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I export a directory on a linux box and I can mount it from another linux box using

# mount -t nfs kurush:/media/lynk /mnt/kurush/

The same command fails on Mac OS X:

$ sudo mount -t nfs kurush:/media/lynk /Volumes/lynk
mount_nfs: can't mount /media/lynk from kurush onto /Volumes/lynk: Operation not permitted

At the same time, kurush:/var/logs/syslog records this line:

rpc.mountd[7943]: authenticated mount request from sds-MacBook-Pro.home:1009 for /media/lynk (/media/lynk)

When I try to go though the GUI (finder->connect to server->nfs://kurush/media/lynk->connect), I get an immediate failure (unable to connect &c) and the linux box syslog records the authenticated mount request.

The problem is solved by using a privileged port:

Command line:

sudo mount -o resvport -t nfs kurush:/media/lynk /Volumes/lynk

To enable GUI:

sudo vifs

then add a line

kurush:/media/lynk /Volumes/lynk nfs resvport,ro,user,noauto

The questions are:

  • Why do I need to use a privileged port? Is it something I do on the linux side? I seem to recall that once upon a time I did mount that share without the aforementioned magic.

  • How do I tell MacOSX to use the privileged port without using the command line? I thought Apple was for the "non-techie" crowd, so it must be possible!

|improve this question
  • Hi. Normally we close questions that exist to ask "Why did Apple do X?" but there's some nice technical details here. Your question might work better if you ask the question simply (edit it down) and then put all the answer in the answer section. If you need to ask a follow on question explaining what the problem is - perhaps it could work. What will you eventually do with the story of "why" Apple designed it thusly? – bmike♦ Aug 21 '14 at 21:47
  • 1
    @bmike: I changed the "why" to "how". – sds Aug 21 '14 at 21:57
9

Why do you have to? Tradition, mostly. Once upon a time, restricting NFS to privileged ports (<1023) was considered a security measure. Back when people were using mainframe computers, this made sure that the NFS software on the client side was part of the OS/approved by the administrator, since a program can only use a privileged port if it's run by the root user. Today, this makes no sense because anyone can own a computer and have root access, so this doesn't mean anything in terms of security.

By default, many NFS servers don't allow non-privileged source ports. Some NFS clients (such as Ubuntu's), default to using a privileged source port unless otherwise specified, which is why your Linux client works without issue. Clearly, the OS X client doesn't do this. I don't know if that was an Apple design choice or something inherited from BSD. I know that Solaris also defaults to a non-privileged port.

The two ways of avoiding this problem are, telling the OS X client to use a privileged port, as you discovered, or configuring your NFS server to allow non-privileged ports (look it up in your server's documentation).

How do you get OS X to use a privileged port using a GUI? As far as I know, you can't on versions > 10.6. One used to be able to mount NFS shares in Disk Utility and type in extra options, but that was removed. (details) It was never a simple button or anything. NFS is hardly something most of the "non-techy" crowd need, so I guess it wasn't a priority and there are reasons routinely using privileged ports isn't a great idea.

I haven't tried it, but http://www.bresink.com/osx/NFSManager.html seems to allow configuration of OS X's NFS features without the command line.

|improve this answer
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    About "or configuring your NFS server to allow non-privileged ports": for nfs-kernel-server it's the insecure options in /etc/exports. For example: /media/sda3 192.168.1.0/24(rw,async,no_subtree_check,insecure) – tungd Sep 16 '15 at 16:01
  • thanks, insecure allows Mac connect to NFS using Finder -> Go -> Connect to server – waza123 Mar 20 '18 at 12:10
  • This is an active security concern for systems today, typically within an intranet rather than over the internet. Because systems tend to mount NFS shares within the file system, there is a lot of room for abuse. Requiring privileged ports still keeps users from manipulating the file system when they shouldn't. Of course if the user has root already it doesn't matter. – jtpereyda Jul 11 '18 at 19:06

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