1. Linux Installation and Administration – Lesson 5 Tutor: George Papamarkos Topic: Devices in Linux

2. Lesson Outline Managing Filesystems –Mounting Disks Managing Devices –Device Files –Loading Device Drivers –Loading Modules Automatically

3. 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 1 st serial port –/dev/hda2 for the 2 nd partition of the 1 st IDE HDD drive

4. 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

5. Managing Devices – Device Files In ls –l command in /dev dir, the size of the files has been replaced by two numbers separated by a comma.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 1 st 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

6. 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

7. 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

8. Loading Device Drivers The modules are stored (in most of the systems) in /lib/modules/kernel- version where different dirs per module category exist

9. Load a Module Command: insmod –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

10. Working with modules List the already loaded drivers with: –lsmod Remove a loaded driver with: –Rmmod –E.g. rmmod usbcore

11. Mounting Filesystems on Devices Filesystem is the way the data are organised and stored (in physical level) on disks Common Filesystems in Linux 1.Ext2/ext3 2.ReiserFS 3.Swap 4.NFS 5.Vfat 6./proc filesystem

12. 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.

13. 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

14. 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, e.g. umount mnt/windows

15. /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

16. /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.

17. /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