破除MySQL打开的文件描述符限制-数据库Too many open files问题

由于挖站否免费CN2空间用户增多,近期总是出现半夜Mysql进程挂掉的情况,查询了一下Mysql的错误日志,提示有:[ERROR] Error in accept: Too many open files,原来是因为open files不足导致数据库挂掉了,尤其是晚上DirectAdmin系统备份时更是如此。

Linux系统默认的opens file是1024,可以使用ulimit -a 查看,这个是系统级的限制,另外在mysql中默认的open files也是1024,很多时候这个数值无法满足我们的建站需要,尤其是一个大型的网站和巨大型的数据库中心,很容易就会出现Too many open files问题。

破除MySQL打开的文件描述符限制-解决数据库Too many open files问题

这篇文章就是来分享一下如何解决错误:[ERROR] Error in accept: Too many open files的问题,更多的关于服务器优化以及问题解决方法,参考:

  1. 让图片飞一会儿!网站图片WebP格式批量转换设置及加速效果体验
  2. 巧用又拍云FTP和坚果云WebDAV-打造个人文件备份和数据云存储
  3. VPS主机和服务器安全防护:SSH修改端口,添加白名单,仅限密钥登录

一、数据库问题详情

查看数据库错误日志,如果用的是DirectAdmin面板,相关的日志路径如下:

#DirectAdmin:
/var/log/directadmin/error.log
/var/log/directadmin/errortaskq.log
/var/log/directadmin/system.log
/var/log/directadmin/security.log


#Apache:
/var/log/httpd/error_log
/var/log/httpd/access_log
/var/log/httpd/suexec_log
/var/log/httpd/fpexec_log
/var/log/httpd/domains/domain.com.error.log
/var/log/httpd/domains/domain.com.log
/var/log/messages (generic errors)


#Proftpd:
/var/log/proftpd/access.log
/var/log/proftpd/auth.log
/var/log/messages (generic errors)


#PureFTPd:
/var/log/pureftpd.log


#Dovecot and vm-pop3d:
/var/log/maillog
/var/log/messages


#named (bind):
/var/log/messages


#exim:
/var/log/exim/mainlog
/var/log/exim/paniclog
/var/log/exim/processlog
/var/log/exim/rejectlog

#(on FreeBSD, they have "exim_" in front of the filenames)

#mysqld:
#RedHat:
/var/lib/mysql/server.hostname.com.err

#FreeBSD and Debian:
/usr/local/mysql/data/server.hostname.com.err


#crond:
/var/log/cron


#To view a log file, run:
less /var/log/filename

#Where /var/log/filename is the path of the log you wish to view.  If the log is too large you can use the "tail" command:
tail -n 30 /var/log/filename

#Where 30 is the number of lines from the end you wish to view.

打开Mysql错误日志,一般会提示如下错误:

190902  3:16:52 [ERROR] Error in accept: Too many open files
190902  3:21:08 [ERROR] Error in accept: Too many open files
190902  3:25:24 [ERROR] Error in accept: Too many open files
190902  3:29:40 [ERROR] Error in accept: Too many open files
190902  3:33:56 [ERROR] Error in accept: Too many open files
190902  3:38:12 [ERROR] Error in accept: Too many open files
190902  3:42:28 [ERROR] Error in accept: Too many open files
190902  3:46:44 [ERROR] Error in accept: Too many open files
190902  3:51:00 [ERROR] Error in accept: Too many open files
190902  3:55:16 [ERROR] Error in accept: Too many open files
190902  3:59:32 [ERROR] Error in accept: Too many open files
190902  4:03:48 [ERROR] Error in accept: Too many open files
190902  4:08:04 [ERROR] Error in accept: Too many open files
190902  4:12:20 [ERROR] Error in accept: Too many open files
190902  4:16:37 [ERROR] Error in accept: Too many open files
190902  4:20:53 [ERROR] Error in accept: Too many open files
190902  4:25:09 [ERROR] Error in accept: Too many open files
190902  4:29:25 [ERROR] Error in accept: Too many open files
190902  4:33:41 [ERROR] Error in accept: Too many open files
190902  4:37:57 [ERROR] Error in accept: Too many open files
190902  4:42:13 [ERROR] Error in accept: Too many open files
190902  4:46:29 [ERROR] Error in accept: Too many open files
190902  4:50:45 [ERROR] Error in accept: Too many open files

二、数据库问题分析

2.1 查看限制

使用命令:ulimit -a可以查看到本机的open_files_limit:

[root@sc3 ~]# ulimit -a
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 15675
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
open files                      (-n) 1024
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 15675
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

或者使用以下命令仅查看某一项进程的open_files_limit:

#直接查看 open files限制数字
ulimit -n

#仅查看soft 和 hard open files limits :
ulimit -Hn
ulimit -Sn

#仅查看Mysql的open files limits:

su mysql ulimit -a

2.2 修改limits.conf

方法一:

你可以使用以下命令来修改/etc/security/limits.conf文件,命令如下:

#To set the ceiling of the limits available (the max a soft or hard limit can be set by each user).
#NOTE: this is set by a PAM during authentication, and NOT at boot. 
#编辑文件

vi /etc/security/limits.conf

#Add the following to bottom of file to set for everything *:
#添加以下谷贱伤农

* soft nofile 1024000
* hard nofile 1024000
* soft nproc 10240
* hard nproc 10240

#To set only a specific user, like mysql then put in:
#或者指定Mysql

mysql hard nofile 1024000
mysql soft nofile 1024000

#Repeat for /etc/security/limits.d/90-nproc.conf
#同样对90-nproc.conf也是一样的操作

vi /etc/security/limits.d/90-nproc.conf

#Add the following:

* soft nofile 1024000
* hard nofile 1024000
* soft nproc 10240
* hard nproc 10240

#root soft nproc unlimited
#I selected '1024000', which is fairly high; you can surely set this lower to something like '102400',请根据自己的实际情况来设定数字

或者使用root账号登录,然后使用以下命令临时修改/etc/security/limits.conf:

ulimit -Hn 1024000


#Edit /etc/init.d/mysqld and add this to the top, after #!/bin/sh
#或者编辑修改/etc/init.d/mysqld,加入以下代码:
ulimit -HSn 1024
ulimit -HSn 32768
ulimit -HSn 1024000

方法二:

打开vi /etc/security/limits.conf文件,在文件里添加一行:* - nofile 32768,这样就把open files调整到了32768

数据库Too many open files修改配置

2.3 修改my.cnf文件

编辑:vi /etc/my.cnf,添加以下代码在 [mysqld]下方:

[mysqld]
open_files_limit = 1024000

然后重启Mysql,如下:

/etc/init.d/mysqld restart
#或者
service mysqld restart

2.4 查看是否生效

执行以下命令:

mysql -u root -p 
show global variables like 'open%';
#如果是DirectAdmin面板
mysql -u da_admin -p 
show global variables like 'open%';

可以查看到open_files_limit已经修改成功了:

数据库Too many open files修改成功

三、重启后失效问题

如果你发现系统重启后open files又恢复到了1024,按照以下命令修改配置 :

#One fix: simply restart mysqld after the system boots up.
#最简单的方法再次重启Mysql

service mysqld restart

#另一种方法
#Another fix is to set these values at boot time before everything else (permanent):
vi /etc/init.d/mysqld

#Add the following:
#添加以下内容:
ulimit -S -n ${DAEMON_FILES_LIMIT:-102400} >/dev/null 2>&1

#然后在 /etc/my.cnf 中添加以下内容:
[myqld_safe]
open_files_limit = 102400
#或者是
[myqld]
open_files_limit = 102400

四、总结

MySQL打开的文件描述符限制都是Linux操作系统的文件描述符限制,即默认为1024,和Mysql配置文件中open_files_limit的设置没有关系。所以要想修改open_files_limit,必须先修改操作系统的open_files_limit。

当然,如果你不想修改系统设置,也可以使用root帐号,运行mysqld_safe脚本启动MySQL(或者使用mysql.server启动),加上命令:–open-files-limit是可以成功设置的,因为mysqld_safe启动MySQL时,其实是在启动mysqld程序之前,调用了ulimit -n $open_files来实现文件描述符的限制。

./mysqld_safe --open-files-limit=25000 &
root@(none) 02:50:54>show variables like "%open_files_limit%";
+------------------+-------+
| Variable_name    | Value |
+------------------+-------+
| open_files_limit | 25000 |
+------------------+-------+

文章出自:挖站否 https://wzfou.com/mysql-too-files/,版权所有。本站文章除注明出处外,皆为作者原创文章,可自由引用,但请注明来源。部分内容参考自:orczhouduntuk


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Avatar for Qi
关于站长(Qi),2008年开始混迹于免费资源圈中,有幸结识了不少的草根站长。之后自己摸爬滚打潜心学习Web服务器、VPS、域名等,兴趣广泛,杂而不精,但愿将自己经验与心得分享出来与大家共勉。
已有 6 条评论
  1. Avatar for C C

    优化方法:1.使用SSD硬盘,加快读写速度。2.优化网站程序,减少查询写入次数和资源占用。

    1月25日 16:36 回复
  2. Avatar for aaa123 aaa123

    哈哈。我之前也遇到过这样的情况。不过现在新系统默认就很大了。

    2019年12月23日 11:02 回复
    • Avatar for Qi Qi

      是的,用户一多负载就开始大,还是得提高性能。

      2019年12月23日 12:54 回复
  3. Avatar for No No

    优化还是要看服务器性能

    2019年12月21日 18:53 回复
  4. Avatar for Nie Nie

    免费空间还是挺稳定的。

    2019年12月21日 12:15 回复
  5. 沙发。[鼓掌]

    2019年12月21日 11:11 回复

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