cannot write files to a mounted nfs partition

I mounted an nfs partition from a remote server to this host (thea). I wrote this line to /etc/fstab file and mounted with -a option. all things looks ok except when I tried to write file to this partition. it doesn't let me create file to this partition even with "root" permission, please help.  

[root@thea titanbackup]# touch testfile
touch: cannot touch `testfile': Permission denied

[root@thea mnt]# ls -alt
total 20
dr-xr-xr-x. 28 root root 4096 Aug 21 08:48 ..
drwxr-xr-x   2 root root    6 Jun 17 14:31 titanbackup
drwxr-xr-x.  6 root root 4096 Jun 14 21:07 .
drwxr-xr-x.  2 root root 4096 Feb 11  2014 hgfs
drwxr-xr-x.  2 root root 4096 Feb 10  2014 cdrom
drwxr-xr-x.  2 root root 4096 Feb  5  2014 ExternalHD
[root@thea mnt]#

[root@thea titanbackup]# mount
/dev/sda3 on / type ext4 (rw)
proc on /proc type proc (rw)
sysfs on /sys type sysfs (rw)
devpts on /dev/pts type devpts (rw,gid=5,mode=620)
tmpfs on /dev/shm type tmpfs (rw)
/dev/sda1 on /boot type ext4 (rw)
/dev/mapper/vg_OS-home on /home type ext4 (rw)
/dev/mapper/vg_OS-tmp on /tmp type ext4 (rw)
/dev/mapper/vg_Gentran-LogVol00 on /u1 type ext4 (rw)
/dev/mapper/vg_OS-usr on /usr type ext4 (rw)
/dev/mapper/vg_OS-var on /var type ext4 (rw)
none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw)
sunrpc on /var/lib/nfs/rpc_pipefs type rpc_pipefs (rw) on /u1/nfsbackup type nfs (rw,vers=4,addr=,clientaddr= on /mnt/titanbackup type nfs (rw,vers=4,addr=,clientaddr=
[root@thea titanbackup]# cat /etc/*-release
Red Hat Enterprise Linux Server release 6.5 (Santiago)
Red Hat Enterprise Linux Server release 6.5 (Santiago)
[root@thea titanbackup]#

root@thea titanbackup]# cat /etc/fstab

# /etc/fstab
# Created by anaconda on Mon Feb  3 23:20:58 2014
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
UUID=011240a7-1286-43ef-9e77-889eada1b760 /                       ext4    defaults        1 1
UUID=8678f3c4-d9a0-44fe-96ea-f292b022c84e /boot                   ext4    defaults        1 2
/dev/mapper/vg_OS-home  /home                   ext4    defaults        1 2
/dev/mapper/vg_OS-tmp   /tmp                    ext4    defaults        1 2
/dev/mapper/vg_Gentran-LogVol00 /u1                     ext4    defaults        1 2
/dev/mapper/vg_OS-usr   /usr                    ext4    defaults        1 2
/dev/mapper/vg_OS-var   /var                    ext4    defaults        1 2
UUID=969cf12d-482f-4b54-a6e0-79a8600509aa swap                    swap    defaults        0 0
tmpfs                   /dev/shm                tmpfs   defaults        0 0
devpts                  /dev/pts                devpts  gid=5,mode=620  0 0
sysfs                   /sys                    sysfs   defaults        0 0
proc                    /proc                   proc    defaults        0 0   /u1/nfsbackup nfs     _netdev         0 0
titan:/u1/backup/thea/nfsbackup   /mnt/titanbackup nfs    _netdev         0 0
[root@thea titanbackup]#
Jason YuAsked:
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Seth SimmonsSr. Systems AdministratorCommented:
on the titan server, what is the output of /etc/exports?
for that export (titanbackup) does it have the option no_root_squash?
if not, that is your problem since by default root over an nfs share will be like nobody
adding no_root_squash to your export options will allow root access over nfs

example: /u1/backup/thea/nfsbackup *(no_root_squash)
you want to add that option there with whatever other options you already have

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Jason YuAuthor Commented:
I just added the no_root_sqush to this titan server but it's still not working, could you check?

[root@titan ~]# cat /etc/exports
/u1/backup/jupiter    ,sync)
/u1/backup/halo                 halobk(rw,sync)
/u1/backup/ora9igl    ,sync)
/u1/centos                      *(rw,sync)
/u1/centos/centos-6_32          *(rw,sync)
/u3/appsperi          ,sync),sync) elysium(rw,sync) phobos(rw,sync)
/u1/centos/rhel64_5.5           *(rw,sync)
/u2/backup/luna       ,sync)
/u1/backup/thea       ,sync,no_root_squash)
[root@titan ~]#

[root@thea titanbackup]# mount titan:/u1/backup/thea/nfsbackup   /mnt/titanbackup
mount.nfs: /mnt/titanbackup is busy or already mounted
[root@thea titanbackup]# umount -f /u1/nfsbackup
umount2: Invalid argument
umount: /u1/nfsbackup: not mounted
[root@thea titanbackup]# cd ..
[root@thea mnt]# umount -f /mnt/titanbackup/
[root@thea mnt]# mount -a
[root@thea mnt]# cd titanbackup/
[root@thea titanbackup]# touch test
touch: cannot touch `test': Permission denied
[root@thea titanbackup]#
Seth SimmonsSr. Systems AdministratorCommented:
after you change the exports file, you need to run exportfs -a on titan for the nfs server to refresh the export list
remove the mount on thea and mount again
the syntax you added in exports is correct
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Jason YuAuthor Commented:
It's working now, wonderful job.

[root@thea titanbackup]# touch test
[root@thea titanbackup]# ls -alt
total 4
-rw-r--r--  1 root root    0 Aug 21  2014 test
drwxr-xr-x  2 root root   17 Aug 21  2014 .
drwxr-xr-x. 6 root root 4096 Jun 14 21:07 ..
[root@thea titanbackup]# rm -rf test
[root@thea titanbackup]#
Jason YuAuthor Commented:
what is exportfs command for? and option -a -r?
Jason YuAuthor Commented:
thanks, I figured it out by google. have a nice night.
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