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LPI Linux Certification/Control Mounting And Unmounting Of Filesystems

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Detailed Objectives

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(LPIC-1 Version 5.0)

Weight: 3

Description:
Candidates should be able to configure the mounting of a filesystem.

Key Knowledge Areas:

  • Manually mount and unmount filesystems.
  • Configure filesystem mounting on bootup.
  • Configure user mountable removeable filesystems.
  • Use of labels and UUIDs for identifying and mounting file systems.
  • Awareness of systemd mount units.

The following is a partial list of the used files, terms and utilities:

  • /etc/fstab
  • /media/
  • mount
  • umount
  • blkid
  • lsblk

Attach a filesystem

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The mount command serves to attach the file system found on some device to the big file tree. 

mount [options]
mount [options] [-t vfstype] [-o options] device dir

If the device or directory is listed in /etc/fstab you can use the following: 

mount [options] [-o options [,...]] device | dir

Normally only root has the privilege to mount devices unless it is specified in the /etc/fstab file. Examples: 

# Print all the mounted filesystems (/etc/mtab).
mount

# Mount devices or dirs listed in /etc/fstab.
mount -a

# Mount /dev/hdc partition in read only mode without updating /etc/mtab.
mount -n -o ro /dev/hdc /mnt

# Allow a user to mount the CDROM if the following line is in /etc/fstab:
# /dev/cdrom /media/cdrom iso9660 ro,user,noauto,unhide
mount /media/cdrom 
mount /dev/cdrom

# Sync in realtime
mount -o sync /dev/sdb1 /mnt/usb

Detach a filesystem

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To detach a filesystem from the file tree, use umount. 

umount [options]
umount [options] [-o options [,...]] device | dir

A busy filesystem cannot be unmounted.

  • Open files
  • Working directory of a process.

Examples: 

umount -a # Unmount devices or dirs listed in /etc/fstab.
umount /mnt # Unmount the filesystem attached to /mnt.
umount /media/cdrom  # Allow a user to unmount the CDROM if the following line is in /etc/fstab:
/dev/cdrom  /media/cdrom  iso9660  ro,user,noauto,unhide

File system information

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The file /etc/fstab contains all the file systems and related information that will be used when doing a mount -a. (Boot time)

The file /etc/mtab is maintained by the kernel and keeps track on what is or isn't mounted. The /etc/fstab format is: 

#Device     Mount point    Fs type  Options             1 2
/dev/hda3   /              reiserfs defaults            1 2
/dev/hda1   /boot          ext2     defaults            1 2
/dev/cdrom  /media/cdrom   auto     ro,noauto,user,exec 0 0
usbdevfs    /proc/bus/usb  usbdevfs noauto              0 0
/dev/hda2   swap           swap     pri=42              0 0

Common options:

ro: read only
noauto: Don't mount automatically
exec: Can execute binary on the filesystem
suid: Allow to setuser bit
user: Allow a user to mount/unmount it
unhide: hidden file visible
async: All operations will be done asynchronously
default: rw, suid, dev, exec, auto, nouser, and async

Exercises

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  1. Create a line in /etc/fstab that allows any user to access the floppy disk. Check that you can mount the floppy and can create a file with touch.
  2. Do the following manipulation:
    • Create a ext2 file system on the floppy.
    • Mount the floppy.
    • Copy all the files /etc/*.conf into the floppy.
    • Unmount it. What's happening?
    • Mount it back and check that all the files are there.
    • Issue the following command:
    • Tar cvf /dev/fd0 /etc/*.conf
    • Try to mount it back. What's happening?
    • Use tar to view the contents of the floppy.


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