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From: Neil Zanella <nzanella@cs.mun.ca>
Subject: BLFAQ: Brief Linux FAQ with answers
Date: Fri, 13 Mar 1998 12:25:38 -0330
Copyright Notice:
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Copyright (c) 1998 by Neil Zanella. This document may be distributed under the
terms set forth in the LDP license at http://sunsite.unc.edu/LDP/COPYRIGHT.html
Intro:
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Welcome to the Brief Linux FAQ (BLFAQ)!
Here is a brief list of some frequently asked Linux questions with their
answers. I hope that these will be of some help to Linux users, especially to
newbies. Also, I invite you to modify and add to this list anything that you
might think would be helpful to Linux users in general. If you modify this list
please be sure to mail me a copy of the modified list so that I can include
your changes in future postings.
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 username
and password to do this?
A: No, anonymous ftp means that you log in with the username "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 username.
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Q: I plan to use the fips program to shrink a FAT32 partition (such
as one devoted to MS-Windows 95) and hence create space for my
Linux operating system. Can this be done?
A: Yes, but in order to do this you will need a version of fips
at least as up to date as fips15c. You can get the latest
version of fips by anonymous ftp from bmrc.berkeley.edu
in the directory /pub/linux/fat32
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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.
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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 old and you have an IDE (or EIDE) hard drive then
you must install your root partition completely below cylinder 1023
which means below 512MB 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 get
around this problem by enabling LBA mode.
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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 runlevel) to
another number like 4. Which number should be clear by reading the comments
in the file /etc/inittab . Alternatively, yo might have to change a link
in /etc/rc[2345].d . Runlevels 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 obtain more virtual screen space.
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Q: I would like to have xdm run multiple local diplays 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
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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
at the command prompt. For more information see the Visual-Bell-mini-HOWTO
at http://www.linux.org/
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Q: I have access to a 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 using dip or whatever you use. If the machine is called
foo.bar.edu you can type xhost +foo.bar.edu
from your own machine's shell prompt. Once you're there if your machine
is called kiwi.remote.net then you must export the display on
foo.bar.edu
with a command like export DISPLAY=kiwi.remote.net:0.0 or
set DISPLAY=kiwi.remote.net:0.0 . You should be now ready to run the
remote application from your own machine.
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Q: I have more than 64 MB of RAM, so, how do I get Linux to recognize the
additional RAM?
A: Linux uses a BIOS function call to detect the amount of available RAM.
At the present time the BIOS call reports a maxmium of 64 MB. If you have a
stable version of the Linux kernel prior to 2.2.x then you can get Linux
to detect all of the RAM by adding the line:
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 get Linux to detect all of the
RAM by adding the line:
append = "mem=128M"
to the file /etc/lilo.conf if you use LILO or to the end of the LOADLIN
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.
Any stable version of Linux at least as new as 2.1.x fixes this having to
do this by having the BIOS do multiple fuc\nction calls.
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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: No, you cannot undelete a file under Linux. Once you remove a file its
contents are permanently expunged from the hard drive. To prevent significant
loss of data in this manner you must ensure that your system is backed up
regularly. Also, 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.
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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 prgrams 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 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, I get
mumble
bash: mumble: command not found
A: The current directory is not in your path. Either type the command followed by
the full path to the file as in
./mumble
or
/home/your-username-here/mumble
or edit your PATH variable to contain . or the full path to your file.
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: 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 roots 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 filesystem.
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 itt to be executed even if . is the last
entry in root's path. Finally, the mailicious 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 accidently deleted a file. How do I undelete it?
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. Sorry.
If you are really desparate, read the Ext2fs-Undeletion mini-howto,
which might work.
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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
privliage. 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 have read the Brielf 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.
Hope this helps,
--
maintained by: Neil Zanella
mail: nzanella@ganymede.cs.mun.ca