recently we were booting up a system in rescue mode but after doing chroot to that system I was not able to see any filesystem there as running df -h was giving error no file system processed. As there was no proc system we have mounted the proc system in the chroot environment using below commands first.
mount -t proc proc proc/ mount -t sysfs sys sys/ mount -o bind /dev dev/
Once the proc filesystem was mounted we have have access to file called /proc/mounts I have checked its output using cat command
Now to fix the issue of df no file systems processed I have copied the content of /proc/mounts to the file /etc/mtab
cat /proc/mounts > /etc/mtab
After adding those entries in mtab file I was able to access the filesystem fine and df command was working perfectly fine.