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An NFS client is a system that mounts
remote directories using NFS. When a client mounts a remote filesystem,
it does not make a copy of the filesystem. The mounting process
uses a series of remote procedure calls that enable the client to
transparently access the filesystem on the server’s disk.
To users, these mounted remote directories appear as if they are
a part of the local filesystem. An NFS client can also be an NFS server.
NFS filesystems can also be automounted using AutoFS. For information
on how to automount a filesystem, see Chapter 3 “Configuring and Administering AutoFS”. NFS
Client Configuration Files and Daemons | |
This section describes the NFS client configuration files
and daemons. Configuration FilesTable 2-5 “NFS client configuration files” describes the NFS
configuration files and their functions. Table 2-5 NFS client configuration files File Name | Function |
|---|
| /etc/mnttab | Contains the list of filesystems that are currently
mounted. | | /etc/dfs/fstypes | Contains the default distributed filesystem
type. | /etc/fstab | Contains the list of filesystems that
are automatically mounted at system boot time. |
DaemonsTable 2-5 describes the NFS client daemons and their functions. Table 2-6 NFS client daemons Daemon Name | Function |
|---|
| rpc.lockd | Supports record lock and share lock operations
on the NFS files. | rpc.statd | Maintains a list of clients that have
performed the file locking operation over NFS against the server.
These clients are monitored and notified in the event of a system
crash. |
Following are the tasks involved in configuring and administering
an NFS client. Configuring
the NFSv4 Client Protocol Version | |
By default, the version of the NFS protocol used between the
client and the server is the highest one available on both systems.
On HP-UX 11i v3, the default maximum protocol version of the NFS
server and client is 3. The default minimum protocol version of
the NFS server and client is 2. To configure the NFS client to enable it to mount filesystems
using protocol version 4 (NFSv4), follow this step: Set the value of the NFS_CLIENT_VERSMAX variable to 4 in the /etc/default/nfs file, as follows: The NFS_CLIENT_VERSMAX variable specifies the maximum version of the NFS protocol
for communication. You can also configure the client protocol version to NFSv4
by specifying vers=4 while mounting the directory.
For example, to set the client protocol version to NFSv4 while mounting
the /usr/kc directory, enter the following command: mount -o vers=4 serv:/usr/kc /usr/kc |
For more information on NFSv4, see nfsd(1m), mount_nfs(1m), nfsmapid(1m), and nfs4cbd(1m). Deciding
Between Standard-Mounted Directories and Automounted Directories | |
Before you mount any remote directories on a local system,
decide whether you want each directory to be standard-mounted or automounted.
You can automount directories using AutoFS. For more information
on AutoFS, see Chapter 3 “Configuring and Administering AutoFS”. Table 2-7 “Standard-Mounted Versus Automounted Directories” lists the differences
between the Standard-Mounted and the Automounted directories. Table 2-7 Standard-Mounted Versus Automounted Directories Standard-Mounted Directory | Automounted
Directory (Using AutoFS) |
|---|
The directory stays mounted. You do not
have to wait for it to be mounted after you issue a read or write
request. | Automounted
directories stay mounted until they are left idle for 10 minutes.
The 10 minute time interval is the default value and is configurable. | If a directory is configured to be standard-mounted
when the client system boots, and the NFS server for the directory
is not booted yet, system startup is delayed until the NFS server becomes
available. If the client and the server are configured to mount
directories from each other at boot time, standard mounts can cause
both systems to hang indefinitely. | A
directory automounted with AutoFS is not mounted until a user or
a process requests access to it. As a result, both the client and
the NFS server are able to complete the boot process before attempting
to mount the directory. | You must maintain the configuration file
for standard mounts (/etc/fstab) separately on each NFS client. | You
can manage AutoFS configuration files (maps) centrally through NIS
and LDAP. | If you have to configure many similar standard
mounts, you must configure them individually, because you cannot
use wildcard characters or environment variables when you configure
standard NFS mounts. | AutoFS
allows you to use wildcard characters and environment variables
in configuration files (maps) as shortcuts, when you are configuring
many similar automounts. | Standard
NFS mounts provide no shortcut for configuring all available remote
directories. You must configure each directory separately. If the NFS
servers change the directories they are exporting, you must change
your local NFS client configuration. | AutoFS
allows you to configure a special “built-in” map
known as the -hosts map. This built-in map automounts all the exported directories
from any NFS server on the network on the client system whenever
anyone requests access to a directory on that server. The servers
can change which directories they export, but your configuration remains
valid. |
Enabling
an NFS Client | |
To enable an NFS client, follow these steps: In the /etc/rc.config.d/nfsconf file, set the value of NFS_CLIENT variable to 1, as follows: Enter the following command to run the NFS client
startup script: /sbin/init.d/nfs.client start |
The NFS client startup script starts the necessary NFS client
daemons, and mounts the remote directories configured in the /etc/fstab file. Mounting
Remote Directories | |
The mount command mounts a shared NFS directory from a remote system
(NFS server). You can mount a filesystem using the following methods: Automatic Mounting at System Boot
time To set up a filesystem for automatic mounting at system boot
time, you must configure it in the /etc/fstab file. All filesystems specified in the /etc/fstab file are mounted during system reboot. Manual Mounting When you manually mount a filesystem, it is not persistent
across reboots or when NFS client restarts. If the NFS client is
restarted or the system is rebooted, the filesystem must be mounted
again after the reboot. To mount filesystems manually, you must
run the mount command. For a list of mount options, see mount_nfs(1M).
Consider the following points before you mount a directory: Before you mount a remote directory
on a client system, you must configure the remote system as an NFS
server and share the directory. You must configure a local directory as the mount
point for the NFS filesystem. HP recommends that the mount point
not contain files and directories. However, if the local directory
contains files and directories, they will be hidden and inaccessible
while the remote directory is mounted.
Mounting
a Remote Directory on an NFS clientTo mount a directory on an NFS client, select one of the following methods: Automatic MountTo configure a remote directory to be automatically mounted
at system boot, follow these steps: Add an entry to the /etc/fstab file, for each remote directory you want to mount
on the client. Following is the syntax for the entry in the /etc/fstab file: server:remote_directory local_directory nfs defaults 0 0 |
or server:remote_directory local_directory nfs option[,option...] 0 0 |
Mount all the NFS file systems specified in the /etc/fstab file by entering the following command: /usr/sbin/mount -a -F nfs |
Verify that your filesystem is mounted by entering
the following command: An output similar to the following output is displayed: /mnt/nfs149 from nfs149:/Flags:vers=4,proto=tcp,sec=sys,hard,intr,link,symlink,devs,rsize=32768,wsize=32768,retrans=5,timeo=600Attr cache:acregmin=3,acregmax=60,acdirmin=30,acdirmax=60 |
The directory that you have mounted must be present in this
list.
Manual MountTo mount your directories manually, follow these steps: To mount a remote directory manually,
enter the following command: mount serv:directory_name directory-name |
Verify if your filesystem is mounted by entering
the following command: An output similar to the following output is displayed: /opt/nfstest from hpnfsweb:/home/tester Flags: vers=3,proto=udp,sec=sys,hard,intr,link,symlink,acl,devs,rsize=32768,wsize=32768,retrans=5,timeo=11 Attr cache: acregmin=3,acregmax=60,acdirmin=30,acdirmax=60 Lookups: srtt=33 (82ms), dev=33 (165ms), cur=20 (400ms) |
The directory that you have mounted must be present in this
list.
For a list of mount options, see mount_nfs(1M). Enabling
Client-Side Failover | |
Using client-side failover, an NFS client can switch to another
server if the server supporting a replicated filesystem becomes
unavailable. The failover is usually transparent to the user. Failover
can occur at any time without disrupting the processes running on
the client. Failover is only supported on read-only fileystems. To mount a directory that has been replicated on multiple
servers, enter the following command: mount -o ro svr:dir_name srv:dir_name dir_name |
If the first NFS server is down, the client accesses the second
NFS server. For example, to mount the Casey directory to replicated servers, enter the following
command: mount -o ro onc21:/home/Casey onc23:/home/Casey /Clay |
If the NFS server onc21 is down, the client accesses NFS server onc23. To verify if the failover is in effect, enter the following
command: An output similar to the following output is displayed: /Clay from onc21:/home/Casey,onc23:/home/CaseyFlags: vers=3,proto=tcp,sec=sys,hard,intr,llock,link,symlink,acl,
devs,rsize=32768,wsize=32768,retrans=5,timeo=600Attr cache: acregmin=3,acregmax=60,acdirmin=30,acdirmax=60Failover: noresponse=0,failover=0,remap=0,currserver=onc21 |
The Failover line in the above output indicates that the failover
is working. Mounting a directory as read-only
with no set userid privileges mount -r -o nosuid broccoli:/usr/share/man /usr/share/man |
In this example, the NFS clients mount the /usr/share/man directory from the NFS server broccoli. The local mount point is also /usr/share/man. The directory is mounted as read-only. Figure 2-3 “NFS
Mount of manpages” illustrates this
example. Mounting a Home directory mount -r -o nosuid broccoli:/home/broccoli /home/broccoli mount -r -o nosuid cauliflower:/home/cauliflower /home/cauliflower |
In this example, the NFS client mounts the home directories
from NFS servers broccoli and cauliflower . The nosuid option prevents programs with setuid permission
from executing on the local client. Figure 2-4 “NFS
Mount of Home Directories” illustrates this
example. Mounting an NFS Version 2 filesystem using the UDP
Transport mount -o vers=2,proto=udp onc21:/var/mail /var/mail |
In this example, the NFS client mounts the /var/mail directory from the NFS server, onc21, using NFSv2 and the UDP protocol. Mounting an NFS filesystem using an NFS URL mount nfs://onc31/Casey/mail /Casey/mail |
In this example, the NFS client mounts the /Casey/mail directory from NFS server, onc31, using the WebNFS protocol. Mounting an NFS filesystem by using a public file
handle mount -o public nfs://onc31/usr/%A0abc /Casey/Clay |
If the public option or a URL is specified,
the mount command attempts to connect to the server using the public
file handle. The daemons rpcbind and mountd are not contacted. In this example, the NFS client mounts /Casey/Clay directory by using a public file handle, and an NFS
URL that has a non 7-bit ASCII escape sequence from the NFS server, onc31. Mounting an NFS filesystem using native path mount -o public onc31:C:Casey:test1 /Casey/test |
A native path is a pathname that is interpreted according
to conventions used on the native operating system of the NFS server. In this example, the NFS client mounts the /Casey/test directory using a native path and a public file handle. Mounting a replicated set of NFS filesystems with
same pathnames mount -r onc21,onc23,onc25:/Casey/Clay /Casey/Clay |
In this example, the NFS client mounts a single filesystem, /Casey/Clay that has been replicated to a number of servers with the
same pathnames. This enables the NFS client to failover to either
server onc21, onc23, or onc25 if the current server has become unavailable. Mounting replicated set of NFS file systems with
different pathnames mount -r onc21:/Casey/Clay,onc23:/Var/Clay,nfs://srv-z/Clay /Casey/Clay |
In this example, the NFS client mounts a replicated set of
NFS file systems with different pathnames.
Secure
Mounting of Directories | |
The mount command enables you to specify the security mode for
each NFS mount point. This allows the NFS client to request a specific security
mode. However, if the specific mode does not exist on the server, then
the mount fails. Use the sec option to specify
the security mode. If sec is not specified in NFSv2, then the
AUTH_SYS mode is used by default. If sec is not
specified in NFSv3, then the default action is for the NFS client
to query the server about the security mode to be used. The resulting
security mode is negotiated between the NFS client and server. For
more information on the available security modes, see
nfssec(5). An
Example for Securely Mounting a directoryIn the following example, the NFS client forces the use of krb5 as
the secure mode. The krb5 secure mode uses the Kerberos V5 protocol to authenticate
users before granting access to the shared filesystems. In this
example, the NFS server, onc21, also supports the same secure mode. mount -F nfs -o sec=krb5 onc21:/casey/nfs /casey/nfs |
Changing
the Default Mount Options | |
To change the default mount options, follow these steps: Modify the NFS mount options in the /etc/fstab file, or the AutoFS map, as needed. For more information
on the different mount options that NFS supports, see mount_nfs(1M). If you changed the mount options for a directory that is currently mounted,
you must unmount and remount it before the changes take effect.
To unmount and remount the directory, enter the following commands: /usr/sbin/umount local_directory
/usr/sbin/mount local_directory |
If you change the mount options in the AutoFS master
map, you must restart AutoFS for the changes to take effect. For
information on restarting AutoFS, see “Restarting AutoFS”.
For more information on the different caching mount options,
see mount_nfs(1M). Unmounting
(Removing) a Mounted Directory | |
You can temporarily unmount a directory using the umount command. If you want to stop a directory from being automatically
mounted upon server restart or system reboot, remove it from the /etc/fstab file. | | | |  | NOTE: Before you unmount a directory, run the fuser -cu command to determine whether the directory is currently
in use. The fuser command lists the process IDs and user names of all the
processes who are using the mounted directory. If users are accessing
the mounted directories, they must exit the directories before you
unmount the directory. | | | | |
To unmount a mounted directory and prevent it from being automatically
mounted, follow these steps: Automatic UnmountTo check for any processes accessing the mounted directory,
enter the following command: fuser -cu mounted_directory |
To kill the processes, enter
the following command: fuser -ck local_mount_point |
Unmount the filesystem as follows: /usr/sbin/umount mounted_directory |
If the unmount fails, use the forcible option to
unmount the filesystem: /usr/sbin/umount -f mounted_directory |
Verify whether all the directories are unmounted
by entering the following command: The directories that you have unmounted must not be present
in the list displayed. If you do not want the directory to be automatically
mounted when the system is rebooted, remove the directory entry
from the /etc/fstab file.
Disabling
NFS Client Capability | |
To disable the NFS client, follow these steps: On the NFS client, enter the following command to get a list
of all the mounted NFS filesystems on the client For every NFS mounted directory listed by the nfsstat command, enter the following command to determine
whether the directory is currently in use: /usr/sbin/fuser -cu local_mount_point |
This command lists the process IDs and user names of all processes currently
using the mounted directory. To kill all processes that are using the mounted
directory, enter the following command: /usr/sbin/fuser -ck local_mount_point |
To unmount all NFS mounted directories, enter the
following command: To disable the NFS client and Autofs, edit the /etc/rc.config.d/nfsconf file on the client to set the NFS_CLIENT and AUTOFS variables to 0, as follows: NFS_CLIENT=0
AUTOFS=0
This prevents the client processes from starting up again when you reboot the client. |
Enter the following command to disable NFS client
capability: /sbin/init.d/nfs.client stop |
For more information, see umount (1M),
mount(1M), and fuser(1M).
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