The Linux BLFAQ
Neil Zanella <nzanella@ganymede.cs.mun.ca>
v0.2.5, Sep 30 2000

Copyright Notice:
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Copyright (c) 1998-2000 by Neil Zanella. This document may be distributed under
the terms set forth in the LDP license at
<http://www.linuxdoc.org/COPYRIGHT.html>

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 must configure your BIOS settings so that booting from the CD-ROM
   drive is enabled and so that the boot sequence forces the computer to
   boot from the CD-ROM drive instead of from some other device such as
   a hard drive or floppy drive. On most systems the BIOS settings can be
   accessed by entering a keystroke shortly after the computer powers up.
   The required keystroke varies from system to system and typical values
   include <del>, <f2>, and <ctrl>-<esc>.

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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. For example to
   convert the xterm man page to postscript you can use

   man xterm | a2ps -M Letter -m -o xterm.ps

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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 /tmp 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 startup file
   called "~/.xinitrc" otherwise if you start your X session with a session
   manager such as "xdm" then you need a startup file called "~/.xsession".
   The startup file should contain the command to execute your window manager.
   You must make your startup file executable with "chmod +x ~/.xinitrc" or
   "chmod +x ~/.xsession". For more information look at the files located
   under /etc/X11 and /usr/X11R6/lib/X11 as well as your window manager's
   documentation files.
   
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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
   # rm -f linux; tar zxpvf linux-x.y.z.tar.gz
   # mv linux linux-x.y.z; ln -s linux-x.y.z linux
   # cd linux
   # make menuconfig
   # make dep
   # make clean
   # make bzImage (or better, insert a floppy and do a "make bzdisk").
   # make bzlilo (or if this doesn't work,
                 cp /usr/src/linux-x.y.z/arch/i386/boot/bzImage /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
   # make modules; make modules_install

   This should do it.

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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>

   As "xv" is shareware you may want to try "qiv" which you may obtain from
   <http://www.klografx.net/qiv/>.

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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
