mount: mount to NFS server '192.168.29.100' failed: System Error: Connection refused.

遇到这个问题，原因是nfs没启动。而且无论如何也启动不了。
解决方法：
yum install  portmap
然后
/etc/init.d/portmap start
/etc/init.d/nfs start
然后
mount -a
一切ok！

另外，转一篇文章

Linux下配置NFS(rpc服务启动必须NFS服务先起来)

环境：

    client: 主机rac2,ip 192.168.0.6

    server: 主机rac1,ip 192.168.0.5

    1) 在客户端启动portmap和nfs服务，单起nfs进程是无法启动的。

    [root@rac2 init.d]# ./nfs start

    Starting NFS services: [ OK ]

    Starting NFS quotas: Cannot register service: RPC: Unable to receive; errno = Connection refused

    rpc.rquotad: unable to register (RQUOTAPROG, RQUOTAVERS, udp).

    [FAILED]

    Starting NFS daemon:

    [FAILED]

    Starting NFS mountd: Cannot register service: RPC: Unable to receive; errno = Connection refused

    mountd: unable to register (mountd, 1, udp).

    [FAILED]

    Starting RPC idmapd: [ OK ]

    [root@rac2 init.d]# ps -ef|grep nfs

    证明nfs没有启动。

    [root@rac2 init.d]# /etc/init.d/portmap start

    Starting portmap: [ OK ]

    [root@rac2 init.d]# ps -ef|grep portmap

    rpc 3198 1 0 02:39 ? 00:00:00 portmap

    root 3202 2998 0 02:39 pts/0 00:00:00 grep portmap

    [root@rac2 init.d]# /etc/init.d/nfs start

    Starting NFS services: [ OK ]

    Starting NFS quotas: [ OK ]

    Starting NFS daemon: [ OK ]

    Starting NFS mountd: [ OK ]

    启动正常，检查一下nfs进程是否在。

    [root@rac2 init.d]# ps -ef|grep nfs

    root 3222 1 0 02:39 ? 00:00:00 [nfsd]

    root 3223 1 0 02:39 ? 00:00:00 [nfsd]

    root 3224 1 0 02:39 ? 00:00:00 [nfsd]

    root 3225 1 0 02:39 ? 00:00:00 [nfsd]

    root 3226 1 0 02:39 ? 00:00:00 [nfsd]

    root 3227 1 0 02:39 ? 00:00:00 [nfsd]

    root 3228 1 0 02:39 ? 00:00:00 [nfsd]

    root 3231 1 0 02:39 ? 00:00:00 [nfsd]

    root 3260 2998 0 02:45 pts/0 00:00:00 grep nfs

    rac1上有一个/disk0分区，看从rac2能否直接连接上rac1

    [root@rac1 ~]# df -h

    Filesystem Size Used Avail Use% Mounted on

    /dev/sda5 2.9G 2.3G 503M 83% /

    /dev/sda1 99M 12M 83M 12% /boot

    none 125M 0 125M 0% /dev/shm

    /dev/sda2 7.7G 2.3G 5.1G 32% /home

    /dev/sda3 3.9G 2.3G 1.4G 62% /usr

    /dev/sda7 2.8G 1.1G 1.6G 40% /var

    /dev/sdb5 1004M 1.3M 952M 1% /disk0

    [root@rac2 init.d]# mount 192.168.0.5:/disk0 /wyl (/wyl目录必须已存在)

    mount: mount to NFS server '192.168.0.5' failed: System Error: Connection refused.

    报错信息指的是server端(Rac1)的nfs进程没起来！

    在服务端启动nfs进程(实际上是要启动portmap和nfs进程)

    [root@rac1 ~]# /etc/init.d/portmap start

    Starting portmap: [ OK ]

    [root@rac1 ~]# /etc/init.d/nfs start

    Starting NFS services: [ OK ]

    Starting NFS quotas: [ OK ]

    Starting NFS daemon: [ OK ]

    Starting NFS mountd: [ OK ]

    Starting RPC idmapd: [ OK ]