NFS (简体中文)

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翻译状态: 本文是英文页面 NFS翻译,最后翻译时间:2016-06-15,点击这里可以查看翻译后英文页面的改动。

来自维基百科:NFS 网络文件系统(Network File System) 是由Sun公司1984年发布的分布式文件系统协议。它允许客户端上的用户像访问本地文件一样地访问网络上的文件。

安装

客户端和服务端都只需要安装 nfs-utils 包。

强烈建议在所有节点机上使用如 ntp 之类的时间同步守护进程以保持客户端/服务器之间的时间同步,如果各个节点上没有精确同步的时钟,NFS 可能产生非预期的延迟。建议采用网络时间协议守护进程并使用互联网上的高精度 NTP 服务器同步服务端和客户端的时钟。

注意: nfs-utils for Arch Linux ARM starting with update 1.3.2-4 (possibly earlier) has been reported by one user to behave differently from the x86_64 or i686 package. See the discussion page for a recipe for client mounts.

配置

服务端

NFS 需要查看 /etc/exports 文件中定义的共享(“导出”)列表。共享的对象可以是文件系统中的任意目录。出于安全考虑,建议指定一个 NFS 共享输出的根(目录),来限制用户的可用挂载点。下面的例子遵循此原则。

/etc/exports 中定义的任何 NFS 共享都关联到 NFS 根目录。本例中,NFS 根目录是 /srv/nfs4 ,将要共享的目录是 /mnt/music

# mkdir -p /srv/nfs4/music /mnt/music

客户端可能会对 music 目录做写操作,因此必须开放读/写权限。

现在用 mount --bind 命令将实际的 music 目录挂载到 NFS 的共享根目录。

# mount --bind /mnt/music /srv/nfs4/music

为了让服务器重启后共享仍旧有效,增加绑定到 fstab 文件增加绑定到 fstab 文件:

/etc/fstab
/mnt/music /srv/nfs4/music  none   bind   0   0
注意: ZFS 文件系统对于 bindmounts 方式挂载要特殊处理,参阅 ZFS#Bindmount

增加允许被挂载的目录和主机到exports

/etc/exports
/srv/nfs4/ 192.168.1.0/24(rw,fsid=root,no_subtree_check)
/srv/nfs4/music 192.168.1.0/24(rw,no_subtree_check,nohide) # note the nohide option which is applied to mounted directories on the file system.

不必要对整个子网都开放共享,也可以仅指定单一 IP 地址或主机名。 更多信息及可用选项请查阅 man 5 exports

如果服务运行时修改了 /etc/exports 文件, 你需要重新导出使其生效。

# exportfs -ra

开始运行服务

启用运行 nfs-server.service 服务。对于较老的 V2 和 V3 版也要开启 rpcbind.service 服务。如果仅运行 V4 版,请参阅这里的讨论确认完全禁用 V2 和 V3 版:

/etc/conf.d/nfs-server.conf
NFSD_OPTS="-N 2 -N 3"

否则,必须开启 rpcbind.service 服务。

杂项

可选配置

/etc/conf.d/nfs-server.conf holds optional configurations for options to pass to rpc.nfsd, rpc.mountd, or rpc.svcgssd. Users setting up a simple configuration may not need to edit this file.

NFSv3 版静态导出

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/conf.d/nfs-common.conf to set STATD_OPTS:

/etc/conf.d/nfs-common.conf
STATD_OPTS="-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/conf.d/nfs-server.conf to set MOUNTD_OPTS:

/etc/conf.d/nfs-server.conf
MOUNTD_OPTS="-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 版兼容

Users needing to support clients using NFSv2 (for example U-Boot), should set NFSD_OPTS="-V 2" in /etc/conf.d/nfs-server.conf.

配置防火墙

To enable access through a firewall, tcp and udp ports 111, 2049, and 20048 need to be opened when using the default configuration; use rpcinfo -p to examine the exact ports in use on the server. To configure this for iptables, execute this commands:

# 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
Note: This command will override the current iptables start configuration with the current iptables configuration!

If using NFSv3 and the above listed static ports for rpc.statd and lockd these 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

If using V4-only setup, only tcp port 2049 need to be opened. Therefore only one line need.

/etc/iptables/iptables.rules
-A INPUT -p tcp -m tcp --dport 2049 -j ACCEPT

To apply changes, Restart iptables.service.

客户端

Start rpcbind.service,nfs-client.target and remote-fs.target and enable them to start at boot.

Users intending to use NFS4 with Kerberos, also need to start and enable rpc-gssd.service. Setting up /etc/krb5.keytab /etc/krb5.conf are beyond the scope of this article.

Error from systemd

Users experiencing the following may consider turning off the service using system's masking feature: "Dependency failed for pNFS block layout mapping daemon."

Example:

# systemctl mask nfs-blkmap.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:/full/path/to/music /mountpoint/on/client
Note: Server name needs to be a valid hostname (not just IP address). Otherwise mounting of remote share will hang.

通过 /etc/fstab 挂载

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   nfs4   rsize=8192,wsize=8192,timeo=14,_netdev	0 0
Note: Consult the NFS and mount man pages for more mount options.

Some additional mount options to consider are include:

rsize and wsize
rsize 的值是从服务器读取的字节数。wsize 是写入到服务器的字节数。默认都是1024, 如果使用比较高的值,如8192,可以提高传输速度。这并非通用设置,建议测试确定。参阅 #性能调优.
timeo
The timeo value is the amount of time, in tenths of a second, to wait before resending a transmission after an RPC timeout. 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 performance can be achieved by increasing this timeout value.
_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, but anyway it is good practice to use it for all types of networked file systems
Note: Setting the sixth field (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.

Tip:
  • The noauto mount option will not mount the NFS share until it is accessed: use auto for it to be available immediately.
    If experiencing any issues with the mount failing due to the network not being up/available, enable NetworkManager-wait-online.service. It will ensure that network.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 as noexec 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.
Note: Users trying to automount a NFS-share via systemd which is mounted the same way on the server may experience a freeze when handling larger amounts of data.

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.

提示与技巧

性能调优

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.

Automounting shares with systemd-networkd

Users making use of systemd-networkd might notice nfs mounts the fstab are not mounted when booting; errors like the following are common:

mount[311]: mount.nfs4: Network is unreachable

The solution is simple; force systemd to wait for the network to be completely configured by enabling systemd-networkd-wait-online.service. In theory this slows down the boot-process because less services run in parallel.

Automatic mount handling

This trick is useful for laptops that require nfs shares from a local wireless network. If the nfs host becomes unreachable, the nfs share will be unmounted to hopefully prevent system hangs when using the hard mount option. See https://bbs.archlinux.org/viewtopic.php?pid=1260240#p1260240

Make sure that the NFS mount points are correctly indicated in /etc/fstab:

$ cat /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
Note: You must use hostnames in /etc/fstab for this to work, not IP addresses.

The noauto mount option tells systemd not to automatically mount the shares at boot. systemd would otherwise attempt to mount the nfs shares that may or may not exist on the network causing the boot process to appear to stall on a blank screen.

In order to mount NFS shares with non-root users the user option has to be added.

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 $MOUNT_POINT
    fi
  fi
done
Note: If you want to test using a TCP probe instead of ICMP ping (default is tcp port 2049 in NFS4) then replace the line:
 # Check if the server is reachable
 ping -c 1 "${SERVER}" &>/dev/null

with:

 # Check if the server is reachable
 timeout 1 bash -c ": < /dev/tcp/${SERVER}/2049"
in the auto_share script above.
# chmod +x /usr/local/bin/auto_share

Create a cron entry or a systemd/Timers timer to check every minute if the server of the shares are reachable.

Cron

# crontab -e
* * * * * /usr/local/bin/auto_share

systemd/Timers

# /etc/systemd/system/auto_share.timer
[Unit]
Description=Check the network mounts

[Timer]
OnCalendar=*-*-* *:*:00

[Install]
WantedBy=timer.target
# /etc/systemd/system/auto_share.service
[Unit]
Description=Check the network mounts

[Service]
Type=simple
ExecStart=/usr/local/bin/auto_share
# systemctl enable auto_share.timer

Mount at startup via systemd

A systemd unit file can also be used to mount the NFS shares at startup. The unit file is not necessary if NetworkManager is installed and configured on the client system. See #NetworkManager dispatcher.

/etc/systemd/system/auto_share.service
[Unit]
Description=NFS automount
After=syslog.target network.target

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/usr/local/bin/auto_share

[Install]
WantedBy=multi-user.target

Now enable the auto_share.service.

NetworkManager dispatcher

In addition to the method described previously, NetworkManager can also be configured to run a script on network status change: Enable and start the NetworkManager-dispatcher.service.

The easiest method for mount shares on network status change is to just symlink to 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:

Note: This script ignores mounts with the noauto option.
/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

Make the script executable with chmod and 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

The above script can be modified to mount different shares (even other than NFS) for different connections.

See also: NetworkManager#Use dispatcher to handle mounting of CIFS shares.

排错

参阅 NFS 排错

参阅