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18.2. Mounting a File System

Important

Note

18.2.1. Specifying the File System Type

Table 18.1. Common File System Types

Type	Description
ext2	The ext2 file system.
ext3	The ext3 file system.
ext4	The ext4 file system.
iso9660	The ISO 9660 file system. It is commonly used by optical media, typically CDs.
nfs	The NFS file system. It is commonly used to access files over the network.
nfs4	The NFSv4 file system. It is commonly used to access files over the network.
udf	The UDF file system. It is commonly used by optical media, typically DVDs.
vfat	The FAT file system. It is commonly used on machines that are running the Windows operating system, and on certain digital media such as USB flash drives or floppy disks.

Example 18.2. Mounting a USB Flash Drive

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19.2. Mounting a File System

Important

Note

19.2.1. Specifying the File System Type

Table 19.1. Common File System Types

Type	Description
ext2	The ext2 file system.
ext3	The ext3 file system.
ext4	The ext4 file system.
btrfs	The btrfs file system.
xfs	The xfs file system.
iso9660	The ISO 9660 file system. It is commonly used by optical media, typically CDs.
nfs	The NFS file system. It is commonly used to access files over the network.
nfs4	The NFSv4 file system. It is commonly used to access files over the network.
udf	The UDF file system. It is commonly used by optical media, typically DVDs.
vfat	The FAT file system. It is commonly used on machines that are running the Windows operating system, and on certain digital media such as USB flash drives or floppy disks.

Example 19.2. Mounting a USB Flash Drive

19.2.2. Specifying the Mount Options

Table 19.2. Common Mount Options

Option	Description
async	Allows the asynchronous input/output operations on the file system.
auto	Allows the file system to be mounted automatically using the mount -a command.
defaults	Provides an alias for async,auto,dev,exec,nouser,rw,suid .
exec	Allows the execution of binary files on the particular file system.
loop	Mounts an image as a loop device.
noauto	Default behavior disallows the automatic mount of the file system using the mount -a command.
noexec	Disallows the execution of binary files on the particular file system.
nouser	Disallows an ordinary user (that is, other than root ) to mount and unmount the file system.
remount	Remounts the file system in case it is already mounted.
ro	Mounts the file system for reading only.
rw	Mounts the file system for both reading and writing.
user	Allows an ordinary user (that is, other than root ) to mount and unmount the file system.

Example 19.3. Mounting an ISO Image

19.2.3. Sharing Mounts

Example 19.4. Creating a Shared Mount Point

Example 19.5. Creating a Slave Mount Point

Example 19.6. Creating a Private Mount Point

Example 19.7. Creating an Unbindable Mount Point

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Chapter 3. Mounting NFS shares

As a system administrator, you can mount remote NFS shares on your system to access shared data.

3.1. Introduction to NFS

This section explains the basic concepts of the NFS service.

A Network File System (NFS) allows remote hosts to mount file systems over a network and interact with those file systems as though they are mounted locally. This enables you to consolidate resources onto centralized servers on the network.

The NFS server refers to the /etc/exports configuration file to determine whether the client is allowed to access any exported file systems. Once verified, all file and directory operations are available to the user.

3.2. Supported NFS versions

This section lists versions of NFS supported in Red Hat Enterprise Linux and their features.

Currently, Red Hat Enterprise Linux 8 supports the following major versions of NFS:

• NFS version 3 (NFSv3) supports safe asynchronous writes and is more robust at error handling than the previous NFSv2; it also supports 64-bit file sizes and offsets, allowing clients to access more than 2 GB of file data.
• NFS version 4 (NFSv4) works through firewalls and on the Internet, no longer requires an rpcbind service, supports Access Control Lists (ACLs), and utilizes stateful operations.

NFS version 2 (NFSv2) is no longer supported by Red Hat.

Default NFS version

The default NFS version in Red Hat Enterprise Linux 8 is 4.2. NFS clients attempt to mount using NFSv4.2 by default, and fall back to NFSv4.1 when the server does not support NFSv4.2. The mount later falls back to NFSv4.0 and then to NFSv3.

Features of minor NFS versions

Following are the features of NFSv4.2 in Red Hat Enterprise Linux 8:

Following are the features of NFSv4.1:

• Enhances performance and security of network, and also includes client-side support for pNFS.
• No longer requires a separate TCP connection for callbacks, which allows an NFS server to grant delegations even when it cannot contact the client: for example, when NAT or a firewall interferes.
• Provides exactly once semantics (except for reboot operations), preventing a previous issue whereby certain operations sometimes returned an inaccurate result if a reply was lost and the operation was sent twice.

3.3. Services required by NFS

This section lists system services that are required for running an NFS server or mounting NFS shares. Red Hat Enterprise Linux starts these services automatically.

Red Hat Enterprise Linux uses a combination of kernel-level support and service processes to provide NFS file sharing. All NFS versions rely on Remote Procedure Calls (RPC) between clients and servers. To share or mount NFS file systems, the following services work together depending on which version of NFS is implemented:

This process provides NFSv4 client and server upcalls, which map between on-the-wire NFSv4 names (strings in the form of user @ domain ) and local UIDs and GIDs. For idmapd to function with NFSv4, the /etc/idmapd.conf file must be configured. At a minimum, the Domain parameter should be specified, which defines the NFSv4 mapping domain. If the NFSv4 mapping domain is the same as the DNS domain name, this parameter can be skipped. The client and server must agree on the NFSv4 mapping domain for ID mapping to function properly.

Only the NFSv4 server uses rpc.idmapd , which is started by the nfs-idmapd service. The NFSv4 client uses the keyring-based nfsidmap utility, which is called by the kernel on-demand to perform ID mapping. If there is a problem with nfsidmap , the client falls back to using rpc.idmapd .

The RPC services with NFSv4

The mounting and locking protocols have been incorporated into the NFSv4 protocol. The server also listens on the well-known TCP port 2049. As such, NFSv4 does not need to interact with rpcbind , lockd , and rpc-statd services. The nfs-mountd service is still required on the NFS server to set up the exports, but is not involved in any over-the-wire operations.

Additional resources

3.4. NFS host name formats

This section describes different formats that you can use to specify a host when mounting or exporting an NFS share.

You can specify the host in the following formats:

Either of the following:

• A fully-qualified domain name (that can be resolved by the server)
• Host name (that can be resolved by the server)
• An IP address.

Either of the following formats is valid:

• a.b.c.d/z , where a.b.c.d is the network and z is the number of bits in the netmask; for example 192.168.0.0/24 .
• a.b.c.d/netmask , where a.b.c.d is the network and netmask is the netmask; for example, 192.168.100.8/255.255.255.0 .

3.5. Installing NFS

This procedure installs all packages necessary to mount or export NFS shares.

Procedure

Install the nfs-utils package:

3.6. Discovering NFS exports

This procedure discovers which file systems a given NFSv3 or NFSv4 server exports.

Procedure

With any server that supports NFSv3, use the showmount utility:

With any server that supports NFSv4, mount the root directory and look around:

On servers that support both NFSv4 and NFSv3, both methods work and give the same results.

Additional resources

3.7. Mounting an NFS share with mount

This procedure mounts an NFS share exported from a server using the mount utility.

Procedure

To mount an NFS share, use the following command:

This command uses the following variables:

Additional resources

3.8. Common NFS mount options

This section lists options commonly used when mounting NFS shares. These options can be used with manual mount commands, /etc/fstab settings, and autofs .

Specifies which version of the NFS protocol to use, where version is 3 , 4 , 4.0 , 4.1 , or 4.2 . This is useful for hosts that run multiple NFS servers, or to disable retrying a mount with lower versions. If no version is specified, NFS uses the highest version supported by the kernel and the mount utility.

The option vers is identical to nfsvers , and is included in this release for compatibility reasons.

noacl Turns off all ACL processing. This may be needed when interfacing with older versions of Red Hat Enterprise Linux, Red Hat Linux, or Solaris, because the most recent ACL technology is not compatible with older systems. nolock Disables file locking. This setting is sometimes required when connecting to very old NFS servers. noexec Prevents execution of binaries on mounted file systems. This is useful if the system is mounting a non-Linux file system containing incompatible binaries. nosuid Disables the set-user-identifier and set-group-identifier bits. This prevents remote users from gaining higher privileges by running a setuid program. port= num Specifies the numeric value of the NFS server port. If num is 0 (the default value), then mount queries the rpcbind service on the remote host for the port number to use. If the NFS service on the remote host is not registered with its rpcbind service, the standard NFS port number of TCP 2049 is used instead. rsize= num and wsize= num

These options set the maximum number of bytes to be transferred in a single NFS read or write operation.

There is no fixed default value for rsize and wsize . By default, NFS uses the largest possible value that both the server and the client support. In Red Hat Enterprise Linux 8, the client and server maximum is 1,048,576 bytes. For more details, see the What are the default and maximum values for rsize and wsize with NFS mounts? KBase article.

Security flavors to use for accessing files on the mounted export. The flavors value is a colon-separated list of one or more security flavors.

By default, the client attempts to find a security flavor that both the client and the server support. If the server does not support any of the selected flavors, the mount operation fails.

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