= Do not use Edit(GUI) button. =

[[TableOfContents(4)]]

Copyright 2007, 2008  Osamu Aoki GPL, (Please agree to GPL, GPL2, and any version of GPL which is compatible with DSFG if you update any part of wiki page)

I welcome your contributions to update the wiki pages. You must follow these rules:
 * Do not use Edit(GUI) button of MoinMoin.
 * You can update anytime for:
  * grammar errors
  * spelling errors
  * moved URL location
  * package name transition adjustment (emacs23 etc.)
  * clearly broken script.
 * Before updating real contents:
  * Read "[http://wiki.debian.org/DebianReference/Test Guide for contributing to Debian Reference]".

= System tips =

Here, I will describe basic tips to configure and manage system from the console.  

== The screen program ==

The {{{screen}}} program (popcon: @@@pop-screen@@@) 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.

=== The use scenario for the screen command ===

Here is a typical use scenario of the {{{screen}}}(1) program.

 1. You login to a remote machine.
 1. You start the {{{screen}}} command on a single console.
 1. You execute multiple programs in {{{screen}}} windows created with {{{^A c}}} ("Control-A" followed by "c").
 1. You switch among the multiple {{{screen}}} windows by {{{^A n}}} ("Control-A" followed by "n").
 1. Suddenly you need to leave your terminal, but you don't want to lose your active work by keeping the connection.
 1. 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.
 1. You log in again to the same remote machine (even from a different terminal).
 1. You enter the "{{{screen -r}}}" command.
 1. 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.

=== Key bindings for the screen command ===

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:

|| List of key bindings for screen. ||
|| '''key binding''' || '''meaning''' ||
|| {{{^A ?}}} || show a help screen (display key bindings) ||
|| {{{^A c}}} || create a new window and switch to it ||
|| {{{^A n}}} || go to next window ||
|| {{{^A p}}} || go to previous window ||
|| {{{^A 0}}} || go to window number 0 ||
|| {{{^A 1}}} || go to window number 1 ||
|| {{{^A w}}} || show a list of windows ||
|| {{{^A a}}} || send a Ctrl-A to current window as keyboard input ||
|| {{{^A h}}} || write a hardcopy of current window to file ||
|| {{{^A H}}} || begin/end logging current window to file ||
|| {{{^A ^X}}} || lock the terminal (password protected) ||
|| {{{^A d}}} || detach screen session from the terminal ||
|| {{{^A DD}}} || detach screen session and log out ||

See {{{screen}}}(1) for details.

=== The screen like program for the X ===

Install the {{{xmove}}} package to enable support for mobile X11 clients.  See {{{xmove}}}(1).

== Data recording and presentation ==

=== The log daemon ===

Many programs record their activities under the {{{/var/log/}}} directory.
 * The kernel log daemon: {{{klogd}}}(8)
 * The system log daemon: {{{syslogd}}}(8)

See @{@thesystemmessage@}@ and @{@thekernelmessage@}@.

=== Log analyzer ===

Here are notable log analyzers ("{{{~Gsecurity::log-analyzer}}}" in {{{aptitude}}}).

|| List of system log analyzers. || 1 || 2 || 3 ||
|| '''package''' || '''popcon''' || '''size''' || '''description''' ||
|| {{{logwatch}}} || - || - ||log analyser with nice output written in Perl  ||
|| {{{fail2ban}}} || - || - || bans IPs that cause multiple authentication errors ||
|| {{{analog}}} || - || - || web server log analyzer ||
|| {{{awstats}}} || - || - ||  powerful and featureful web server log analyzer||
|| {{{sarg}}} || - || - || squid analysis report generator ||
|| {{{pflogsumm}}} || - || - || Postfix log entry summarizer ||
|| {{{syslog-summary}}} || - || - || summarize the contents of a syslog log file ||
|| {{{lire}}} || - || - || full-featured log analyzer and report generator ||
|| {{{fwlogwatch}}} || - || - || Firewall log analyzer ||
|| {{{squidview}}} || - || - || monitors and analyses squid access.log files ||
|| {{{visitors}}} || - || - || fast web server log analyzer ||
|| {{{swatch}}} || - || - || Log file viewer with regexp matching, highlighting, & hooks ||
|| {{{crm114}}} || - || - || The Controllable Regex Mutilator and Spam Filter (CRM114) ||
|| {{{icmpinfo}}} || - || - || Interpret ICMP messages ||

(!) [http://crm114.sourceforge.net/ CRM114] provides language infrastructure to write '''fuzzy''' filters with the [http://www.laurikari.net/tre/ TRE regex library].  Its popular use is spam mail filter but it can be used as log analyzer.

## only I greater than or equal to 0.2 are visible.  Rests say below.
##|| {{{acidbase}}} || - || - || Basic Analysis and Security Engine ||
##|| {{{acidlab}}} || - || - || Analysis Console for Intrusion Databases ||
##|| {{{anteater}}} || - || - || MTA log analyser written 100% in C++ ||
##|| {{{asql}}} || - || - || Run SQL queries against apache logs ||
##|| {{{awffull}}} || - || - || web server log analysis program ||
##|| {{{fwanalog}}} || - || - || firewall log-file report generator (using analog) ||
##|| {{{graphdefang}}} || - || - || grapher for MIMEDefang spam and virus logs ||
##|| {{{ip2host}}} || - || - || Resolve IPs to hostnames in web server logs ||
##|| {{{isoqlog}}} || - || - || Mail Transport Agent log analysis program ||
##|| {{{jdresolve}}} || - || - || fast alternative to apache logresolve ||
##|| {{{logtool}}} || - || - || Syslog-style logfile parser with lots of output options ||
##|| {{{logtools}}} || - || - || Russell's misc tools for managing log files. ||
##|| {{{lwatch}}} || - || - || A simple log colorizer ||
##|| {{{modlogan}}} || - || - || A modular logfile analyzer ||
##|| {{{prelude-lml}}} || - || - || Hybrid Intrusion Detection System [ Log Monitoring Lackey ] ||
##|| {{{prom-mew}}} || - || - || procmail reader for Mew ||
##|| {{{rmagic}}} || - || - || Report Magic for Analog ||
##|| {{{sma}}} || - || - || Sendmail log analyser ||
##|| {{{squidtaild}}} || - || - || Squid log monitoring program ||
##|| {{{tcpxtract}}} || - || - || extracts files from network traffic based on file signatures ||
##|| {{{tenshi}}} || - || - || log monitoring and reporting tool ||
##|| {{{tua}}} || - || - || The UUCP Analyzer ||
##|| {{{uutraf}}} || - || - || an UUCP traffic analyzer and cost estimator ||
##|| {{{wflogs}}} || - || - || The modular firewall log analyzer of the WallFire project ||
##|| {{{wwwstat}}} || - || - || httpd logfile analysis package ||

=== Recording the shell activities cleanly ===

The simple use of the {{{script}}}(1) command (see: @{@recordingtheshellactivities@}@) 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
}}}

{i} Some {{{x-terminal-emulator}}} such as {{{gnome-terminal}}} have recording capability.  You may wish to extend line buffer for scrollback. 

{i} You may use {{{screen}}} command with "{{{^A H}}}" (see @{@keybindingsforthescreencommand@}@) to perform recording of console.  

{i} You may use {{{emacs}}}  with "{{{M-x shell}}}", "{{{M-x eshell}}}", or "{{{M-x term}}}" to perform recording of console.  You may later use "{{{C-x C-w}}}" to write the buffer to a file.

=== Customized display of text data ===

Although pager tools such as {{{more}}}(1) and {{{less}}}(1) (see @{@thepager@}@) and custom tools for highlighting and formatting @{@highlightingandfingplaintextdata@}@ can display text data nicely, general purpose editors (see @{@thetexteditor@}@) are most versatile and customizable.

{i} For {{{vim}}}(1) and its pager mode alias {{{view}}}(1), "{{{:set hls}}}" will enable highlighted search.

=== Colorizing commands ===

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}}}".

{i} You can turn off these colorizing aliases in the interactive environment by invoking shell with "{{{TERM=dumb bash}}}".

=== Customizing program to be started ===

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 @{@settingadefaulttexteditor@}@).
 * the "{{{$HOME/.mailcap}}}" and "{{{/etc/mailcap}}}" file contents which associate [http://en.wikipedia.org/wiki/MIME MIME] type with program (see {{{mailcap}}}(5)).
 * the the "{{{$HOME/.mime.types}}}" and "{{{/etc/mime.types}}}" file contents which associate file name extension with [http://en.wikipedia.org/wiki/MIME MIME] type (see {{{run-mailcap}}}(1)).

{i} The {{{update-mime}}}(8) command updates the "{{{/etc/mailcap}}}" file using "{{{/etc/mailcap.order}}}" file (see {{{mailcap.order}}}(5)).

{i} The {{{debianutils}}} package provides {{{sensible-browser}}}(1), {{{sensible-editor}}}(1), and {{{sensible-pager}}}(1) commands which make sensible decisions on which editor, pager, and web browser to call, respectively.  I recommend you to read these shell commands.

=== Recording the graphic image of an X application  ===

There are few ways to record the graphic image of an X application, including an {{{xterm}}} display.

|| List of graphic image manipulation tools. || 1 || 2 || 3 ||
|| '''package''' || '''popcon''' || '''size''' || '''command''' ||
|| {{{xbase-clients}}} ||  25829 || - || {{{xwd}}}(1) ||
|| {{{gimp}}} || 8489 || - || GUI menu  ||
|| {{{imagemagick}}} || 5479 || - || {{{import}}}(1) ||
|| {{{scrot}}} || 134 || - || {{{scrot}}}(1) ||

=== Recording changes in configuration files ===

Changes in configuration files can be nicely recorded using DVCS system (see @{@gitforrecordingcigurationhistory@}@). 

== System maintenance tips ==

=== System integrity check ===

Poor system maintenance may expose your system to external exploitation.  

For system security check, you should start with:
 * {{{debsums}}} package: See {{{debsums}}}(1) and @{@toplevelreleasefileandauthenticity@}@.
 * {{{chkrootkit}}} package: See {{{chkrootkit}}}(1).
 * {{{clamav}}} package family: See {{{clamscan}}}(1) and {{{freahclam}}}(1).
 * [http://www.debian.org/security/faq Debian security FAQ].
 * [http://www.debian.org/doc/manuals/securing-debian-howto/ Securing Debian Manual].

Here is a simple script to check for typical world writable incorrect file permissions.
{{{
# find / -perm 777 -a \! -type s -a \! -type l -a \! \( -type d -a -perm 1777 \)
}}}

=== The hardware identification ===

For the [http://en.wikipedia.org/wiki/Peripheral_Component_Interconnect PCI]-like devices ([http://en.wikipedia.org/wiki/Accelerated_Graphics_Port AGP], [http://en.wikipedia.org/wiki/PCI_Express PCI-Express], [http://en.wikipedia.org/wiki/PC_Card#CardBus CardBus], [http://en.wikipedia.org/wiki/ExpressCard 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 @{@procfsandsysfs@}@).

|| List of hardware identification tools. || 1 || 2 || 3 ||
|| '''package''' || '''popcon''' || '''size''' || '''description''' ||
|| {{{pciutils}}} || - || - || Linux PCI Utilities, {{{lspci}}}(8) ||
|| {{{usbutils}}} || - || - || Linux USB utilities, {{{lsusb}}}(8) ||
|| {{{pcmciautils}}} || - || - || PCMCIA utilities for Linux 2.6, {{{pccardctl}}}(8) ||
|| {{{scsitools}}} || - || - || Collection of tools for SCSI hardware management, {{{lsscsi}}}(8) ||
|| {{{pnputils}}} || - || - || Plug and Play BIOS utilities, {{{lspnp}}}(8) ||
|| {{{procinfo}}} || - || - || Displays system information from {{{/proc}}}, {{{lsdev}}}(8) ||
|| {{{lshw}}} || - || - || Information about hardware configuration, {{{lshw}}}(1) ||
|| {{{discover}}} || - || - || Hardware identification system, {{{discover}}}(8) ||

=== The hardware configuration ===

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.

|| List of hardware configuration tools. || 1 || 2 || 3 ||
|| '''package''' || '''popcon''' || '''size''' || '''description''' ||
|| {{{hal}}} || - || - || Hardware Abstraction Layer, {{{lshal}}}(1) ||
|| {{{console-tools}}} || || - || Linux console font and keytable utilities. ||
|| {{{x11-xserver-utils}}} || || - || X server utilities. {{{xset}}}(1) and {{{xmodmap}}}(1) commands. ||
|| {{{acpid}}} || 24513 || - || Daemon to manage events delivered by the Advanced Configuration and Power Interface (ACPI) ||
|| {{{acpi}}} || 2563 || - || Utilities for ACPI devices ||
|| {{{apmd}}} || 1222  || - || Daemon to manage events delivered by the Advanced Power Management (APM) ||
|| {{{powersaved}}} || 1038 || - || Daemon to manage battery, temperature, ac, cpufreq (SpeedStep, Powernow!) control and monitor with ACPI and APM supports. ||
|| {{{noflushd}}} || 95 || - || Allow idle hard disks to spin down ||
|| {{{sleepd}}} || 75 || - || Puts a laptop to sleep during inactivity ||
|| {{{hdparm}}} || 5192 || - || Hard disk access optimization.  Very effective but dangerous.  You must read {{{hdparm}}}(8) first. ||
|| {{{smartmontools}}} || 3526 || - || Control and monitor storage systems using S.M.A.R.T. ||
|| {{{setserial}}} || 2619 || - || Collection of tools for serial port management. ||
|| {{{memtest86+}}} || 406 || - || Collection of tools for memory hardware management. ||
|| {{{scsitools}}} || 185 || - || Collection of tools for SCSI hardware management. ||
|| {{{tpconfig}}} || 276 || - || A program to configure touchpad devices ||
|| {{{setcd}}} || 82 || - || Compact disc drive access optimization. ||
|| {{{big-cursor}}} || *121 || - || Larger mouse cursors for X ||
|| {{{lspowertweak}}} || - || - || Simple front end to powertweak, {{{lspowertweak}}}(8) ||

Here, ACPI is a newer framework for the power management system than APM.

=== The time ===

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:
 * [http://www.tldp.org/HOWTO/TimePrecision-HOWTO/index.html Managing Accurate Date and Time HOWTO] .
 * [http://www.ntp.org/ NTP Public Services Project] .
 * The {{{ntp-doc}}} package

=== The terminal configuration ===

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}}}.

=== The sound infrastructure ===

Device drivers for sound cards for current Linux 2.6 are provided by [http://en.wikipedia.org/wiki/Advanced_Linux_Sound_Architecture Advanced Linux Sound Architecture (ALSA)].  ALSA provides emulation mode for previous [http://en.wikipedia.org/wiki/Open_Sound_System 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.

{i} Use "{{{cat /dev/urandom > /dev/audio}}}" or the {{{speaker-test}}}(1) command to test speaker. (^C to stop)

{i} If you can not get sound, your speaker may be connected to a muted output.  Modern sound system has many outputs.  The {{{alsamixer}}}(1) command in the {{{alsa-utils}}} package is useful to configure volume and mute settings.

Application softwares may be configured not only to access sound devices directly but also to access them via some standardized sound server system.

## UPDATE FOLLOWING PACKAGE NAME as you see new ones released

|| List of sound packages || 1 || 2 || 3 ||
|| '''package''' || '''pocon''' || '''size''' || '''description''' ||
|| {{{linux-sound-base}}} || - || - || Base package for ALSA and OSS sound systems ||
|| {{{alsa-base}}} || - || - || ALSA driver configuration files ||
|| {{{alsa-utils}}} || - || - || Utilities for configuring and using ALSA ||
|| {{{esound-common}}} || - || - || [http://en.wikipedia.org/wiki/Enlightened_Sound_Daemon Enlightened Sound Daemon (ESD)] common (Enlightenment and GNOME) ||
|| {{{esound}}} || - || - || [http://en.wikipedia.org/wiki/Enlightened_Sound_Daemon Enlightened Sound Daemon (ESD)] server (Enlightenment and GNOME) ||
|| {{{esound-clients}}} || - || - || [http://en.wikipedia.org/wiki/Enlightened_Sound_Daemon Enlightened Sound Daemon (ESD)] client (Enlightenment and GNOME) ||
|| {{{libesd-alsa0}}} || - || - || [http://en.wikipedia.org/wiki/Enlightened_Sound_Daemon Enlightened Sound Daemon (ESD)] library Enlightenment and GNOME) ||
|| {{{libesd0}}} || - || - || [http://en.wikipedia.org/wiki/Enlightened_Sound_Daemon Enlightened Sound Daemon (ESD)] library (Enlightenment and GNOME) - OSS ||
|| {{{arts}}} || - || - || [http://en.wikipedia.org/wiki/ARts aRts] server (KDE) ||
|| {{{libarts1c2a}}} || - || - || [http://en.wikipedia.org/wiki/ARts aRts] library (KDE) ||
|| {{{libartsc0}}} || - || - || [http://en.wikipedia.org/wiki/ARts aRts] library (KDE) ||
|| {{{jackd}}} || - || - || [http://en.wikipedia.org/wiki/JACK_Audio_Connection_Kit JACK Audio Connection Kit. (JACK)] server (low latency) ||
|| {{{libjack0}}} || - || - || [http://en.wikipedia.org/wiki/JACK_Audio_Connection_Kit JACK Audio Connection Kit. (JACK)] library (low latency) ||
|| {{{libjack0.100.0-0}}} || - || - || [http://en.wikipedia.org/wiki/JACK_Audio_Connection_Kit JACK Audio Connection Kit. (JACK)] library (low latency) ||
|| {{{nas}}} || - || - || [http://en.wikipedia.org/wiki/Network_Audio_System Network Audio System (NAS)] server ||
|| {{{libaudio2}}} || - || - || [http://en.wikipedia.org/wiki/Network_Audio_System Network Audio System (NAS)]  library ||
|| {{{pulseaudio}}} || - || - || [http://en.wikipedia.org/wiki/PulseAudio PulseAudio] server, replacement for ESD ||
|| {{{libpulse0}}} || - || - || [http://en.wikipedia.org/wiki/PulseAudio PulseAudio] client library, replacement for ESD ||
|| {{{libpulsecore5}}} || - || - || [http://en.wikipedia.org/wiki/PulseAudio PulseAudio] server library, replacement for ESD ||
|| {{{libgstreamer0.10-0}}} || - || - || [http://en.wikipedia.org/wiki/GStreamer GStreamer]: Gnome sound engine ||
|| {{{libxine1}}} || - || - ||  [http://en.wikipedia.org/wiki/Xine xine]: KDE older sound engine ||
|| {{{libphonon4}}} || - || - ||  [http://en.wikipedia.org/wiki/Phonon_(KDE) 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.

=== Disable the screen saver ===

For disabling the screen saver, use following commands.

|| List of commands for disabling the screen saver. || ||
|| '''environment''' || '''command''' ||
|| The Linux console || {{{setterm -powersave off}}} ||
|| The X Window by turning off screensaver || {{{xset s off}}} ||
|| The X Window by disabling dpms || {{{xset -dpms}}} ||
|| The X Window by GUI configuration of screen saver || {{{xscreensaver-command -prefs}}} ||

=== Disable the sound (beep) ===

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
}}}

=== Storage device hints ===

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).

=== Memory usage ===

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): 

|| 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.

=== Invisible disk space consumption ===

All deleted but open files consumes disk space although they are not visible from normal {{{du}}}(1).  They can be listed with their size by:
{{{
# lsof -s -X / |grep deleted
}}}

== Process operation ==

=== Time a process ===

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
}}}

=== The scheduling priority ===

A nice value is used to control the scheduling priority for the process.

|| 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) ||

|| List of tools for the scheduling priority. || 2 || 3 || 4 ||
|| '''command''' || '''package''' || '''popcon''' || '''size''' || '''function''' ||
|| {{{nice}}} || {{{coreutils}}} || - || - || run a program with the modified scheduling priority ||
|| {{{renice}}} || {{{bsdutils}}} || - || - || 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 command ===

The {{{ps}}}(1) command on the Debian support both BSD and SystemV features and helps to identify the process activity statically.

|| List of ps command styles. || ||
|| '''style''' || '''typical command''' || '''feature''' ||
|| BSD || {{{ps aux}}} || display %CPU %MEM ||
|| System V || {{{ps -efH}}} || display PPID ||

For the zombie (defunct) children process, you can kill them by the parent process ID identified in the ({{{PPID}}}) field.

=== The top command ===

The {{{top}}}(1) command on the Debian has rich features and helps to identify what process is acting funny dynamically.  

|| List of commands for top. || ||
|| '''command key''' || '''response''' ||
|| {{{h}}} or {{{?}}} || To show help. ||
|| {{{f}}} || To set/reset display field. ||
|| {{{o}}} || To reorder display field. ||
|| {{{F}}} || To set sort key field. ||
|| {{{k}}} || To kill a process. ||
|| {{{r}}} || To renice a process. ||
|| {{{q}}} || To quit the {{{top}}} command. ||

=== Kill a process ===

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.

|| 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 ||

=== Schedule tasks once ===

Run the {{{at}}}(1) command to schedule a one-time job:
{{{
$ echo 'command -args'| at 3:40 monday
}}}

=== Schedule tasks regularly ===

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
}}}

{i} For the system not running continuously, install the {{{anacron}}} package to schedule periodic command at the specified intervals as closely as machine-uptime permits.

=== Alt-SysRq ===

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:

|| List of SAK command keys. || ||
|| '''key following Alt-SysRq''' || '''function''' ||
|| {{{r}}} || Un'''r'''aw restores the keyboard after things like X crashes. ||
|| {{{0}}} || Changing the console loglevel to '''0''' reduces error messages. ||
|| {{{k}}} || SAK (system attention key) '''k'''ills all processes on the '''current virtual console'''. ||
|| {{{e}}} || Send a SIGT'''E'''RM to all processes, except for {{{init}}}. ||
|| {{{i}}} || Send a SIGK'''I'''LL to all processes, except for {{{init}}}. ||
|| {{{s}}} || '''S'''ync all mounted filesystems. ||
|| {{{u}}} || Remount all mounted filesystems read-only ('''u'''mount). ||
|| {{{b}}} || Re'''b'''oot 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}}} .

<!> The Alt-SysRq feature may be considered a security risk by allowing users access to root-privileged functions.  Placing "{{{echo 0 >/proc/sys/kernel/sysrq}}}" in {{{/etc/rc.local}}} or "{{{kernel.sysrq = 0}}}" in {{{/etc/sysctl.conf}}} will disable the Alt-SysRq feature.

{i} From SSH terminal etc., you can use the Alt-SysRq feature by writing to the {{{/proc/sysrq-trigger}}}. For example, "{{{echo s > /proc/sysrq-trigger; echo u > /proc/sysrq-trigger}}}" from the root shell prompt will '''s'''ync and '''u'''mount all mounted filesystems.

== The kernel ==

Debian distributes modularized Linux kernel as packages for supported architectures.  

=== Linux kernel 2.6 ===

There are few notable features on Linux kernel 2.6 compared to 2.4.
 * Devices are created by the udev system (see @{@theudevsystem@}@).
 * Read/write accesses to IDE CD/DVD devices do not use the {{{ide-scsi}}} module.
 * Network packet filtering functions use {{{iptable}}} kernel modules.

=== Kernel headers ===

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.

(!) For compiling some kernel-specific programs such as the kernel modules from the external source and the automounter daemon ({{{amd}}}), you must include path to the corresponding kernel headers, e.g. {{{-I/usr/src/linux-particular-version/include/}}} , to your command line.  The {{{module-assistant}}} package helps users to build and install module package(s) easily for one or more custom kernels with the {{{m-a}}}(8) command.

=== Kernel and module compile ===

Debian has its own method of compiling the kernel and related modules.

|| List of key packages to be installed for the kernel recompilation on the Debian system || 1 || 2 || 3 ||
|| '''package''' || '''popcon''' || '''size''' || '''description''' ||
|| {{{build-essential}}} || - || - || essential packages for building Debian packages: {{{make}}}, {{{gcc}}}, ... ||
|| {{{bzip2}}} || - || - || compress and decompress utilities for bz2 files ||
|| {{{libncurses5-dev}}} || - || - || developer's libraries and docs for ncurses ||
|| {{{git-core}}} || - || - || git: distributed revision control system used by the Linux kernel ||
|| {{{fakeroot}}} || - || - || provide fakeroot environment for building package as non-root ||
|| {{{initramfs-tools}}} || - || - || tool to build an initramfs (Debian specific) ||
|| {{{kernel-package}}} || - || - || tool to build Linux kernel packages (Debian specific) ||
|| {{{module-assistant}}} || - || - || tool to help build module packages (Debian specific) ||
|| {{{devscripts}}} || - || - || helper scripts for a Debian Package maintainer (Debian specific) ||
|| {{{linux-tree-2.6.*}}} || - || - || Linux kernel source tree for building Debian kernel images (Debian specific) ||

If you use {{{initrd}}} in @{@stagecthebootloader@}@, make sure to read the related information in {{{initramfs-tools}}}(8), {{{update-initramfs}}}(8), {{{mkinitramfs}}}(8) and {{{initramfs.conf}}}(5). 

/!\ Do not put symlinks to the directories in the source tree (e.g. {{{/usr/src/linux*}}}) from {{{/usr/include/linux}}} and {{{/usr/include/asm}}} when compiling the Linux kernel source. (Some outdated documents suggest this.)

(!) When compiling the latest Linux kernel on the Debian {{{stable}}} system, the use of backported latest tools from the Debian {{{unstable}}} may be needed.

=== Kernel source compile: Debian standard method ===

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}}}" .

<!> When you intend to create a non-modularized kernel compiled only for one machine, invoke {{{make-kpkg}}} command without "{{{--initrd}}}" option since initrd is not used. Invocation of "{{{make oldconfig}}}" and "{{{make dep}}}" are not required since "{{{make-kpkg kernel_image}}}" invokes them.

=== Module source compile: Debian standard method ===

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
}}}

=== Kernel source compile: classic method ===

You can still build [http://www.kernel.org/ 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>
}}}

 * set up bootloader
  * 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}}}" .

=== Non-free hardware drivers ===

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/Softmodem
 * http://en.wikipedia.org/wiki/Comparison_of_open_source_wireless_drivers
 * [http://www.google.com/search?q=Linmodem Linmodem with google] or similar.
 * http://ndiswrapper.sourceforge.net
 * http://linuxwireless.org/
 * http://madwifi.org/ (there is ath5k which is free drivers)

== The chroot ==

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 [http://en.wikipedia.org/wiki/Chroot chroot] systems in the following as examples.

For serious chroot setup with the detail configuration, please consider to use the specialized {{{schroot}}} package.

=== Run a different Debian distribution with chroot ===

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.

<!> 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 "{{{rm -rf /sid-root}}}" '''without unbinding''' their home directory in the chroot. A '''bind mount''' is not normally visible with "{{{df}}}", you need to execute "{{{df -a}}}" to see it.  

This {{{debootstrap}}} trick can also be used to [http://www.debian.org/releases/stable/installmanual install Debian] to a system without using a Debian install disk, but instead from another GNU/Linux distribution.

=== Setting up login for chroot ===

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

=== Setting up X for chroot ===

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!

=== Run other distributions with chroot ===

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
}}}

=== Build packages under chroot ===

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.

=== Other virtualization tools ===

There are several system [http://en.wikipedia.org/wiki/Virtualization virtualization] and [http://en.wikipedia.org/wiki/Emulator emulation] related packages in Debian beyond simple [http://en.wikipedia.org/wiki/Chroot chroot].

|| List of virtualization tools || 1 || 2 || 3 ||
|| '''package''' || '''pocon''' || '''size''' || '''description''' ||
|| {{{schroot}}} || - || - || Specialized tool for executing Debian binary packages in chroot ||
|| {{{sbuild}}} || - || - || Tool for building Debian binary packages from Debian sources ||
|| {{{pbuilder}}} || - || - || Personal package builder for Debian packages ||
|| {{{debootstrap}}} || - || - || Bootstrap a basic Debian system (written in sh) ||
|| {{{cdebootstrap}}} || - || - || Bootstrap a Debian system (written in C) ||
|| {{{rootstrap}}} || - || - || A tool for building complete Linux filesystem images ||
|| {{{user-mode-linux}}} || - || - || User-mode Linux (kernel) ||
|| {{{xen-tools}}} || - || - || Tools to manage debian XEN virtual server ||
|| {{{bochs}}} || - || - || IA-32 PC emulator ||
|| {{{qemu}}} || - || - || Fast generic processor emulator ||
|| {{{virtualbox-ose}}} || - || - || A x86 virtualization solution on i386 and amd64 ||
|| {{{wine}}} || - || - || Windows API Implementation (standard suite) ||
|| {{{dosbox}}} || - || - || 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.
