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:
cat /proc/sys/fs/file-max -- 显示单个登陆会话允许打开的 fd 数目Output:
7500075000 files normal user can have open in single login session . To see the hard and soft values, issue the command as follows:
# ulimit -Hn
# ulimit -SnTo 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。
# su - usernameIn this example, su to oracle user, enter:
# 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。
# 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。
# vi /etc/sysctl.confAppend a config directive as follows:
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:
# sysctl -p -- 不用重启系统令修改生效的方法Verify your settings with command:
# cat /proc/sys/fs/file-maxOR
# 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。
# vi /etc/security/limits.confSet httpd user soft and hard limits as follows:
httpd soft nofile 4096 -- 针对 httpd 用户做 fd 限制
httpd hard nofile 10240Save and close the file. To see limits, enter:
# su - httpd
$ ulimit -Hn
$ ulimit -Sn
来源：oschina
链接：https://my.oschina.net/u/617889/blog/199596