導致java掛掉的元兇，我們把cron進程手動kill掉，這樣就不會執(zhí)行定時任務(wù)了，這次我們在驗證下Java進程是否會掛掉

果不其然，Java進程并沒有掛掉，看來真的是cron任務(wù)導致的

高版本CentOS是否也會出現(xiàn)類似問題？

按理說oom killer應(yīng)該只kill掉占用內(nèi)存最高的才對，Java進程占用內(nèi)存又不是最高的，高版本的CentOS系統(tǒng)oom killer策略會不會有升級？

Java服務(wù)總在半夜掛，背后的真相竟然是...

讓我們來一起驗證下高版本的CentOS系統(tǒng)是否有這個問題

當前鏡像的CentOS版本是CentOS release 6.6 (Final)，為了驗證高版本的CentOS是否也有類似的問題，我們將增加兩個實驗組，分別升級基礎(chǔ)鏡像至CentOS release 6.10 (Final)和CentOS Linux release 7.9.2009 (Core)，也添加相同的cron任務(wù)

結(jié)果發(fā)現(xiàn)CentOS release 6.10 (Final)和CentOS Linux release 7.9.2009 (Core)都沒有kill掉Java進程，只kill掉了cron的子進程

Java服務(wù)總在半夜掛，背后的真相竟然是...

結(jié)論

Java服務(wù)總在半夜掛，背后的真相竟然是...

由于容器limit open files(系統(tǒng)最大句柄數(shù))設(shè)置不合理導致cron執(zhí)行任務(wù)時使容器內(nèi)存飆升，存在內(nèi)存溢出的風險，linux由于保護機制會kill掉占用內(nèi)存高的進程，導致cron子任務(wù)進程和Java進程一起被kill（但是問題來了，這個jdos基礎(chǔ)鏡像為什么會執(zhí)行一個完全不存在的shell腳本，而且還是執(zhí)行兩次？？？），高版本的CentOS系統(tǒng)不會kill java進程，猜測不同版本的CentOS的kill選擇策略略有不同

問題分析

Cron任務(wù)執(zhí)行邏輯

在Linux中，crontab工具是由croine軟件包提供的，讓我們一起看下cron的執(zhí)行過程

Java服務(wù)總在半夜掛，背后的真相竟然是...

其中child_process（）執(zhí)行了cron子進程，cron執(zhí)行子進程時會有發(fā)送mail的動作

Java服務(wù)總在半夜掛，背后的真相竟然是...

cron_popen在執(zhí)行時會按照open files(系統(tǒng)最大句柄數(shù))清除內(nèi)存

Java服務(wù)總在半夜掛，背后的真相竟然是...

綜上，cron oom的原因找到了，是由于open files設(shè)置過大且cron任務(wù)沒有標準輸出，導致執(zhí)行了發(fā)送mail邏輯，而清除的內(nèi)存大小超出了容器本身內(nèi)存的大小，導致oom。

croine 1.5.4 版本之后修復了該問題，如果想查看當前容器croine版本可執(zhí)行如下命令：

rpm -q cronie

Java服務(wù)總在半夜掛，背后的真相竟然是...

Linux內(nèi)核OOM killer機制

Linux 內(nèi)核有個機制叫OOM killer(Out Of Memory killer)，該機制會監(jiān)控那些占用內(nèi)存過大，尤其是瞬間占用內(nèi)存很快的進程，然后防止內(nèi)存耗盡而自動把該進程殺掉。內(nèi)核檢測到系統(tǒng)內(nèi)存不足、挑選并殺掉某個進程的過程可以參考內(nèi)核源代碼linux/mm/oom_kill.c，當系統(tǒng)內(nèi)存不足的時候，out_of_memory()被觸發(fā)，然后調(diào)用select_bad_process()選擇一個”bad”進程殺掉。

以下是一些主要的進程選擇策略：

內(nèi)存使用情況：OOM Killer首先傾向于選擇占用內(nèi)存最多的進程，因為終止這些進程可以釋放最多的內(nèi)存。
OOM分數(shù)：每個進程都有一個OOM分數(shù)，該分數(shù)是基于其內(nèi)存使用情況和其他因素計算出來的。OOM Killer傾向于終止OOM分數(shù)最高的進程。
進程優(yōu)先級：在選擇要終止的進程時，OOM Killer通常會避免終止對系統(tǒng)至關(guān)重要的系統(tǒng)進程。這些進程通常具有較高的優(yōu)先級，因此它們更不容易成為終止目標。
進程資源需求：OOM Killer還會考慮進程的資源需求。它傾向于終止那些請求較少資源的進程，以最小化影響其他進程的運行。
進程屬性：某些進程可能被標記為不可終止，例如通過設(shè)置/proc/[PID]/oom_score_adj的值來調(diào)整OOM分數(shù)。這些進程通常不容易被OOM Killer終止。

注：不同版本的Linux oom killer機制可能會存在一些差異

解決方案

使用高版本穩(wěn)定的CentOS系統(tǒng)，如果業(yè)務(wù)無法升級CentOS，則需要設(shè)置合理的limit open files數(shù)量，application_worker類型應(yīng)用可以在啟動腳本中手動修改limit，web_tomcat類型應(yīng)用沒法修改啟動腳本，可以選擇kill掉cron進程或刪除系統(tǒng)cron任務(wù)，也可以手動升級cronie的版本至1.5.7-5

寫在后面

open files這個坑很大，栽這個坑兩次了，大家一定要檢查自己服務(wù)對應(yīng)容器的CentOS版本和limit設(shè)置是否合理，本次案例發(fā)生在測試環(huán)境，尚不會引起事故，如果在生產(chǎn)出現(xiàn)類似情況，后果不堪設(shè)想

由于測試環(huán)境新增的這批機器都存在這個問題，我們團隊已經(jīng)聯(lián)系機器提供方上報了該問題，后續(xù)這批機器會由提供方統(tǒng)一修改系統(tǒng)最大句柄數(shù)，如果當前問題影響到了業(yè)務(wù)的正常使用，可以臨時刪除容器中/etc/crontab中的任務(wù)