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nfs.systemd \- managing NFS services through systemd.
.I etc
.I nfs-utils
package provides a suite of
.I systemd
unit files which allow the various services to be started and
managed. These unit files ensure that the services are started in the
correct order, and the prerequisites are active before dependant
services start. As there are quite few unit files, it is not
immediately obvious how best to achieve certain results. The
following subsections attempt to cover the issues that are most likely
to come up.
.SS Configuration
The standard systemd unit files do not provide any easy way to pass
any command line arguments to daemons so as to configure their
behavior. In many case such configuration can be performed by making
changes to
.I /etc/nfs.conf
or other configuration files. When that is not convenient, a
distribution might provide systemd "drop-in" files which replace the
.B ExecStart=
setting to start the program with different arguments. For example a
drop-in file
.B systemd/system/nfs-mountd.service.d/local.conf
ExecStart= /usr/sbin/rpc.mountd $RPCMOUNTDOPTS
would cause the
.B nfs-mountd.service
unit to run the
.I rpc.mountd
program using, for arguments, the value given for
.IR /etc/sysconfig/nfs .
This allows for seamless integration with existing configuration
.SS Enabling unit files
There are three unit files which are designed to be manually enabled.
All others are automatically run as required. The three are:
This should be enabled on any host which ever serves as an NFS client.
There is little cost in transparently enabling it whenever NFS client
software is installed.
.B nfs-server.service
This must be enabled to provide NFS service to clients. It starts and
configures the required daemons in the required order.
.B nfs-blkmap.service
.B blkmapd
daemon is only required on NFS clients which are using pNFS (parallel
NFS), and particularly using the
.B blocklayout
layout protocol. If you might use this particular extension to NFS,
.B nfs-blkmap.service
unit should be enabled.
Several other units which might be considered to be optional, such as
.I rpc-gssd.service
are careful to only start if the required configuration file exists.
.I rpc-gssd.service
will not start if the
.I krb5.keytab
file does not exist (typically in
.IR /etc ).
.SS Restarting NFS services
Most NFS daemons can be restarted at any time. They will reload any
state that they need, and continue servicing requests. This is rarely
necessary though.
When configuration changesare make, it can be hard to know exactly
which services need to be restarted to ensure that the configuration
takes effect. The simplest approach, which is often the best, is to
restart everything. To help with this, the
.B nfs-utils.service
unit is provided. It declares appropriate dependencies with other
unit files so that
.B systemctl restart nfs-utils
will restart all NFS daemons that are running. This will cause all
configuration changes to take effect
.I except
for changes to mount options lists in
.I /etc/fstab
.IR /etc/nfsmount.conf .
Mount options can only be changed by unmounting and remounting
filesystem. This can be a disruptive operation so it should only be
done when the value justifies the cost. The command
.B umount -a -t nfs; mount -a -t nfs
should unmount and remount all NFS filesystems.
.SS Masking unwanted services
Rarely there may be a desire to prohibit some services from running
even though there are normally part of a working NFS system. This may
be needed to reduce system load to an absolute minimum, or to reduce
attack surface by not running daemons that are not absolutely
Three particular services which this can apply to are
.IR rpcbind ,
.IR idmapd ,
.IR rpc-gssd .
.I rpcbind
is not part of the
.I nfs-utils
package, but it used by several NFS services. However it is
.B not
needed when only NFSv4 is in use. If a site will never use NFSv3 (or
NFSv2) and does not want
.I rpcbind
to be running, the correct approach is to run
.B systemctl mask rpcbind
This will disable
.IR rpcbind ,
and the various NFS services which depend on it (and are only needed
for NFSv3) will refuse to start, without interfering with the
operation of NFSv4 services. In particular,
.I rpc.statd
will not run when
.I rpcbind
is masked.
.I idmapd
is only needed for NFSv4, and even then is not needed when the client
and server agree to use user-ids rather than user-names to identify the
owners of files. If
.I idmapd
is not needed and not wanted, it can be masked with
.B systemctl mask idmapd
.I rpc-gssd
is assumed to be needed if the
.I krb5.keytab
file is present. If a site needs this file present but does not want
.I rpc-gssd
running, it can be masked with
.B systemctl mask rpc-gssd
.BR systemd.unit (5),
.BR nfs.conf (5),
.BR nfsmount.conf (5).