详解Docker无法正常启动的原因及解决办法

一、Docker启动异常表现：

1.状态反复restaring，用命令查看

$docker ps -a
CONTAINER ID  IMAGE COMMAND    CREATED   STATUS    PORTS  NAMES
21c09be88c11   docker.xxxx.cn:5000/xxx-tes/xxx_tes:1.0.6  "/usr/local/tomcat..."  9 days ago     Restarting (1) Less than a second ago           xxx10

2.Docker日志有明显问题：

$docker logs [容器名/容器ID]

二、Docker启动异常的可能原因：

2.1.内存不够

Docker 启动至少需要2G内存，首先执行free -mh命令查看剩余内存是否足够

直接查看内存

$free -mh
      total    used    free   shared buff/cache  available
Mem:     15G     14G     627M    195M    636M   726M
Swap:     0B     0B     0B

分析日志

有时候一瞬间内存过载溢出，导致部分进程被杀死，看起来内存也是够用的，事实上docker还是会反复重启，就需要通过docker日志和系统日志信的息来进一步分析：

分析docker日志

查看docker日志看到内存溢出的信息，要仔细翻阅才能找到信息，并不是在最下面

$docker logs [容器名/容器ID]|less 
Java HotSpot(TM) 64-Bit Server VM warning: INFO: os::commit_memory(0x0000000769990000, 1449590784, 0) failed; error='Cannot allocate memory' (errno=12)
#
# There is insufficient memory for the Java Runtime Environment to continue.
# Native memory allocation (malloc) failed to allocate 1449590784 bytes for committing reserved memory.
# An error report file with more information is saved as:
# //hs_err_pid1.log
Java HotSpot(TM) 64-Bit Server VM warning: INFO: os::commit_memory(0x0000000769990000, 1449590784, 0) failed; error='Cannot allocate memory' (errno=12)
#
# There is insufficient memory for the Java Runtime Environment to continue.
# Native memory allocation (malloc) failed to allocate 1449590784 bytes for committing reserved memory.
# An error report file with more information is saved as:
# /tmp/hs_err_pid1.log
Java HotSpot(TM) 64-Bit Server VM warning: INFO: os::commit_memory(0x0000000769990000, 1449590784, 0) failed; error='Cannot allocate memory' (errno=12)
#
# There is insufficient memory for the Java Runtime Environment to continue.
# Native memory allocation (malloc) failed to allocate 1449590784 bytes for committing reserved memory.
# Can not save log file, dump to screen..
#
# There is insufficient memory for the Java Runtime Environment to continue.
# Native memory allocation (malloc) failed to allocate 1449590784 bytes for committing reserved memory.
# Possible reasons:
#  The system is out of physical RAM or swap space
#  In 32 bit mode, the process size limit was hit
# Possible solutions:
#  Reduce memory load on the system
#  Increase physical memory or swap space
#  Check if swap backing store is full
#  Use 64 bit Java on a 64 bit OS
#  Decrease Java heap size (-Xmx/-Xms)
#  Decrease number of Java threads
#  Decrease Java thread stack sizes (-Xss)
#  Set larger code cache with -XX:ReservedCodeCacheSize=
# This output file may be truncated or incomplete.
#
# Out of Memory Error (os_linux.cpp:2756), pid=1, tid=140325689620224
#
# JRE version: (7.0_79-b15) (build )
# Java VM: Java HotSpot(TM) 64-Bit Server VM (24.79-b02 mixed mode linux-amd64 compressed oops)
# Core dump written. Default location: //core or core.1
#

分析系统日志

查看系统日志，发现有大量由于内存溢出，进程被杀死的记录

$grep -i 'Out of Memory' /var/log/messages
Apr 7 10:04:02 centos106 kernel: Out of memory: Kill process 1192 (java) score 54 or sacrifice child
Apr 7 10:08:00 centos106 kernel: Out of memory: Kill process 2301 (java) score 54 or sacrifice child
Apr 7 10:09:59 centos106 kernel: Out of memory: Kill process 28145 (java) score 52 or sacrifice child
Apr 7 10:20:40 centos106 kernel: Out of memory: Kill process 2976 (java) score 54 or sacrifice child
Apr 7 10:21:08 centos106 kernel: Out of memory: Kill process 3577 (java) score 47 or sacrifice child
Apr 7 10:21:08 centos106 kernel: Out of memory: Kill process 3631 (java) score 47 or sacrifice child
Apr 7 10:21:08 centos106 kernel: Out of memory: Kill process 3634 (java) score 47 or sacrifice child
Apr 7 10:21:08 centos106 kernel: Out of memory: Kill process 3640 (java) score 47 or sacrifice child
Apr 7 10:21:08 centos106 kernel: Out of memory: Kill process 3654 (java) score 47 or sacrifice child
Apr 7 10:27:27 centos106 kernel: Out of memory: Kill process 6998 (java) score 51 or sacrifice child
Apr 7 10:27:28 centos106 kernel: Out of memory: Kill process 7027 (java) score 52 or sacrifice child
Apr 7 10:28:10 centos106 kernel: Out of memory: Kill process 7571 (java) score 42 or sacrifice child
Apr 7 10:28:10 centos106 kernel: Out of memory: Kill process 7586 (java) score 42 or sacrifice child

2.2.端口冲突

该docker监听端口已经被其他进程占用，一般此种问题容易出现在新部署的服务，或在原有机器上部署新的后台服务，所以在部署之前应该执行命令检查端口是否已经被占用，如果上线后发现占有则应改为可用端口再重启之。

检查命令：    $netstat -nltp|grep [规划的端口号]

三、对策

3.1.内存不够的对策：

对策1:
    3.1.1 saltstack的minion在运行过久之后，可能占用大量内存，需要将其重启。重启命令可能有时并不起作用。主要检查运行状态，如果未成功停止，则重新重启；

对策2:
    3.2.2 ELK日志收集程序或者其他java进程占用过高，用top和ps命令排查，谨慎确定进程的作用，在确保不影响业务的情况下，停止相关进程；

对策3:
   释放被占用的内存（buff/cache）：
   $sync  #将内存数据写入磁盘
   $echo 3 > /proc/sys/vm/drop_caches  #释放被占用的内存

对策4:
    有时候并不是buff/cache过高导致内存不够用，确实是被很多必要的进程消耗掉了内存，那就需要从机器资源分配使用的层面去考虑和解决了。

3.2 端口冲突的对策

对策1:
 一般此种问题容易出现在新部署的服务，或在原有机器上部署新的后台服务，所以在部署之前应该执行命令检查端口是否已经被占用，如果上线后发现占有则应改为可用端口再重启之。
检查命令：    $netstat -nltp|grep [规划的端口号]

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