Mounting (either internal or external) hard drives in Linux
When using Linux headless, such as via SSH or with no desktop environment, accessing a newly installed hard drive (not just external USB drives, but additional internal HDDs too) is not obvious, and most people end up having to Google it. I know I did. So let's have a quick and dirty guide on how.
When using Linux headless, such as via SSH or with no desktop environment, accessing a newly So how do we access a newly added hard drive in Linux? In Windows and most Linux desktop environments, a newly connected internal or external hard drive will be automatically detected, mounted and show up in file explorer (or your desktop environment’s equivalent), but how does it work over command line with no GUI?
For purposes of this explanation, let’s assume you have a Linux server you just installed a new internal hard drive in. (The process is nearly identical for external drives.) This server has no desktop environment, so we’re using only the command line. In Linux, all devices connected to the computer, including hard drives, are located in the root /dev directory. Each hard drive, whether internal or external, are given their own sub-directory within it. If your hard drives use SCSI (and they likely do if built in the last decade) then your boot drive will be /sda. On the off chance you’re still using IDE hard drives, the master drive will be /hda, and the slave drive will be /hdb.
First, let’s list out our hard drives on the terminal. There are several ways to do this, but the one I find most user friendly is lsblk — using it will output a nicely formatted list of all devices, including hard drives and their partitions. Partitions within a hard drive are named, for example, sda1, sda2, etc. Let’s see the output of lsblk:
The output shows this computer has a primary hard drive, /sda, with two partitions. /sdb is an additional 1TB hard drive installed. In my case this drive was previously partitioned, has data on it, but the data is inaccessible because it is not mounted. If you need to partition the hard drive, use the following command:
sudo fdisk /dev/sdb
This will change the terminal to a prompt, press m to bring up a list of commands. You’ll see that you use d to delete partitions and n to create new ones. We’ll create a new one here and give it the default number of 1, then use w to save and quit. Now when you use the lsblk command you’ll see the _sdb1_ partition listed.
To access and interact with files, the partition needs a file system. Since this is on Linux, we’ll just use ext4. Use the following command:
sudo mkfs -t ext4 /dev/sdb1
Now you mount that partition onto a specific directory. Common practice is to mount internal hard drives that will stay at work long-term to /mnt in the root directory. Or at least I heard that somewhere and adopted it as a common practice for myself. I’ll create a sub-directory within like this: mkdir /mnt/DATA
Now we mount the sdb1 partition to that new directory with this command:
mount /dev/sdb1 /mnt/DATA
Let’s check out our list of devices again, but it’s refine the output of lsblk by piping it into grep like so:
lsblk | grep -v 7:
The -v option will filter out any lines with the character 7:. Without getting into the weeds of device numbers, in the prior output of lsblk it shows block devices have the major number 7 while hard drives have the major number 8, both separated from the minor number by a colon. So by piping 7: through grep I can list only hard drives. Here’s the output:
There it is! In my case I made a primary partition taking up the entire 1TB hard drive. Now I can see the contents by using ls /mnt/DATA. But there’s one last thing to do. This drive will not stay mounted on reboot by default, so let’s make sure we make it stay. This is done by editing the fstab file. Let’s do that with sudo nano /etc/fstab.
It gives you the instructions right there, very plainly. Let’s do as it says and use the command blkid. (If there’s no output, do it with sudo.)
Since the drive is mounted, it’s helpfully labeled, so you can figure out which one it is at a glance. Copy the UUID, then paste it into the fstab file and add the other options as instructed:
Simple. We’re using ext4 as the file system, which is how I partitioned it, but if it the file system is different use the correct one — e.g ntfs, zfs, etc. We are using the same options as the swap partition for this hard drive, let’s call these basic options.
The number at the end of each line is important, its the order filesystems are checked at boot time. Make sure your root drive is always set to
1, non-root mount points should be set to2.
Save and close the fstab file. Now when you reboot, the second hard drive should always auto-mount to /mnt/DATA. This guide was for an internal hard drive specifically, but as I said before, everything is identical for external USB drives; they show up as sdb, sdc, and so on. The HDDs inside the external drives are SCSI, and so are USB sticks. Mount all the things!