What is linux NFS and how to use it

nfs is the abbreviation of network file system, that is, network file system. The network file system is one of the file systems supported by freebsd, also known as nfs. nfs allows a system to share directories and files with others on the network. By using NFS, users and programs can access files on remote systems as if they were local files.

nfs is based on the rpc protocol. nfs itself only plays a role in sharing, while connection and data transmission with the client are the functions of the rpc protocol.

nfs mainly uses two daemons. Control:
1.rpc.nfsd ------- It is used to control whether the client can connect to, nfs server
2.rpc.mountd----It is used to control the client connection Whether you have permission to operate the file is mainly based on the settings of the /etc/exports file

To enable nfs, you need to enable portmap and nfs-utils
1.portmap is mainly used to control what is requested when the client connects Port
2.nfs-utils is the executable file of rpc.nfsd and rpc.mountd

/etc/exports     The main configuration file of nfs service
/usr/sbin/exportfs    Management commands of nfs service
/usr/sbin/showmount Client view command
/var/lib/nfs/xtab Record the customer information that has logged in

/etc/exports file setting format
[Shared Directory] ip or host (parameter 1, parameter 2) ip or host (parameter 3, parameter 4)
The parameters mainly include the following
rw: read and write
ro: read only
no_root_squash: If the client login is root, he will have root permissions after logging into the shared directory
root_squash: After root login, the identity is compressed to nfsnobody (by default)
all_squash: After all users log in, the identity is compressed into nfsnobody (by default) Next)
anonuid: If you do not want the user to be compressed into nfsnobody after logging in, the user can change this
anongid: Same as above (this is a group)
sync: Data is written to the hard disk synchronously
async: Data first Store in memory

Analysis on permissions

1. When the client connects, check for ordinary users, no.1 if it is explicitly set that ordinary users will be compressed identity, then the identity of the client user is converted to the specified user at this time, no.2 If there is a user with the same name on the nfs server, then the identity of the client login account is converted to the user with the same name on the nfs server, no.3 if there is no If it is explicitly specified and there is no user with the same name, then the user identity will be compressed into nfsnobody
2. When the client connects, root will be checked, no.1. If no_root_squash is set, then the root user identity will be compressed into Root on the nfs server, no.2 if all_squash, anonuid, and anongid are set, then the root identity is compressed to the specified user, no.3 if not explicitly specified, then the root user is compressed to nfsnobody, no.4 if both Specifying no_root_squash and all_squash users will be compressed into nfsnobody. If anonuid and anongid are set, they will be compressed into the specified user and group

Start the service
service portmap start or /etc /rc.d/init.d/portmap start
service nfs start or /etc/rc.d/init.d/nfs start

exportfs command usage
- a Mount or unmount all
-r Reread the information in /etc/exports and synchronously update /etc/exports, /var/lib/nfs/xtab
-u Unmount a single directory (with -a Use together to uninstall all directories in the /etc/exports file)
-v Output detailed information on the screen

showmount command usage
-a Display connected to the client Directory information on
-e ip or hostname displays the directory shared by this IP address

Use netstat to check that the nfs service has opened many ports. Among them, nfs opens 2049, portmap opens 111, and the rest It is enabled by rpc
Use rpcinfo -p to check out the programs provided by the port opened by rpc
Use mount -t nfs ip (hostname): shared directory mount point method to complete the mounting
Finally, note two points. Although ordinary users can access it through permission settings, only root can mount by default when mounting (ordinary users can execute sudo)

nfs server when shutting down One thing to make sure is that the nfs service is closed and no clients are connected! ! You can view it through showmount -a. If there is any, use kill killall pkill to end it (-9 forces the end)

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