Table of Contents
Here, I will describe basic tips to configure and manage system from the console.
The screen
program (popcon: V:10, I:28) enables to have multiple terminals on a single physical terminal.
It also accommodates remote shell process to survive the interrupted connection. This is the essential tool for people to access remote sites via the unreliable connection.
Here is a typical use scenario of the screen
(1) program.
You login to a remote machine.
You start the screen
command on a single console.
You execute multiple programs in screen
windows created with ^A c
("Control-A" followed by "c").
You switch among the multiple screen
windows by ^A n
("Control-A" followed by "n").
Suddenly you need to leave your terminal, but you don't want to lose your active work by keeping the connection.
You detach the screen
session by any methods such as:
brutally unplugging your network connection,
typing ^A d
("Control-A" followed by "d") and manually logging out from the remote connection, or
typing ^A DD
("Control-A" followed by "DD") to have screen
detach and log you out.
You log in again to the same remote machine (even from a different terminal).
You enter the "screen -r
" command.
The screen
program will magically reattach all previous screen
windows with all actively running programs.
This is good way to save connection fee if you are on the dial-up network connection.
In screen
session, all keyboard inputs are sent to your current window except for the command keystroke, by default ^A
("Control-A"). All screen
commands are entered by typing ^A
plus a single key [plus any parameters]. Here are important ones to remember:
Table 10.1. List of key bindings for screen.
key binding |
meaning |
---|---|
|
show a help screen (display key bindings) |
|
create a new window and switch to it |
|
go to next window |
|
go to previous window |
|
go to window number 0 |
|
go to window number 1 |
|
show a list of windows |
|
send a Ctrl-A to current window as keyboard input |
|
write a hardcopy of current window to file |
|
begin/end logging current window to file |
|
lock the terminal (password protected) |
|
detach screen session from the terminal |
|
detach screen session and log out |
See screen
(1) for details.
Many programs record their activities under the /var/log/
directory.
The kernel log daemon: klogd
(8)
The system log daemon: syslogd
(8)
See Section 4.5.8, “The system message” and Section 4.5.9, “The kernel message”.
Here are notable log analyzers ("~Gsecurity::log-analyzer
" in aptitude
).
Table 10.2. List of system log analyzers.
package |
popcon |
size |
description |
---|---|---|---|
|
V:2, I:2 |
2312 |
log analyser with nice output written in Perl |
|
V:2, I:2 |
616 |
bans IPs that cause multiple authentication errors |
|
V:1.2, I:18 |
4520 |
web server log analyzer |
|
V:1.5, I:3 |
4892 |
powerful and featureful web server log analyzer |
|
V:1.4, I:1.5 |
1500 |
squid analysis report generator |
|
V:0.3, I:0.8 |
164 |
Postfix log entry summarizer |
|
V:0.2, I:1.1 |
80 |
summarize the contents of a syslog log file |
|
V:0.17, I:0.2 |
5048 |
full-featured log analyzer and report generator |
|
V:0.16, I:0.3 |
432 |
Firewall log analyzer |
|
V:0.10, I:0.6 |
260 |
monitors and analyses squid access.log files |
|
V:0.09, I:0.3 |
224 |
fast web server log analyzer |
|
V:0.07, I:0.2 |
196 |
Log file viewer with regexp matching, highlighting, & hooks |
|
V:0.07, I:0.2 |
1120 |
The Controllable Regex Mutilator and Spam Filter (CRM114) |
|
V:0.07, I:0.4 |
84 |
Interpret ICMP messages |
![]() |
Note |
---|---|
CRM114 provides language infrastructure to write fuzzy filters with the TRE regex library. Its popular use is spam mail filter but it can be used as log analyzer. |
The simple use of the script
(1) command (see: Section 2.4.9, “Recording the shell activities”) to record the shell activity produces a file with control characters. This can be avoided by using the col
(1) command:
$ script Script started, file is typescript
do whatever ...
Press Ctrl-D
to exit script
$ col -bx <typescript >cleanedfile $ vim cleanedfile
In some odd environment where you lack access to the script
command, for example, during the boot process in the initramfs, you can use following instead:
$ sh -i 2>&1 | tee typescript
![]() |
Tip |
---|---|
Some |
![]() |
Tip |
---|---|
You may use |
![]() |
Tip |
---|---|
You may use |
Although pager tools such as more
(1) and less
(1) (see Section 2.4.5, “The pager”) and custom tools for highlighting and formatting Section 12.1.7, “Highlighting and formatting plain text data” can display text data nicely, general purpose editors (see Section 2.4.6, “The text editor”) are most versatile and customizable.
![]() |
Tip |
---|---|
For |
Colorized commands are handy for inspecting their output in the interactive environment. I include following in my ~/.bashrc
.
if [ "$TERM" != "dumb" ]; then eval "`dircolors -b`" alias ls='ls --color=always' alias ll='ls --color=always -l' alias la='ls --color=always -A' alias less='less -R' alias ls='ls --color=always' alias grep='grep --color=always' alias egrep='egrep --color=always' alias fgrep='fgrep --color=always' alias zgrep='zgrep --color=always' else alias ll='ls -l' alias la='ls -A' fi
The use of alias limits color effects to the interactive command usage. It has advantage over exporting environment variable "export GREP_OPTIONS='--color=auto'
" since color can be seen under pager programs such as "less
".
![]() |
Tip |
---|---|
You can turn off these colorizing aliases in the interactive environment by invoking shell with " |
Some programs start another program automatically. Here are check points for customizing this process:
configuration file of the parent program such as "/etc/mc/mc.ext
".
system configuration menu such as "Sysyem" -> "Preferences" -> "Preferred Application" for Gnome.
environment variables such as "BROWSER
", "EDITOR
", "VISUAL
", and "PAGER
" (see eviron
(7)).
the update-alternatives
(8) system for programs such as "editor
", "view
", "x-www-browser
", "gnome-www-browser
", and "www-browser
" (see Section 2.4.7, “Setting a default text editor”).
the "$HOME/.mailcap
" and "/etc/mailcap
" file contents which associate MIME type with program (see mailcap
(5)).
the the "$HOME/.mime.types
" and "/etc/mime.types
" file contents which associate file name extension with MIME type (see run-mailcap
(1)).
![]() |
Tip |
---|---|
The |
![]() |
Tip |
---|---|
The |
There are few ways to record the graphic image of an X application, including an xterm
display.
Table 10.3. List of graphic image manipulation tools.
package |
popcon |
size |
command |
---|---|---|---|
|
V:33, I:67 |
52 |
|
|
V:13, I:56 |
11720 |
GUI menu |
|
V:14, I:30 |
4464 |
|
|
V:0.19, I:0.9 |
88 |
|
Changes in configuration files can be nicely recorded using DVCS system (see Section 11.5.4.4, “Git for recording configuration history”).
Poor system maintenance may expose your system to external exploitation.
For system security check, you should start with:
debsums
package: See debsums
(1) and Section 3.2.2, “Top level Release file and authenticity”.
chkrootkit
package: See chkrootkit
(1).
clamav
package family: See clamscan
(1) and freahclam
(1).
Here is a simple script to check for typical world writable incorrect file permissions.
# find / -perm 777 -a \! -type s -a \! -type l -a \! \( -type d -a -perm 1777 \)
For the PCI-like devices (AGP, PCI-Express, CardBus, ExpressCard, etc.), lspci
(8) command (probably with "-nn
" option) is a good start for the hardware identification
Alternatively, you can identify the hardware by reading contents of /proc/bus/pci/devices
or browsing directory tree under /sys/bus/pci
(see Section 2.2.12, “procfs and sysfs”).
Table 10.4. List of hardware identification tools.
package |
popcon |
size |
description |
---|---|---|---|
|
V:44, I:92 |
460 |
Linux PCI Utilities, |
|
V:22, I:97 |
520 |
Linux USB utilities, |
|
V:1.0, I:16 |
172 |
PCMCIA utilities for Linux 2.6, |
|
V:0.2, I:1.5 |
476 |
Collection of tools for SCSI hardware management, |
|
V:0.03, I:0.18 |
108 |
Plug and Play BIOS utilities, |
|
V:0.7, I:5 |
120 |
Displays system information from |
|
V:1.0, I:5 |
804 |
Information about hardware configuration, |
|
V:4, I:13 |
928 |
Hardware identification system, |
Although most of the hardware configuration on modern GUI desktop systems such as Gnome and KDE can be managed through accompanying GUI configuration tools, it is a good idea to know some basics methods to configure them.
Table 10.5. List of hardware configuration tools.
package |
popcon |
size |
description |
---|---|---|---|
|
V:43, I:60 |
1972 |
Hardware Abstraction Layer, |
|
V:60, I:97 |
948 |
Linux console font and keytable utilities. |
|
V:16, I:23 |
616 |
X server utilities. |
|
V:54, I:88 |
184 |
Daemon to manage events delivered by the Advanced Configuration and Power Interface (ACPI) |
|
V:3, I:34 |
92 |
Utilities for ACPI devices |
|
V:1.4, I:13 |
252 |
Daemon to manage events delivered by the Advanced Power Management (APM) |
|
V:1.2, I:1.6 |
1800 |
Daemon to manage battery, temperature, ac, cpufreq (SpeedStep, Powernow!) control and monitor with ACPI and APM supports. |
|
V:0.13, I:0.2 |
244 |
Allow idle hard disks to spin down |
|
V:0.09, I:0.13 |
140 |
Puts a laptop to sleep during inactivity |
|
V:10, I:34 |
272 |
Hard disk access optimization. Very effective but dangerous. You must read |
|
V:4, I:12 |
828 |
Control and monitor storage systems using S.M.A.R.T. |
|
V:3, I:6 |
176 |
Collection of tools for serial port management. |
|
V:0.5, I:4 |
236 |
Collection of tools for memory hardware management. |
|
V:0.2, I:1.5 |
476 |
Collection of tools for SCSI hardware management. |
|
V:0.4, I:0.5 |
208 |
A program to configure touchpad devices |
|
V:0.09, I:0.5 |
64 |
Compact disc drive access optimization. |
|
I:0.2 |
68 |
Larger mouse cursors for X |
|
V:0.02, I:0.11 |
88 |
Simple front end to powertweak, |
Here, ACPI is a newer framework for the power management system than APM.
The following will set system and hardware time to MM/DD hh:mm, CCYY.
# date MMDDhhmmCCYY # hwclock --utc --systohc # hwclock --show
Times are normally displayed in the local time on the Debian system but the hardware and system time usually use UTC.
If the hardware (BIOS) time is set to GMT, change the setting to UTC=yes
in the /etc/default/rcS
.
If you wish to update system time via network, consider to use the NTP service with the packages such as ntp
, ntpdate
, and chrony
. See:
The ntp-doc
package
There are several components to configure character console and ncurses
(3) system features:
the terminfo
(5) file
the TERM
(7) environment variable
the setterm
(1) command
the stty
(1) command
the tic
(1) command
the toe
(1) command
If the terminfo
entry for xterm
doesn't work with a non-Debian xterm
, change your terminal type from xterm
to one of the feature-limited versions such as xterm-r6
when you log in to a Debian system remotely. See /usr/share/doc/libncurses5/FAQ
for more. dumb
is the lowest common denominator for terminfo
.
Device drivers for sound cards for current Linux 2.6 are provided by Advanced Linux Sound Architecture (ALSA). ALSA provides emulation mode for previous Open Sound System (OSS) for compatibility.
Run "dpkg-reconfigure linux-sound-base
" to select the sound system to use ALSA. Unless you have very new sound hardware, udev infrastructure should configure your sound system.
![]() |
Tip |
---|---|
Use " |
![]() |
Tip |
---|---|
If you can not get sound, your speaker may be connected to a muted output. Modern sound system has many outputs. The |
Application softwares may be configured not only to access sound devices directly but also to access them via some standardized sound server system.
Table 10.6. List of sound packages
package |
pocon |
size |
description |
---|---|---|---|
|
V:15, I:59 |
132 |
Base package for ALSA and OSS sound systems |
|
I:59 |
444 |
ALSA driver configuration files |
|
V:39, I:59 |
1984 |
Utilities for configuring and using ALSA |
|
V:25, I:68 |
68 |
Enlightened Sound Daemon (ESD) common (Enlightenment and GNOME) |
|
V:5, I:40 |
84 |
Enlightened Sound Daemon (ESD) server (Enlightenment and GNOME) |
|
V:10, I:19 |
168 |
Enlightened Sound Daemon (ESD) client (Enlightenment and GNOME) |
|
V:2, I:3 |
96 |
Enlightened Sound Daemon (ESD) library Enlightenment and GNOME) |
|
V:40, I:64 |
92 |
Enlightened Sound Daemon (ESD) library (Enlightenment and GNOME) - OSS |
|
I:16 |
36 |
aRts server (KDE) |
|
V:23, I:47 |
6180 |
aRts library (KDE) |
|
V:22, I:51 |
72 |
aRts library (KDE) |
|
V:1.6, I:7 |
412 |
JACK Audio Connection Kit. (JACK) server (low latency) |
|
V:12, I:22 |
360 |
JACK Audio Connection Kit. (JACK) library (low latency) |
|
I:38 |
48 |
JACK Audio Connection Kit. (JACK) library (low latency) |
|
V:0.17, I:0.2 |
324 |
Network Audio System (NAS) server |
|
V:27, I:65 |
204 |
Network Audio System (NAS) library |
|
V:0.6, I:1.8 |
1240 |
PulseAudio server, replacement for ESD |
|
V:2, I:25 |
496 |
PulseAudio client library, replacement for ESD |
|
V:0.5, I:1.4 |
604 |
PulseAudio server library, replacement for ESD |
|
V:14, I:61 |
2644 |
GStreamer: Gnome sound engine |
|
V:6, I:54 |
24 |
xine: KDE older sound engine |
|
I:2 |
468 |
Phonon: KDE new sound engine |
There is usually a common sound engine for each popular desktop environment. Each sound engine used by the application can choose to connect to different sound servers.
For disabling the screen saver, use following commands.
Table 10.7. List of commands for disabling the screen saver.
environment |
command |
---|---|
The Linux console |
|
The X Window by turning off screensaver |
|
The X Window by disabling dpms |
|
The X Window by GUI configuration of screen saver |
|
One can always unplug the PC speaker. Removing pcspkr
kernel module does this for you.
The following will prevent the readline
program used by the bash
to beep when encountering "\a" (ASCII=7):
$ echo "set bell-style none">> ~/.inputrc
You can test disk access speed of harddisk, e.g. /dev/hda
, by "hdparm -tT /dev/hda
".
You may be able to speed up a harddisk connected with (E)IDE with "hdparm -q -c3 -d1 -u1 -m16 /dev/hda
". Please check your hardware and read manpage of hdparam
(8) before playing with harddisk configuration because this may be quite dangerous for the data integrity.
You may be able to read badly pressed cdroms on modern high head CD-ROM drive by slowing it down with "setcd -x 2
.
Mounting a filesystem with the noatime
option is also very effective in speeding up read access to the file. See fstab
(5) and mount
(8).
The kernel boot message in the /var/log/dmesg
contains the total exact size of available memory.
The free
(1) and top
(1) commands display information on memory resources on the running system.
$ grep '^Memory' /var/log/dmesg Memory: 990528k/1016784k available (1975k kernel code, 25868k reserved, 931k data, 296k init) $ free -k total used free shared buffers cached Mem: 997184 976928 20256 0 129592 171932 -/+ buffers/cache: 675404 321780 Swap: 4545576 4 4545572
For my MacBook with 1GB=1048576k DRAM (video system steals some of this):
Table 10.8. List of memory sizes reported.
report |
size |
---|---|
Total size in dmesg |
1016784k = 1GB - 31792k |
Free in dmesg |
990528k |
Total under shell |
997184k |
Free under shell |
20256k |
Do not worry about the large size of "used
" and the small size of "free
" in the "Mem:
" line, but read the one under them (675404 and 321780 in the example below) and relax.
Display time used by the process invoked by the command.
# time some_command >/dev/null real 0m0.035s # time on wall clock (elapsed real time) user 0m0.000s # time in user mode sys 0m0.020s # time in kernel mode
A nice value is used to control the scheduling priority for the process.
Table 10.9. List of nice values for the scheduling priority.
nice value |
scheduling priority |
---|---|
19 |
lowest priority process (nice) |
0 |
very high priority process for user. |
-20 |
very high priority process for root. (not-nice) |
Table 10.10. List of tools for the scheduling priority.
command |
package |
popcon |
size |
function |
---|---|---|---|---|
|
|
V:86, I:99 |
11448 |
run a program with the modified scheduling priority |
|
|
V:62, I:99 |
168 |
modify the scheduling priority of a running processes |
# nice -19 top # very nice # nice --20 wodim -v -eject speed=2 dev=0,0 disk.img # very fast
Sometimes an extreme nice value does more harm than good to the system. Use this command carefully.
The ps
(1) command on the Debian support both BSD and SystemV features and helps to identify the process activity statically.
Table 10.11. List of ps command styles.
style |
typical command |
feature |
---|---|---|
BSD |
|
display %CPU %MEM |
System V |
|
display PPID |
For the zombie (defunct) children process, you can kill them by the parent process ID identified in the (PPID
) field.
The top
(1) command on the Debian has rich features and helps to identify what process is acting funny dynamically.
Table 10.12. List of commands for top.
command key |
response |
---|---|
|
To show help. |
|
To set/reset display field. |
|
To reorder display field. |
|
To set sort key field. |
|
To kill a process. |
|
To renice a process. |
|
To quit the |
Use the kill
(1) command to kill (or send a signal to) a process by the process ID.
Use the killall
(1) command to do the same by the process command name.
Table 10.13. List of frequently used signals for kill command.
signal value |
signal name |
function |
---|---|---|
1 |
HUP |
restart daemon |
15 |
TERM |
normal kill |
9 |
KILL |
kill hard |
Run the at
(1) command to schedule a one-time job:
$ echo 'command -args'| at 3:40 monday
Use cron
(8) to schedule tasks regularly. See crontab
(1) and crontab
(5).
Run the command "crontab -e
" to create or edit a crontab file to set up regularly scheduled events.
Example of a crontab file:
# use /bin/sh to run commands, no matter what /etc/passwd says SHELL=/bin/sh # mail any output to paul, no matter whose crontab this is MAILTO=paul # Min Hour DayOfMonth Month DayOfWeek command (Day... are OR'ed) # run at 00:05, every day 5 0 * * * $HOME/bin/daily.job >> $HOME/tmp/out 2>&1 # run at 14:15 on the first of every month -- output mailed to paul 15 14 1 * * $HOME/bin/monthly # run at 22:00 on weekdays(1-5), annoy Joe. % for newline, last % for cc: 0 22 * * 1-5 mail -s "It's 10pm" joe%Joe,%%Where are your kids?%.%% 23 */2 1 2 * echo "run 23 minutes after 0am, 2am, 4am ..., on Feb 1" 5 4 * * sun echo "run at 04:05 every sunday" # run at 03:40 on the first Monday of each month 40 3 1-7 * * [ "$(date +%a)" == "Mon" ] && command -args
![]() |
Tip |
---|---|
For the system not running continuously, install the |
Insurance against system malfunction is provided by the kernel compile option "Magic SysRq key" (SAK key) which is now the default for the Debian kernel. Pressing Alt-SysRq followed by one of the following keys does the magic of rescuing control of the system:
Table 10.14. List of SAK command keys.
key following Alt-SysRq |
function |
---|---|
|
Unraw restores the keyboard after things like X crashes. |
|
Changing the console loglevel to 0 reduces error messages. |
|
SAK (system attention key) kills all processes on the current virtual console. |
|
Send a SIGTERM to all processes, except for |
|
Send a SIGKILL to all processes, except for |
|
Sync all mounted filesystems. |
|
Remount all mounted filesystems read-only (umount). |
|
Reboot the system without syncing or unmounting. |
The combination of "Alt-SysRq s", "Alt-SysRq u", and "Alt-SysRq r" is good for getting out of really bad situations.
See /usr/share/doc/linux-doc-2.6.*/Documentation/sysrq.txt.gz
.
![]() |
Caution |
---|---|
The Alt-SysRq feature may be considered a security risk by allowing users access to root-privileged functions. Placing " |
![]() |
Tip |
---|---|
From SSH terminal etc., you can use the Alt-SysRq feature by writing to the |
Debian distributes modularized Linux kernel as packages for supported architectures.
There are few notable features on Linux kernel 2.6 compared to 2.4.
Devices are created by the udev system (see Section 4.5.10, “The udev system”).
Read/write accesses to IDE CD/DVD devices do not use the ide-scsi
module.
Network packet filtering functions use iptable
kernel modules.
Most normal programs don't need kernel headers and in fact may break if you use them directly for compiling. They should be compiled against the headers in /usr/include/linux
and /usr/include/asm
provided by the libc6-dev
package (created from the glibc
source package) on the Debian system.
![]() |
Note |
---|---|
For compiling some kernel-specific programs such as the kernel modules from the external source and the automounter daemon ( |
Debian has its own method of compiling the kernel and related modules.
Table 10.15. List of key packages to be installed for the kernel recompilation on the Debian system
package |
popcon |
size |
description |
---|---|---|---|
|
I:38 |
48 |
essential packages for building Debian packages: |
|
V:53, I:81 |
132 |
compress and decompress utilities for bz2 files |
|
V:4, I:28 |
6780 |
developer's libraries and docs for ncurses |
|
V:3, I:6 |
7164 |
git: distributed revision control system used by the Linux kernel |
|
V:4, I:26 |
456 |
provide fakeroot environment for building package as non-root |
|
V:16, I:95 |
408 |
tool to build an initramfs (Debian specific) |
|
V:3, I:19 |
2192 |
tool to build Linux kernel packages (Debian specific) |
|
V:4, I:21 |
512 |
tool to help build module packages (Debian specific) |
|
V:2, I:13 |
1536 |
helper scripts for a Debian Package maintainer (Debian specific) |
|
I:0.03 |
120 |
Linux kernel source tree for building Debian kernel images (Debian specific) |
If you use initrd
in Section 4.3, “Stage 2: the boot loader”, make sure to read the related information in initramfs-tools
(8), update-initramfs
(8), mkinitramfs
(8) and initramfs.conf
(5).
![]() |
Warning |
---|---|
Do not put symlinks to the directories in the source tree (e.g. |
![]() |
Note |
---|---|
When compiling the latest Linux kernel on the Debian |
The Debian standard method for compiling kernel source to create a custom kernel package uses make-kpkg
(1) command. The official documentation is in (the bottom of) /usr/share/doc/kernel-package/README.gz
. See kernel-pkg.conf
(5) and kernel-img.conf
(5) for customization.
Here is an example for amd64 system:
# aptitude install linux-tree-<version> $ cd /usr/src $ tar -xjvf linux-source-<version>.tar.bz2 $ cd linux-source-<version> $ cp /boot/config-<oldversion> .config $ make menuconfig ... $ make-kpkg clean $ fakeroot make-kpkg --append_to_version -amd64 --initrd --revision=rev.01 kernel_image modules_image $ cd .. # dpkg -i linux-image*.deb
reboot to new kernel with "shutdown -r now
" .
![]() |
Caution |
---|---|
When you intend to create a non-modularized kernel compiled only for one machine, invoke |
The Debian standard method for creating and installing a custom module package for a custom kernel package uses module-assistant
(8) command and module-source packages. For example, following will build the unionfs
kernel module package and installs it.
$ sudo aptitude install module-assistant ... $ sudo aptitude install unionfs-source unionfs-tools unionfs-utils $ sudo m-a update $ sudo m-a prepare $ sudo m-a auto-install unionfs ... $ sudo apt-get autoremove
You can still build Linux kernel from the pristine sources with the classic method. You must take care the details of the system configuration manually.
$ cd /usr/src $ wget http://www.kernel.org/pub/linux/kernel/v2.6/linux-<version>.tar.bz2 $ tar -xjvf linux-<version>.tar.bz2 $ cd linux-<version> $ cp /boot/config-<version> .config $ make menuconfig ... $ make dep; make bzImage $ make modules # cp ./arch/x86_64/boot/bzImage /boot/vmlinuz-<version> # make modules_install # depmod -a # update-initramfs -c -k <version>
edit /etc/lilo.conf
and run /sbin/lilo
, if you use lilo
.
edit /boot/grub/menu.lst
, if you use grub
.
reboot to new kernel with "shutdown -r now
" .
Although most of hardware drivers are available as free software and as a part of the Debian system, you may need to load some non-free external drivers to support some hardwares, such as Winmodem, on your system.
Check pertinent resources:
http://en.wikipedia.org/wiki/Comparison_of_open_source_wireless_drivers
Linmodem with google or similar.
http://madwifi.org/ (there is ath5k which is free drivers)
The chroot
(8) program is most basic way to run different instances of the GNU/Linux environment on a single system simultaneously without rebooting. I will explain simple chroot systems in the following as examples.
For serious chroot setup with the detail configuration, please consider to use the specialized schroot
package.
A chroot Debian environment can easily be created by the debootstrap
or cdebootstrap
command.
For example, the following will create a sid
chroot on /sid-root
while having fast Internet access:
main # debootstrap sid /sid-root http://ftp.debian.org/debian/
watch it download the whole system
main # echo "proc-sid /sid-root/proc proc none 0 0" >> /etc/fstab main # echo "devpts-sid /sid-root/dev/pts devpts defaults 0 0" >> /etc/fstab main # mount -a main # cp -f /etc/passwd /sid-root/etc/passwd main # cp -f /etc/shadow /sid-root/etc/shadow main # cp -f /etc/group /sid-root/etc/group main # cp -f /etc/hosts /sid-root/etc/hosts main # chroot /sid-root /bin/bash chroot # cd /dev; /sbin/MAKEDEV generic ; cd - chroot # vi /etc/apt/sources.list
point the source to unstable
chroot # aptitude update ... chroot # aptitude install locales ...
add "en_US.UTF-8" as locale and make it default
Do you want to continue? [Y/n/?] y chroot # aptitude install mc vim ... Do you want to continue? [Y/n/?] y ... chroot # exit main #
At this point you should have a fully working Debian sid system, where you can play around without fear of affecting your main Debian installation.
![]() |
Caution |
---|---|
If you use bind mount for directories such as home directory in the chroot, you must be careful for its side effects. I heard people lost their home directory after executing " |
This debootstrap
trick can also be used to install Debian to a system without using a Debian install disk, but instead from another GNU/Linux distribution.
Typing "chroot /sid-root /bin/bash
" is easy, but it retains all sorts of environment variables that you may not want, and has other issues. A much better approach is to run another login process on a separate virtual terminal where you can log in to the chroot directly.
Since on default Debian systems tty1
to tty6
run Linux consoles and tty7
runs the X Window System, let's set up tty8
for a chrooted console as an example. After creating a chroot system, type from the root shell of the main system:
main # echo "8:23:respawn:/usr/sbin/chroot /sid-root /sbin/getty 38400 tty8" >> /etc/inittab main # init q
reload init
You want to run the latest X and GNOME safely in your chroot? That's entirely possible! The following example will make GDM run on virtual terminal vt9
.
First install a chroot system. From the root of the main system, copy key configuration files to the chroot system.
main # cp /etc/X11/xorg.conf /sid-root/etc/X11/xorg.conf main # chroot /sid-root chroot # cd /dev; /sbin/MAKEDEV generic ; cd - chroot # aptitude install gdm gnome x-window-system chroot # vim /etc/gdm/gdm.conf
change "[servers]
" section with "s/vt7/vt9/
" to make the first virtual console in the chroot from vt7
to vt9
.
chroot # /etc/init.d/gdm start
Now you can easily switch back and forth between full X environments in your chroot and your main system just by switching between Linux virtual terminals; e.g. by using Ctrl-Alt-F7 and Ctrl-Alt-F9. Have fun!
A chroot environment for another Linux distribution can easily be created. You install a system into separate partitions using the installer of the other distribution. If its root partition is in /dev/hda9
:
main # cd / ; mkdir /other-dist main # mount -t ext3 /dev/hda9 /other-dist main # chroot /other-dist /bin/bash
There is a more specialized chroot package, pbuilder
, which constructs a chroot system and builds a package inside the chroot. It is an ideal system to use to check that a package's build-dependencies are correct, and to be sure that unnecessary and wrong build dependencies will not exist in the resulting package.
There are several system virtualization and emulation related packages in Debian beyond simple chroot.
Table 10.16. List of virtualization tools
package |
pocon |
size |
description |
---|---|---|---|
|
V:1.1, I:1.7 |
1900 |
Specialized tool for executing Debian binary packages in chroot |
|
V:0.07, I:0.3 |
452 |
Tool for building Debian binary packages from Debian sources |
|
V:0.6, I:2 |
1116 |
Personal package builder for Debian packages |
|
V:1.6, I:11 |
260 |
Bootstrap a basic Debian system (written in sh) |
|
V:0.5, I:2 |
156 |
Bootstrap a Debian system (written in C) |
|
V:0.03, I:0.2 |
156 |
A tool for building complete Linux filesystem images |
|
V:0.07, I:0.5 |
17816 |
User-mode Linux (kernel) |
|
V:0.3, I:2 |
976 |
Tools to manage debian XEN virtual server |
|
V:0.10, I:0.7 |
3072 |
IA-32 PC emulator |
|
V:1.2, I:5 |
30724 |
Fast generic processor emulator |
|
V:1.6, I:2 |
22108 |
A x86 virtualization solution on i386 and amd64 |
|
V:2, I:15 |
96 |
Windows API Implementation (standard suite) |
|
V:0.6, I:3 |
2240 |
A x86 emulator with Tandy/Herc/CGA/EGA/VGA/SVGA graphics, sound and DOS |
See Wikipedia article http://en.wikipedia.org/wiki/Comparison_of_virtual_machines for detail comparison of different virtualization solutions.