Script to check for read only filesystem

awk '$4~/(^|,)ro($|,)/' /proc/mounts

I've used the following in the past

grep ' ro ' /proc/mounts

In some instances you may want to skip any remote mounts which may be RO by design

grep ' ro ' /proc/mounts | grep -v ':'

You also may want to skip things that are mounted via automount

grep ' ro ' /proc/mounts | egrep -v 'automount|autofs'

If you intent is to find filesystems with problems (i.e. the mounting status has been changed to READ-ONLY due to a filesystem error), then I'd do the following (assumming ext* filesystems):

 tune2fs -e panic [raw-disk-partition-name]

EX:

 tune2fs -e panic /dev/sda1

What this does is panic the system, thus rebooting the server, possibly invoking a fsck on the problem filesystem to fix it. Thus a serious filesystem problem is handled by having the system fix it automatically, instead of dumping it into Read-ONLY mode which I have not found very helpful. Besides I'd rather panic a problem filesystem, fixing it than attempting to run with it damaged which as time goes on might cause more damage.

cat /proc/mounts|sort|awk '{print $1 "\011" toupper(substr($4,0,2))}'

Produces tab delimited output with mount name and mode.

As other answers suggest, you can parse /proc/mounts with grep or awk, for example you can list the read-only mounts:

$ grep "\sro[\s,]" /proc/mounts

or

$ awk '$4~/(^|,)ro($|,)/' /proc/mounts

An alternative to parsing the content of /proc/mounts that you could try is

$  grep '^ro$' /proc/fs/*/<device>/options

where <device> is the filesystem's device node name under /dev. For example

$ grep '^ro$' /proc/fs/*/sdc1/options

would return ro if /dev/sdc1 is mounted read-only.

If you want to check for a read-only block device (instead of a mounted filesystem) you can use

$ cat /sys/block/<device>/ro

which returns 1 if the filesystem is read-only or 0 if read-write.

Note that <device> above refers to the real device node. If you want to check a symlink device (such as those created by device-mapper or by-uuid references) then you can use basename and readlink to get the device node name. Like these examples:

$ grep '^ro$' /proc/fs/*/$(basename $(readlink -f /dev/mapper/foo)/options
$ cat /sys/block/$(basename $(readlink -f /dev/mapper/foo)/ro

An approach that works even for remote file systems (which can be mounted rw even if they're exported ro, resulting in a read only file system) is to simply create a test file on each file system and test the return code of that command.

But if this is something that happens regularly you need to look into the cause rather than trying to keep up fixing the symptoms.

I'm a little late but this is how I handle it.

#!/bin/bash

FILE=/tmp/test.txt

# Check health of LXD host machine
touch ${FILE}

if [ -f ${FILE} ];
then
   rm ${FILE}
   echo "File System is Good!"
else
   message="File System is R/O !"
   echo ${message} >> /var/log/lxd/health.log >&2
   send_twilio "${TWILIO_ACCOUNT_SID}" "${TWILIO_ACCOUNT_TOKEN}" "${TWILIO_NUMBER}" "${to_twilio}" "${HOST}" "${message}"