2018-01-08T01:34:44.515973Z 0 [Warning] Changed limits: max_open_files: 5000 (requested 10240)
2018-01-08T01:34:44.516402Z 0 [Warning] Changed limits: table_open_cache: 1471 (requested 2000)		
		
		

提出出現在 CentOS 7 ulimit 配置沒有問題的情況下mysql日誌提示 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        
		
		

動態改變

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

問題的出現出現原因是systemctl啟動腳本覆蓋了ulimit配置

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

解決方法，直接修改上面的數值，不建議修改mysqld.service，這樣會影響你下次升級。請採用下面的方案完美解決：

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

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

重啟 MySQL

systemctl daemon-reload
systemctl restart mysqld
		

檢查是否生效

		
mysql> show variables like 'open_files_limit';
+------------------+-------+
| Variable_name    | Value |
+------------------+-------+
| open_files_limit | 65535 |
+------------------+-------+
1 row in set (0.01 sec)