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本教程操作环境：linux7.3系统、docker19.03版、Dell G3电脑。
docker start起不来怎么办？
Docker无法正常启动的原因及解决办法
概述
Docker启动异常表现
状态反复restaring，用命令查看
$docker ps -aCONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES21c09be88c11 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
Docker日志有明显问题：
$docker logs [容器名/容器ID]比如：docker logs openresty
Docker启动异常的可能原因
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 availableMem: 15G 14G 627M 195M 636M 726MSwap: 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.logJava 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.logJava 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/messagesApr 7 10:04:02 centos106 kernel: Out of memory: Kill process 1192 (java) score 54 or sacrifice childApr 7 10:08:00 centos106 kernel: Out of memory: Kill process 2301 (java) score 54 or sacrifice childApr 7 10:09:59 centos106 kernel: Out of memory: Kill process 28145 (java) score 52 or sacrifice childApr 7 10:20:40 centos106 kernel: Out of memory: Kill process 2976 (java) score 54 or sacrifice childApr 7 10:21:08 centos106 kernel: Out of memory: Kill process 3577 (java) score 47 or sacrifice childApr 7 10:21:08 centos106 kernel: Out of memory: Kill process 3631 (java) score 47 or sacrifice childApr 7 10:21:08 centos106 kernel: Out of memory: Kill process 3634 (java) score 47 or sacrifice childApr 7 10:21:08 centos106 kernel: Out of memory: Kill process 3640 (java) score 47 or sacrifice childApr 7 10:21:08 centos106 kernel: Out of memory: Kill process 3654 (java) score 47 or sacrifice childApr 7 10:27:27 centos106 kernel: Out of memory: Kill process 6998 (java) score 51 or sacrifice childApr 7 10:27:28 centos106 kernel: Out of memory: Kill process 7027 (java) score 52 or sacrifice childApr 7 10:28:10 centos106 kernel: Out of memory: Kill process 7571 (java) score 42 or sacrifice childApr 7 10:28:10 centos106 kernel: Out of memory: Kill process 7586 (java) score 42 or sacrifice child
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]
解决方案
内存不够的方案
进程在运行一段时间后占用大量内存，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；
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；
释放被占用的内存（buff/cache）
[root]# sync #将内存数据写入磁盘 [root]# echo 3 > /proc/sys/vm/drop_caches #释放被占用的内存
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。
端口冲突的对策
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]
推荐学习：《docker视频教程》
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