Exporting NFS File Systems
Sharing files from an NFS server is known as exporting the
directories. The NFS Server Configuration Tool can be used to
configure a system as an NFS server.
To use the NFS Server Configuration Tool, you must by running the X
Window System. To start the application, select (on the Panel) => =>
, or type the command
redhat-config-nfs.
To add an NFS share, click the Add button. The
dialog box shown in Figure 15-2 will appear.
The Basic tab requires the following information:
Directory — Specify the directory to
share, such as /tmp.
Host(s) — Specify the host(s) to
which to share the directory. Refer to the Section called Hostname Formats for an explanation of possible
formats.
Basic permissions — Specify whether
the directory should have read-only or read/write permissions.
The General Options tab allows the following
options to be configured:
Allow connections from port 1024 and higher
— Services started on port numbers less than 1024 must be
started as root. Select this option to allow the NFS service to be
started by a user other than root. This option corresponds to
insecure.
Allow insecure file locking — Do not
require a lock request. This option corresponds to
insecure_locks.
Disable subtree checking — If a
subdirectory of a file system is exported, but the entire file
system is not exported, the server checks to see if the requested
file is in the subdirectory exported. This check is called
subtree checking. Select this option to
disable subtree checking. It the entire file system is exported,
selecting to disable subtree checking can increase the transfer
rate. This option corresponds to
no_subtree_check.
Sync write operations on request —
Enabled by default, this option does not allow the server to reply
to requests before the changes made by the request are written to
the disk. This option corresponds to sync. If
this is not selected, the async option is
used.
The User Access tab allows the following options to
be configured:
Treat remote root user as local root
— By default, the user and group IDs of the root user are both
0. Root squashing maps the user ID 0 and the group ID 0 to the user
and group IDs of anonymous so that root on the client does not have
root privileges on the NFS server. If this option is selected, root
is not mapped to anonymous, and root on a client has root
privileges to exported directories. Selecting this option can
greatly decrease the security of the system. Do not select it unless
it is absolutely necessary. This option corresponds to
no_root_squash.
Treat all client users as anonymous users
— If this option is selected, all user and group IDs are
mapped to the anonymous user. This option corresponds to
all_squash.
Specify local user ID for anonymous
users — If Treat all client users
as anonymous users is selected, this option lets
you specify a user ID for the anonymous user. This option
corresponds to anonuid.
Specify local group ID for anonymous
users — If Treat all client users as
anonymous users is selected, this option lets you
specify a group ID for the anonymous user. This option corresponds
to anongid.
To edit an existing NFS share, select the share from the list, and click
the Properties button. To delete an existing NFS
share, select the share from the list, and click the
Delete button.
After adding, modifying, or deleting shares, the nfs
service must be restarted for the changes to take effect. To apply the
changes to the configuration file and restart the service, click the
Apply button. If the nfs
service is not already running, you will be prompted to start the
service. Select Yes to start the daemon. The
daemon must be running to export the configured directories. The old
configuration file will be saved as
/etc/exports.bak, and the new configuration will be
written to /etc/exports.
NFS Server Configuration Tool reads and writes directly to the
/etc/exports configuration file. Thus, the file can
be modified manually after using the tool, and the tool can be used
after modifying the file manually (provided the file was modified with
correct syntax).
Command Line Configuration
If you prefer editing configuration files using a text editor or if
you do have have the X Window System installed, you can modify the
configuration file directly.
The /etc/exports file controls what directories the
NFS server exports. Its format is as follows:
directory hostname(options) |
The (options) are
not required. For example:
/misc/export speedy.redhat.com |
would allow users from speedy.redhat.com to mount
/misc/export with the default read-only permissions, but:
/misc/export speedy.redhat.com(rw) |
would allow users from speedy.redhat.com to mount
/misc/export with read/write privileges.
Refer to the Section called Hostname Formats for an explanation
of possible hostname formats.
Refer to the Official Red Hat Linux Reference Guide for a list of options that
can be specified.
 | Caution |
|---|
| | Be careful with spaces in the /etc/exports
file. If there are no spaces between the hostname and the options in
parentheses, the options apply only to the hostname. If there is a
space between the hostname and the options, the options apply to the
rest of the world. For example, examine the following lines:
/misc/export speedy.redhat.com(rw)
/misc/export speedy.redhat.com (rw) |
The first line grants users from
speedy.redhat.com read-write access and denies
all other users. The second line grants users from
speedy.redhat.com read-only access (the default)
and allows the rest of the world read-write access.
|
Each time you change /etc/exports, you must
inform the NFS daemon of the change, or reload the configuration file
with the following command:
Hostname Formats
The host(s) can be in the following forms:
Single machine — A fully qualified domain name (that can
be resolved by the server), hostname (that can be resolved by the
server), or an IP address
Series of machines specified with wild cards — Use the *
or ? character to specify a string match. For example,
192.168.100.* specifies any IP
address that begins with 192.168.100. When specifying wild cards in
fully qualified domain names, dots (.) are not included in the
wild card. For example,
*.example.com includes
one.example.com but does not include one.two.example.com.
IP networks — Use 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). Another acceptable format is
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).
Netgroups — In the format
@group-name, where
group-name is the NIS netgroup
name.
Starting and Stopping the Server
On the server that is exporting NFS file systems, the
nfs service must be running.
View the status of the NFS daemon with the following command:
Start the NFS daemon with the following command:
Stop the NFS daemon with the following command:
To start the nfs service at boot time, use the command:
/sbin/chkconfig --level 345 nfs on |
You can also use chkconfig,
ntsysv or the
Services Configuration Tool to configure which
services start at boot time. Refer to Chapter 13 for
details.
