How To Restore Partition Table on Running Linux Mint Ubuntu Debian Machine

Here is an easy way to restore things if you have the starting point and size of each partition using fdisk:

In this example we pretend that /dev/sda was wiped out, but the running system still has the info in /sys/class/block/sda

Go into each partition and record the "start" and "size"

hostdev@box /sys/class/block/sda/sda1 $ cat start 2048 hostdev@box /sys/class/block/sda/sda1 $ cat size 2097152

hostdev@box /sys/class/block/sda $ cat sda2/start 2099200 hostdev@box /sys/class/block/sda $ cat sda2/size 62914560

hostdev@box /sys/class/block/sda $ cat sda3/start 65013760 hostdev@box /sys/class/block/sda $ cat sda3/size 520923740

Now create the same 3 partitions at the same starting point and with the same size using fdisk:

Welcome to fdisk (util-linux 2.34). Changes will remain in memory only, until you decide to write them. Be careful before using the write command. Device does not contain a recognized partition table. Created a new DOS disklabel with disk identifier 0x8e7672df. Command (m for help): n Partition type p primary (0 primary, 0 extended, 4 free) e extended (container for logical partitions) Select (default p): Using default response p. Partition number (1-4, default 1): First sector (2048-585524838, default 2048): 2048 Last sector, +/-sectors or +/-size{K,M,G,T,P} (2048-585524838, default 585524838): 2097152 Created a new partition 1 of type 'Linux' and of size 1023 MiB. Command (m for help): n Partition type p primary (1 primary, 0 extended, 3 free) e extended (container for logical partitions) Select (default p): Using default response p. Partition number (2-4, default 2): First sector (2097153-585524838, default 2099200): 2099200 Last sector, +/-sectors or +/-size{K,M,G,T,P} (2099200-585524838, default 585524838): 62914560 Created a new partition 2 of type 'Linux' and of size 29 GiB. Command (m for help): n Partition type p primary (2 primary, 0 extended, 2 free) e extended (container for logical partitions) Select (default p): Using default response p. Partition number (3,4, default 3): 65013760 Value out of range. Partition number (3,4, default 3): First sector (2097153-585524838, default 62916608): 65013760 Last sector, +/-sectors or +/-size{K,M,G,T,P} (65013760-585524838, default 585524838): 520923740 Created a new partition 3 of type 'Linux' and of size 217.4 GiB.