Κεφάλαιο 16. Διάφορες Ερωτήσεις

16.1. FreeBSD uses far more swap space than Linux®. Why?
16.2. Why does top show very little free memory even when I have very few programs running?
16.3. Why will chmod not change the permissions on symlinks?
16.4. Can I run DOS binaries under FreeBSD?
16.5. What do I need to do to translate a FreeBSD document into my native language?
16.6. Why does my email to any address at FreeBSD.org bounce?
16.7. Where can I find a free FreeBSD account?
16.8. What is sup, and how do I use it?
16.9. What is the cute little red guy's name?
16.10. Can I use the BSD daemon image?
16.11. Do you have any BSD daemon images I could use?
16.12. I have seen an acronym or other term on the mailing lists and I do not understand what it means. Where should I look?
16.13. Why should I care what color the bikeshed is?

16.1.

FreeBSD uses far more swap space than Linux®. Why?

FreeBSD only appears to use more swap than Linux®. In actual fact, it does not. The main difference between FreeBSD and Linux® in this regard is that FreeBSD will proactively move entirely idle, unused pages of main memory into swap in order to make more main memory available for active use. Linux® tends to only move pages to swap as a last resort. The perceived heavier use of swap is balanced by the more efficient use of main memory.

Note that while FreeBSD is proactive in this regard, it does not arbitrarily decide to swap pages when the system is truly idle. Thus you will not find your system all paged out when you get up in the morning after leaving it idle overnight.

16.2.

Why does top show very little free memory even when I have very few programs running?

The simple answer is that free memory is wasted memory. Any memory that your programs do not actively allocate is used within the FreeBSD kernel as disk cache. The values shown by top(1) labeled as Inact, Cache, and Buf are all cached data at different aging levels. This cached data means the system does not have to access a slow disk again for data it has accessed recently, thus increasing overall performance. In general, a low value shown for Free memory in top(1) is good, provided it is not very low.

16.3.

Why will chmod not change the permissions on symlinks?

Symlinks do not have permissions, and by default, chmod(1) will not follow symlinks to change the permissions on the target file. So if you have a file, foo, and a symlink to that file, bar, then this command will always succeed.

% chmod g-w bar

However, the permissions on foo will not have changed.

You have to use either -H or -L together with the -R option to make this work. See the chmod(1) and symlink(7) manual pages for more info.

Προειδοποίηση:

The -R option does a RECURSIVE chmod(1). Be careful about specifying directories or symlinks to directories to chmod(1). If you want to change the permissions of a directory referenced by a symlink, use chmod(1) without any options and follow the symlink with a trailing slash (/). For example, if foo is a symlink to directory bar, and you want to change the permissions of foo (actually bar), you would do something like:

% chmod 555 foo/

With the trailing slash, chmod(1) will follow the symlink, foo, to change the permissions of the directory, bar.

16.4.

Can I run DOS binaries under FreeBSD?

Yes, you can use emulators/doscmd, a DOS emulation program, available in the FreeBSD Ports Collection.

Σημείωση:

The doscmd program used to be an integrated part of FreeBSD, but was removed before the release of FreeBSD 5.3.

If doscmd will not suffice, the add-on utility emulators/pcemu emulates an 8088 and enough BIOS services to run many DOS text mode applications. It requires the X Window System.

16.5.

What do I need to do to translate a FreeBSD document into my native language?

See the Translation FAQ in the FreeBSD Documentation Project Primer.

16.6.

Why does my email to any address at FreeBSD.org bounce?

The FreeBSD.org mail system implements some of the stricter Postfix checks on incoming mail and rejects mail that is either misconfigured or is potential spam. Your mail might bounce for one of the following reasons:

  • The email is being sent from a known spam domain or IP block.

    The FreeBSD mail servers reject email from known spam sources. If you have service through a company or domain who generates or relays spam, please switch to a service provider who does not.

  • The body of the email only contains HTML.

    Mail should be sent in plain text only. Please configure your mail user agent to send plain text.

  • The mailer at FreeBSD.org cannot resolve the IP address of the connecting host back to a symbolic name.

    Working reverse DNS is a standard requirement for accepting mail from a host. Set up reverse DNS for your mail server's IP address. Many home services (DSL, cable, dialup, etc.) will not give you this option. In this case, relay your email through your service provider's mail server.

  • The hostname given in the EHLO/HELO part of the SMTP exchange cannot be resolved to an IP address.

    A fully qualified, resolvable host name is necessary in this part of the SMTP dialogue before mail will be accepted. If you do not have a host name that is registered in the DNS, then you should use your service provider's mail server to relay your mail.

  • Your message had a message ID ending with the string «localhost».

    Some mail user agents generate bad message IDs which will not be accepted. You will need to persuade your mail user agent to generate a valid message ID or else configure your mail transfer agent to rewrite them.

16.7.

Where can I find a free FreeBSD account?

While FreeBSD does not provide open access to any of their servers, others do provide open access UNIX® systems. The charge varies and limited services may be available.

Arbornet, Inc, also known as M-Net, has been providing open access to UNIX® systems since 1983. Starting on an Altos running System III, the site switched to BSD/OS in 1991. In June of 2000, the site switched again to FreeBSD. M-Net can be accessed via telnet and SSH and provides basic access to the entire FreeBSD software suite. However, network access is limited to members and patrons who donate to the system, which is run as a non-profit organization. M-Net also provides an bulletin board system and interactive chat.

Grex provides a site very similar to M-Net including the same bulletin board and interactive chat software. However, the machine is a Sun™ 4M and is running SunOS™.

16.8.

What is sup, and how do I use it?

SUP stands for Software Update Protocol, and was developed by CMU for keeping their development trees in sync. We used it to keep remote sites in sync with our central development sources.

SUP is not bandwidth friendly, and has been retired. The current recommended method to keep your sources up to date is CVSup

16.9.

What is the cute little red guy's name?

He does not have one, and is just called «the BSD daemon». If you insist upon using a name, call him «beastie». Note that «beastie» is pronounced «BSD».

You can learn more about the BSD daemon on his home page.

16.10.

Can I use the BSD daemon image?

Perhaps. The BSD daemon is copyrighted by Marshall Kirk McKusick. You will want to check his Statement on the Use of the BSD Daemon Figure for detailed usage terms.

In summary, you are free to use the image in a tasteful manner, for personal use, so long as appropriate credit is given. If you want to use him commercially, you must contact Kirk McKusick. More details are available on the BSD Daemon's home page.

16.11.

Do you have any BSD daemon images I could use?

You will find eps and Xfig drawings under /usr/share/examples/BSD_daemon/.

16.12.

I have seen an acronym or other term on the mailing lists and I do not understand what it means. Where should I look?

Please see the FreeBSD Glossary.

16.13.

Why should I care what color the bikeshed is?

The really, really short answer is that you should not. The somewhat longer answer is that just because you are capable of building a bikeshed does not mean you should stop others from building one just because you do not like the color they plan to paint it. This is a metaphor indicating that you need not argue about every little feature just because you know enough to do so. Some people have commented that the amount of noise generated by a change is inversely proportional to the complexity of the change.

The longer and more complete answer is that after a very long argument about whether sleep(1) should take fractional second arguments, Poul-Henning Kamp posted a long message entitled «A bike shed (any color will do) on greener grass...». The appropriate portions of that message are quoted below.

 

«What is it about this bike shed?» Some of you have asked me.

It is a long story, or rather it is an old story, but it is quite short actually. C. Northcote Parkinson wrote a book in the early 1960s, called «Parkinson's Law», which contains a lot of insight into the dynamics of management.

[snip a bit of commentary on the book]

In the specific example involving the bike shed, the other vital component is an atomic power-plant, I guess that illustrates the age of the book.

Parkinson shows how you can go into the board of directors and get approval for building a multi-million or even billion dollar atomic power plant, but if you want to build a bike shed you will be tangled up in endless discussions.

Parkinson explains that this is because an atomic plant is so vast, so expensive and so complicated that people cannot grasp it, and rather than try, they fall back on the assumption that somebody else checked all the details before it got this far. Richard P. Feynmann gives a couple of interesting, and very much to the point, examples relating to Los Alamos in his books.

A bike shed on the other hand. Anyone can build one of those over a weekend, and still have time to watch the game on TV. So no matter how well prepared, no matter how reasonable you are with your proposal, somebody will seize the chance to show that he is doing his job, that he is paying attention, that he is here.

In Denmark we call it «setting your fingerprint». It is about personal pride and prestige, it is about being able to point somewhere and say «There! I did that.» It is a strong trait in politicians, but present in most people given the chance. Just think about footsteps in wet cement.

 
 --Poul-Henning Kamp on freebsd-hackers, October 2, 1999

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