How can I mount a partition on every reboot?

You need to make an entry in /etc/fstab for the mount, something like:

/dev/sda3 /foo                       ext3    defaults        1 1

For more information see:

https://help.ubuntu.com/community/Fstab

Sometimes, one may face critical issues due to /etc/fstab entries. So, the alternative is crontab.

Just add below entry in root's crontab.

$ sudo crontab -e

@reboot mount -t ext3 /dev/sda3 /foo

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