61.12. [Warning] Changed limits: max_open_files: 5000 (requested 20480)

提出出现在 CentOS 7 ulimit 配置没有问题的情况下mysql日志提示 Warning

# ulimit -Sa | grep "open files"
open files                      (-n) 40960		
		

[root@netkiller ~]# cat /proc/`pidof mysqld`/limits
Limit                     Soft Limit           Hard Limit           Units     
Max cpu time              unlimited            unlimited            seconds   
Max file size             unlimited            unlimited            bytes     
Max data size             unlimited            unlimited            bytes     
Max stack size            8388608              unlimited            bytes     
Max core file size        0                    unlimited            bytes     
Max resident set          unlimited            unlimited            bytes     
Max processes             63494                63494                processes 
Max open files            5000                 5000                 files     
Max locked memory         65536                65536                bytes     
Max address space         unlimited            unlimited            bytes     
Max file locks            unlimited            unlimited            locks     
Max pending signals       63494                63494                signals   
Max msgqueue size         819200               819200               bytes     
Max nice priority         0                    0                    
Max realtime priority     0                    0                    
Max realtime timeout      unlimited            unlimited            us        
		
		

[root@netkiller ~]# egrep '^(Limit|Max open files)' /proc/`pidof mysqld`/limits
Limit                     Soft Limit           Hard Limit           Units     
Max open files            5000                 5000                 files  
		

问题的出现出现原因是systemctl启动脚本覆盖了ulimit配置

# cat /usr/lib/systemd/system/mysqld.service | grep -A2 open_files_limit
# Sets open_files_limit
LimitNOFILE = 5000
		

解决方法，直接修改上面的数值，不建议修改mysqld.service，这样会影响你下次升级。请采用下面的方案完美解决：

		
mkdir /usr/lib/systemd/system/mysqld.service.d

cat >> /usr/lib/systemd/system/mysqld.service.d/override.conf <<EOF
[Service]
LimitNOFILE=40960
EOF
		
		

systemctl daemon-reload
systemctl restart mysqld
		

原文出处：Netkiller 系列 手札
本文作者：陈景峯
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