不可行的方法

最初我直接修改catalina.sh, 將JAVA_OPTS變數加上了

-server -Xms1G -Xmx1G -XX:+UserG1GC

最初看起來沒啥問題，但是當伺服器執行幾天後，發現執行shutdown.sh無法關閉tomcat， 錯誤資訊如下：

# [email protected]:~/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
#

關閉個tomcat要請求1G的記憶體， 當時伺服器就剩下200M記憶體，所以Out Of Memory了。檢視shutdown.sh，發現它其實還是呼叫了catalina.sh，只是傳入了一個stop引數。而catalina.sh是執行了

org.apache.catalina.startup.Bootstrap stop

來向tomcat傳送關閉資訊的。由於上面我們設定了JAVA_OPTS使用1G的堆，因此執行該類時JVM會向系統申請1G多的記憶體，直接導致Out Of Memory。

可行的方法

在catalina.sh的第二行新增：

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

這些VM引數就會只應用到catalina而不是所有Tomcat程序。