Chapter 9 General Linux Administration 311

as the chown command. The chgrp command allows group ownership of a file to be changed independent of the permissions on the file or ownership of the file.

Mounting and Managing File Systems

4.5 Manage and navigate the Linux hierarchy (e.g., /etc, /usr, /bin, /var)

4.8 Mount and manage filesystems and devices (e.g., /mnt, /dev, du, df, mount, umount)

The Linux system administrator must daily mount and manage the file systems. This task also includes the mounting and un-mounting of devices. The administrator must determine the available resources in order to manage the file systems properly. The administrator can perform these tasks by using the tools provided by the Linux operating system.

Mount

The mount command is a powerful tool used to mount directories and devices on a Linux system. The simplest application of the mount command is to use it with no options or arguments. If the command is used on its own, it will return information similar to the following:

[user@dhcppc1 user]$ mount /dev/hda1 on / type reiserfs (rw) none on /proc type proc (rw)

none on /dev/pts type devpts (rw,mode=0620)

/mnt/cdrom on /mnt/cdrom type supermount (rw,fs=iso9660,dev=/dev/cdrom) /mnt/floppy on /mnt/floppy type supermount (rw,fs=vfat,dev=/dev/fd0) /dev/hda6 on /usr type reiserfs (rw)

/dev/hda7 on /var type reiserfs (rw)

/proc/bus/usb on /proc/bus/usb type usbdevfs (rw,devmode=0664,devgid=43)

This example shows the currently mounted devices and directories. Notice that the first device, hda1, is the primary IDE controller-master device, which contains the / or root directory. Mounts for the CD-ROM drive, FDD, /usr directory, /var directory, and USB on /proc/bus/usb are also available to the system. The mount command shows all the mounted devices on the system, and the hardware path for file systems, such as /var on partition /dev/hda7. This partition is commonly used to determine currently mounted devices and directories. The options available for the mount command are listed in Table 9-15.

312 Part IV Administration

These options are used to mount a device. The following is a common command, which is used to mount the diskette drive on a Linux system.

[root@dhcppc1 user]# mount -v /mnt/floppy

/mnt/floppy on /mnt/floppy type supermount (rw,fs=vfat,dev=/dev/fd0)

Notice that the file system type is listed and can be assigned by the -t option.

The -t option

The -t option is used to indicate the file system type to be mounted. This allows you to mount other types of file system formats, such as msdos and vfat for Microsoft Windows. For most types, the mount program issues a simple mount system call; no detailed knowledge of the filesystem type is required because the mount command will probe the file system. If the probe fails, then the file /etc/filesystems is checked and those file types are attempted.

Chapter 9 General Linux Administration 313

The -o option

The -o option has many available arguments that allow it to provide the mount command more flexibility, as shown in Table 9-16.

Umount

The opposite of mounting a drive is to unmount it, so that it cannot be accessed. Use the umount command to unmount a file system. If a floppy diskette drive is mounted, unmount the diskette before removing it. To perform this task, use the following umount command :

[root@dhcppc1 user]# umount -v /mnt/floppy /mnt/floppy umounted

314 Part IV Administration

The umount command uses the normal structure of umount [options] argument. The arguments are devices, directories, or -t [file system type]. The options available for the umount command are shown in Table 9-17.

Mounted file systems

One of the main reasons for adding a new mounted file system is that the current file systems don’t provide the required resources for the users. Before adding a new file system via the mount command, however, you should view the systems that are currently being used. Linux has several ways to view this information — the most common are the du and df commands.

The du command

The du command is used to summarize disk usage of each file and recursively for directories. This command provides an extensive list of all the files and their usage of storage space. You may use the du command to determine the space used on a diskette as shown in the following:

[root@dhcppc1 floppy]# ls picture.bmp* [root@dhcppc1 floppy]# du 769 .

The picture file uses 769 kilobytes of the space on the diskette. The available options for the du command are shown in Table 9-18.

Chapter 9 General Linux Administration 315

You can use the du command to estimate the free space used in the directory, as shown in the following.

[root@dhcppc1 /]# du /home/user

0/home/user/tmp

0/home/user/.kde/share/apps/RecentDocuments

0/home/user/.kde/share/apps/konqiconview/kpartplugins

316 Part IV Administration

1/home/user/.kde/share/apps/konqiconview

8/home/user/.kde/share/apps/konqueror/dirtree/remote/

8/home/user/.kde/share/apps/konqueror/dirtree/remote/

4/home/user/.kde/share/fonts/override

5/home/user/.kde/share/fonts

0/home/user/.kde/share/icons/favicons

1/home/user/.kde/share/icons

4/home/user/.netscape/xover-cache/host-localhost

5/home/user/.netscape/xover-cache

0/home/user/.netscape/archive

467 /home/user/.netscape

0/home/user/mydir

4/home/user/Desktop/Trash

57 /home/user/Desktop

0/home/user/nsmail

0/home/user/.bluefish/projects 5 /home/user/.bluefish

3764 /home/user

Although the du command is capable of much more, it is ideal for determining the file usage in a single directory, such as how much space and which files are using what space in a user’s home directory.

The df comand

The df command is similar to the du command but provides information about the amount of disk space available on the file system. The following is an example of the information provided by the df command:

The additional options available to the df command are shown in Table 9-19.

Chapter 9 General Linux Administration 317

The ability to easily check usage of the created partitions with the df command is a valuable tool for anyone using the Linux system.

Most current systems have plenty of disk space, but you can use the df command to verify the current usage of that space displayed by percentage of used space.