RHEL7: Provide NFS network shares to specific clients.

Note: This is an RHCE 7 exam objective.

In this tutorial, the NFS server is called nfsserver.example.com and the NFS client nfsclient.example.com.

NFS Server Configuration

Install the file-server package group:

# yum groupinstall -y file-server

Add a new service to the firewall:

# firewall-cmd --permanent --add-service=nfs
success

Note: NFSv4 is the version used at the exam and doesn’t need any extra firewall configuration. However, beyond the exam objectives, if you plan to use NFSv3, you will also need to run these commands:

# firewall-cmd --permanent --add-service=mountd
# firewall-cmd --permanent --add-service=rpc-bind

Reload the firewall configuration:

# firewall-cmd --reload
success

Activate the NFS services at boot:

# systemctl enable rpcbind nfs-server

Note: The nfs-idmap/nfs-idmapd (changes happened with RHEL 7.1) and nfs-lock services are automatically started by the nfs-server service. nfs-idmap/nfs-idmapd is required by NFSv4 but doesn’t allow you any UID/GID mismatches between clients and server. It is only used when setting ACL by names or to display user/group names. All permission checks are still done with the UID/GID used by the server (see this thread about nfs-idmap for more details).

Start the NFS services:

# systemctl start rpcbind nfs-server

Note1: By default, 8 NFS threads are used (RPCNFSDCOUNT=8 in the /etc/sysconfig/nfs file). This should be increased in a production environment to at least 32 (source: http://initrd.org/wiki/NFS_Setup). Note2: Optionally, to enable SELinux Labeled NFS Support, edit the /etc/sysconfig/nfs file and paste the following line (source): RPCNFSDARGS=”-V 4.2″

Create directories to export and assign access rights:

# mkdir -p /home/tools
# chmod 0777 /home/tools
# mkdir -p /home/guests
# chmod 0777 /home/guests

Assign the correct SELinux contexts to the new directories:

# yum install -y setroubleshoot-server
# semanage fcontext -a -t public_content_rw_t "/home/tools(/.*)?"
# semanage fcontext -a -t public_content_rw_t "/home/guests(/.*)?"
# restorecon -R /home/tools
# restorecon -R /home/guests

Note: The public_content_rw_t context is not the only available, you can also use the public_content_ro_t (only read-only) or nfs_t (more limited) contexts according to your needs.

Check the SELinux booleans used for NFS:

# semanage boolean -l | egrep "nfs|SELinux"
SELinux boolean                State  Default Description
xen_use_nfs                    (off  ,  off)  Allow xen to use nfs
virt_use_nfs                   (off  ,  off)  Allow virt to use nfs
mpd_use_nfs                    (off  ,  off)  Allow mpd to use nfs
nfsd_anon_write                (off  ,  off)  Allow nfsd to anon write
ksmtuned_use_nfs               (off  ,  off)  Allow ksmtuned to use nfs
git_system_use_nfs             (off  ,  off)  Allow git to system use nfs
virt_sandbox_use_nfs           (off  ,  off)  Allow virt to sandbox use nfs
logrotate_use_nfs              (off  ,  off)  Allow logrotate to use nfs
git_cgi_use_nfs                (off  ,  off)  Allow git to cgi use nfs
cobbler_use_nfs                (off  ,  off)  Allow cobbler to use nfs
httpd_use_nfs                  (off  ,  off)  Allow httpd to use nfs
sge_use_nfs                    (off  ,  off)  Allow sge to use nfs
ftpd_use_nfs                   (off  ,  off)  Allow ftpd to use nfs
sanlock_use_nfs                (off  ,  off)  Allow sanlock to use nfs
samba_share_nfs                (off  ,  off)  Allow samba to share nfs
openshift_use_nfs              (off  ,  off)  Allow openshift to use nfs
polipo_use_nfs                 (off  ,  off)  Allow polipo to use nfs
use_nfs_home_dirs              (off  ,  off)  Allow use to nfs home dirs
nfs_export_all_rw              (on   ,   on)  Allow nfs to export all rw
nfs_export_all_ro              (on   ,   on)  Allow nfs to export all ro

Note1: The State column respectively shows the current boolean configuration and the Default column the permanent boolean configuration. Note2: Here we are interested in the nfs_export_all_rw, nfs_export_all_ro and potentially use_nfs_home_dirs booleans. Note3: The nfs_export_all_ro boolean allows files to be shared through NFS in read-only mode but doesn’t restrict them from being used in read-write mode. It’s the role of the nfs_export_all_rw boolean to allow read-write mode.

If necessary, assign the correct setting to the SELinux booleans:

# setsebool -P nfs_export_all_rw on
# setsebool -P nfs_export_all_ro on
# setsebool -P use_nfs_home_dirs on

Edit the /etc/exports file and add the following lines with the name (or IP address) of the client(s):

/home/tools nfsclient.example.com(rw,no_root_squash)
/home/guests nfsclient.example.com(rw,no_root_squash)

Note: Please, don’t put any space before the opening parenthesis, this would completely change the meaning of the line!

Export the directories:

# exportfs -avr
exporting nfsclient.example.com:/home/guests
exporting nfsclient.example.com:/home/tools
# systemctl restart nfs-server

Note: This last command shouldn’t be necessary in the future. But, for the time being, it avoids rebooting.

Check your configuration:

# showmount -e localhost
Export list for localhost:
/home/guests nfsclient.example.com
/home/tools  nfsclient.example.com

Note: You can test what is exported by the NFS server from a remote client with the command showmount -e nfsserver.example.com but you first need to stop Firewalld on the NFS server (or open the 111 udp and 20048 tcp ports on the NFS server).

NFS Client Configuration

On the client side, the commands are:

# yum install -y nfs-utils
# mount -t nfs nfsserver.example.com:/home/tools /mnt

Additional Resources

The GeekDiary website provides a tutorial about Configuring a NFS server and NFS client.