高并发下linux ulimit优化

水深无声 2022-08-12 16:20 188阅读 0赞

系统性能一直是一个受关注的话题，如何通过最简单的设置来实现最有效的性能调优，如何在有限资源的条件下保证程序的运作，ulimit 是我们在处理这些问题时，经常使用的一种简单手段。ulimit 是一种 linux 系统的内键功能，它具有一套参数集，用于为由它生成的 shell 进程及其子进程的资源使用设置限制。

ulimit 用于限制 shell 启动进程所占用的资源，支持以下各种类型的限制：所创建的内核文件的大小、进程数据块的大小、Shell 进程创建文件的大小、内存锁住的大小、常驻内存集的大小、打开文件描述符的数量、分配堆栈的最大大小、CPU 时间、单个用户的最大线程数、Shell 进程所能使用的最大虚拟内存。同时，它支持硬资源和软资源的限制。  
**ulimit 指令参数**：

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      <code style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; background:none!important">选项 [options]&nbsp;&nbsp;&nbsp; 含义&nbsp; </code> 
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      <code style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; background:none!important">-H&nbsp;&nbsp; 设置硬资源限制，一旦设置不能增加。&nbsp; </code> 
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      <code style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; background:none!important">-a&nbsp;&nbsp; 显示当前所有的 limit 信息。&nbsp;&nbsp; </code> 
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     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; white-space:pre!important"> 
      <code style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; background:none!important">-c&nbsp;&nbsp; 最大的 core 文件的大小， 以 blocks 为单位。&nbsp; </code> 
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      <code style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; background:none!important">-d&nbsp;&nbsp; 进程最大的数据段的大小，以 Kbytes 为单位。&nbsp; </code> 
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      <code style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; background:none!important">-f&nbsp;&nbsp; 进程可以创建文件的最大值，以 blocks 为单位。</code> 
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     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; white-space:pre!important"> 
      <code style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; background:none!important">-l&nbsp;&nbsp; 最大可加锁内存大小，以 Kbytes 为单位。&nbsp;&nbsp;&nbsp; </code> 
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     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; white-space:pre!important"> 
      <code style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; background:none!important">-m&nbsp;&nbsp; 最大内存大小，以 Kbytes 为单位。</code> 
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     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; white-space:pre!important"> 
      <code style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; background:none!important">-n&nbsp;&nbsp; Linux操作系统对一个进程可以打开最大文件描述符的数量。&nbsp; </code> 
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     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; white-space:pre!important"> 
      <code style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; background:none!important">-p&nbsp;&nbsp; 管道缓冲区的大小，以 Kbytes 为单位。&nbsp; </code> 
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      <code style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; background:none!important">-s&nbsp;&nbsp; 线程栈大小，以 Kbytes 为单位。&nbsp;&nbsp;&nbsp; </code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; white-space:pre!important"> 
      <code style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; background:none!important">-t&nbsp;&nbsp; 最大的 CPU 占用时间，以秒为单位。&nbsp;&nbsp;&nbsp;&nbsp; </code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; white-space:pre!important"> 
      <code style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; background:none!important">-u&nbsp;&nbsp; 用户最大可用的进程数。&nbsp;&nbsp;&nbsp; </code> 
     </div> 
     <div style="margin:0px!important; padding:0px 1em!important; border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:inherit!important; white-space:pre!important"> 
      <code style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; font-size:1em!important; min-height:inherit!important; background:none!important">-v&nbsp;&nbsp; 进程最大可用的虚拟内存，以 Kbytes 为单位。</code> 
     </div> 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

在我的centos 6.3 32位系统输入 ulimit -a 结果如下

[![ulimit-n][]][ulimit-n]

这边重点描述下红色部分  
**ulimit -n**

问题： Can’t open so many files 对于linux运维的同学们，相信都遇到过这个问题。  
在Linux下一切资源皆文件，普通文件是文件，磁盘打印机是文件，socket 当然也是文件。系统默认设置成1024，但是这个数字对于服务器特别是大并发的远远是不够的，所以，我们需要结合实际情况修改成一个更大更合理的值。

**修改方法**

vim /etc/security/limits.conf

保存，然后重启  
注：65536 是我这边的设定值，读者也可以自行设置一个合适的值，\* 代表针对所有用户  
同时还有个要注意的值 file-max 是设置 系统所有进程一共可以打开的文件数量 ,可以通过如下方法进行修改  
echo 6553560 > /proc/sys/fs/file-max  
或修改 /etc/sysctl.conf, 加入  
fs.file-max = 6553560 重启生效

另外还有一个，/proc/sys/fs/file-nr，可以看到整个系统目前使用的文件句柄数量

**ulimit -u**  
比如我们在模拟大规模http并发测试的时候，客户端会报一个无法fork new proc异常，原因是受到了最大进程1024的限制  
解除 Linux 系统的最大进程数  
方法如下  
vim /etc/security/limits.d/90-nproc.conf

转自：https://gitsea.com/2013/05/23/linux-ulimit%E8%AF%A6%E8%A7%A3/

\----好一个无聊的分割线----

tomcat优化：http://feihan21.blog.51cto.com/1364153/1320295

[ulimit-n]: https://gitsea.com/wp-content/uploads/2013/05/ulimit-n.jpg