“OS has enough file descriptors”代表什么？

qiaoruzhi78

Security.maxConnections
The security.maxConnections directive gets set to the
maximum number of socket connections that Apache JServ is to be permitted to
handle simultaneously. When making alterations to this directive, you need to be
sure that the OS has enough file descriptors to allow for the number to which
this gets set. It defaults to 50 and this should be enough to handle most
configurations. security.maxConnections=50

在设定Jserv.properties 参数文件时，遇到这个描述，现在问题有二个：
1）不懂“OS has enough file descriptors”是代表什么意思？
2）怎么确认OS的 file descriptors是多少？

请各位帮忙！多谢！