Date: Wed, 7 Nov 2001 09:09:22 -0500 (EST) From: mwlucas@blackhelicopters.org To: FreeBSD-gnats-submit@freebsd.org Subject: docs/31821: new FAQ: du/df Message-ID: <200111071409.JAA01617@blackhelicopters.org>
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>Number: 31821
>Category: docs
>Synopsis: new FAQ: du/df
>Confidential: no
>Severity: non-critical
>Priority: low
>Responsible: freebsd-doc
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: change-request
>Submitter-Id: current-users
>Arrival-Date: Wed Nov 07 06:10:00 PST 2001
>Closed-Date:
>Last-Modified:
>Originator: Michael Lucas
>Release: FreeBSD 3.5-STABLE i386
>Organization:
None
>Environment:
yesterday's -doc tree
>Description:
People have asked several times about the difference between du and
df; specifically, the example cited below keeps happening.
>How-To-Repeat:
read -questions
>Fix:
*** en_US.ISO8859-1/books/faq/book.sgml-dist Mon Nov 5 10:49:36 2001
--- en_US.ISO8859-1/books/faq/book.sgml Wed Nov 7 09:05:22 2001
***************
*** 5869,5874 ****
--- 5869,5921 ----
</qandaentry>
<qandaentry>
+ <question id="du-vs-df">
+ <para>The <command>du</command> and <command>df</command>
+ commands show different amounts of disk space available?
+ What's going on?</para>
+ </question>
+
+ <answer>
+ <para>You need to understand what <command>du</command> and
+ <command>df</command> really do. <command>du</command>
+ shows how much of the disk is designated <emphasis>used by
+ files</emphasis>. <command>df</command> shows how much of
+ the disk is designated <emphasis>free</emphasis>. While
+ they seem to be opposite, that isn't exactly true.</para>
+
+ <para>When a program has a file open, and you delete the
+ file, it isn't really deleted until the program releases
+ the file. You can see this easily enough with a program
+ such as <command>more</command>. If you delete a file
+ while using <command>more</command> on it,
+ <command>more</command> doesn't immediately choke and
+ complain that it cannot view the file. You cannot access
+ the file from anywhere except that <command>more</command>
+ window. If the file is large enough,
+ <command>df</command> will show that it is gone. The
+ space the file took up is now designated free.
+ <command>du</command> will show that it is still there, as
+ the space the file uses is still technically in use. Once
+ you end the <command>more</command> session,
+ <command>du</command> and <command>df</command> will
+ agree.</para>
+
+ <para>Note that softupdates can delay the freeing of disk
+ space; you might need to wait up to 30 seconds for the
+ change to be visible!</para>
+
+ <para>This situation is common on web servers. Many people
+ set up a FreeBSD web server and forget to rotate the log
+ files. The access log fills up <filename>/var</filename>.
+ The new administrator deletes the file, but the system
+ still complains that the partition is full. Stopping and
+ restarting the web server program would free the file,
+ allowing the system to release the disk space. To prevent
+ this from happening, set up &man.newsyslog.8;.</para>
+ </answer>
+ </qandaentry>
+
+ <qandaentry>
<question id="add-swap-space">
<para>How can I add more swap space?</para>
</question>
>Release-Note:
>Audit-Trail:
>Unformatted:
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