【原创】如何在 Linux 下调整可打开文件/文件描述符数目

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【原创】如何在 Linux 下调整可打开文件/文件描述符数目

摩云飞 2016-05-11 14:26:13 浏览2014
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How do I increase the maximum number of open files under CentOS Linux? How do I open more file descriptors under Linux? 

The ulimit command provides control over the resources available to the shell and/or to processes started by it, on systems that allow such control. The maximum number of open file descriptors displayed with following command (login as the root user). 
ulimit 命令提供了针对 shell  和/或由该 shell 启动的进程占用资源的控制。 

Command To List Number Of Open File Descriptors 

Use the following command to display maximum number of open file descriptors: 
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cat /proc/sys/fs/file-max    -- 显示单个登陆会话允许打开的 fd 数目
Output: 
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75000
75000 files normal user can have open in single login session . To see the hard and soft values, issue the command as follows: 
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# ulimit -Hn
# ulimit -Sn
To see the hard and soft values for httpd or oracle user, issue the command as follows: 
通过切换登陆用户,可以查看针对特定登陆用户所设置的 fd 限制数目。 
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# su - username
In this example, su to oracle user, enter: 
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# su - oracle
$ ulimit -Hn
$ ulimit -Sn

System-wide File Descriptors (FD) Limits 

The number of concurrently open file descriptors throughout the system can be changed via /etc/sysctl.conf file under Linux operating systems. 
系统范围级别的 fd 数量控制需要编辑 /etc/sysctl.conf 内核参数配置文件。 

The Number Of Maximum Files Was Reached, How Do I Fix This Problem? 

Many application such as Oracle database or Apache web server needs this range quite higher. So you can increase the maximum number of open files by setting a new value in kernel variable /proc/sys/fs/file-max as follows (login as the root): 
通过调整内核参数  /proc/sys/fs/file-max 来增加可打开 fd 数目。 
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# sysctl -w fs.file-max=100000   -- 这种方式只能临时修改 fd 数目限制
Above command forces the limit to 100000 files. You need to edit /etc/sysctl.conf file and put following line so that after reboot the setting will remain as it is: 
通过修改 /etc/sysctl.conf 文件,可以在令针对 fd 的修改一直生效。 
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# vi /etc/sysctl.conf
Append a config directive as follows: 
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fs.file-max = 100000  -- 系统范围内修改 fd 数目
Save and close the file. Users need to log out and log back in again to changes take effect or just type the following command: 
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# sysctl -p   -- 不用重启系统令修改生效的方法
Verify your settings with command: 
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# cat /proc/sys/fs/file-max
OR 
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# sysctl fs.file-max

User Level FD Limits 

The above procedure sets system-wide file descriptors (FD) limits. However, you can limit httpd (or any other users) user to specific limits by editing /etc/security/limits.conf file, enter: 
通过修改 /etc/security/limits.conf 文件可以在用户级别对 fd 进行限制。 
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# vi /etc/security/limits.conf
Set httpd user soft and hard limits as follows: 
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httpd soft nofile 4096   -- 针对 httpd 用户做 fd 限制
httpd hard nofile 10240
Save and close the file. To see limits, enter: 
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# su - httpd
$ ulimit -Hn
$ ulimit -Sn

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