Date: Wed, 7 Nov 2001 08:20:02 -0800 (PST) From: Michael Lucas <mwlucas@blackhelicopters.org> To: freebsd-doc@freebsd.org Subject: Re: docs/31821: new FAQ: du/df Message-ID: <200111071620.fA7GK2O26503@freefall.freebsd.org>
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The following reply was made to PR docs/31821; it has been noted by GNATS. From: Michael Lucas <mwlucas@blackhelicopters.org> To: Dima Dorfman <dima@trit.org> Cc: FreeBSD-gnats-submit@freebsd.org Subject: Re: docs/31821: new FAQ: du/df Date: Wed, 7 Nov 2001 11:10:34 -0500 --3V7upXqbjpZ4EhLz Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Wed, Nov 07, 2001 at 03:06:27PM +0000, Dima Dorfman wrote: > This is backwards. 'du' typically reports less space is in use, not > df (if you wrote this looking at the recent thread on -stable, note > that the originator misnamed the output; what he claimed was from du > was from df, and vice versa). Aha! That confused me, but I'm not going to argue with actual output. You've gone to a lot of trouble to prove me wrong, but I'm a tech writer. I assume that I will be proven wrong. :) Here's another patch, addressing your points. ==ml -- Michael Lucas mwlucas@blackhelicopters.org http://www.blackhelicopters.org/~mwlucas/ Big Scary Daemons: http://www.oreillynet.com/pub/q/Big_Scary_Daemons --3V7upXqbjpZ4EhLz Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename=du-vs-df *** 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 11:09:10 2001 *************** *** 5869,5874 **** --- 5869,5929 ---- </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> + goes through the directory tree, measures how large each + file is, and presents the totals. <command>df</command> + just asks the filesystem how much space it has left. They + seem to be the same thing, but a file without a directory + entry will affect <command>df</command> but not + <command>du</command>.</para> + + <para>When a program is using a file, and you delete the + file, the file isn't really removed from the filesystem + until the program stops using it. The file is immediately + deleted from the directory listing, however. You can see + this easily enough with a program such as + <command>more</command>. Assume you have a file large + enough that its presence affects the output of + <command>du</command> and <command>df</command>. (Since + disks can be so large today, this might be a + <emphasis>very</emphasis> large file!) If you delete this + file while using <command>more</command> on it, + <command>more</command> doesn't immediately choke and + complain that it cannot view the file. The entry is + simply removed from the directory so no other program or + user can access it. <command>du</command> shows that it + is gone -- it has walked the directory tree and the file + isn't listed. <command>df</command> shows that it is + still there, as the filesystem knows that + <command>more</command> is still using that space. 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> --3V7upXqbjpZ4EhLz-- To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-doc" in the body of the message
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