How to configure and manage NFS server on Linux/centos?

1 Basic understanding of NFS

• NFS（Network File System）That is, file operating system;
• NFSAllows different computers in the network to share resources with each other.

1.1 NFS Overview

• A method of file sharing between systems SUNdeveloped in 1980 ;UNIX&Linux
• It is a file system protocol that supports applications on the client side to access data located on the server disk through the network;
• NFSOnly provides network file sharing and does not provide data transmission functions;
• NFSThe client and server need to RPC（Remote Procedure Calls）implement data transmission;
• NFSThe access to the server directory is called export ( export), and the process of the client accessing the export directory is called mount ( mount) or import ( import).

1.2 NFS workflow

Step 1: To access NFS shared resources, the NFS client sends a query request, that is, the client RPC service sends a query request to the 111 port of the server RPC service through the network.

Step 2: The NFS server RPC finds the corresponding registered NFSdaemon port and notifies the client RPC;

Step 3: The NFS client obtains the port and directly stores data online with the NFSNFSdaemon.

Step 4: After the NFS client successfully stores the data, notify the user of the result.

2 Install and start the NFS service

2.1 Install NFS server

• In general, NFS has been installed on the system;
• First check whether NFS is installed. The following two are related dependency packages:

rpm -qa | grep nfs-utils
rpm -qa | grep rpcbind

• After checking, it is already installed:
  
• If the system does not have NFS dependency packages installed, you need to install them:

yum clean all
yum -y install nfs-utils rpcbind

2.2 Start NFS service

• Check NFS status:

systemctl status rpcbind.service
systemctl status nfs.service 

• Start the NFS service:

systemctl start rpcbind.service
systemctl start nfs.service 

• Check the status again, they are all started:
  
• Stop the NFS service:

systemctl stop nfs.service

• Restart the NFS service:

systemctl restart nfs.service

• Set the NFS service to start automatically at boot:

systemctl enable rpcbind.service 
systemctl enable nfs.service

3 Configure NFS server and client

3.1 Configure NFS server

• The configuration file is in /etc/exports;
• The format is:

共享目录 [客户端1(参数)] [客户端2（参数）] 

Shared directory: The actual path (absolute path) required by the NFS server to be shared;
Client: A computer that can access the shared directory.

• Common forms of clients:

client	illustrate
192.168.1.111	Host with specified IP address
192.168.1.0/24	All hosts on the specified subnet
192.168.1.*	All hosts on the specified subnet
www.xxx.com	Host of specified domain name
*.xxx.com	All hosts in the specified domain
*	All hosts

Access permission parameters: access permission settings.

• Common access rights:

access permission	illustrate
ro	read only
rw	Read and write

User mapping parameters

• User mapping parameter table:

User mapping	illustrate
all_squash	Map all remote access users to anonymous users or user groups ( nfsnobody)
no_all_squash	Opposite of above (default setting)
root_squash	Set root user to… (default setting)
no_root_squash	Contrary to the above
anonuid=xxx	Convert the anonymous account to a local account ( UID=xxx)
anongid=xxx	Configure the anonymous user group as a local user group (GID=xxx）

Other parameters: control the output directory.

• Other commonly used parameters:

Other parameters	illustrate
secure	Restrict clients to connect to NFS from TCP/IP ports less than 1024
insecure	Word order client connects to NFS with a TCP/IP port greater than 1024
sync	Synchronously write data to the memory buffer and disk
async	Save the data in the buffer first and then write it to disk when necessary
wdelay	Check if there are any related write operations
no_wdelay	A write operation is executed immediately, syncused in conjunction with
subtree_check	If the output directory is a subdirectory, the NFS server will check the permissions of the parent directory
no_subtree_check	If the output directory is a subdirectory, the NFS server does not check the permissions of the parent directory

• For example /mnt/temp, give the directory only 172.16.1.33read and write permissions to the computer with the IP address:

/mnt/temp 172.16.1.33 (rw, sync)

• For example, give the directory read and write permissions /mnt/temp01only to the computers in the subnet , and give other computer mechanisms only read permissions:172.16.1.0/24

/mnt/temp0 172.16.1.0/24 (rw, async) * (ro)

3.2 Configure NFS client

• View NFS server information:

showmount [选项] （参数）

-d: Only display shared directories that have been loaded by the NFS client;
-e: Display all shared directories on the NFS server.

showmount -e 192.168.0.190

When using showmount, it is recommended to turn off the firewall and set SELinux to allow.

systemctl stop firewalld.service
setenforce 0
getenforce

• Mount the shared directory on the NFS server:

Mount the NFS shared directory locally:
mount -t NFS server IP: the output directory is mounted locally.

• for example:

mkdir /mnt/mytemp
mount -t nfs 192.168.0.190:/mnt/mytemp /mnt/mytemp

• Uninstall the NFS server:

umount 挂载点

• Automatically mount the NFS shared directory at startup:

192.168.0.190： /mnt/temp /mnt/mytemp nfs defaults 0 0

4 Practical examples

4.1 Basic requirements

• NFS server 192.168.0.190;

• Requirement 1: The shared directory /mnt/temp is allowed to be accessed by computers in the 192.168.0.0/24 network segment;
• Requirement 2: The shared directory /mnt/share is allowed to be accessed by user zhang, and the IP is 192.168.0.10;
• Requirement 3: The shared directory /mnt/upload allows the 192.168.0.0/24 network segment to be used as the upload directory, the group it belongs to is nfsupload, and the UID and GID are both 666;
• Requirement 4: The shared directory /mnt/nfs, except for user access in the 192.168.0.0/24 network segment, is read-only and can provide data content to the Internet;

4.2 Case implementation

• Install NFS service:

yum -y install rpcbind
yum -y install nfs-utils

• Create directory and test files:

# 创建目录：
mkdir -p /mnt/temp
mkdir -p /mnt/share
mkdir -p /mnt/upload
mkdir -p /mnt/nfs

# 创建测试文件
touch /mnt/temp/temp1.txt /mnt/temp/temp2.txt 
touch /mnt/share/data1.txt /mnt/share/data2.txt
touch /mnt/upload/upload.txt
touch /mnt/nfs/nfs1.txt /mnt/nfs/nfs2.txt

• Set shared directory permission attributes:

# 要求1：
chmod 1777 /mnt/temp/
ll -d /mnt/temp/

# 要求2：
useradd zhang
passwd zhang
cat /etc/passwd | grep zhang
chmod 700 /mnt/share/
chown -R zhang:zhang /mnt/share/
ll -d /mnt/share/

# 要求3：
groupadd -g 666 nfsupload
useradd -g 666 -u 666 -M nfsupload
cat /etc/passwd | grep nfs
chown -R nfsupload:nfsupload /mnt/upload
ll -d /mnt/upload/

# 要求4：
ll -d /mnt/nfs/

• Edit /etc/exports:

/mnt/temp 192.168.0.0/24 (rw,no_root_squash)
/mnt/share 192.168.0.10 (rw)
/mnt/upload 192.168.0.0/24 (rw,all_squash,anonuid = 666,anongid = 666)
/mnt/nfs 192.168.0.0/24 (ro) * (rw,all_squash)

• Close the firewall, set Selinux to allow, and restart the NFS service:

systemctl stop firewalld.service
setenforce 0
getenforce
systemctl restart nfs

• NFS client installs client software:

yum -y install nfs-utils

• View the shared directories on the NFS server:

showmount -e 192.168.0.190

• Create a directory on the client machine and mount the NFS directory to the directory:

mkdir /mnt/ClientNFS
mount -t nfs 192.168.0.190:/mnt/nfs/ /mnt/ClientNFS/

• Just use the same method to mount other NFS directories;
• And create group 666 on the client machine:

groupaddd -g 666 nfsupload
useradd -g 666 -u 666 -M nfsupload

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