Linux Faq

Intro, intermediate and advanced HOWTOs and discussion.

Linux Faq

Postby weazy » Fri May 30, 2003 5:21 pm

Intro:
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Welcome to the Brief Linux FAQ (BLFAQ)!

This document contains a list of some frequently asked Linux questions and their
answers. It is meant to provide general help to Linux users, especially newbies.
I invite you to modify and add to this list but if you do so please be sure to
mail me so that I can include your changes in future releases. Finally, I hope
that this document will prove helpful to all Linux users, newbies especially.
Current releases of this document can be found at:
<ftp://metalab.unc.edu/pub/Linux/docs/faqs/BLFAQ>

FAQs:
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Q: I am trying to use the text based ftp program to download some stuff via
anonymous ftp from an ftp site. I have never done this before and the ftp
server doesn't seem to be letting me log in. Do I need a special user name
and password to do this?

A: To use anonymous ftp services log in with user name "anonymous" without
quotations and your full e-mail address as your password.
Some ftp sites will also accept the words "ftp" or "guest" instead of the
word "anonymous" as user name.

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Q: I plan to use the FIPS program to shrink a FAT32 partition (such as one used
by MS-Windows 95/98) and hence create space for my Linux operating system.
Can this be done?

A: Yes, but in order to do so you will need a version of FIPS at least as recent
as FIPS 1.5c. You can get the latest version of FIPS by anonymous ftp from
the official FIPS web site at <http://www.igd.fhg.de/~aschaefe/fips/>.

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Q: I am using the DOS Fdisk utility to destructively repartition my hard drive.
How should I deal with the question pertaining to whether or not I should
"enable large disk support"?

A: That question really has to do with whether you want to use a FAT32 or a
FAT16 file system with your DOS/Windows partition. Linux will coexist equally
well with both file systems except that in order to see a FAT32 file system
from your Linux partition you will need a version of the kernel at least
as recent as 2.0.35 .

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Q: I have upgraded to kernel 2.0.35 or later but still can't see my FAT32
partition. What went wrong?

A: You must ensure that you have an entry for your DOS partition in your
/etc/fstab file resembling the line:

/dev/hda1 /dos vfat auto,user,rw 0 0

Once the line is there you can just issue the command "umount -a;mount -a"
to mount your DOS partition under the /dos directory.

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Q: I am trying to install Linux via CD-ROM. I have made space for Linux on my
hard drive but inserting the Linux CD into the CD-ROM drive and rebooting
has no effect.

A: You might have to tell your BIOS (Basic I/O System) to enable booting
from CD-ROM by changing the default BIOS settings. On most systems you may
access the BIOS settings by pressing the <del> key on your keyboard shortly
after rebooting. If implemented by the BIOS as a separate feature you may
also have to change the BIOS's boot sequence.

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Q: I have completed the installation process but upon reboot I get a LI
prompt or a bunch of zeros and ones.

A: If your machine is somewhat old and you have an IDE (or EIDE) hard drive then
you must install your root partition completely below cylinder 1023
which means below 512 MB of disk space. On SCSI drives this means
your root partition must be contained within approximately one GB.
If your machine is fairly new and your BIOS supports it you may be able to
get around this problem by enabling LBA mode in the BIOS settings.

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Q: I can log in and out of my system but how do I shut it down / reboot it?

A: There are various ways. The most popular ones are logging in as root and
issuing the command "/sbin/shutdown -h now" or "/sbin/halt" to shut it
down or "/sbin/shutdown -r now" or "/sbin/reboot" to reboot.
On most systems while using a text based console pressing the <ctrl>, <alt>
and <del> keys simultaneously will also reboot the system.

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Q: I have shut down my system with the "halt" command and gotten to a message
saying "System Halted" but why is my computer still on?

A: If you want it to power off on shutdown then you must recompile the kernel to
enable support for that feature by selecting the appropriate entry in the
APM options.

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Q: My new video card is listed at <http://www.linux.org/> as a card which the
X Window System supports under Linux but I cannot get it to work.

A: Make sure that you have the newest version of XFree86 and that you installed
the right X Server. If all else fails you might want to try selecting the
generic SVGA server as your X Server.

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Q: I have successfully installed the X Window System and use the startx
command to run it from a text based virtual console. How can I have the X
Window System run at all times so that I don't have to use the startx
command?

A: If you are running Red Hat then you can edit the file /etc/inittab on
your system and replace the entry

id:3:initdefault:

with the entry

id:5:initdefault:

and reboot.
On other systems you might have to change the number 5 (the run level) to
another number like 4. How to choose the correct run level should be clear
by reading the comments in the file /etc/inittab . Alternatively, you might
have to change a link in /etc/rc[2345].d . Run levels 2-5 don't have really
strong conventions behind them like 0, 1, and 6 do. It depends on the
distribution.

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Q: When I use the X Window system and open multiple windows I find that my
screen size is insufficient. How can I use more virtual screen space?

A: Most window managers running under X Window have a built in feature known as
a pager which allows you to have more virtual screen space.

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Q: I would like to have xdm run multiple local displays on my system and switch
back and forth by pressing <ctrl><alt><F*> where * is a number between
1 and 12.

A: If you wanted to run 6 virtual consoles accessible by pressing the keys
<ctrl><alt><F7> through <ctrl><alt><F12> then you could put the following
entries in the file /usr/X11R6/lib/X11/xdm/Xservers

:0 local /usr/X11R6/bin/X vt07 :0
:1 local /usr/X11R6/bin/X vt08 :1
:2 local /usr/X11R6/bin/X vt09 :2
:3 local /usr/X11R6/bin/X vt10 :3
:4 local /usr/X11R6/bin/X vt11 :4
:5 local /usr/X11R6/bin/X vt12 :5

I would limit myself to only a few of these though as X seems to eat up
quite a lot of memory when multiple displays are running.

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Q: I hate the sound of the bell. I would prefer to disable it perhaps enabling
the visual bell as an alternative.

A: If you are running X then you can simply type "xset -b" without quotation
marks at the command prompt. Alternatively, if you are running the bash
shell then you can add the command "xset -b 2> /dev/null" without quotation
marks at the end of your .bash_profile file in your home directory to have
the audible bell disabled each time you log in.
For more information see the Visual-Bell-mini-HOWTO at
<http://www.linux.org/>

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Q: I have access to a remote Unix machine that has some commercial software that
uses X which I would like to run remotely on my display. How do I do it?

A: First connect to the remote machine using dip or whatever you use. If the
remote machine is called grasshopper.uvw.edu and your machine is called
kiwi.fruit.org then first type

xhost +grasshopper.uvw.edu

from your own machine's shell prompt while running X. If you telnet to the
remote machine and you're using a modem to connect then your machine name
on the Internet may be different from your actual machine name at home
so be sure to use the finger command on the remote machine with your remote
user name as an argument to find out what your machine name is on the
Internet. Assuming your machine name has not changed you must type

export DISPLAY=kiwi.fruit.org:0.0

on the remote machine if it uses the Korn shell or the equivalent if it uses
another shell. You should be now ready to fire up the remote application
from your machine.

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Q: I am sick of having to type in my password interactively each time I want to
start a shell on a remote server. Is there a way to avoid this.

A: Surprisingly yes. Simply replace the words "remote-host", "username", and
"password" in the following expect script and do a "chmod +x name-of-script".
You can then simply invoke the script to log into the remote host.

#!/usr/bin/expect
eval spawn telnet remote-host
set timeout 20
expect ogin:
send "username\r"
expect assword:
send "password\r"
sleep 2
interact

Alternatively you can try out the ktelnet program.

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Q: Is it possible to make recursive downloads to mirror ftp or web sites or
just download a file, perhaps while not even logged in?

A: Yes, use the wget program. See <ftp://sunsite.auc.dk/pub/infosystems/wget/>
for the latest version of the software.

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Q: I use the lp or lpr programs to print ASCII files and man pages. Is there
any way that I can get more text on one page, hence less pages of output?

A: Yes. If you have a printer which can print postscript files you could
try the a2ps program. Make sure you specify the -M option for the paper's
size and the -m option in case you're printing man pages.

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Q: I have more than 64 MB of RAM but when I use the "free" command to check
the amount of available memory on my system only slightly less than 64MB
show up. How do I get Linux to recognize the additional RAM?

A: Linux uses the BIOS to detect the amount of available RAM. At the present
time there are two separate function calls available to do the job. Any
version of Linux prior to 2.1.x uses the old call which is limited to 64M.
The newer call (used by 95/NT and Linux 2.1.x) can return more than 64M.
This problem should be fixed in the next stable release of the Linux kernel
(release 2.2.0). For now it is possible to have Linux detect all of your
RAM by adding the line:

append = "mem=128M"

to the file /etc/lilo.conf if you use LILO or to the end of the respective
LOADLIN file if you use LOADLIN. This will enable 128MB of RAM, for example.
You will need to rerun LILO for the changes to take effect. The next time you
boot up, Linux will see all of your memory.

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Q: I have used the rm command to delete a file. Is it possible to undelete the
file and hence recover its contents?

A: In theory there is a way to undelete a file if you are using the ext2fs
file system (most common). In practice, it is rarely possible. To prevent
significant loss of data in this manner you must ensure that your system
is backed up regularly. Alternatively if you had installed the program
midnight commander before deleting and compiled a version with undelf
then you could use cd undel:/dev/hda8 to see your deleted files (without
names). Alternatively, some users like to have a shell script that moves
a file to a directory like /tmp each time it is removed or just before
it is overwritten. If you are really desperate, read the Ext2fs-Undeletion
mini-HOWTO, which might work.

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Q: I am trying to run a script file named script or test but I am getting some
unexpected results.

A: The names script and test are names of executable programs on your system so
you should not use them for your own executables. If you got unexpected
it's because the system binaries got to be executed before your own binaries.

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Q: I (re/)installed windows on the same hard drive as Linux but now I no longer
get the LILO prompt and can't boot into Linux. What should I do?

A: Most likely windows overwrote the MBR (Master Boot Record) hence deleting
LILO. If you manually installed the kernel and used "make zdisk" then you
can boot from the floppy, otherwise you can download a boot/root floppy
distribution of Linux like the one at <http://www.toms.net/rb/> or some
other one. Once you get to your hard drive don't forget to rerun /sbin/lilo
so that you won't have to boot from the floppy again. If you are using a
floppy that boots its own file system then you must first mount your hard
drive with something like "mount /dev/hda1 /mnt" and change to the hard
drive with "chroot /mnt /bin/sh" before rerunning "/sbin/lilo".

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Q: I removed Linux from my system, but now DOS won't boot because LILO is still
there. How do I remove LILO?

A: If you have a version of DOS at least as recent as DOS 5.0 then you can
insert your DOS boot diskette and boot from it. At the DOS prompt, type

fdisk /mbr

to remove LILO from the Master Boot Record (MBR).

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Q: I want to add '.' to root's PATH, to allow me to not have to put ./ in
front of every local command I type. But I hear this is a bad thing. Why?

A: Adding '.' to root's PATH would be a security risk. Imagine the case where a
malicious user creates a file called /tmp/ls containing a command sequence
such as

# Caution: This script removes everything from the Linux file system.
cat /tmp/ls
rm -Rf /

and you as root wander into temp and want to see what files are there. If
the . occurs in root's path before /bin then typing ls at the shell prompt
will execute the malicious command instead. Alternatively, the malicious
command could be named mroe, ls-l, caat, lss, or similar in which case a
typo on root's behalf would cause it to be executed even if . is the last
entry in root's path. Finally, the malicious command may be set to copy
/bin/bash to a hidden spot and change permissions of the copy to
suid ( -rws---r-x ) so that anyone executing the hidden copy would have
root permissions.

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Q: I can't execute my script/program. I can list the file with ls -l and
it is there with the correct permissions:

ls -l mumble
-rwxrw-r-- 1 me user 104 Feb 14 15:46 mumble

but when I type mumble at the command prompt I get the response:

bash: mumble: command not found

A: Most probably the current directory (CWD) is not in your path. The best
thing to do in such situations is probably to type the full path to the
script/program followed by the name of the script/program .
If you are work in a directory that you alone use and which is not shared
then you might want to take the risk of editing your PATH variable to
contain CWD. Alternatively you could keep all your executables in a directory
called ~/bin and put it in your path. You can look at your path by typing
echo $PATH at the shell prompt.

echo $PATH
/usr/local/bin:/bin:/usr/bin:/usr/X11R6/bin:/home/me/bin

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Q: Why can't I telnet or rsh in to my Linux system as Root?

A: This is a security feature meant to protect you. Malicious users must
know a valid user password, as well as the root password in order to
get in to the system and do anything as root. Log in as a user, and
use the su command to then become root. Better still is to use the ssh
command (if installed) which encrypts your session to prevent anyone
from seeing the root password.
If your network is totally local (you have only a terminal connected
to a serial port), you can edit /etc/securetty to add that port as one
considered secure enough for root to log in.

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Q: Why can't I ftp as root?

A: This is a security feature meant to protect you. No user listed in
/etc/ftpuser is allowed to use ftp. Always ftp as a regular user.

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Q: I've tried to create a shell script and made it setuid root so the users
can execute it. But no matter what I do, it doesn't execute with root
privilege. Why?

A: Shell scripts are a notorious security hole. To protect you, the kernel
purposely ignores setuid and setgid in scripts. Create a C or Pearl
program to do the task.

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Q: Why should I create ordinary user accounts. I'm the only user on this
machine. Why not just work as root?

A: Root, commonly called the super-user, is for system administration tasks
only. The normal protection mechanisms are eliminated for this account
(indeed for any user with UID or GID equal to 0). So if you make any
little mistake (for example the classic "rm * myfile" -- note the
space between the wild-card and myfile) the system will do _exactly_
what you told it to do, not what you meant it to do. In the classic mistake
above, the system will remove all files in the current directory, then
complain because it can't remove 'myfile' which doesn't exist.

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Q: I am able to establish a dial up connection but when I use telnet to
connect to remote hosts telnet understands IP address but not host names.
What can I do to have telnet and other programs understand host names?

A: You should be able to get rid of this problem by adding an entry for a
name server in the file /etc/resolv.conf . If you have more than one name
server then you should put your primary dns first as nameserver entries
get read from top to bottom. The 'search' or 'domain' line should have
your isp's domain name. Your /etc/resolv.conf should look something like:

search virtual-impact.com
domain virtual-impact.com
nameserver 205.162.94.51
nameserver 205.162.88.33
nameserver 134.153.2.90

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Q: I don't like having to type the full host name when using telnet.
How can I resolve this problem?

A: Edit the file /etc/hosts and add entries like the following:

127.0.0.1 localhost localhost.localdomain
134.153.1.200 riemann riemann.math.mun.ca
134.153.39.1 ganymede ganymede.cs.mun.ca
134.153.1.1 garfield garfield.cs.mun.ca
134.153.2.151 plato plato.ucs.mun.ca
129.128.88.12 vega vega.math.ualberta.ca

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Q: I am logged into a host. I would like to find out its IP address
and a few other ones. How can I do this?

A: You could use the hosts command as follows:

ganymede $ host ganymede.cs.mun.ca
ganymede.cs.mun.ca has address 134.153.39.1
ganymede.cs.mun.ca mail is handled (pri=5) by garfield.cs.mun.ca
ganymede $

The programs nslookup and /sbin/ifconfig can also be used for this
purpose.

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Q: How can I have the "useradd" or "adduser" command automatically place some
default files in a user's directory when that user is added to the system?

A: Edit the contents of the files located under /etc/skel to suit your needs.
These files will be added to a user's home directory each time that user
is added.

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Q: I am trying to build a new kernel. Why is it that "make menuconfig" does not
display any colors when running under an xterm?

A: You could either use "make xconfig" or if you have the terminfo library
installed you could say "export TERM=xterm-color" or something similar.
Look at the entries in the terminfo library to chooses an appropriate value
for the TERM environment variable.

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Q: I am trying to get X to read my window manager's configuration file but with
no success.

A: If you start X with "startx" or "xinit" then you need a "~/.xinitrc" file
containing a command to execute your window manager and make the file
executable with "chmod u+x .xsession". If you start your session with xdm
though, your file will have to be named "~/.xsession" instead of
"~/.xinitrc".

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Q: Are the modules part of the Linux kernel or are they distributed separately?

A: They come with the kernel. There used to be an old package called
modules-x.y.z.tar.gz that you could download. This did not consist of the
modules themselves but the module utilities needed to handle modules.
For obvious reasons this package was renamed to modutils-x.y.z.tar.gz.

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Q: What is the quickest and safest way to recompile the kernel?

A: In short, as root issue the following commands after downloading a kernel:

# mv linux-x.y.z.tar.gz /usr/src; cd /usr/src
# tar zxpvf linux-x.y.z.tar.gz
# cd linux-x.y.z
# make menuconfig
# make dep
# make clean
# make bzImage (or better, insert a floppy and do a "make zdisk").
# make zlilo (or if this doesn't work,
cp /usr/src/linux-2.0.x/arch/i386/boot/zImage /boot/vmlinuz
Edit /etc/lilo.conf and change the image label to point to
/boot/vmlinuz-x.y.z and rerun /sbin/lilo)
reboot (here you may use the disk you made if something goes wrong)
# cd /usr/src/linux-x.y.z
# make modules; make modules_install

... and your kernel and modules should be all done.

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Q: I am trying to set up a home page. How do I go about doing that and where
should I put my web files to view them on my Linux box?

A: If you are running the Apache web server then look in
/etc/httpd/conf/srm.conf . There you should see lines like:

UserDir public_html
DirectoryIndex index.html index.shtml index.cgi

This means that your web files should be stored under a directory called
~/public_html and the first file to be read when a user accesses your web
site with http://x1.x2.x3.x4/~<your-username> must be one of ~/index.html ,
~/index.shtml , or ~/index.cgi . If you have an entry like:

127.0.0.1 localhost

in your /etc/hosts directory (ie. you have loopback enabled) than you can
make sure everything is OK by pointing your browser to
http://127.0.0.1/~<your-username> . Of course all files must have the right
permissions, in particular you probably want to do
a "chmod a+x ~/public_html" and a "chmod a+r index.html".
If you are not on the Internet this enables you to edit a whole web site on
a Linux box without having to be dialed up to your ISP. You can later upload
the pages to the Internet. This method will pay off in browser speed when
editing your web page.

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Q: I would like to have more lines and/or columns displayed when I use the text
consoles. Is there a way I can do this?

A: Yes. If you are using LILO to boot your system then you can do it by
inserting the vga option in your /etc/lilo.conf file. For example a line
saying "vga=ask" will let you choose the text mode at boot time (type
"man lilo.conf" for more details). Don't forget to rerun /sbin/lilo after
you modify /etc/lilo.conf .
Alternatively you could get the SVGATextMode program by anonymous ftp from
<ftp://metalab.unc.edu/pub/linux/utils/console/>.

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Q: I have two Linux boxes but they're not networked. What's a good way to
transfer data from one to another.

A: Get a bunch of floppies (one might be enough) and use:

$ tar cvMf /dev/fd0 <file/directory to be archived>

move the floppies to the other PC's floppy drive and do a:

$ tar xvMf /dev/fd0

Alternatively you can use the "split" command to split your file into many
files of a particular size with the "-b" option, copy them to a floppy
with a DOS file system with "mcopy", move the floppies to the other PC, copy
them to the hard drive and redirect the output of "cat" to merge them.

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Q: What's the cheapest way to network two Linux boxes?

A: Probably your best bet is to get an Interlink/Laplink/Bi-Directional cable
to connect the parallel ports. This method makes use of the PLIP protocol.
This will allow your PCs to communicate at a speed of approximately 47kB
per second. This is of course somewhat slower than a connection that makes
use of Ethernet cards. See the relevant HOWTOs and mini HOWTOs for more
detail.

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Q: I am running X. What's an easy way to put an image file in the background.

A: If you have "xv" installed then you may want to use:

xv -root -max -quit <absolute-path-to-image-file/image-file>

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Q: I have read the Brief Linux FAQ (BLFAQ) but could not find what I was
looking for. Where else should I look?

A: Other places include links under <http://www.linux.org/> including the Linux
FAQ (LFAQ) and the various HOWTOs and mini-HOWTOs. Other sites of interest
might include <http://www.xfree86.org/> for X related things and
<ftp://metalab.unc.edu/> if you're looking for interesting applications to
run under Linux.

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A big thank you to all those people who contributed to this FAQ.
Send me e-mail for corrections and enhancements.

--
maintained by: Neil Zanella
e-mail: nzanella@ganymede.cs.mun.ca



The Linux BLFAQ
Neil Zanella <nzanella@ganymede.cs.mun.ca>
v0.2.1, Jun 4 1999

Copyright Notice:
--------------------------------------------------------------------------------
Copyright (c) 1998-1999 by Neil Zanella. This document may be distributed under
the terms set forth in the LDP license at
<http://www.linuxdoc.org/COPYRIGHT.html>
--The Devil is in the Details--
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