diff [options] file1 file2
The diff command compares the contents of any two les. The output produced
by the program lists all lines that do not match. This is frequently used by pro-
grammers who need only to send their program alterations and not the entire
source code.
-q
Only reports whether the two les dier
-u
Produces a “unied” di, which makes the output more readable
7.12.1.3 File Systems
mount [options] [device] mountpoint
This command can be used to mount any data media, such as hard disks, CD-
ROM drives, and other drives, to a directory of the Linux le system.
-r
Mount read-only
-t filesystem
Specify the le system, commonly ext2 for Linux hard disks, msdos for MS-DOS
media, vfat for the Windows le system, and iso9660 for CDs
For hard disks not dened in the le /etc/fstab, the device type must also be
specied. In this case, only root can mount it. If the le system needs to also be
mounted by other users, enter the option user in the appropriate line in the /etc/
fstab le (separated by commas) and save this change. Further information is
available in the mount(1) man page.
umount [options] mountpoint
This command unmounts a mounted drive from the le system. To prevent data
loss, run this command before taking a removable data medium from its drive.
Normally, only root is allowed to run the commands mount and umount. To enable
other users to run these commands, edit the /etc/fstab le to specify the option
user for the relevant drive.
7.12.2 System Commands
The following section lists a few of the most important commands needed for retriev-
ing system information and controlling processes and the network.
7.12.2.1 System Information
df [options] [directory]
The df (disk free) command, when used without any options, displays information
about the total disk space, the disk space currently in use, and the free space on
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