专题：NFSv4 file server

　　Network File System (NFS) is a file system protocol that allows client machines to access network attached filesystems. The newest version is version 4.

<A> Kernel requirements:

　　NFS server support is not required for NFS clients, and NFS client support is not required for NFS servers. Dnotify support is only required for NFSv4. NFSv3 is only required for compatibility with legacy clients e.g.

File systems --->
  [*] Dnotify support
  [*] Network File Systems --->
        <*>   NFS client support
        <*>     NFS client support for NFS version
        <*>     NFS client support for NFS version
        [*]   NFS client support for NFSv4.
        <*>   NFS server support
        [*]     NFS server support for NFS version
        [*]     NFS server support for NFS version
        [*]       NFSv4. server support for Parallel NFS (pNFS)

<B> Install "net-fs/nfs-utils"(Gentoo) or "nfs-utils.x86_64"(RedHat)

　　After installation, set the "rpcbind" and "nfs" service start with your OS:

root # rc-update add nfs default && rc-update add rpcbind default
OR
root # systemctl enable nfs.service && systemctl enable rpcbind.service

<C> Virtual root

　　The filesystems to be exported must be made available under a single directory. This directory is known as the virtual root directory, and it is required for NFSv4:

root #mkdir /export
#The dir_name "/export" can be changed it to any other.

　　Create directories in the virtual root directory for the filesystems that are to be exported:

root #mkdir /export/distfiles

　　Write to "/etc/fstab"

/PATH/TO/distfiles    /export/distfiles    none    bind     

<D> Exports

　　The filesystems to be made accessible for clients are specified in /etc/exports. This file consists of the directories to be exported, the clients allowed to access those directories, and a list options for each client:

/export    　　　　　　10.1.0.0/(sync,rw,insecure,no_subtree_check,crossmnt,fsid=root)
/export/distfiles    *(sync,ro,insecure,no_subtree_check)

　　The following table briefly describes the client options used in the configuration above:

 insecure    The server will require that client requests originate on unprivileged ports (those above ). This option is required when mounting exported directories from OS X. The default is to use privileged ports.
 rw    The client will have read and write access to the exported directory. The default is to allow read-only access.
 sync    The server must wait until filesystem changes are committed to storage before responding to further client requests. This is the default.
 no_subtree_check    The server will not verify the requests from clients(wether it's in the appropriate filesystem or has the correct permissions). This is the default in NFSv4.
 crossmnt    The server will reveal filesystems that are mounted under the virtual root directory that would otherwise be hidden when a client mounts the virtual root directory.
 fsid=root    This option is required to uniquely identify the virtual root directory.

　　If changes are made to /etc/exports after the NFS server has started, execute the following command:

root #exportfs -rv
OR
root #/etc/init.d/nfs reload
OR
root #systemctl reload nfs.service

<E> Daemon

　　The NFS daemon is configured via /etc/conf.d/nfs:

# /etc/conf.d/nfs
# Options to pass to rpc.nfsd
OPTS_RPC_NFSD="8 -N 2 -V 3 -V 4 -p 8888"

　　The option 8 is the number of NFS server threads to start.The option -N 2 disables NFS version 2, while options -V 3 and -V 4 enable NFS versions 3 and 4, The option -p 8888 change listening port from the default 2049 to 8888.

<F> Client Service

　　To be able to mount exported directories, start the NFS client:

root # service rpcbind start
OR
root # systemctl start rpcbind

<G> Mount on Client

root # mount [-t nfs] 113.114.115.116:/ /mnt    #"-t nfs" argument is not necessary

<H>Troubeshooting

　　The system may become unresponsive during shutdown when the NFS client attempts to unmount exported directories after udev has stopped. To prevent this, a local.d script(Gentoo) can be used to forcibly unmount the exported directories during shutdown:

#write in "/etc/local.d/NFS_umount.stop"
/bin/umount -a -f -t nfs

　　Remember to add "x" permission:

chmod +x NFS_umount.stop

　　Verify which NFS daemons are running:

Gentoo > rpcinfo -p
   program vers proto   port  service
           tcp      portmapper
           udp      portmapper
           udp    status
           tcp    status
           udp    mountd
           tcp    mountd
           tcp     nfs
           tcp     nfs
           udp     nfs
           udp     nfs
           udp    nlockmgr

　　List the exported directories from the NFS server:

Gentoo > exportfs -v
/export           10.1.7.0/(rw,wdelay,crossmnt,insecure,root_squash,no_subtree_check,fsid=,sec=sys,rw,insecure,root_squash,no_all_squash)

　　List the established connections:

Gentoo > ss -tuanp | grep
udp    UNCONN                    *:                  *:*
udp    UNCONN                   :::                 :::*
tcp    LISTEN                   *:                  *:*
tcp    LISTEN                  :::                 :::*