Linux Installation and
Administration – Lesson 5
Tutor: George Papamarkos
Topic: Devices in Linux
Lesson Outline
• Managing Filesystems
– Mounting Disks
• Managing Devices
– Device Files
– Loading Device Drivers
– Loading Modules Automatically
Managing Devices – Device
Files
• Device Files allow user programs access
hw devices on the system through
Linux kernel
• Device Drives in Linux/Unix are part of
the monolithic kernel
• Devices are located under the /dev dir
– E.g. /dev/ttyS0 for the 1st serial port
– /dev/hda2 for the 2nd partition of the 1st
IDE HDD drive
Managing Devices – Device
Files
• Some device files do not correspond to actual
devices
– E.g. /dev/null acts as a byte sink.Write on this
device succeeds always but what is written is
ignored
• Devices are divided to:
– Block Devices: Data are read and written in
“blocks”
• E.g. the IDE hard drives
– Character Devices: Data are read and written
sequentially
• E.g. serial port
Managing Devices – Device
Files
• In ls –l command in /dev dir, the size of
the files has been replaced by two
numbers separated by a comma.
– brw-rw---- 1 root disk 3, 0 November 2 2004 /dev/hda
– The 1st value is called major number and the second is
called minor number
– Major Num: Specifies a particular driver within the kernel
– Minor Num: Specifies a particular devices handled by the
driver
– E.g. All USB devices are handled by the same driver with
one major num although for each of them there is a minor
num
Working with Device Files
• Create a device file:
mknod -m permissions name type major minor
where:
• name is the full pathname of the device to create, such as /dev/rft0
• type is either c for a character device or b for a block device
• major is the major number of the device
• minor is the minor number of the device
• -m permissions is an optional argument that sets the permission bits of
the new device file to permissions
– E.g. mknod /dev/test b 42 0
• Remove a device file:
rm /dev/test
• You can of course create links between devices using ln
command
Loading Device Drivers
• Drivers are cooperating with kernel and
they are:
– Compiled within the kernel, or
– Loaded like external modules to the kernel
(like .dll files in Windows) at runtime
• A module is simply a single object file
containing all the code for the driver.
– E.g. usbcore.o the module for usb
devices 
Loading Device Drivers
• The modules are stored (in most of the
systems) in /lib/modules/kernelversion where different dirs per
module category exist
Load a Module
• Command: insmod <module_name>
– insmod usbcore.o
• The module may fail to load due to dependencies from
other modules
• You have to find by your own and resolve this
• To avoid this, create a module database with the
command: depmod –a, to store all the info about the
module
• After that you can replace insmod with modprobe
command, which checks the create database and
resolves the module dependencies automatically
Working with modules
• List the already loaded drivers with:
– lsmod
• Remove a loaded driver with:
– Rmmod <module_name>
– E.g. rmmod usbcore
Mounting Filesystems on
Devices
•
•
Filesystem is the way the data are organised
and stored (in physical level) on disks
Common Filesystems in Linux
1.
2.
3.
4.
5.
6.
Ext2/ext3
ReiserFS
Swap
NFS
Vfat
/proc filesystem
Mounting filesystems
• In order to access any filesystem under Linux, you
must mount it on a certain directory.
• The mount command is used to do this and usually
must be executed as root.
• The format of this command is:
mount -t type device mount-point
where type is the type name of the filesystem,
device is the physical device where the filesystem
resides (the device file in /dev), and mount-point is
the directory on which to mount the filesystem.
• You have to create the directory before issuing mount.
Mounting Filesystems
• E.g.
– mount -t vfat /dev/hda2 /mnt/windows
To mount the windows hda2 FAT32 partition
• There are many options to the mount command,
which can be specified with the -o switch.
• One common option to mount is -o ro, which
mounts the filesystem as read-only. E.g.
CDROMs
mount -t iso9660 -r /dev/cdrom /mnt/cdrom
Unmounting Filesystems
•
•
The inverse of mounting a filesystem is,
naturally, unmounting it.
Unmounting a filesystem has two effects:
– synchronizes the system's buffers with the actual
contents of the filesystem on disk
– it makes the filesystem no longer available from
its mount point.
•
Unmounting is done with the umount
command
–
umount <mount_dir>, e.g. umount mnt/windows
/etc/fstab
• You can find out what devices are mounted,
and where, using the mount command with
no arguments
• The system automatically mounts several
filesystems when the system boots.
• This is handled by the file /etc/fstab
– Each line in this file is of the format:
device mount-point type options
e.g. /dev/hda2 /mnt/windows vfat defaults
/etc/fstab
• The option defaults should be used for
most filesystems; it enables a number of
other options, such as rw (read-write access),
async (buffer I/O to the filesystem in memory
asynchronously), and so forth.
• Another potentially useful option is umask,
which lets you set the default mask for the
permission bits, something that is especially
useful with some foreign filesystems.
/etc/fstab
• At boot time mount –a command is
called that mounts everything listed in
/etc/fstab
• A filesystem does not need to be listed
in /etc/fstab in order to be mounted,
but it does need to be listed there in
order to be mounted "automatically" by
mount -a