NFS mount failed server Permission denied解决方法
在linux中，在一台IP为192.168.65.215的服务器上挂载nfs服务器的目录时报permission denied错。
错误信息如下所示：
- [root@webdg1 ~]# mount -t nfs 192.168.15.56:/u02 /u02
- mount: 192.168.15.56:/u02 failed, reason given by server: Permission denied
第一反应是nfs server的权限没配对或可能没授权此IP接入。但是去检查nfs server上配置情况是对15网段都是授权了的。
- [root@htwebapp1 ~]# more /etc/exports
- /u02 192.168.15.*(rw)
这种配置是根据经验和网上很多文档介绍的案例来写的，并且一直以来都是运行都是正确的。这里也不是所有的15网段的服务器都不能挂载这个目录的。在本环境中，一个15网段的服务器就能挂载这个nfs服务器的目录。
(miki西游 @mikixiyou 原文链接: http://mikixiyou.iteye.com/blog/1731208 )
两者的区别在于出问题的服务器的网卡是双IP配置，而正常的服务器是单个IP配置。
那么，问题就可能是一个网卡多个IP导致的。
如果在nfs服务器上/etc/exports中，将需要挂载的服务器IP地址写死，如下所示：
[root@htwebapp1 ~]# more /etc/exports
/u02 192.168.15.215(rw)
这样就可以在215上挂载nfs服务器的u02目录了。
但需要挂载该目录的服务器有很多，是不能一一列出的。
因此这个方法不适用。
在nfs服务器上的/etc/hosts下也有挂载服务器15.215的主机名IP解析，根据网络上建议，将此条目注释掉，也能挂载。
这是另一种解决方法，但nfs服务器上hosts中是必须配置这个主机名IP解析条目的，此服务器上还有其他应用需要用到它。
因此，这个方法也不能采纳。
分析
我们猜测可能是NFS SERVER在 client请求挂载时解析 /etc/exports 时出错了。
我们并不很清楚NFS的原理，也没有能力去看它的源代码。但有一点，我们可以去看一下exports的帮助。
使用man exports一下，得到结果如下：
- EXPORTS(5) Linux File Formats Manual EXPORTS(5)
- NAME
- exports - NFS file systems being exported (for Kernel based NFS)
- SYNOPSIS
- /etc/exports
- DESCRIPTION
- The file /etc/exports serves as the access control list for file systems which may be exported to NFS
- clients. It is used by exportfs(8) to give information to mountd(8) and to the kernel based NFS file
- server daemon nfsd(8).
- The file format is similar to the SunOS exports file. Each line contains an export point and a whitespace-
- separated list of clients allowed to mount the file system at that point. Each listed client may be imme-
- diately followed by a parenthesized, comma-separated list of export options for that client. No whitespace
- is permitted between a client and its option list.
- Blank lines are ignored. A pound sign ("#") introduces a comment to the end of the line. Entries may be
- continued across newlines using a backslash. If an export name contains spaces it should be quoted using
- double quotes. You can also specify spaces or other unusual character in the export name using a backslash
- followed by the character code as three octal digits.
- Machine Name Formats
- NFS clients may be specified in a number of ways:
- single host
- This is the most common format. You may specify a host either by an abbreviated name recognized be
- the resolver, the fully qualified domain name, or an IP address.
- netgroups
- NIS netgroups may be given as @group. Only the host part of each netgroup members is consider in
- checking for membership. Empty host parts or those containing a single dash (-) are ignored.
- wildcards
- Machine names may contain the wildcard characters * and ?. This can be used to make the exports
- file more compact; for instance, *.cs.foo.edu matches all hosts in the domain cs.foo.edu. As these
- characters also match the dots in a domain name, the given pattern will also match all hosts within
- any subdomain of cs.foo.edu.
- IP networks
- You can also export directories to all hosts on an IP (sub-) network simultaneously. This is done
- by specifying an IP address and netmask pair as address/netmask where the netmask can be specified
- in dotted-decimal format, or as a contiguous mask length (for example, either ??/255.255.252.0?ˉ or
- ??/22?ˉ appended to the network base address result in identical subnetworks with 10 bits of host).
- Wildcard characters generally do not work on IP addresses, though they may work by accident when
- reverse DNS lookups fail.
从帮助文档中看，机器名称格式只有四种，我们使用192.168.15.*(rw)中"*"做通配符，是第一种"single host"用法。
但它没有说可以使用"*"，只是我们根据习惯和网上得到经验配置出来的。
这种需要给多个nfs client挂载的需求，是可以这样配置。在/etc/exports中写入/u02 192.168.15.0/255.255.255.0(rw)或/u02 192.168.15.0/24(rw)。
小结
通过帮助文档的分析和这个问题解决过程可以得到这样的结论,很多nfs服务器上exports的配置都是不规范的，只是通配符"*"碰巧能用而已。规范的配置应是192.168.15.0/24或192.168.15.0/255.255.255.0。
原帖地址：http://mikixiyou.iteye.com/blog/1731208