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Sometimes, things go wrong, and the system you've carefully installed is no
longer bootable. Perhaps the boot loader configuration broke while trying
out a change, or perhaps a new kernel you installed won't boot, or perhaps
cosmic rays hit your disk and flipped a bit in
/sbin/init. Regardless of the cause, you'll need to
have a system to work from while you fix it, and rescue mode can be useful
for this.
To access rescue mode, type rescue at the
boot: prompt, or boot with the
rescue/enable=true boot parameter. You'll be shown
the first few screens of the installer, with a note in the corner of the
display to indicate that this is rescue mode, not a full installation. Don't
worry, your system is not about to be overwritten! Rescue mode simply takes
advantage of the hardware detection facilities available in the installer to
ensure that your disks, network devices, and so on are available to you
while repairing your system.
Instead of the partitioning tool, you should now be presented with a list of
the partitions on your system, and asked to select one of them. Normally,
you should select the partition containing the root file system that you
need to repair. You may select partitions on RAID and LVM devices as well as
those created directly on disks.
If possible, the installer will now present you with a shell prompt in the
file system you selected, which you can use to perform any necessary
repairs.
For example, if you need to reinstall the GRUB boot loader into the master
boot record of the first hard disk, you could enter the command
grub-install '(hd0)' to do so.
... Read more »
Why would someone want to compile a new kernel? It is often not
necessary since the default kernel shipped with Ubuntu handles most
configurations. Also, Ubuntu often offers several alternative kernels.
So you may want to check first if there is an alternative kernel image
package that better corresponds to your hardware. However, it can be
useful to compile a new kernel in order to:
handle special hardware needs, or hardware conflicts with the
pre-supplied kernels
use options of the kernel which are not supported in the pre-supplied
kernels (such as high memory support)
optimize the kernel by removing useless drivers to speed up boot time
create a monolithic instead of a modularized kernel
run an updated or development kernel
learn more about linux kernels
Kernel Image Management
Don't be afraid to try compiling the kernel. It's fun and profitable.
To compile a kernel the Debian/Ubuntu way, you need some packages:
fakeroot, kernel-package,
linux-source-2.6
and a few others which are probably already installed (see
/usr/share/doc/kernel-package/README.gz for the
complete list).
This method will make a .deb of your kernel source, and, if you have
non-standard modules, make a synchronized dependent .deb of those
too. It's a better way to manage kernel images;
/boot will hold the kernel, the System.map, and a
log of the active config file for the build.
Note that you don't have to compile your kernel
the "Debian/Ubuntu way”; but we find that using the packaging system
to manage your kernel is actually safer and easier. In fact, you can get
your kernel sources right from Linus instead of
linux-source-2.6,
yet still use the kernel-package compilation method.
Note that you'll find complete documentation on using
kernel-package under
/usr/share/doc/kernel-package. This section just
contains a brief tutorial.
Hereafter, we'll assume you have free rein over your machine and will
extract your kernel source to somewhere in your home directory. We'll also assume that your kernel version is
2.6.35. Make sure you are in the directory to where you want to
unpack the kernel sources, extract them using
tar xjf /usr/src/linux-source-2.6.35.tar.bz2
and change to the directory linux-source-2.6.35
that will have been created.
... Read more »
Today, email is an important part of many people's life. As there are
many options as to how to set it up, and as having it set up correctly is
important for some Ubuntu utilities, we will try to cover the basics in
this section.
There are three main functions that make up an e-mail system. First there is
the Mail User Agent (MUA) which is the program a user
actually uses to compose and read mails. Then there is the Mail
Transfer Agent (MTA) that takes care of transferring messages
from one computer to another. And last there is the Mail
Delivery Agent (MDA) that takes care of delivering incoming mail
to the user's inbox.
These three functions can be performed by separate programs, but they can
also be combined in one or two programs. It is also possible to have
different programs handle these functions for different types of mail.
On Linux and Unix systems mutt is historically a very
popular MUA. Like most traditional Linux programs it is text based. It is
often used in combination with exim or
sendmail as MTA and procmail as MDA.
With the increasing popularity of graphical desktop systems, the use of
graphical e-mail programs like GNOME's evolution,
KDE's kmail or Mozilla's thunderbird
is becoming more popular. These programs combine the function
of a MUA, MTA and MDA, but can — and often are — also be used
in combination with the traditional Linux tools.
... Read more »
If you need information about a particular program, you should first
try man program, or
info program.
There is lots of useful documentation in
/usr/share/doc as well. In particular,
/usr/share/doc/HOWTO and
/usr/share/doc/FAQ contain lots of interesting
information. To submit bugs, look at
/usr/share/doc/debian/bug*. To read about
Debian/Ubuntu-specific issues for particular programs, look at
/usr/share/doc/(package name)/README.Debian.
Ubuntu is a little different from other distributions. Even if you're
familiar with Linux in other distributions, there are things you
should know about Ubuntu to help you to keep your system in a good,
clean state. This chapter contains material to help you get oriented;
it is not intended to be a tutorial for how to use Ubuntu, but just a
very brief glimpse of the system for the very rushed.
Ubuntu Packaging System
The most important concept to grasp is the Ubuntu packaging system, which
may be familiar to those who have already used Debian GNU/Linux.
In essence, large parts of your system should be considered under the
control of the packaging system. These include:
/usr (excluding /usr/local)
/var (you could make
/var/local and be safe in there)
/bin
/sbin
/lib
For instance, if you replace /usr/bin/perl, that
will work, but then if you upgrade your perl
package, the file you put there will be replaced. Experts can get
around this by putting packages on "hold” in
aptitude.
One of the best installation methods is apt. You can use the command
line version apt-get, the full-screen text version
aptitude, or the graphical version
synaptic. Note apt will also let you merge
main, contrib, and non-free so you can have export-restricted packages
as well as standard versions.
... Read more »
If you are new to Unix, you probably should go out and buy some books
and do some reading. A lot of valuable information can also be found
in the Debian Reference.
This list of Unix FAQs contains a
number of UseNet documents which provide a nice historical reference.
Linux is an implementation of Unix. The
Linux Documentation Project (LDP)
collects a number of HOWTOs and online books
relating to Linux. Most of these documents can be installed locally;
just install the doc-linux-html package (HTML
versions) or the doc-linux-text package (ASCII
versions), then look in /usr/share/doc/HOWTO.
International versions of the LDP HOWTOs are also available as Ubuntu
packages.
To shut down a running Linux system, you must not reboot with the
reset switch on the front or back of your computer, or just turn off
the computer. Linux should be shut down in a controlled manner,
otherwise files might get lost and/or disk damage might occur. If you run a
desktop environment, there is usually an option to "log out”
available from the application menu that allows you to shutdown (or reboot)
the system.
Alternatively you can press the key combination Ctrl+Alt+Del
. A last option is to log in as root and type one of the
commands poweroff, halt or
shutdown -h now if either of the key combinations do not
work or you prefer to type commands; use reboot to reboot
the system.
Once your system boots, you'll be presented with the login
prompt. Log in using the personal login and password you
selected during the installation process. Your system is now ready for use.
If you are a new user, you may want to explore the documentation which
is already installed on your system as you start to use it. There are
currently several documentation systems, work is proceeding on
integrating the different types of documentation. Here are a few
starting points.
Documentation accompanying programs you have installed can be found in
/usr/share/doc/, under a subdirectory named after the
program (or, more precise, the Debian package that contains the program).
However, more extensive documentation is often packaged separately in
special documentation packages that are mostly not installed by default.
For example, documentation about the package management tool
apt can be found in the packages
apt-doc or apt-howto.
In addition, there are some special folders within the
/usr/share/doc/ hierarchy. Linux HOWTOs are
installed in .gz (compressed) format, in
/usr/share/doc/HOWTO/en-txt/. After installing
dhelp, you will find a browsable index of
documentation in /usr/share/doc/HTML/index.html.
... Read more »
If you created encrypted volumes during the installation and assigned
them mount points, you will be asked to enter the passphrase for each
of these volumes during the boot. The actual procedure differs
slightly between dm-crypt and loop-AES.
dm-crypt
For partitions encrypted using dm-crypt you will be shown the following
prompt during the boot:
Starting early crypto disks... part_crypt(starting)
Enter LUKS passphrase:
In the first line of the prompt, part is the
name of the underlying partition, e.g. sda2 or md0.
You are now probably wondering
for which volume you are actually entering the
passphrase. Does it relate to your /home? Or to
/var? Of course, if you have just one encrypted
volume, this is easy and you can just enter the passphrase you used
when setting up this volume. If you set up more than one encrypted
volume during the installation, the notes you wrote down as the last
step in the section called "Configuring Encrypted Volumes” come in handy. If you did not
make a note of the mapping between
part_crypt and the mount
points before, you can still find it
in /etc/crypttab
and /etc/fstab of your new system.
The prompt may look somewhat different when an encrypted root file system is
mounted. This depends on which initramfs generator was used to generate the
initrd used to boot the system. The example below is for an initrd generated
using initramfs-tools:
No characters (even asterisks) will be shown while entering the passphrase.
If you enter the wrong passphrase, you have two more tries to correct it.
After the third try the boot process will skip this volume and continue to
mount the next filesystem. Please see the section called "Troubleshooting”
for further information.
After entering all passphrases the boot should continue as usual.
... Read more »
Your system's first boot on its own power is what electrical engineers
call the "smoke test”.
If you did a default installation, the first thing you should see when you
boot the system is the menu of the grub or possibly
the lilo bootloader.
The first choices in the menu will be for your new Ubuntu system. If you
had any other operating systems on your computer (like Windows) that were
detected by the installation system, those will be listed lower down in the
menu.
If the system fails to start up correctly, don't panic. If the installation
was successful, chances are good that there is only a relatively minor
problem that is preventing the system from booting Ubuntu. In most cases
such problems can be fixed without having to repeat the installation.
One available option to fix boot problems is to use the installer's
built-in rescue mode (see the section called "Recovering a Broken System”).
If you had any other operating systems on your computer that were not detected
or not detected correctly, please file an installation report.
