I know mount and df lists all mounts. But I would like to list the mounts which failed to establish on boot, too. How do I get them?
There is no such command, since there is no list of "attempted mounts". You can compare the current mount list (/etc/mtab) to the list of shares registered to be mounted though (/etc/fstab).
Alternatively you could try to grep through the system log files to find failed mount attempts.