关于file-max和file-nr

     2012年11月10日       teddy.sun       运维笔记->系统管理       sysctl file-max file-nr 

Linux的/proc/sys/fs/file-max决定了当前内核可以打开的最大的文件句柄数。
查看当前的值:
cat /proc/sys/fs/file-max
这个值在kernel的文档里是这样描述的:
The value  in  file-max  denotes  the  maximum number of file handles that the
Linux kernel will allocate. When you get a lot of error messages about running
out of  file handles, you might want to raise this limit. The default value is
10% of  RAM in kilobytes.  To  change it, just  write the new number  into the
file:
意思是file-max一般为内存大小(KB)的10%来计算,如果使用shell,可以这样计算:
grep -r MemTotal /proc/meminfo | awk '{printf("%d",$2/10)}'
一般我们不需要主动设置这个值,除非这个值确实较小(可能有各种其他原因导致file-max没有设置为内存的10%)
如何查看当前kernel的句柄;
cat /proc/sys/fs/file-nr
file-nr在内核文档里得解释如下:
Historically, the three values in file-nr denoted the number of allocated file
handles,  the number of  allocated but  unused file  handles, and  the maximum
number of file handles. Linux 2.6 always  reports 0 as the number of free file
handles -- this  is not an error,  it just means that the  number of allocated
file handles exactly matches the number of used file handles.