Linux下Tomcat VM參数改动

不可行的方法

最初我直接改动catalina.sh, 将JAVA_OPTS变量加上了

-server -Xms1G -Xmx1G -XX:+UserG1GC

最初看起来没啥问题，可是当服务器运行几天后，发现运行shutdown.sh无法关闭tomcat， 错误信息例如以下：

# root@iZ94hjppdqzZ:~/projects/taolijie# cat hs_err_pid5519.log 
# There is insufficient memory for the Java Runtime Environment to continue.
# Native memory allocation (mmap) failed to map 1073741824 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:2673), pid=5519, tid=3061726064
#
# JRE version:  (8.0_45-b14) (build )
# Java VM: Java HotSpot(TM) Server VM (25.45-b02 mixed mode linux-x86 )
# Failed to write core dump. Core dumps have been disabled. To enable core dumping, try "ulimit -c unlimited" before starting Java again
#

关闭个tomcat要请求1G的内存， 当时服务器就剩下200M内存，所以Out Of Memory了。查看shutdown.sh，发现它事实上还是调用了catalina.sh，仅仅是传入了一个stop參数。而catalina.sh是运行了

org.apache.catalina.startup.Bootstrap stop

来向tomcat发送关闭信息的。因为上面我们设置了JAVA_OPTS使用1G的堆。因此运行该类时JVM会向系统申请1G多的内存，直接导致Out Of Memory。

可行的方法

在catalina.sh的第二行加入：

CATALINA_OPTS="$CATALINA_OPTS -server -Xms1G -Xmx1G -XX:+UseG1GC"

这些VM參数就会仅仅应用到catalina而不是全部Tomcat进程。