I did tried auto option but it did not work either.
Somehow I feel that eth-0 and eth-1 interfaces are up after syetm trying to mount nfs during system power up inititalization. Is it a possiblity? CompactRio power up console log is shown below. I could see n/w interface details are listed at the end. Not sure if that means those are up only at the end.
Rebooting... [236433.339130] Restarting system.
Booting LabVIEW RT...
INIT: version 2.88 booting
[ 5.485962] generic-usb 0003:0835:8501.0001: claimed by neither input, hiddev nor hidraw
[ 6.803155] generic-usb 0003:0835:8502.0002: claimed by neither input, hiddev nor hidraw
Applying large UDP packet fix to devices: eth0 eth1... done.
vm.overcommit_ratio = 81
INIT: Entering runlevel: 5
Starting NI Service Locator: done
Starting NiRioRpcServer: done
BDS: Loading NiRioSrv (NiRioSrv) ... done.
BDS: Loading bb_libk (bb_libk) ... done.
BDS: Loading niriozynqk (niriozynqk) ... done.
Starting systemWebServer: done
Starting NIAuth: done
Starting lkads: done
Starting applicationWebServer: done
Starting NI-VISA Server...
NI-VISA Server 5.4 started successfully.
Interface eth0 - MAC addr: 00:80:2f:15:46:93 - 10.35.13.191/16 (primary - static)
Interface eth1 - MAC addr: 00:80:2f:15:46:94 - 126.96.36.199/24 (static)
compactRio-9068 login: NI Scan Engine initialized.
Welcome to LabVIEW Real-Time 13.0
Finally I got the solution. The issue was related to the absence of mountnfs service. CompactRio boots up with runlevel 5. After digging deeper, it was found that '/etc/init.d/mountnfs.sh' service is not not connected in /etc/rc5.d/ and was not getting executed.
I used following commands to connect it to rc5.d:
# cd /etc/init.d
# update-rc.d mountnfs.sh start 69 5 .
Adding system startup for /etc/init.d/mountnfs.sh.
Note: Sequence number '69' is used here as at reboot level 6 (/etc/rc6.d/) the umountnfs.sh is running at sequence: 31. (standard rule: 100 - 31 = 69)
# ls -rtl /etc/rc5.d
S69mountnfs.sh -> ../init.d/mountnfs.sh
After next power boot-up, I could see that my nfs share (defined in /etc/fstab) was mounted without any issue: (shown below)
rootfs on / type rootfs (rw)
ubi1:rootfs on / type ubifs (rw,relatime)
188.8.131.52:/tmp on /mnt/iasHome type nfs (rw,relatime,vers=3,rsize=524288,wsize=524288,namlen=255,hard,nolock,proto=tcp,port=2049,timeo=70,retrans=3,sec=sys,local_lock=all,addr=184.108.40.206)
Thank you BradM and TD for your help on guiding towards right direction.