Disks, Mounting & fstab

Managing disks and partitions is a core skill in Ubuntu 26.04 system administration. This article explains how to view disk information, manually mount partitions, and configure automatic mounting at boot via fstab.

Viewing Disk and Partition Information

lsblk - List Block Devices


# Basic usage
lsblk
 
# Example output:
# NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
# sda      8:0    0   500G  0 disk
# ├─sda1   8:1    0   512M  0 part /boot/efi
# ├─sda2   8:2    0   488G  0 part /
# └─sda3   8:3    0  11.5G  0 part [SWAP]
# sdb      8:16   0     2T  0 disk
# └─sdb1   8:17   0     2T  0 part
 
# Show filesystem types and UUIDs
lsblk -f
 
# Show more detailed information
lsblk -o NAME,SIZE,FSTYPE,MOUNTPOINT,UUID,LABEL

Other Disk Information Tools


# View partition table
sudo fdisk -l
 
# View disk usage
df -h
 
# View disk usage of a specific directory
du -sh /var/log
 
# View UUIDs of all partitions
sudo blkid

Partitioning

Using fdisk for MBR Partitioning


# Partition /dev/sdb
sudo fdisk /dev/sdb
 
# fdisk interactive commands:
# n - Create a new partition
# p - Print partition table
# d - Delete a partition
# t - Change partition type
# w - Write changes and exit

Using gdisk for GPT Partitioning


sudo apt install gdisk
sudo gdisk /dev/sdb

Using parted


# Interactive mode
sudo parted /dev/sdb
 
# Non-interactive example: create a GPT partition table and one partition
sudo parted /dev/sdb mklabel gpt
sudo parted /dev/sdb mkpart primary ext4 0% 100%

Formatting Partitions


# Format as ext4
sudo mkfs.ext4 /dev/sdb1
 
# Format as XFS
sudo mkfs.xfs /dev/sdb1
 
# Format as Btrfs
sudo mkfs.btrfs /dev/sdb1
 
# Format as NTFS (requires ntfs-3g)
sudo mkfs.ntfs /dev/sdb1
 
# Set a volume label
sudo e2label /dev/sdb1 "DataDisk"

Mounting and Unmounting

mount - Mounting a Partition


# Create a mount point
sudo mkdir -p /mnt/data
 
# Mount a partition
sudo mount /dev/sdb1 /mnt/data
 
# Mount as read-only
sudo mount -o ro /dev/sdb1 /mnt/data
 
# Mount an ISO file
sudo mount -o loop ubuntu-26.04.iso /mnt/iso
 
# Mount an NFS share
sudo mount -t nfs 192.168.1.100:/shared /mnt/nfs
 
# Mount a CIFS/SMB share
sudo mount -t cifs //192.168.1.100/share /mnt/smb -o username=user,password=pass
 
# View all current mounts
mount | column -t
findmnt

umount - Unmounting a Partition


# Unmount a partition
sudo umount /mnt/data
 
# If the device is busy, find the processes using it
sudo lsof +f -- /mnt/data
sudo fuser -mv /mnt/data
 
# Force unmount (use with caution)
sudo umount -l /mnt/data    # Lazy unmount
sudo umount -f /mnt/data    # Force unmount (NFS)

/etc/fstab Auto-Mount

Warning

Configuration errors in /etc/fstab (such as typos in UUIDs or non-existent mount points) can prevent the system from booting normally. Always back up the file before editing (sudo cp /etc/fstab /etc/fstab.bak), and verify the configuration with sudo mount -a and sudo findmnt --verify after making changes. For non-critical partitions, consider adding the nofail option to prevent boot failures.

fstab File Format

/etc/fstab defines partitions that are automatically mounted at boot. Each line contains six fields:


# <device>           <mount point>  <filesystem>  <options>         <dump>  <fsck>
UUID=xxxx-xxxx    /mnt/data   ext4        defaults        0       2

Field descriptions:

Field	Description
Device	Partition identifier; UUID is recommended
Mount point	Directory path to mount to
Filesystem	ext4, xfs, btrfs, ntfs, etc.
Options	Mount options, separated by commas
Dump	Backup flag, usually 0
Fsck	Boot check order: 1 for root, 2 for others, 0 to skip

Getting the UUID


# Method 1: blkid
sudo blkid /dev/sdb1
# Output: /dev/sdb1: UUID="a1b2c3d4-e5f6-7890-abcd-ef1234567890" TYPE="ext4"
 
# Method 2: lsblk
lsblk -f /dev/sdb1
 
# Method 3: ls symlinks
ls -la /dev/disk/by-uuid/

fstab Configuration Examples


# Edit fstab (back up before modifying)
sudo cp /etc/fstab /etc/fstab.bak
sudo nano /etc/fstab

Common configurations:


# ext4 data partition
UUID=a1b2c3d4-e5f6-7890-abcd-ef1234567890  /mnt/data  ext4  defaults  0  2

# Mount with specific options
UUID=b2c3d4e5-f6a7-8901-bcde-f12345678901  /mnt/ssd   ext4  defaults,noatime,discard  0  2

# NTFS partition (Windows data drive)
UUID=1234567890ABCDEF  /mnt/windows  ntfs-3g  defaults,uid=1000,gid=1000,umask=022  0  0

# NFS network share
192.168.1.100:/shared  /mnt/nfs  nfs  defaults,_netdev  0  0

# tmpfs (in-memory filesystem)
tmpfs  /tmp  tmpfs  defaults,noatime,size=2G  0  0

# swap partition
UUID=c3d4e5f6-a7b8-9012-cdef-123456789012  none  swap  sw  0  0

Common Mount Options

Option	Description
`defaults`	Equivalent to rw,suid,dev,exec,auto,nouser,async
`noatime`	Do not update access time; improves performance
`nodiratime`	Do not update directory access time
`discard`	Enable TRIM (recommended for SSDs)
`nofail`	Do not block boot if the device is absent
`_netdev`	Wait for network before mounting
`ro`	Mount as read-only
`noexec`	Prevent execution of binaries
`nosuid`	Ignore SUID/SGID bits

Verifying fstab Configuration


# Mount all entries in fstab that are not yet mounted (tests if configuration is correct)
sudo mount -a
 
# Verify with findmnt
sudo findmnt --verify
 
# If there are errors, restore the backup
sudo cp /etc/fstab.bak /etc/fstab

Swap Management


# View current swap
swapon --show
free -h
 
# Create a swap file
sudo fallocate -l 4G /swapfile
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile
 
# Add to fstab to make it persistent
echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab
 
# Disable swap
sudo swapoff /swapfile

LVM Logical Volume Management


# Install LVM tools
sudo apt install lvm2
 
# Create a physical volume
sudo pvcreate /dev/sdb1
 
# Create a volume group
sudo vgcreate mydata /dev/sdb1
 
# Create a logical volume
sudo lvcreate -L 100G -n myvolume mydata
 
# Format and mount
sudo mkfs.ext4 /dev/mydata/myvolume
sudo mount /dev/mydata/myvolume /mnt/data
 
# Online extend a logical volume
sudo lvextend -L +50G /dev/mydata/myvolume
sudo resize2fs /dev/mydata/myvolume
 
# View LVM status
sudo pvs
sudo vgs
sudo lvs

Troubleshooting

fstab Mount Failure at Boot

If an fstab misconfiguration prevents booting, use GRUB recovery mode:


# Remount root partition as read-write
mount -o remount,rw /
 
# Edit and fix fstab
nano /etc/fstab
 
# Reboot
reboot

Troubleshooting Insufficient Disk Space


# View partition usage
df -h
 
# Find large files
sudo find / -type f -size +100M -exec ls -lh {} \;
 
# View directory space usage (sorted)
sudo du -sh /* | sort -rh | head -20
 
# Clean APT cache
sudo apt clean
sudo apt autoremove