mount: attach file systems

Updated November 2026

Unix has a single directory tree. To use a disk, USB stick or network share, you mount it on a directory, the mount point, and its files appear there.

mount [-t type] [-o options] device directory umount directory

Find the device

lsblk -f                    # disks, partitions, file system types, labels, UUIDs, mount points
sudo blkid                  # UUIDs and types of every partition
findmnt                     # what is mounted where, as a tree
findmnt -T /var             # which file system holds /var

Examples

sudo mkdir -p /mnt/usb
sudo mount /dev/sdb1 /mnt/usb                       # type is detected automatically
sudo mount -o ro /dev/sdb1 /mnt/usb                 # read-only
sudo umount /mnt/usb                                # unmount before unplugging

sudo mount -o loop,ro ubuntu.iso /mnt/iso           # an ISO image
sudo mount -t nfs fileserver:/export/data /mnt/data # NFS share
sudo mount -t cifs //nas/share /mnt/share -o username=anna,uid=$(id -u)   # Windows/Samba share
sudo mount -o remount,rw /                          # make a read-only root writable (rescue mode)
sudo mount --bind /srv/data /var/www/data           # make a directory appear in a second place

USB sticks formatted for Windows use exFAT or NTFS; current Linux kernels mount both. Network mounts need the client tools: nfs-common (Debian) or nfs-utils (RHEL) for NFS, cifs-utils for SMB.

Permanent mounts in /etc/fstab

Each line in /etc/fstab describes a file system to mount at boot. Use the UUID rather than /dev/sdb1, because device names can change when disks are added.

# <device>                                 <mount point>  <type>  <options>                 <dump> <fsck>
UUID=3f1c2a9e-8d6b-4b6e-9c55-0d2a7e1f4b21  /srv/data      ext4    defaults,noatime          0      2
fileserver:/export/backup                  /mnt/backup    nfs     defaults,_netdev,nofail   0      0
tmpfs                                      /tmp           tmpfs   nosuid,nodev,size=2G      0      0

sudo findmnt --verify      # check fstab for mistakes
sudo mount -a              # mount everything in fstab that is not mounted yet
sudo systemctl daemon-reload   # systemd systems: after editing fstab

Test before you reboot

A wrong line in /etc/fstab can stop the system from booting into normal mode. Run sudo mount -a and findmnt --verify after every change, and add nofail to disks that might be missing.

Useful mount options

Option	Effect
`ro` / `rw`	Read-only / read-write
`noatime`	Do not record access times (fewer writes)
`nosuid`, `nodev`, `noexec`	Security restrictions; see file system security
`nofail`	Do not fail the boot if the device is missing
`_netdev`	Wait for the network (for network file systems)
`uid=`, `gid=`, `umask=`	Owner and permissions for file systems without Unix permissions (FAT, exFAT, CIFS)

"target is busy"

umount refuses while any process uses a file or has its working directory on the file system. Find out who:

sudo fuser -vm /mnt/usb      # processes using the mount
sudo lsof +f -- /mnt/usb

Often it is your own shell: cd out of the directory first. umount -l (lazy) removes it from the directory tree at once and finishes unmounting when it is no longer in use; do not unplug a USB drive before that has happened.

To see how full mounted file systems are, use df.