EC2 error: cannot create temp file for here-document: Read-only file system

Looks like my Ubuntu 14.04 EC2 made the fs read-only.

cd /var/  (pressing tab for autocomplete)

cannot create temp file for here-document: Read-only file system

But I have plenty of free space and memory is not full either:

Welcome to Ubuntu 14.04.2 LTS (GNU/Linux 3.13.0-48-generic x86_64) * Documentation:  https://help.ubuntu.com/  System information as of Wed Feb  3 14:40:58 UTC 2016  System load:  0.0                Processes:           126  Usage of /:   14.9% of 11.67GB   Users logged in:     0  Memory usage: 19%                IP address for eth0: 172.31.15.38  Swap usage:   0%

df -hi:

/dev/xvda1       768K   85K  684K   12% /none             251K     2  251K    1% /sys/fs/cgroupudev             249K   387  249K    1% /devtmpfs            251K   309  250K    1% /runnone             251K     1  251K    1% /run/locknone             251K     1  251K    1% /run/shmnone             251K     2  251K    1% /run/user

free:

             total       used       free     shared    buffers     cachedMem:       2048484    1199420     849064       6248     180300     635596-/+ buffers/cache:     383524    1664960

du -sch /tmp*

9.9M    /tmp9.9M    total

What's the solution here? How can I fix the fs without losing my data?

Should I run:

mount -o remount,rw /

or should I reboot?

Thanks in advance!