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<!-- ISBN=0672311623 //-->
<!-- TITLE=SAMS TEACH YOURSELF LINUX IN 24 HOURS //-->
<!-- AUTHOR=BILL BALL, STEPHEN SMOOGEN //-->
<!-- PUBLISHER=MACMILLAN //-->
<!-- IMPRINT=SAMS //-->
<!-- PUBLICATION DATE=1998 //-->
<!-- CHAPTER=20 //-->
<!-- PAGES=0291-0312 //-->
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<P><CENTER>
<a href="0291-0295.html">Previous</A> | <a href="../ewtoc.html">Table of Contents</A> | <a href="0299-0301.html">Next</A>
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<A NAME="PAGENUM-296"><P>Page 296</P></A>
<P>The df (free disk space) command will gather and summarize some important
statistics about all currently mounted filesystems. The
df command is easy to use, for example:
</P>
<!-- CODE //-->
<PRE>
# df
Filesystem 1024-blocks Used Available Capacity Mounted on
/dev/hda3 497699 443871 28124 94% /
/dev/hda1 509856 469632 40224 92% /mnt/dos
/dev/hdc1 3868 2596 1272 67% /mnt/flash
/dev/hdb 644324 644324 0 100% /mnt/cdrom
</PRE>
<!-- END CODE //-->
<P>This output shows four different filesystems on three different devices mounted
under Linux. The first is the root partition at the
/ directory on /dev/hda3; the second is a DOS partition under
/mnt/dos on /dev/hda1; the third is a flashcard under
/mnt/flash on /dev/hdc1; and the fourth is a CD-ROM, mounted under
/mnt/cdrom on /dev/dev/hdb. The df command also
lists the size of the storage device, how much has been used, how much is available, and
the current capacity of the device. Notice that the CD-ROM has no space left. This is
because it is mounted read-only, meaning you can't save or delete files on this device. The
command shown in the next example will let you know.
</P>
<P>One handy way to find out about the different filesystems you have mounted is to use
the mount command. This command is usually used during startup, and by the root
operator to mount and unmount filesystems, but you can use
mount to show what type of filesystems are in use, and how the filesystems are mounted, for example:
</P>
<!-- CODE //-->
<PRE>
# mount
/dev/hda3 on / type ext2 (rw)
/dev/hda1 on /mnt/dos type msdos (rw)
none on /proc type proc (rw)
/dev/hdc1 on /mnt/flash type msdos (rw)
/dev/hdb on /mnt/cdrom type iso9660 (ro)
</PRE>
<!-- END CODE //-->
<P>This shows that your root partition, on the / directory, is a Linux
ext2 filesystem mounted read-write, whereas
/mnt/dos and /mnt/flash contain DOS partitions, also read-write. (The
/proc filesystem is a special directory Linux uses for process reporting, such as
running applications, system state, and so on.)
Finally, mount reports that your CD-ROM is mounted as a read-only iso9660 filesystem.
</P>
<P>You can use this information from mount to get specific information with the
df command, by using the df command's -t, or filesystem, option, as follows:
</P>
<!-- CODE SNIP //-->
<PRE>
# df -t ext2
Filesystem 1024-blocks Used Available Capacity Mounted on
/dev/hda3 497699 443873 28122 94% /
</PRE>
<!-- END CODE SNIP //-->
<P>This tells df to just show information about any mounted Linux filesystems. You can
get a list of valid filesystems to specify with the
df command by looking at the mount manual page. The
mount command is covered in more detail in Hour 21, "Handling Files." You can
see
</P>
<A NAME="PAGENUM-297"><P>Page 297</P></A>
<P>that by using the df and mount command, you can get reports on the type of mounted
devices, how the devices are mounted, and how much room you have left on each.
</P>
<H4><A NAME="ch20_ 7">
Getting Filesystem Disk Usage with the du Command
</A></H4>
<P>The du (disk usage) command conveniently summarizes how your disk is being used,
by reporting the amount of space required by each directory or specified path. Although
the du command has more than 20 command-line options, this section presents some of
the common ones, and leaves it up to you to experiment. You can use the
du command by itself, or specify a directory or path, for example:
</P>
<!-- CODE //-->
<PRE>
# du
904 ./book
12080 ./mail
1 ./.tin/.mailidx
1 ./.tin/.index
10 ./.tin
...
589 ./News
9 ./.index
7 ./.procmail
5 ./.ncftp
418 ./reading
778 ./documents
27199 .
</PRE>
<!-- END CODE //-->
<P>This report (for brevity, not all the directories are listed) shows the contents of a
home directory, with a total for 27,199 1-kilobyte blocks. If you find this hard to
understand, you can have du report the size in bytes, for example:
</P>
<!-- CODE //-->
<PRE>
# du -b
897606 ./book
12294410 ./mail
1024 ./.tin/.mailidx
1024 ./.tin/.index
9382 ./.tin
561715 ./News
4033 ./.index
4139 ./.procmail
2791 ./.ncftp
424037 ./reading
784216 ./documents
26785752 .
</PRE>
<!-- END CODE //-->
<P>If this is too much information for you, then you can use the
--summarize option to get the total in either kilobytes or bytes, as follows:
</P>
<!-- CODE SNIP //-->
<PRE>
# du -b --summarize
26786903 .
</PRE>
<!-- END CODE SNIP //-->
<P>The du command can also help you keep track of directories which, unattended,
sometimes grow out of control or use a lot of disk space. If you specify a path,
du will report on the
</P>
<A NAME="PAGENUM-298"><P>Page 298</P></A>
<P>
different size of the directories, pinpointing any that may contain too much
information, for example:
</P>
<!-- CODE //-->
<PRE>
# du --summarize -b /var/* | sort -nr
6474535 /var/lib
2336494 /var/log
868163 /var/catman
76362 /var/spool
14591 /var/dt
2385 /var/run
2048 /var/lock
2048 /var/local
1024 /var/tmp
1024 /var/preserve
1024 /var/nis
</PRE>
<!-- END CODE //-->
<P>Here I've combined the du command, which has been instructed to summarize the
number of bytes in each directory, with the sort command, which has been set to use a
numerical sort in reverse order. This one-liner, which uses pipes (discussed in Hour 6, "Using
the Shell"), will automatically print the largest directories at
the top of the output list. You can see that the
/var/log directory is getting pretty big. The
/var/lib directory will be large because it contains the
rpm databases (rpm is discussed in Hour 22, "Red Hat Tools").
</P>
<P>Although the du command does not, like the df command, have a
-t option to specify which filesystem to report on, you can use the
-x option to exclude other filesystems. Or, you
can have du report on other filesystems by specifying a usage report at the
mount point. For example, du will merrily chug along and summarize how much room your
Windows directories take up:
</P>
<!-- CODE //-->
<PRE>
# du -b --summarize /mnt/dos/* | sort -nr
129486405 /mnt/dos/windows
23929345 /mnt/dos/msoffice
20811654 /mnt/dos/photoenf
7744046 /mnt/dos/tranxit
6828902 /mnt/dos/org2
6647520 /mnt/dos/laplink
5556496 /mnt/dos/acrobat3
4041127 /mnt/dos/pcdr
3753962 /mnt/dos/psp
3603469 /mnt/dos/insync
3176769 /mnt/dos/antvirus
2669335 /mnt/dos/airlite
2408920 /mnt/dos/winfax
...
</PRE>
<!-- END CODE //-->
<P>This (shortened) report shows that next to the operating system, the largest space is
taken up by certain applications. This information can be helpful in making a decision on
what applications to uninstall if you need more disk space.
</P>
<H4><A NAME="ch20_ 8">
Checking Symbolic Links with the stat Command
</A></H4>
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