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=== Client === | === Client === | ||
− | Users intending to use NFS4 with [[Kerberos]] | + | Users intending to use NFS4 with [[Kerberos]] need to [[start]] and [[enable]] {{ic|nfs-client.target}}, which starts {{ic|rpc-gssd.service}}. |
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==== Manual mounting ==== | ==== Manual mounting ==== |
Revision as of 18:04, 10 June 2018
From Wikipedia:
- Network File System (NFS) is a distributed file system protocol originally developed by Sun Microsystems in 1984, allowing a user on a client computer to access files over a network in a manner similar to how local storage is accessed.
- NFS is not encrypted. Tunnel NFS through an encrypted protocol like Kerberos, or tinc when dealing with sensitive data.
- Unlike Samba, NFS doesn't have any user authentication by default, client access is restricted by their IP-address/hostname.
- NFS expects the user and/or group ID's are the same on both the client and server. It is however possible to overrule the UID/GID by using
anonuid
/anongid
withall_squash
in/etc/exports
.
Contents
Installation
Both client and server only require the installation of the nfs-utils package.
It is highly recommended to use a time sync daemon to keep client/server clocks in sync. Without accurate clocks on all nodes, NFS can introduce unwanted delays.
Configuration
Server
The NFS server needs a list of exports (shared directories) which are defined in /etc/exports
. NFS shares defined in /etc/exports
are relative to the so-called NFS root. A good security practice is to define an NFS root in a discrete directory tree under the server's root file system which will keep users limited to that mount point. Bind mounts are used to link the share mount point to the actual directory elsewhere on the filesystem.
Consider this following example wherein:
- The NFS root is
/srv/nfs
. - The export is
/srv/nfs/music
via a bind mount to the actual target/mnt/music
.
# mkdir -p /srv/nfs/music /mnt/music # mount --bind /mnt/music /srv/nfs/music
To make it stick across reboots, add the bind mount to fstab:
/etc/fstab
/mnt/music /srv/nfs/music none bind 0 0
Add directories to be shared and limit them to a range of addresses via a CIDR or hostname(s) of client machines that will be allowed to mount them in /etc/exports
, e.g.:
/etc/exports
/srv/nfs 192.168.1.0/24(rw,sync,crossmnt,fsid=0) /srv/nfs/music 192.168.1.0/24(rw,sync) /srv/nfs/home 192.168.1.0/24(rw,sync,nohide) /srv/nfs/public 192.168.1.0/24(ro,all_squash,insecure) desktop(rw,sync,all_squash,anonuid=99,anongid=99) # map to user/group - in this case nobody
It should be noted that modifying /etc/exports
while the server is running will require a re-export for changes to take effect:
# exportfs -rav
To view the current loaded exports state in more detail, use:
# exportfs -v
For more information about all available options see exports(5).
fsid=1
option is required.Starting the server
Start and enable nfs-server.service
.
Miscellaneous
Optional configuration
Advanced configuration options can be set in /etc/nfs.conf
. Users setting up a simple configuration may not need to edit this file.
When using NFS on a network with a significant of clients one may increase the default NFS threads from 8 to 16 or even a higher, depending on the server/network requirements.
Restricting NFS to interfaces/IPs
By default, starting nfs-server.service
will listen for connections on all network interfaces, regardless of /etc/exports
. This can be changed by defining which IPs and/or hostnames to listen on.
/etc/nfs.conf
[nfsd] host=192.168.1.123 # Alternatively, you can use your hostname. # host=myhostname
Restarting the service will apply the changes immediately.
# systemctl restart nfs-server.service
Enable NFSv4 idmapping
The NFSv4 protocol represents the local system's UID and GID values on the wire as strings of the form user@domain
. The process of translating from UID to string and string to UID is referred to as ID mapping [1].
Even though idmapd may be running, it may not be fully enabled. Verify if /sys/module/nfsd/parameters/nfs4_disable_idmapping
returns N
, on disabled run:
# echo "N" | tee /sys/module/nfsd/parameters/nfs4_disable_idmapping
Set as module option to make this change permanent, e.g.:
/etc/modprobe.d/nfsd.conf
options nfsd nfs4_disable_idmapping=0
To fully use idmapping, make sure the domain is configured in /etc/idmapd.conf
on both the server and the client.
Static ports for NFSv3
Users needing support for NFSv3 clients, may wish to consider using static ports. By default, for NFSv3 operation rpc.statd
and lockd
use random ephemeral ports; in order to allow NFSv3 operations through a firewall static ports need to be defined. Edit /etc/sysconfig/nfs
to set STATDARGS
:
/etc/sysconfig/nfs
STATDARGS="-p 32765 -o 32766 -T 32803"
The rpc.mountd
should consult /etc/services
and bind to the same static port 20048 under normal operation; however, if it needs to be explicity defined edit /etc/sysconfig/nfs
to set RPCMOUNTDARGS
:
/etc/sysconfig/nfs
RPCMOUNTDARGS="-p 20048"
After making these changes, several services need to be restarted; the first writes the configuration options out to /run/sysconfig/nfs-utils
(see /usr/lib/systemd/scripts/nfs-utils_env.sh
), the second restarts rpc.statd
with the new ports, the last reloads lockd
(kernel module) with the new ports. Restart these services now: nfs-config
, rpcbind
, rpc-statd
, and nfs-server
.
After the restarts, use rpcinfo -p
on the server to examine the static ports are as expected. Using rpcinfo -p <server IP>
from the client should reveal the exact same static ports.
NFSv2 compatibility
Users needing to support clients using NFSv2 (for example U-Boot), should set RPCNFSDARGS="-V 2"
in /etc/sysconfig/nfs
.
Firewall configuration
To enable access through a firewall, TCP and UDP ports 111
, 2049
, and 20048
may need to be opened when using the default configuration; use rpcinfo -p
to examine the exact ports in use on the server:
$ rpcinfo -p | grep nfs
100003 3 tcp 2049 nfs 100003 4 tcp 2049 nfs 100227 3 tcp 2049 nfs_acl
When using NFSv4, make sure TCP port 2049
is open. No other port opening should be required:
/etc/iptables/iptables.rules
-A INPUT -p tcp -m tcp --dport 2049 -j ACCEPT
When using an older NFS version, make sure other ports are open:
# iptables -A INPUT -p tcp -m tcp --dport 111 -j ACCEPT # iptables -A INPUT -p tcp -m tcp --dport 2049 -j ACCEPT # iptables -A INPUT -p tcp -m tcp --dport 20048 -j ACCEPT # iptables -A INPUT -p udp -m udp --dport 111 -j ACCEPT # iptables -A INPUT -p udp -m udp --dport 2049 -j ACCEPT # iptables -A INPUT -p udp -m udp --dport 20048 -j ACCEPT
To have this configuration load on every system start, edit /etc/iptables/iptables.rules
to include the following lines:
/etc/iptables/iptables.rules
-A INPUT -p tcp -m tcp --dport 111 -j ACCEPT -A INPUT -p tcp -m tcp --dport 2049 -j ACCEPT -A INPUT -p tcp -m tcp --dport 20048 -j ACCEPT -A INPUT -p udp -m udp --dport 111 -j ACCEPT -A INPUT -p udp -m udp --dport 2049 -j ACCEPT -A INPUT -p udp -m udp --dport 20048 -j ACCEPT
The previous commands can be saved by executing:
# iptables-save > /etc/iptables/iptables.rules
If using NFSv3 and the above listed static ports for rpc.statd
and lockd
the following ports may also need to be added to the configuration:
/etc/iptables/iptables.rules
-A INPUT -p tcp -m tcp --dport 32765 -j ACCEPT -A INPUT -p tcp -m tcp --dport 32803 -j ACCEPT -A INPUT -p udp -m udp --dport 32765 -j ACCEPT -A INPUT -p udp -m udp --dport 32803 -j ACCEPT
To apply changes, Restart iptables.service
.
Client
Users intending to use NFS4 with Kerberos need to start and enable nfs-client.target
, which starts rpc-gssd.service
.
Manual mounting
For NFSv3 use this command to show the server's exported file systems:
$ showmount -e servername
For NFSv4 mount the root NFS directory and look around for available mounts:
# mount server:/ /mountpoint/on/client
Then mount omitting the server's NFS export root:
# mount -t nfs -o vers=4 servername:/music /mountpoint/on/client
If mount fails try including the server's export root (required for Debian/RHEL/SLES, some distributions need -t nfs4
instead of -t nfs
):
# mount -t nfs -o vers=4 servername:/srv/nfs/music /mountpoint/on/client
Mount using /etc/fstab
Using fstab is useful for a server which is always on, and the NFS shares are available whenever the client boots up. Edit /etc/fstab
file, and add an appropriate line reflecting the setup. Again, the server's NFS export root is omitted.
/etc/fstab
servername:/music /mountpoint/on/client nfs defaults,soft,rsize=32768,wsize=32768,timeo=900,retrans=5,_netdev 0 0
Some additional mount options to consider:
- rsize and wsize
- The
rsize
value is the number of bytes used when reading from the server. Thewsize
value is the number of bytes used when writing to the server. The default for both is 1024, but using higher values such as 8192 can improve throughput. This is not universal. It is recommended to test after making this change, see #Performance tuning.
- soft or hard
- Determines the recovery behaviour of the NFS client after an NFS request times out. If neither option is specified (or if the
hard
option is specified), NFS requests are retried indefinitely. If thesoft
option is specified, then the NFS client fails a NFS request after retrans retransmissions have been sent, causing the NFS client to return an error to the calling application.
- timeo
- The
timeo
value is the amount of time, in tenths of a second, to wait before resending a transmission after an RPC timeout. The default value for NFS over TCP is 600 (60 seconds). After the first timeout, the timeout value is doubled for each retry for a maximum of 60 seconds or until a major timeout occurs. If connecting to a slow server or over a busy network, better stability can be achieved by increasing this timeout value.
- retrans
- The number of times the NFS client retries a request before it attempts further recovery action. If the
retrans
option is not specified, the NFS client tries each request three times. The NFS client generates a "server not responding" message after retrans retries, then attempts further recovery (depending on whether the hard mount option is in effect).
- _netdev
- The
_netdev
option tells the system to wait until the network is up before trying to mount the share - systemd assumes this for NFS, although automount may be a more preferred solution.
fs_passno
) to a nonzero value may lead to unexpected behaviour, e.g. hangs when the systemd automount waits for a check which will never happen.Mount using /etc/fstab with systemd
Another method is using the systemd automount
service. This is a better option than _netdev
, because it remounts the network device quickly when the connection is broken and restored. As well, it solves the problem from autofs, see the example below:
/etc/fstab
servername:/home /mountpoint/on/client nfs noauto,x-systemd.automount,x-systemd.device-timeout=10,timeo=14,x-systemd.idle-timeout=1min 0 0
One might have to reboot the client to make systemd aware of the changes to fstab. Alternatively, try reloading systemd and restarting mountpoint-on-client.automount
to reload the /etc/fstab
configuration.
- The
noauto
mount option will not mount the NFS share until it is accessed: useauto
for it to be available immediately.
If experiencing any issues with the mount failing due to the network not being up/available, enableNetworkManager-wait-online.service
. It will ensure thatnetwork.target
has all the links available prior to being active. - The
users
mount option would allow user mounts, but be aware it implies further options asnoexec
for example. - The
x-systemd.idle-timeout=1min
option will unmount the NFS share automatically after 1 minute of non-use. Good for laptops which might suddenly disconnect from the network. - If shutdown/reboot holds too long because of NFS, enable
NetworkManager-wait-online.service
to ensure that NetworkManager is not exited before the NFS volumes are unmounted. You may also try to add thex-systemd.requires=network-online.target
mount option if shutdown takes too long. - Using mount options as
noatime
,nodiratime
,noac
,nocto
may be used to increase NFS performance.
Mount using autofs
Using autofs is useful when multiple machines want to connect via NFS; they could both be clients as well as servers. The reason this method is preferable over the earlier one is that if the server is switched off, the client will not throw errors about being unable to find NFS shares. See autofs#NFS network mounts for details.
Tips and tricks
Performance tuning
In order to get the most out of NFS, it is necessary to tune the rsize
and wsize
mount options to meet the requirements of the network configuration.
In recent linux kernels (>2.6.18) the size of I/O operations allowed by the NFS server (default max block size) varies depending on RAM size, with a maximum of 1M (1048576 bytes), the max block size of the server will be used even if nfs clients requires bigger rsize
and wsize
. See https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/5/html/5.8_Technical_Notes/Known_Issues-kernel.html
It is possible to change the default max block size allowed by the server by writing to the /proc/fs/nfsd/max_block_size
before starting nfsd. For example, the following command restores the previous default iosize of 32k:
# echo 32767 > /proc/fs/nfsd/max_block_size
To make the change permanent, create a systemd-tmpfile:
/etc/tmpfiles.d/nfsd-block-size.conf
w /proc/fs/nfsd/max_block_size - - - - 32768
To mount with the increased rsize
and wsize
mount options:
# mount -t nfs -o rsize=32768,wsize=32768,vers=4 servername:/srv/nfs/music /mountpoint/on/client
Automatic mount handling
This trick is useful for NFS-shares on a wireless network and/or on a network that may be unreliable. If the NFS host becomes unreachable, the NFS share will be unmounted to hopefully prevent system hangs when using the hard
mount option [4].
Make sure that the NFS mount points are correctly indicated in fstab:
/etc/fstab
lithium:/mnt/data /mnt/data nfs noauto,noatime,rsize=32768,wsize=32768 0 0 lithium:/var/cache/pacman /var/cache/pacman nfs noauto,noatime,rsize=32768,wsize=32768 0 0
Create the auto_share
script that will be used by cron or systemd/Timers to use ICMP ping to check if the NFS host is reachable:
/usr/local/bin/auto_share
#!/bin/bash function net_umount { umount -l -f $1 &>/dev/null } function net_mount { mountpoint -q $1 || mount $1 } NET_MOUNTS=$(sed -e '/^.*#/d' -e '/^.*:/!d' -e 's/\t/ /g' /etc/fstab | tr -s " ")$'\n'b printf %s "$NET_MOUNTS" | while IFS= read -r line do SERVER=$(echo $line | cut -f1 -d":") MOUNT_POINT=$(echo $line | cut -f2 -d" ") # Check if server already tested if [[ "${server_ok[@]}" =~ "${SERVER}" ]]; then # The server is up, make sure the share are mounted net_mount $MOUNT_POINT elif [[ "${server_notok[@]}" =~ "${SERVER}" ]]; then # The server could not be reached, unmount the share net_umount $MOUNT_POINT else # Check if the server is reachable ping -c 1 "${SERVER}" &>/dev/null if [ $? -ne 0 ]; then server_notok[${#Unix[@]}]=$SERVER # The server could not be reached, unmount the share net_umount $MOUNT_POINT else server_ok[${#Unix[@]}]=$SERVER # The server is up, make sure the share are mounted net_mount $MOUNT_POINT fi fi done
# Check if the server is reachable ping -c 1 "${SERVER}" &>/dev/null
with:
# Check if the server is reachable timeout 1 bash -c ": < /dev/tcp/${SERVER}/2049"in the
auto_share
script above.Make sure the script is executable:
# chmod +x /usr/local/bin/auto_share
Next check configure the script to run every X, in the examples below this is every minute.
Cron
# crontab -e
* * * * * /usr/local/bin/auto_share
systemd/Timers
/etc/systemd/system/auto_share.timer
[Unit] Description=Automount NFS shares every minute [Timer] OnCalendar=*-*-* *:*:00 [Install] WantedBy=timers.target
/etc/systemd/system/auto_share.service
[Unit] Description=Automount NFS shares After=syslog.target network.target [Service] Type=oneshot ExecStart=/usr/local/bin/auto_share [Install] WantedBy=multi-user.target
Finally, enable and start auto_share.timer
.
Using a NetworkManager dispatcher
NetworkManager can also be configured to run a script on network status change.
The easiest method for mount shares on network status change is to symlink the auto_share
script:
# ln -s /usr/local/bin/auto_share /etc/NetworkManager/dispatcher.d/30-nfs.sh
However, in that particular case unmounting will happen only after the network connection has already been disabled, which is unclean and may result in effects like freezing of KDE Plasma applets.
The following script safely unmounts the NFS shares before the relevant network connection is disabled by listening for the pre-down
and vpn-pre-down
events, make the script is executable:
/etc/NetworkManager/dispatcher.d/30-nfs.sh
#!/bin/bash # Find the connection UUID with "nmcli con show" in terminal. # All NetworkManager connection types are supported: wireless, VPN, wired... WANTED_CON_UUID="CHANGE-ME-NOW-9c7eff15-010a-4b1c-a786-9b4efa218ba9" if [[ "$CONNECTION_UUID" == "$WANTED_CON_UUID" ]]; then # Script parameter $1: NetworkManager connection name, not used # Script parameter $2: dispatched event case "$2" in "up") mount -a -t nfs4,nfs ;; "pre-down");& "vpn-pre-down") umount -l -a -t nfs4,nfs >/dev/null ;; esac fi
noauto
option, remove this mount option or use auto
to allow the dispatcher to manage these mounts.Create a symlink inside /etc/NetworkManager/dispatcher.d/pre-down
to catch the pre-down
events:
# ln -s /etc/NetworkManager/dispatcher.d/30-nfs.sh /etc/NetworkManager/dispatcher.d/pre-down.d/30-nfs.sh
Troubleshooting
There is a dedicated article NFS Troubleshooting.
See also
- See also Avahi, a Zeroconf implementation which allows automatic discovery of NFS shares.
- HOWTO: Diskless network boot NFS root
- Microsoft Services for Unix NFS Client info
- NFS on Snow Leopard (Dead Link => Archive.org Mirror)
- http://chschneider.eu/linux/server/nfs.shtml
- How to do Linux NFS Performance Tuning and Optimization
- Linux: Tune NFS Performance