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I am sharing /share/global/usr/share from a server to /usr/share on a client via NFS. When the client writes into it I get "Read-only filesystem" error.

Server

Filesystem permissions ok:

$> ls -la /share/global/usr/ drwxrwxrwx 2 nobody nogroup 4096 Dec 6 14:37 share

Exports are rw for client IP 192.168.101.250, other internal IPs are ro.

$> grep usr /etc/exports /share/global/usr/share 192.168.0.0/16(ro,subtree_check,all_squash) 192.168.101.250(rw,subtree_check,all_squash)

Server can write here:

$> echo HELLO > /share/global/usr/share/REMOVEME && chmod 666 /share/global/usr/share/REMOVEME && echo ok ok

Client

IP address matches (static):

$> ip addr | grep inet inet 192.168.101.250/24 brd 192.168.101.255 scope global enp0s8

fstab specifies rw:

$> grep usr /etc/fstab 192.168.101.254:/share/global/usr/share /usr/share nfs rsize=8192,wsize=8192,timeo=3,intr,rw

and it's mounted rw:

$> mount | grep usr 192.168.101.254:/share/global/usr/share on /usr/share type nfs4 (rw,relatime,vers=4.0,rsize=8192,wsize=8192,namlen=255,hard,proto=tcp,port=0,timeo=3,retrans=2,sec=sys,clientaddr=192.168.101.250,local_lock=none,addr=192.168.101.254)

Read is ok:

$> ls -al /usr/share/REMOVEME -rw-rw-rw-. 1 nfsnobody nfsnobody 7 Dec 6 15:14 /usr/share/REMOVEME

Problem

On client:

$> sudo -i $> echo foo > /usr/share/REMOVEME -bash: /usr/share/REMOVEME: Permission denied

I also can't create new files here.

Everything in the configuration looks okay to me. Why can't I write to the shared directory on the client?

Server is Ubuntu 16.04, client is CentOS 7.

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  • SElinux in play here? Commented Dec 6, 2016 at 16:18

2 Answers 2

Reset to default
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/etc/exports wants the specific IP addresses to appear first, IP ranges after.

i.e.

/share/global/usr/share 192.168.101.250(rw,subtree_check,all_squash) 192.168.0.0/16(ro,subtree_check,all_squash)
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  • I wonder if the ordering in your example is important because your IP range has a more restrictive permission granted than the single host. I think if the IP range was a different subnet from your single host, it could still be listed first. Commented Dec 6, 2016 at 16:34
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You seem to get the error message when writing to the root of the NFS mount on the client. I had a similar issue and to me it seems that NFS server shows the all "disks" as "virtual devices" in the root, which is not really any directory on the server, but a "virtual listing" provided by the NFS server, resulting in "Read-only file system" -error message. Depending on your configuration, you might get the error message when writing to the root of the shared volume.

However, if you have a sub-directory on a shared disk, and try to write there, it works fine.

Demonstration on the client:

 root@dunharg:/mnt/share# touch write-test touch: cannot touch 'write-test': Read-only file system root@dunharg:/mnt/share# ls backup hdd nvme ssd root@dunharg:/mnt/share# cd sdd root@dunharg:/mnt/share/sdd# ls home share root@dunharg:/mnt/share/sdd# touch write-test touch: cannot touch 'write-test': Read-only file system root@dunharg:/mnt/share/sdd# cd share root@dunharg:/mnt/share/sdd/share# touch write-test ok
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