quick-reference/asciidoc/09_systips.txt

== System tips

// vim: set sts=2 expandtab:
// Use ":set nowrap" to edit table

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

=== The screen program

`screen`(1) is a very useful tool for people to access remote sites via unreliable or intermittent connections since it support interrupted network connections.


.List of programs to support interrupted network connections.
[grid="all"]
`--------`-------------`------------`-------------------------------------------------------
package  popcon        size         description                                             
--------------------------------------------------------------------------------------------
`screen` @@@popcon1@@@ @@@psize1@@@ terminal multiplexer with VT100/ANSI terminal emulation 
--------------------------------------------------------------------------------------------

// xmove not in lenny
// || {{{xmove}}} || - || - || allows you to move programs between X Window System displays ||

==== The use scenario for screen(1)

`screen`(1) not only allows one terminal window to work with multiple processes, but also allows **remote shell process to survive interrupted connections**.  Here is a typical use scenario of `screen`(1).

1. You login to a remote machine.
2. You start `screen` on a single console.
3. You execute multiple programs in `screen` windows created with `\^A c` ("Control-A" followed by "c").
4. You switch among the multiple `screen` windows by `\^A n` ("Control-A" followed by "n").
5. Suddenly you need to leave your terminal, but you don\'t want to lose your active work by keeping the connection.
6. 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.
7. You log in again to the same remote machine (even from a different terminal).
8. You start `screen` as "`screen -r`".
9. `screen` will magically **reattach** all previous `screen` windows with all actively running programs.

TIP: You can save connection fees for metered network connections such as dial-up and packet ones, because you can leave a process active while disconnected, and then re-attach it later when you connect again.

==== Key bindings for the screen command

In a `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.
[grid="all"]
`-----------`-------------------------------------------------
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.

// xmove removed from lenny
// === A screen-like program for X Window System ===
// The {{{xmove}}} package enables support for mobile X clients; that is, X clients can move between displays.  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 <<_the_system_message>> and <<_the_kernel_message>>.

==== Log analyzer

Here are notable log analyzers ("`\~Gsecurity::log-analyzer`" in `aptitude`(8)).


.List of system log analyzers.
[grid="all"]
`----------------`-------------`------------`-----------------------------------------------------------
package          popcon        size         description                                                 
--------------------------------------------------------------------------------------------------------
`logwatch`       @@@popcon1@@@ @@@psize1@@@ log analyser with nice output written in Perl               
`fail2ban`       @@@popcon1@@@ @@@psize1@@@ bans IPs that cause multiple authentication errors          
`analog`         @@@popcon1@@@ @@@psize1@@@ web server log analyzer                                     
`awstats`        @@@popcon1@@@ @@@psize1@@@ powerful and featureful web server log analyzer             
`sarg`           @@@popcon1@@@ @@@psize1@@@ squid analysis report generator                             
`pflogsumm`      @@@popcon1@@@ @@@psize1@@@ Postfix log entry summarizer                                
`syslog-summary` @@@popcon1@@@ @@@psize1@@@ summarize the contents of a syslog log file                 
`lire`           @@@popcon1@@@ @@@psize1@@@ full-featured log analyzer and report generator             
`fwlogwatch`     @@@popcon1@@@ @@@psize1@@@ Firewall log analyzer                                       
`squidview`      @@@popcon1@@@ @@@psize1@@@ monitors and analyses squid access.log files                
`visitors`       @@@popcon1@@@ @@@psize1@@@ fast web server log analyzer                                
`swatch`         @@@popcon1@@@ @@@psize1@@@ Log file viewer with regexp matching, highlighting, & hooks 
`crm114`         @@@popcon1@@@ @@@psize1@@@ The Controllable Regex Mutilator and Spam Filter (CRM114)   
`icmpinfo`       @@@popcon1@@@ @@@psize1@@@ Interpret ICMP messages                                     
--------------------------------------------------------------------------------------------------------

NOTE: 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 `script`(1) (see <<_recording_the_shell_activities>>) to record shell activity produces a file with control characters.  This can be avoided by using `col`(1):

--------------------
$ script
Script started, file is typescript
--------------------

- do whatever ...
- Press `Ctrl-D` to exit `script`

--------------------
$ col -bx <typescript >cleanedfile
$ vim cleanedfile
--------------------

If you don\'t have `script` (for example, during the boot process in the initramfs), you can use following instead:

--------------------
$ sh -i 2>&1 | tee typescript
--------------------

TIP: Some `x-terminal-emulator` such as `gnome-terminal` can record.  You may wish to extend line buffer for scrollback. 

TIP: You may use `screen`(1) with "`\^A H`" (see <<_key_bindings_for_the_screen_command>>) to perform recording of console.  

TIP: You may use `emacs`(1) 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 <<_the_pager>>) and custom tools for highlighting and formatting <<_highlighting_and_formatting_plain_text_data>> can display text data nicely, general purpose editors (see <<_the_text_editor>>) are most versatile and customizable.

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

==== Customized display of time and date

The default display format of time and date by the "`ls -l`" command depends on the **locale** (see value <<_timestamps>>).  The "`$LANG`" variable is referred first and it can be overridden by the "`$LC_TIME`" variable. 

The actual default display format for each locale depends on the version of  the standard C library (the `libc6` package) used.  I.e., different releases of Debian had different defaults. 

If you really wish to customize this display format of time and date beyond the **locale**, you should set the **time style value** by the "`--time-style`" argument or by the "`$TIME_STYLE`" value (see `ls`(1), `date`(1), "`info coreutils \'ls invocation\'`").  
 

.Display examples of time and date for the "`ls -l`" command for `lenny`.
[grid="all"]
`-----------------`--------------------`-------------------------------------
time style value  locale               display of time and date              
-----------------------------------------------------------------------------
`iso`             __any__              `01-19 00:15`                         
`long-iso`        __any__              `2009-01-19 00:15`                    
`full-iso`        __any__              `2009-01-19 00:15:16.000000000 +0900` 
`locale`          `C`                  `Jan 19 00:15`                        
`locale`          `en_US.UTF-8`        `2009-01-19 00:15`                    
`locale`          `es_ES.UTF-8`        `ene 19 00:15`                        
`+%d.%m.%y %H:%M` __any__              `19.01.09 00:15`                      
`+%d.%b.%y %H:%M` `C` or `en_US.UTF-8` `19.Jan.09 00:15`                     
`+%d.%b.%y %H:%M` `es_ES.UTF-8`        `19.ene.09 00:15`                     
-----------------------------------------------------------------------------

TIP: You can eliminate typing long option on commandline using command alias, e.g. "`alias ls=\'ls --time-style=+%d.%m.%y\ %H:%M\'`" (see <<_command_alias>>).

TIP: http://en.wikipedia.org/wiki/ISO_8601[ISO 8601] is followed for these iso-formats.

==== Colorized shell echo

Shell echo to most modern terminals can be colorized using http://en.wikipedia.org/wiki/ANSI_escape_code[ANSI escape code] (see "`/usr/share/doc/xterm/ctlseqs.txt.gz`").  E.g.:

--------------------
$ RED=$(printf "\x1b[31m")
$ NORMAL=$(printf "\x1b[0m")
$ REVERSE=$(printf "\x1b[7m")
$ echo "${RED}RED-TEXT${NORMAL} ${REVERSE}REVERSE-TEXT${NORMAL}"
--------------------

// I use "printf" here instead of "echo -e" for shell portability.

==== Colorized 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`(1).  If you wish to surpress color when piping to other programs, use "`--color=auto`" instead in the above example for "`\~/.bashrc`".

TIP: You can turn off these colorizing aliases in the interactive environment by invoking shell with "`TERM=dumb bash`".

==== 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.
[grid="all"]
`---------------`-------------`------------`-----------
package         popcon        size         command     
-------------------------------------------------------
`xbase-clients` @@@popcon1@@@ @@@psize1@@@ `xwd`(1)    
`gimp`          @@@popcon1@@@ @@@psize1@@@ GUI menu    
`imagemagick`   @@@popcon1@@@ @@@psize1@@@ `import`(1) 
`scrot`         @@@popcon1@@@ @@@psize1@@@ `scrot`(1)  
-------------------------------------------------------

==== Recording changes in configuration files

There are specialized tools to record changes in configuration files with help of DVCS system.


.List of packages to record configuration history in VCS.
[grid="all"]
`-------------`-------------`------------`------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
package       popcon        size         description                                                                                                                                                                                                                                
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
`etckeeper`   @@@popcon1@@@ @@@psize1@@@ store configuration files and its metadata with http://en.wikipedia.org/wiki/Git_(software)[Git] (default), http://en.wikipedia.org/wiki/Mercurial_(software)[Mercurial], or http://en.wikipedia.org/wiki/Bazaar_(software)[Bazaar]. (new) 
`changetrack` @@@popcon1@@@ @@@psize1@@@ store configuration files with http://en.wikipedia.org/wiki/Revision_Control_System[RCS]. (old)                                                                                                                                            
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

I recommend to use the `etckeeper` package with `git`(1) which put entire "`/etc`" under VCS control.  Its installation guide and tutorial are found in "`/usr/share/doc/etckeeper/README.gz`".  

Essentially, running "`sudo etckeeper init`" initializes the git repository for "`/etc`" just like the process explained in <<_git_for_recording_configuration_history>>) but with special hook scripts for more thorough setups.  

As you change your configuration, you can use `git`(1) normally to record them.  It will automatically record changes nicely every time you run package management commands, too.

TIP: You can browse the change history of "`/etc`" by executing "`sudo GIT_DIR=/etc/.git gitk`" with clear view for new installed packages, removed packages, and version changes of packages.

=== Data storage tips

Booting your system with Linux http://en.wikipedia.org/wiki/Live_CD[live CDs] or http://www.debian.org/releases/stable/debian-installer/[debian-installer CDs] in rescue mode make it easy for you to reconfigure data storage on your boot device.  See also <<_the_binary_data>>.

==== Partition configuration

For partition configuration, although `fdisk`(8) has been considered standard, `parted`(8) deserves some attention.  "Disk partitioning data", "partition table", "partition map", and "disk label" are all synonyms.

Most PCs use the classic http://en.wikipedia.org/wiki/Master_boot_record[Master Boot Record (MBR)] scheme to hold http://en.wikipedia.org/wiki/Disk_partitioning[disk partitioning] data in the first sector, i.e., http://en.wikipedia.org/wiki/Logical_block_addressing[LBA] sector 0 (512 bytes).

NOTE: Some new PCs with http://en.wikipedia.org/wiki/Extensible_Firmware_Interface[Extensible Firmware Interface (EFI)], including Intel-based Macs, use http://en.wikipedia.org/wiki/GUID_Partition_Table[GUID Partition Table (GPT)] scheme to hold http://en.wikipedia.org/wiki/Disk_partitioning[disk partitioning] data not in the first sector.

Although `fdisk`(8) has been standard for the disk partitioning tool, `parted`(8) is replacing it.


.List of disk partition management packages
[grid="all"]
`------------`-------------`------------`------------------------------------------------------`-------------------------------------------------------------------
package      popcon        size         http://en.wikipedia.org/wiki/GUID_Partition_Table[GPT] description                                                         
-------------------------------------------------------------------------------------------------------------------------------------------------------------------
`util-linux` @@@popcon1@@@ @@@psize1@@@ Not supported                                          Miscellaneous system utilities including `fdisk`(8) and `cfdisk`(8) 
`parted`     @@@popcon1@@@ @@@psize1@@@ Supported                                              The GNU Parted disk partition resizing program                      
`gparted`    @@@popcon1@@@ @@@psize1@@@ Supported                                              GNOME partition editor based on `libparted`                         
`qtparted`   @@@popcon1@@@ @@@psize1@@@ Supported                                              KDE partition editor based on `libparted`                           
`gptsync`    @@@popcon1@@@ @@@psize1@@@ Supported                                              Synchronize classic MBR partition table with the GPT one            
-------------------------------------------------------------------------------------------------------------------------------------------------------------------

// || {{{gnu-fdisk}}} || - || - || GNU replacements of console {{{fdisk}}}(8) and {{{cfdisk}}}(8) based on {{{libparted}}} || Supported () ||
// Exclusion of gnu-fdisk is intentional since it is little used and buggy from BTS.
// It does not list disk label like parted.
// parted family is new and recommended here.

CAUTION: Although `parted`(8) claims to create and to resize filesystem too, it is safer to do such things using best maintained specialized tools such as `mkfs`(8) (`mkfs.msdos`(8), `mkfs.ext2`(8), `mkfs.ext3`(8), ...) and `resize2fs`(8).

NOTE: In order to switch between GPT and MBR, you need to erase first few blocks of disk contents directly (see <<_clear_file_contents>>) and use "`parted /dev/sdx mklabel gpt`" or "`parted /dev/sdx mklabel msdos`" to set it.  Please note "`msdos`" is use here for http://en.wikipedia.org/wiki/Master_boot_record[MBR].

==== Accessing partition using UUID

Although reconfiguration of your partition may yield different names for partitions, you can access them consistently. This is also helpful if you have multiple disks and your BIOS doesn\'t give them consistent device names.


- `mount`(8) with "`-U`" options can mount a block device using http://en.wikipedia.org/wiki/Universally_Unique_Identifier[UUID], instead of using its file name such as "`/dev/sda3`".  
- "`/etc/fstab`" (see `fstab`(5)) can use http://en.wikipedia.org/wiki/Universally_Unique_Identifier[UUID].
- Boot loaders (<<_stage_2_the_boot_loader>>) may use http://en.wikipedia.org/wiki/Universally_Unique_Identifier[UUID] too.

TIP: You can probe http://en.wikipedia.org/wiki/Universally_Unique_Identifier[UUID] of a block special device with `vol_id`(8). 

==== Filesystem configuration

For http://en.wikipedia.org/wiki/Ext3[ext3] filesystem, the `e2fsprogs` package provides:

- `mkfs.ext3`(8) to create new http://en.wikipedia.org/wiki/Ext3[ext3] filesystem,
- `fsck.ext3`(8) to check and to repair existing http://en.wikipedia.org/wiki/Ext3[ext3] filesystem, and
- `tune2fs`(8) to configure superblock of http://en.wikipedia.org/wiki/Ext3[ext3] filesystem.

The `mkfs`(8) and `fsck`(8) commans are provided by the `e2fsprogs` package as front-ends to various filesystem dependent programs (`mkfs.fstype` and `fsck.fstype`). For http://en.wikipedia.org/wiki/Ext3[ext3] filesystem, they are `mkfs.ext3`(8) and `fsck.ext3`(8) (they are hardlinked to `mke2fs`(8) and `e2fsck`(8)).

Similar commands are available for each filesystem supported by Linux.


.List of filesystem management packages
[grid="all"]
`---------------`-------------`------------`------------------------------------------------------------------------------------------------------------------------------------------------------
package         popcon        size         description                                                                                                                                            
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
`e2fsprogs`     @@@popcon1@@@ @@@psize1@@@ Utilities for the http://en.wikipedia.org/wiki/Ext2[ext2]/http://en.wikipedia.org/wiki/Ext3[ext3]/http://en.wikipedia.org/wiki/Ext4[ext4] filesystems. 
`reiserfsprogs` @@@popcon1@@@ @@@psize1@@@ Utilities for the http://en.wikipedia.org/wiki/Reiserfs[Reiserfs] filesystem.                                                                          
`dosfstools`    @@@popcon1@@@ @@@psize1@@@ Utilities for the http://en.wikipedia.org/wiki/File_Allocation_Table[FAT] filesystem. (Microsoft: MS-DOS, Windows)                                     
`xfsprogs`      @@@popcon1@@@ @@@psize1@@@ Utilities for the http://en.wikipedia.org/wiki/XFS[XFS] filesystem. (SGI: IRIX)                                                                        
`ntfsprogs`     @@@popcon1@@@ @@@psize1@@@ Utilities for the http://en.wikipedia.org/wiki/NTFS[NTFS] filesystem. (Microsoft: Windows NT, ...)                                                     
`jfsutils`      @@@popcon1@@@ @@@psize1@@@ Utilities for the http://en.wikipedia.org/wiki/JFS_(file_system)[JFS] filesystem. (IBM: AIX, OS/2)                                                     
`reiser4progs`  @@@popcon1@@@ @@@psize1@@@ Utilities for the http://en.wikipedia.org/wiki/Reiser4[Reiser4] filesystem.                                                                            
`hfsprogs`      @@@popcon1@@@ @@@psize1@@@ Utilities for http://en.wikipedia.org/wiki/Hierarchical_File_System[HFS] and http://en.wikipedia.org/wiki/HFS_Plus[HFS Plus] filesystem. (Apple: Mac OS)   
`btrfs-tools`   @@@popcon1@@@ @@@psize1@@@ Utilities for the http://en.wikipedia.org/wiki/Btrfs[btrfs] filesystem.                                                                                
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

TIP: http://en.wikipedia.org/wiki/Ext3[Ext3] filesystem is the default filesystem for the Linux system and strongly recommended to use it unless you have some specific reasons not to.  After Linux kernel 2.6.28 (Debian `squeeze`), http://en.wikipedia.org/wiki/Ext4[ext4] filesystem will be available and expected to be the default filesystem for the Linux system.  http://en.wikipedia.org/wiki/Btrfs[btrfs] filesystem is expected to be the next default filesystem after http://en.wikipedia.org/wiki/Ext4[ext4] filesystem for the Linux system.

WARNING: You might face some limtations with ext4 since it is new.  For example, you must have Linux kernel 2.6.30 or later if you wish to resizean ext4 partition.

TIP: Some tools allow access to filesystem without Linux kernel support (see <<_manipulating_files_without_mounting_disk>>).

==== Filesystem creation and integrity check

The `mkfs`(8) command creates the filesystem on a Linux system. The `fsck`(8) command provides the filesystem integrity check and repair on a Linux system.  

CAUTION: It is generally not safe to run `fsck` on **mounted filesystems**.

TIP: Check files in "`/var/log/fsck/`" for the result of the `fsck`(8) command run from the boot script.

TIP: Use "`shutdown -F -r now`" to force to run the `fsck`(8) command safely on all filesystems including root file system on reboot. See the `shutdown`(8) manpage for more.

==== Optimization of filesystem by mount options

Performance and characteristics of a filesystem can be optimized by mount options used on it (see `fstab`(5) and `mount`(8)).  For example:


- "`defaults`" option implies default options: "`rw,suid,dev,exec,auto,nouser,async`". (general)
- "`noatime`" or "`relatime`" option is very effective for speeding up the read access. (general)
- "`user`" option allows an ordinary user to mount the file system. This option implies "`noexec,nosuid,nodev`" option combination. (general, used for CD and floppy)
- "`noexec,nodev,nosuid`" option combination is used to enhance security. (general)
- "`noauto`" option limits mounting by explicit operation only. (general)
- "`data=journal`" option for ext3fs can enhance data integrity against power failure with some loss of write speed.

TIP:  You need to provide kernel boot parameter "`rootflags=data=journal`" to deploy "`data=journal`" option for the root file system formatted with ext3fs.

==== Optimization of filesystem via superblock

Characteristics of a filesystem can be optimized via its superblock using the `tune2fs`(8) command.  For example on "`/dev/hda1`":


- Execution of "`sudo tune2fs -l /dev/hda1`" will display the contents of its filesystem superblock.
- Execution of "`sudo tune2fs -c 50 /dev/hda1`" will change frequency of filesystem checks (`fsck` execution during boot-up) to every 50 boots.
- Execution of "`sudo tune2fs -j /dev/hda1`" will add journaling capability to the filesystem, i.e. filesystem conversion from http://en.wikipedia.org/wiki/Ext2[ext2] to http://en.wikipedia.org/wiki/Ext3[ext3].  (Do this on the unmounted filesystem.)
- Execution of "`sudo tune2fs -O extents,uninit_bg,dir_index /dev/hda1 && fsck -pf /dev/hda1`" will convert it from http://en.wikipedia.org/wiki/Ext3[ext3] to http://en.wikipedia.org/wiki/Ext4[ext4].  (Do this on the unmounted filesystem.)

WARNING: Filesystem conversion for the boot device to the http://en.wikipedia.org/wiki/Ext4[ext4] filesystem should be avoided until http://bugs.debian.org/511121[GRUB boot loader supports the ext4 filesystem well] and installed Linux Kernel version is newer than 2.6.28.

TIP: Despite its name, `tune2fs`(8) works not only on the http://en.wikipedia.org/wiki/Ext2[ext2] filesystem but also on the http://en.wikipedia.org/wiki/Ext3[ext3] and http://en.wikipedia.org/wiki/Ext4[ext4] filesystems.

==== Optimization of harddisk

WARNING: 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 can test disk access speed of a harddisk, e.g. "`/dev/hda`", by "`hdparm -tT /dev/hda`". For some harddisk connected with (E)IDE, you can speed it up with "`hdparm -q -c3 -d1 -u1 -m16 /dev/hda`" by enabling the "(E)IDE 32-bit I/O support", enabling the "using_dma flag", setting "interrupt-unmask flag", and setting the "multiple 16 sector I/O" (dangerous!).

You can test write cache feature of a harddisk, e.g. "`/dev/sda`", by "`hdparm -W /dev/sda`". You can disable its write cache feature with "`hdparm -W 0 /dev/sda`".

You may be able to read badly pressed CDROMs on modern high head CD-ROM drive by slowing it down with "`setcd -x 2`.

==== Using SMART to predict harddisk failure

You can monitor and log your harddisk which is compliant to http://en.wikipedia.org/wiki/S.M.A.R.T[SMART] with the `smartd`(8) daemon.

1. Enable http://en.wikipedia.org/wiki/S.M.A.R.T[SMART] feature in http://en.wikipedia.org/wiki/BIOS[BIOS].
2. Install the `smartmontools` package.
3. Identify your harddisk drives by listing them with `df`(1).
 * Let\'s assume a harddisk drive to be monitored as "`/dev/hda`".
4. Check the output of "`smartctl -a /dev/hda`" to see if http://en.wikipedia.org/wiki/S.M.A.R.T[SMART] feature is actually enabled.
 * If not, enable it by "`smartctl -s on -a /dev/hda`".
5. Enable `smartd`(8) daemon to run by:
 * uncomment "`start_smartd=yes`" in the "`/etc/default/smartmontools`" file.
 * restart the `smartd`(8) daemon by "`sudo /etc/init.d/smartmontools restart`".

TIP: The `smartd`(8) daemon can be customized with the `/etc/smartd.conf` file including how to be notified of warnings.

==== Expand usable storage space via LVM

For partitions created on http://en.wikipedia.org/wiki/Logical_Volume_Manager_(Linux)[Logical Volume Manager (Linux)] at install time, they can be resized easily by concatenating extents onto them or truncating extents from them over multiple storage devices without major system reconfiguration.

CAUTION: Deployment of the current LVM system may degrade guarantee against filesystem corruption offered by journaled file systems such as ext3fs unless their system performance is sacrificed by disabling write cache of harddisk.

==== Expand usable storage space by mounting another partition

If you have an empty partition (e.g., "`/dev/sdx`"), you can format it with `mkfs.ext3`(1) and `mount`(8) it to a directory where you need more space. (You need to copy original data contents.)

--------------------
$ sudo mv work-dir old-dir
$ sudo mkfs.ext3 /dev/sdx
$ sudo mount -t ext3 /dev/sdx work-dir
$ sudo cp -a old-dir/* work-dir
$ sudo rm -rf old-dir
--------------------

==== Expand usable storage space using symlink

If you have an empty directory (e.g., "`/path/to/emp-dir`") in another partition with usable space, you can create a symlink to the directory with `ln`(8).

--------------------
$ sudo mv work-dir old-dir
$ sudo mkdir -p /path/to/emp-dir
$ sudo ln -sf /path/to/emp-dir work-dir
$ sudo cp -a old-dir/* work-dir
$ sudo rm -rf old-dir
--------------------
CAUTION: Some software may not function well with "symlink to a directory".  

==== Expand usable storage space using aufs

If you have usable space in another partition (e.g., "`/path/to/`"), you can create a directory in it and stack that on to a directory where you need space with http://en.wikipedia.org/wiki/Aufs[aufs].


--------------------
$ sudo mv work-dir old-dir
$ sudo mkdir -p /path/to/emp-dir
$ sudo mount -t aufs -o br:/path/to/emp-dir:old-dir none work-dir
--------------------

CAUTION: Use of http://en.wikipedia.org/wiki/Aufs[aufs] for long term data storage is not good idea since it is under development and its design change may introduce issues.

TIP: In order to use http://en.wikipedia.org/wiki/Aufs[aufs], its utility package `aufs-tools` and kernel module package for http://en.wikipedia.org/wiki/Aufs[aufs] such as `aufs-modules-2.6-amd64` need to be installed.

TIP: http://en.wikipedia.org/wiki/Aufs[aufs] is used to provide writable root filesystem by many modern http://en.wikipedia.org/wiki/Live_CD[live CD] projects.

=== Data encryption tips

With physical access to your PC, anyone can easily gain root privilege and access all the files on your PC (see <<_securing_the_root_password>>).  This means that login password system can not secure your private and sensitive data against possible theft of your PC.  You must deploy data encryption technology to do it.  Although http://en.wikipedia.org/wiki/GNU_Privacy_Guard[GNU privacy guard] (see <<_data_security_infrastructure>>) can encrypt files, it takes some user efforts.

http://en.wikipedia.org/wiki/Dm-crypt[dm-crypt] and http://ecryptfs.sourceforge.net/[eCryptfs] facilitates automatic data encryption natively via Linux kernel modules with minimal user efforts.

.List of data encryption utilities.
[grid="all"]
`----------------`-------------`------------`----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
package          popcon        size         function                                                                                                                                                                                       
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
`cryptsetup`     @@@popcon1@@@ @@@psize1@@@ Utilities for encrypted block device (http://en.wikipedia.org/wiki/Dm-crypt[dm-crypt] / http://en.wikipedia.org/wiki/Linux_Unified_Key_Setup[LUKS])                                            
`cryptmount`     @@@popcon1@@@ @@@psize1@@@ Utilities forencrypted block device (http://en.wikipedia.org/wiki/Dm-crypt[dm-crypt] / http://en.wikipedia.org/wiki/Linux_Unified_Key_Setup[LUKS]) with focus on mount/unmount by normal users 
`ecryptfs-utils` @@@popcon1@@@ @@@psize1@@@ Utilities for encrypted stacked filesystem (http://ecryptfs.sourceforge.net/[eCryptfs])                                                                                                        
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

http://en.wikipedia.org/wiki/Dm-crypt[Dm-crypt] is a cryptographic filesystem using http://en.wikipedia.org/wiki/Device_mapper[device-mapper]. http://en.wikipedia.org/wiki/Device_mapper[Device-mapper] maps one block device to another.

http://ecryptfs.sourceforge.net/[eCryptfs] is another cryptographic filesystem using stacked filesystem.  Stacked filesystem stacks itself on top of an existing directory of a mounted filesystem.

CAUTION: Data encryption costs CPU time etc.  Please weigh its benefits and costs.

NOTE: Entire Debian system can be installed on a encrypted disk by the http://www.debian.org/devel/debian-installer/[debian installer] (lenny or newer) using http://en.wikipedia.org/wiki/Dm-crypt[dm-crypt]/http://en.wikipedia.org/wiki/Linux_Unified_Key_Setup[LUKS] and initramfs.  

TIP: See <<_data_security_infrastructure>> for user space encryption utility: http://en.wikipedia.org/wiki/GNU_Privacy_Guard[GNU Privacy Guard].

==== Removable disk encryption with dm-crypt/LUKS

You can encrypt contents of removable mass storage devices, e.g. USB memory stick on "`/dev/sdx`", using http://en.wikipedia.org/wiki/Dm-crypt[dm-crypt]/http://en.wikipedia.org/wiki/Linux_Unified_Key_Setup[LUKS].  You simply formatting it as:

--------------------
# badblocks -c 10240 -s -w -t random -v /dev/sdx
# shred -v -n 1 /dev/sdx
# fdisk /dev/sdx
... "n" "p" "1" "return" "return" "w"
# cryptsetup luksFormat /dev/sdx1
...
# cryptsetup luksOpen /dev/sdx1 sdx1
...
# ls -l /dev/mapper/
total 0
crw-rw---- 1 root root  10, 60 2008-10-04 18:44 control
brw-rw---- 1 root disk 254,  0 2008-10-04 23:55 sdx1
# mkfs.vfat /dev/mapper/sdx1
...
# cryptsetup luksClose sdx1
--------------------
Then, it can be mounted just like normal one on to "`/media/<disk_label>`", except for asking password (see <<_removable_mass_storage_device>>) under modern desktop environment, such as GNOME using `gnome-mount`(1).  The difference is that every data written to it is encrypted.  You may alternatively format media in different file format, e.g., ext3 with "`mkfs.ext3 /dev/sdx1`".

NOTE: If you are really paranoid for the security of data, you may need to overwrite multiple times in the above example.  This operation is very time consuming though.

==== Encrypted swap partition with dm-crypt

If your original "`/etc/fstab`" contains:
--------------------
/dev/sda7 swap sw 0 0
--------------------
then you can enable encrypted swap partition using http://en.wikipedia.org/wiki/Dm-crypt[dm-crypt] by as
--------------------
# aptitude install cryptsetup
# swapoff -a
# echo "cswap /dev/sda7 /dev/urandom swap" >> /etc/crypttab
# perl -i -p -e "s/\/dev\/sda7/\/dev\/mapper\/cswap/" /etc/fstab
# /etc/init.d/cryptdisks restart
 ...
# swapon -a
--------------------

==== Automatically encrypting files with eCryptfs

You can encrypt files written under "`\~/Private/`" automatically using http://ecryptfs.sourceforge.net/[eCryptfs] and the `ecryptfs-utils` package.

- run `ecryptfs-setup-private`(1) and set up "`\~/Private/`" by following prompts.
- activate "`\~/Private/`" by running `ecryptfs-mount-private`(1).
- move sensitive data files to "`\~/Private/`" and make symlinks as needed.
 * candidates: "`\~/.fetchmailrc`", "`\~/.ssh/identity`", "`\~/.ssh/id_rsa`", "`\~/.ssh/id_dsa`" and other files with "`go-rwx`".
- move sensitive data directories to a subdirectory in "`\~/Private/`" and make symlinks as needed.
 * candidates: "`\~/.gnupg`" and other directories with "`go-rwx`".
- create symlink from "`\~/Desktop/Private/`" to "`\~/Private/`" for easier desktop operations.
- deactivate "`\~/Private/`" by running `ecryptfs-umount-private`(1).
- activate "`\~/Private/`" by issuing "`ecryptfs-mount-private`" as you need encrypted data.

TIP: Since http://ecryptfs.sourceforge.net/[eCryptfs] selectively encrypt only the sensitive files, its system cost is much less than using http://en.wikipedia.org/wiki/Dm-crypt[dm-crypt] on the entire root or home device.  It does not require any special on-disk storage allocation effort but cannot keep all filesystem metadata confidential.


==== Automatically mounting eCryptfs

If you use your login password for wrapping encryption keys, you can automate mounting eCryptfs via 
Pluggable Authentication Module by having a following line just before "`pam_permit.so`" in "`/etc/pam.d/common-auth`" as:
--------------------
auth required pam_ecryptfs.so unwrap
--------------------
and the last line in "`/etc/pam.d/common-session`" as: 
--------------------
session optional pam_ecryptfs.so unwrap
--------------------
and the first active line in "`/etc/pam.d/common-password`" as: 
--------------------
password required pam_ecryptfs.so
--------------------
This is quite convienient.

WARNING: Configuration errors of PAM may lock you out of your own system. See <<_authentication>>.

CAUTION: If you use your login password for wrapping encryption keys, your encrypted data are as secure as your user login password (see <<_good_password>>).  Unless you are careful to set up a http://en.wikipedia.org/wiki/Password_strength[strong password], your data will be at risk when someone runs http://en.wikipedia.org/wiki/Password_cracking[password cracking] software after stealing your laptop (see <<_securing_the_root_password>>).

=== Monitoring, controlling, and starting program activities

Program activities can be monitored and controlled using specialized tools.


.List of tools for monitoring and controlling program activities
[grid="all"]
`-----------`-------------`------------`-----------------------------------------------------------------------------------------
package     popcon        size         description                                                                               
---------------------------------------------------------------------------------------------------------------------------------
`time`      @@@popcon1@@@ @@@psize1@@@ `time`(1) runs a program to report system resource usages with respect to time.           
`coreutils` @@@popcon1@@@ @@@psize1@@@ `nice`(1) runs a program with modified scheduling priority.                               
`bsdutils`  @@@popcon1@@@ @@@psize1@@@ `renice`(1) modifies the scheduling priority of a running process.                        
`powertop`  @@@popcon1@@@ @@@psize1@@@ `powertop`(1) gives information about system power use on Intel-based laptops.            
`procps`    @@@popcon1@@@ @@@psize1@@@ The "`/proc`" file system utilities: `ps`(1), `top`(1), `kill`(1), `watch`(1), ...        
`psmisc`    @@@popcon1@@@ @@@psize1@@@ The "`/proc`" file system utilities: `killall`(1), `fuser`(1), `pstree`(1)                
`cron`      @@@popcon1@@@ @@@psize1@@@ The `cron`(8) daemon runs processes according to a schedule (in background).              
`at`        @@@popcon1@@@ @@@psize1@@@ `at`(1) or `batch`(1) commands run a job at a specified time or below certain load level. 
`lsof`      @@@popcon1@@@ @@@psize1@@@ `lsof`(8) lists open files by a running process using "`-p`" option.                      
`strace`    @@@popcon1@@@ @@@psize1@@@ `strace`(1) traces system calls and signals.                                              
`ltrace`    @@@popcon1@@@ @@@psize1@@@ `ltrace`(1) traces library calls.                                                         
`xtrace`    @@@popcon1@@@ @@@psize1@@@ `xtrace`(1) traces communication between X11 client and server.                           
---------------------------------------------------------------------------------------------------------------------------------

==== 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.
[grid="all"]
`----------`-----------------------------------------------
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) 
-----------------------------------------------------------


--------------------
# 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.
[grid="all"]
`--------`---------------`-----------------
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 `pstree`(1) command display a tree of processes.

==== The top command

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


.List of commands for top.
[grid="all"]
`-----------`---------------------------
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.  
----------------------------------------

==== List files opened by a process

You can list all files opened by a process with a process ID (PID), e.g. 1 as:

--------------------
$ sudo lsof -p 1
--------------------

PID=1 is usually `init` program.

==== Trace program activities

You can trace program activity with `strace`(1), `ltrace`(1), or `xtrace`(1) for system calls and signals, library calls, or communication between X11 client and server.  For example:

--------------------
$ sudo strace ls
...
--------------------

==== Identify processes using files or sockets

You can also identify processes using files or sockets by `fuser`(1).  For example:

--------------------
$ sudo fuser -v /var/log/mail.log
                     USER        PID ACCESS COMMAND
/var/log/mail.log:   root       2946 F.... syslogd
--------------------
You see that file "`/var/log/mail.log`" is open for writing by the `syslogd`(8) command.


--------------------
$ sudo fuser -v smtp/tcp
                     USER        PID ACCESS COMMAND
smtp/tcp:            Debian-exim   3379 F.... exim4
--------------------
Now you know your system runs `exim4`(8) to handle http://en.wikipedia.org/wiki/Transmission_Control_Protocol[TCP] connections to http://en.wikipedia.org/wiki/Simple_Mail_Transfer_Protocol[SMTP] port (25).

==== Repeating a command with a constant interval

`watch`(1) executes a program repeatedly with a constant interval while showing its output in fullscreen.


--------------------
$ watch w
--------------------
This will display who is logged on to the system updated every 2 seconds.

==== Repeating a command looping over files

There are several ways to repeat a command looping over files matching some condition, e.g. matching glob pattern "`\*.ext`".


- Shell for-loop method (see <<_shell_loops>>):
 +
--------------------
for x in *.ext; do if [ -f "$x"]; then command "$x" ; fi; done
--------------------


- `find`(1) and `xargs`(1) combination:
 +
--------------------
find . -type f -maxdepth 1 -name '*.ext' -print0 | xargs -0 -n 1 command
--------------------


- `find`(1) with "`-exec`" option with a command:
 +
--------------------
find . -type f -maxdepth 1 -name '*.ext' -exec command '{}' \;
--------------------


- `find`(1) with "`-exec`" option with a short shell script:
 +
--------------------
find . -type f -maxdepth 1 -name '*.ext' -exec sh -c "command '{}' && echo 'successful'" \;
--------------------

The above examples are written to ensure proper handling of funny file names such as ones containing spaces.  See <<_idioms_for_the_selection_of_files>> for more advance uses of `find`(1).

==== Starting a program from GUI

You can set up to start a process from http://en.wikipedia.org/wiki/Graphical_user_interface[graphical user interface (GUI)].

Under GNOME desktop environment, a program program can be started with proper argument by **drag-and-drop** of an icon to the launcher icon or by "**Open with ...**" menu with right clicking. KDE can do the equivalent, too. Here is an example for GNOME to set up `mc`(1) started in `gnome-terminal`(1):


- create an executable program "`mc-term`" as:

--------------------
# cat >/usr/local/bin/mc-term <<EOF
#!/bin/sh
gnome-terminal -e "mc \$1"
EOF
# chmod 755 /usr/local/bin/mc-term
--------------------

- create a desktop launcher
 * right clicking desktop space to select "`Create Launcher ...`"
 * set "Type" to "`Application`"
 * set "Name" to "`mc`"
 * set "Command" to "`mc-term %f`"
 * click "OK"
- create an open-with association
 * right click folder to select "`Open with Other Application ...`"
 * click open "Use a custom command" dialog and enter "`mc-term %f`"
 * click "Open".

TIP: Launcher is a file at "`\~/Desktop`" with "`.desktop`" as its extension.

==== Customizing program to be started

Some programs start another program automatically.  Here are check points for customizing this process:

- application configuration menu:
 * GNOME desktop: "System" -> "Preferences" -> "Preferred Application"
 * KDE desktop: "K" -> "Control Center" -> "KDE Components" -> "Component Chooser"
 * Iceweasle browser: "Edit" -> "Preferences" -> "Applications"
 * `mc`(1): "`/etc/mc/mc.ext`"
- 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 <<_setting_a_default_text_editor>>).
- the "`\~/.mailcap`" and "`/etc/mailcap`" file contents which associate http://en.wikipedia.org/wiki/MIME[MIME] type with program (see `mailcap`(5)).
- the the "`\~/.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)).

TIP: `update-mime`(8) updates the "`/etc/mailcap`" file using "`/etc/mailcap.order`" file (see `mailcap.order`(5)).

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

TIP: In order to run a console application such as `mutt` under X as your prefered application, you should create an X application as following and set "`/usr/local/bin/mutt-term`" as your prefered application to be started as described.

--------------------
# cat /usr/local/bin/mutt-term <<EOF
#!/bin/sh
gnome-terminal -e "mutt \$@"
EOF
chmod 755 /usr/local/bin/mutt-term
--------------------

==== Kill a process

Use `kill`(1) to kill (or send a signal to) a process by the process ID.

Use `killall`(1) or `pkill`(1) to do the same by the process command name and other attributes.


.List of frequently used signals for kill command.
[grid="all"]
`------------`-----------`--------------
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
--------------------

TIP: 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" (http://en.wikipedia.org/wiki/Secure_attention_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.
[grid="all"]
`-----------------------`--------------------------------------------------------------------------------------
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`(8).                             
`i`                     Send a SIGK**I**LL to all processes, except for `init`(8).                             
`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`".

CAUTION: 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.

TIP: 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.

=== System maintenance tips

==== Who is logged on

You can check who is logged on to the system with `w`(1) or `who`(1).

==== Warn everyone

You can send message to everyone who is logged on to the system with `wall`(1):

--------------------
$ echo "We are shutting down in 1 hour" | wall
--------------------

==== 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) (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 <<_procfs_and_sysfs>>).


.List of hardware identification tools.
[grid="all"]
`-------------`-------------`------------`-------------------------------------------------------------
package       popcon        size         description                                                   
-------------------------------------------------------------------------------------------------------
`pciutils`    @@@popcon1@@@ @@@psize1@@@ Linux PCI Utilities, `lspci`(8)                               
`usbutils`    @@@popcon1@@@ @@@psize1@@@ Linux USB utilities, `lsusb`(8)                               
`pcmciautils` @@@popcon1@@@ @@@psize1@@@ PCMCIA utilities for Linux 2.6, `pccardctl`(8)                
`scsitools`   @@@popcon1@@@ @@@psize1@@@ Collection of tools for SCSI hardware management, `lsscsi`(8) 
`pnputils`    @@@popcon1@@@ @@@psize1@@@ Plug and Play BIOS utilities, `lspnp`(8)                      
`procinfo`    @@@popcon1@@@ @@@psize1@@@ Displays system information from "`/proc`", `lsdev`(8)        
`lshw`        @@@popcon1@@@ @@@psize1@@@ Information about hardware configuration, `lshw`(1)           
`discover`    @@@popcon1@@@ @@@psize1@@@ Hardware identification system, `discover`(8)                 
-------------------------------------------------------------------------------------------------------

==== 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.
[grid="all"]
`-------------------`-------------`------------`-------------------------------------------------------------------------------------------------------------------------
package             popcon        size         description                                                                                                               
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------
`hal`               @@@popcon1@@@ @@@psize1@@@ Hardware Abstraction Layer, `lshal`(1)                                                                                    
`console-tools`     @@@popcon1@@@ @@@psize1@@@ Linux console font and keytable utilities.                                                                                
`x11-xserver-utils` @@@popcon1@@@ @@@psize1@@@ X server utilities. `xset`(1) and `xmodmap`(1).                                                                           
`acpid`             @@@popcon1@@@ @@@psize1@@@ Daemon to manage events delivered by the Advanced Configuration and Power Interface (ACPI)                                
`acpi`              @@@popcon1@@@ @@@psize1@@@ Utilities for ACPI devices                                                                                                
`apmd`              @@@popcon1@@@ @@@psize1@@@ Daemon to manage events delivered by the Advanced Power Management (APM)                                                  
`powersaved`        @@@popcon1@@@ @@@psize1@@@ Daemon to manage battery, temperature, ac, cpufreq (SpeedStep, Powernow!) control and monitor with ACPI and APM supports. 
`noflushd`          @@@popcon1@@@ @@@psize1@@@ Allow idle hard disks to spin down                                                                                        
`sleepd`            @@@popcon1@@@ @@@psize1@@@ Puts a laptop to sleep during inactivity                                                                                  
`hdparm`            @@@popcon1@@@ @@@psize1@@@ Hard disk access optimization.  Very effective but dangerous.  You must read `hdparm`(8) first.                           
`smartmontools`     @@@popcon1@@@ @@@psize1@@@ Control and monitor storage systems using S.M.A.R.T.                                                                      
`setserial`         @@@popcon1@@@ @@@psize1@@@ Collection of tools for serial port management.                                                                           
`memtest86+`        @@@popcon1@@@ @@@psize1@@@ Collection of tools for memory hardware management.                                                                       
`scsitools`         @@@popcon1@@@ @@@psize1@@@ Collection of tools for SCSI hardware management.                                                                         
`tpconfig`          @@@popcon1@@@ @@@psize1@@@ A program to configure touchpad devices                                                                                   
`setcd`             @@@popcon1@@@ @@@psize1@@@ Compact disc drive access optimization.                                                                                   
`big-cursor`        @@@popcon1@@@ @@@psize1@@@ Larger mouse cursors for X                                                                                                
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------

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

==== System and hardware 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

TIP: `ntptrace`(8) in the `ntp` package can trace a chain of NTP servers back to the primary source.

==== The terminal configuration

There are several components to configure character console and `ncurses`(3) system features:


- the "`/etc/terminfo/\*/\*`" file (`terminfo`(5))
- the "`$TERM`" environment variable (`term`(7))
- `setterm`(1), `stty`(1), `tic`(1), and `toe`(1)

If the `terminfo` entry for `xterm` doesn\'t work with a non-Debian `xterm`, change your terminal type, "`$TERM`", from "`xterm`" to one of the feature-limited versions such as "`xterm-r6`" when you log in to a Debian system remotely.  See "`/usr/share/doc/libncurses5/FAQ`" for more.  "`dumb`" is the lowest common denominator for "`$TERM`".

==== 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 via blacklisting of kernel modules. Unless you have very new sound hardware, udev infrastructure should configure your sound system.

TIP: Use "`cat /dev/urandom > /dev/audio`" or `speaker-test`(1) to test speaker. (\^C to stop)

TIP: If you can not get sound, your speaker may be connected to a muted output.  Modern sound system has many outputs.  `alsamixer`(1) 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
[grid="all"]
`--------------------`-------------`------------`-----------------------------------------------------------------------------------------------------------------------------
package              pocon         size         description                                                                                                                   
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
`linux-sound-base`   @@@popcon1@@@ @@@psize1@@@ Base package for ALSA and OSS sound systems                                                                                   
`alsa-base`          @@@popcon1@@@ @@@psize1@@@ ALSA driver configuration files                                                                                               
`alsa-utils`         @@@popcon1@@@ @@@psize1@@@ Utilities for configuring and using ALSA                                                                                      
`oss-compat`         @@@popcon1@@@ @@@psize1@@@ OSS compatibility under ALSA preventing "`/dev/dsp not found`" errors                                                         
`esound-common`      @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/Enlightened_Sound_Daemon[Enlightened Sound Daemon (ESD)] common (Enlightenment and GNOME)        
`esound`             @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/Enlightened_Sound_Daemon[Enlightened Sound Daemon (ESD)] server (Enlightenment and GNOME)        
`esound-clients`     @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/Enlightened_Sound_Daemon[Enlightened Sound Daemon (ESD)] client (Enlightenment and GNOME)        
`libesd-alsa0`       @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/Enlightened_Sound_Daemon[Enlightened Sound Daemon (ESD)] library Enlightenment and GNOME)        
`libesd0`            @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/Enlightened_Sound_Daemon[Enlightened Sound Daemon (ESD)] library (Enlightenment and GNOME) - OSS 
`arts`               @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/ARts[aRts] server (KDE)                                                                          
`libarts1c2a`        @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/ARts[aRts] library (KDE)                                                                         
`libartsc0`          @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/ARts[aRts] library (KDE)                                                                         
`jackd`              @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/JACK_Audio_Connection_Kit[JACK Audio Connection Kit. (JACK)] server (low latency)                
`libjack0`           @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/JACK_Audio_Connection_Kit[JACK Audio Connection Kit. (JACK)] library (low latency)               
`libjack0.100.0-0`   @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/JACK_Audio_Connection_Kit[JACK Audio Connection Kit. (JACK)] library (low latency)               
`nas`                @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/Network_Audio_System[Network Audio System (NAS)] server                                          
`libaudio2`          @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/Network_Audio_System[Network Audio System (NAS)]  library                                        
`pulseaudio`         @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/PulseAudio[PulseAudio] server, replacement for ESD                                               
`libpulse0`          @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/PulseAudio[PulseAudio] client library, replacement for ESD                                       
`libpulsecore9`      @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/PulseAudio[PulseAudio] server library, replacement for ESD                                       
`libgstreamer0.10-0` @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/GStreamer[GStreamer]: GNOME sound engine                                                         
`libxine1`           @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/Xine[xine]: KDE older sound engine                                                               
`libphonon4`         @@@popcon1@@@ @@@psize1@@@ 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.
[grid="all"]
`-------------------------------------------------`-----------------------------
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`(3) program used by `bash`(1) to beep when encountering "`\a`" (ASCII=7):

--------------------
$ echo "set bell-style none">> ~/.inputrc
--------------------

==== Memory usage

The kernel boot message in the "`/var/log/dmesg`" contains the total exact size of available memory. 

`free`(1) and `top`(1) display information on memory resources on the running system.

--------------------
$ grep '\] Memory' /var/log/dmesg
[    0.004000] 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.
[grid="all"]
`-------------------`-----------------------
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.

==== System security and integrity check

Poor system maintenance may expose your system to external exploitation.  

For system security and integrity check, you should start with:

- the `debsums` package: See `debsums`(1) and <<_top_level_release_file_and_authenticity>>.
- the `chkrootkit` package: See `chkrootkit`(1).
- the `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].


.List of tools for system security and integrity check
[grid="all"]
`------------`-------------`------------`----------------------------------------------------------------
package      popcon        size         description                                                      
---------------------------------------------------------------------------------------------------------
`logcheck`   @@@popcon1@@@ @@@psize1@@@ This mails anomalies in the system logfiles to the administrator 
`debsums`    @@@popcon1@@@ @@@psize1@@@ This verifies installed package files against MD5 checksums.     
`chkrootkit` @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/Rootkit[Rootkit] detector.          
`clamav`     @@@popcon1@@@ @@@psize1@@@ Anti-virus utility for Unix - command-line interface.            
`tiger`      @@@popcon1@@@ @@@psize1@@@ Report system security vulnerabilities                           
`tripwire`   @@@popcon1@@@ @@@psize1@@@ File and directory integrity checker                             
`john`       @@@popcon1@@@ @@@psize1@@@ Active password cracking tool                                    
`aide`       @@@popcon1@@@ @@@psize1@@@ Advanced Intrusion Detection Environment - static binary         
`bastille`   @@@popcon1@@@ @@@psize1@@@ Security hardening tool                                          
`integrit`   @@@popcon1@@@ @@@psize1@@@ A file integrity verification program                            
`crack`      @@@popcon1@@@ @@@psize1@@@ Password guessing program                                        
---------------------------------------------------------------------------------------------------------

Here is a simple script to check for typical world writable incorrect file permissions.

--------------------
# find / -perm 777 -a \! -type s -a \! -type l -a \! \( -type d -a -perm 1777 \)
--------------------

CAUTION: Since the `debsums` package uses MD5 checksums stored locally, it can not be fully trusted as the system security audit tool against malicious attacks.

=== 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 <<_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.

==== 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.

NOTE: 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. `module-assistant`(8) (or its short form `m-a`) helps users to build and install module package(s) easily for one or more custom kernels.

==== 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
[grid="all"]
`-------------------`-------------`------------`----------------------------------------------------------------------------
package             popcon        size         description                                                                  
----------------------------------------------------------------------------------------------------------------------------
`build-essential`   @@@popcon1@@@ @@@psize1@@@ essential packages for building Debian packages: `make`, `gcc`, ...          
`bzip2`             @@@popcon1@@@ @@@psize1@@@ compress and decompress utilities for bz2 files                              
`libncurses5-dev`   @@@popcon1@@@ @@@psize1@@@ developer\'s libraries and docs for ncurses                                  
`git-core`          @@@popcon1@@@ @@@psize1@@@ git: distributed revision control system used by the Linux kernel            
`fakeroot`          @@@popcon1@@@ @@@psize1@@@ provide fakeroot environment for building package as non-root                
`initramfs-tools`   @@@popcon1@@@ @@@psize1@@@ tool to build an initramfs (Debian specific)                                 
`kernel-package`    @@@popcon1@@@ @@@psize1@@@ tool to build Linux kernel packages (Debian specific)                        
`module-assistant`  @@@popcon1@@@ @@@psize1@@@ tool to help build module packages (Debian specific)                         
`devscripts`        @@@popcon1@@@ @@@psize1@@@ helper scripts for a Debian Package maintainer (Debian specific)             
`linux-tree-2.6.\*` N/A           N/A          Linux kernel source tree meta package (Debian specific) 
----------------------------------------------------------------------------------------------------------------------------

If you use `initrd` in <<_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. "`/usr/src/linux\*`") from "`/usr/include/linux`" and "`/usr/include/asm`" when compiling the Linux kernel source. (Some outdated documents suggest this.)

NOTE: 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). 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 `make-kpkg` 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) 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[Google] or other search engines with keyword "Linmodem".
- http://ndiswrapper.sourceforge.net
- http://linuxwireless.org
- http://madwifi-project.org (there is ath5k which contains free drivers)

=== Virtualized system

Use of virtualized system enables us to run multiple instances of system simultaneously on a single hardware.

==== Virtualization tools

Virturization involves 2 steps:

- create file system populated with required package data.  Programs such as `debootstrap` and `cdebootstrap` helps this process.
- run a program under virturized environment.  Most basic method is provided by http://en.wikipedia.org/wiki/Chroot[chroot].

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].  Some packages also help you to setup such system.

.List of virtualization tools
[grid="all"]
`-----------------`-------------`------------`------------------------------------------------------------------------------------------------------------------
package           pocon         size         description                                                                                                        
----------------------------------------------------------------------------------------------------------------------------------------------------------------
`schroot`         @@@popcon1@@@ @@@psize1@@@ Specialized tool for executing Debian binary packages in chroot                                                    
`sbuild`          @@@popcon1@@@ @@@psize1@@@ Tool for building Debian binary packages from Debian sources                                                       
`pbuilder`        @@@popcon1@@@ @@@psize1@@@ Personal package builder for Debian packages                                                                       
`debootstrap`     @@@popcon1@@@ @@@psize1@@@ Bootstrap a basic Debian system (written in sh)                                                                    
`cdebootstrap`    @@@popcon1@@@ @@@psize1@@@ Bootstrap a Debian system (written in C)                                                                           
`rootstrap`       @@@popcon1@@@ @@@psize1@@@ A tool for building complete Linux filesystem images                                                               
`user-mode-linux` @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/User-mode_Linux[User-mode Linux] (kernel)                                             
`xen-tools`       @@@popcon1@@@ @@@psize1@@@ Tools to manage debian http://en.wikipedia.org/wiki/Xen[XEN] virtual server                                        
`bochs`           @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/Bochs[Bochs]: IA-32 PC emulator                                                       
`qemu`            @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/Qemu[Qemu]: fast generic processor emulator                                           
`virtualbox-ose`  @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/VirtualBox[VirtualBox]: x86 virtualization solution on i386 and amd64                 
`wine`            @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/Wine_(software)[Wine]: Windows API Implementation (standard suite)                    
`dosbox`          @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/DOSBox[DOSBox]: x86 emulator with Tandy/Herc/CGA/EGA/VGA/SVGA graphics, sound and DOS 
`util-vserver`    @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/Linux-VServer[Linux-VServer] virtual private servers - user-space tools               
`vzctl`           @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/OpenVZ[OpenVZ] server virtualization solution - control tools                         
`vzquota`         @@@popcon1@@@ @@@psize1@@@ http://en.wikipedia.org/wiki/OpenVZ[OpenVZ] server virtualization solution - quota tools                           
----------------------------------------------------------------------------------------------------------------------------------------------------------------

See Wikipedia article http://en.wikipedia.org/wiki/Comparison_of_virtual_machines[Comparison of virtual machines] for detail comparison of different virtualization solutions.

==== Chroot system

`chroot`(8) offers most basic way to run different instances of the GNU/Linux environment on a single system simultaneously without rebooting.  

CAUTION: Examples below assumes both parent system and chroot system share the same CPU architecture.

You can learn how to setup and use `chroot`(8) by running `pbuilder`(8) program under `script`(1) as follows.

------
$ sudo mkdir /sid-root
$ sudo pbuilder --create --no-targz --debug --buildplace /sid-root
------

You will see how `debootstrap`(8) or `debootstrap`(1) populate system data for `sid` environment under "`/sid-root`".

TIP: These `debootstrap`(8) or `debootstrap`(1) are used to http://www.debian.org/releases/stable/installmanual[install Debian] by the Debian Installer.  These can also be used to install Debian to a system without using a Debian install disk, but instead from another GNU/Linux distribution.

-----
$ sudo pbuilder --login --no-targz  --debug --buildplace /sid-root
-----

You will see how a system shell running under `sid` environment is created:

- copying local configuration (`"/etc/hosts`", `"/etc/hostname`", `"/etc/resolv.conf`")
- mounting "`/proc`" filesystem
- mounting "`/dev/pts`" filesystem
- "`/usr/sbin/policy-rc.d`" created (this always exits with 101)
- run "`chroot /sid-root bin/bash -c @@@sq@@@exec -a -bash bin/bash@@@sq@@@`"

NOTE: Some programs under chroot may require access to more files from the parent system to function than `pbuilder` provides.  For example, "`/sys`", "`/etc/passwd`", "`/etc/group`", "`/var/run/utmp`", "`/var/log/wtmp`", etc.. may need to be bind-mounted or copied.

NOTE: The "`/usr/sbin/policy-rc.d`" file prevents daemon programs to be started automatically on Debian system.  See "`/usr/share/doc/sysv-rc/README.policy-rc.d.gz`".

TIP: The original purpose of the specialized chroot package, `pbuilder` is to construct 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.

TIP: Similar `schroot` package may give you an idea to run `i386` chroot system under `amd64` parent system.

TIP: By installing a system into a separate partition using the installer of other distributions and using this system for `chroot`(8), you can run other distributions under `chroot`(8).

==== Setting up login for chroot

You can run another login process on a separate virtual terminal where you can log in to the chroot system 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 `sid` chroot system under "`/sid-root`" by following steps you learned from `pbuilder`(8), 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
// 
// WARNING: XXX FIXME XXX: until we find stable way to run 2 xservers on different terminal, this is commented out.
