LPI Linux Certification/Control Mounting And Unmounting Of Filesystems

Detailed Objective

Weight: 3

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

• Key knowledge area(s):
  • Manually mount and unmount filesystems.
  • Configure filesystem mounting on bootup.
  • Configure user mountable removeable filesystems.

• The following is a partial list of the used files, terms and utilities:
  • /etc/fstab
  • /media
  • mount
  • umount

Attach a filesystem

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 priviledge to mount devices unless it is specified in the /etc/fstab file. Examples:

# Print all the mouted 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

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

The file /etc/fstab contains all the file sytems 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

• Exercises results

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 happenning?
   • 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 happenning?
   • Use tar to view the contents of the floppy.