To format an SD card in Ubuntu you can use either an external or built-in SD card reader. Additionally, download and install Disk Utility for Ubuntu. Insert the SD card into the reader and connect it to your computer if it's an external device.
Click the Applications icon in Unity to bring up the search box.
Type disks in the search box and then choose Disks in the Applications section of the search results.
Locate the SD drive in the list of devices and click it to highlight it.
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Select the Gear icon and choose Format.
First, select an erase method. For a quick format, choose Don't Overwrite Existing Data (Quick), or you can select Overwrite Existing Data With Zeroes (Slow) to shred the files on the drive.
Then, select a method. Choose Compatible With All Systems and Devices (MBR/DOS) to format for maximum compatibility. If your USB drive is greater than 2TB, choose Compatible With Modern Systems and Hard Disks > 2TB (GPT).
To format without a partition, select No Partitioning (Empty).
Choose Format to continue.
Choose Format to confirm that you want to destroy all the data on the SD card and format it.