/etc目录深入理解

 /etc

This is the nerve center of your system, it contains all system related configuration files in here or in its sub-directories. A "configuration file" is defined as a local file used to control the operation of a program; it must be static and cannot be an executable binary. For this reason, it's a good idea to backup this directory regularly. It will definitely save you a lot of re-configuration later if you re-install or lose your current installation. Normally, no binaries should be or are located here.

/etc/X11/

This directory tree contains all the configuration files for the X Window System. Users should note that many of the files located in this directory are actually symbolic links to the /usr/X11R6 directory tree. Thus, the presence of these files in these locations can not be certain.

/etc/X11/XF86Config, /etc/X11/XF86Config-4

The 'X' configuration file. Most modern distributions possess hardware autodetection systems that enable automatic creation of a valid file. Should autodetection fail a configuration file can also be created manually provided that you have sufficient knowledge about your system. It would be considered prudent not to attempt to type out a file from beginning to end. Rather, use common configuration utilities such as xf86config, XF86Setup and xf86cfg to create a workable template. Then, using suitable documentation commence optimization through intuition and/or trial and error. Options that can be configured via this file include X modules to be loaded on startup, keyboard, mouse, monitor and graphic chipset type. Often, commercial distributions will include their own X configuration utilities such as XDrake on Mandrake and also Xconfiguration on Redhat. Below is a sample X configuration file from the reference system
 

/etc/X11/xdm/

X display manager configuration files. xdm manages a collection of X servers, which may be on the local host or remote machines. It provides services similar to those provided by init, getty, and login on character-based terminals: prompting for login name and password, authenticating the user, and running a session. xdm supports XDMCP (X Display Manager Control Protocol) and can also be used to run a chooser process which presents the user with a menu of possible hosts that offer XDMCP display management. If the xutils package is installed, xdm can use the sessreg utility to register login sessions to the system utmp file; this, however, is not necessary for xdm to function.

/etc/X11/xdm/xdm-config

This is the master 'xdm' configuration file. It determines where all other 'xdm' configuration files will be located. It is almost certain to be left undisturbed.

/etc/X11/gdm/

GNOME Display Manager configuration files. gdm provides the equivalent of a "login:" prompt for X displays- it pops up a login window and starts an X session. It provides all the functionality of xdm, including XDMCP support for managing remote displays. The greeting window is written using the GNOME libraries and hence looks like a GNOME application- even to the extent of supporting themes! By default, the greeter is run as an unprivileged user for security.

/etc/X11/gdm/gdm.conf

This is the primary configuration file for GDM. Through it, users can specify whether they would like their system to automatically login as a certain user, background startup image and also if they would like to run their machine as somewhat of a terminal server by using the XDMCP protocol.

/etc/X11/fonts

Home of xfs fonts.

/etc/X11/fs/

X font server configuration files. xfs is a daemon that listens on a network port and serves X fonts to X servers (and thus to X clients). All X servers have the ability to serve locally installed fonts for themselves, but xfs makes it possible to offload that job from the X server, and/or have a central repository of fonts on a networked machine running xfs so that all the machines running X servers on a network do not require their own set of fonts. xfs may also be invoked by users to, for instance, make available X fonts in user accounts that are not available to the X server or to an already running system xfs.

/etc/X11/fs/config

This is the 'xfs' initialisation file. It specifies the number of clients that are allowed to connect to the 'xfs' server at any one time, the location of log files, default resolution, the location of the fonts, etc.
 

/etc/X11/xinit/

xinit configuration files. 'xinit' is a configuration method of starting up an X session that is designed to used as part of a script. Normally, this is used at larger sites as part of a tailored login process.

/etc/X11/xinit/xinitrc

Global xinitrc file, used by all X sessions started by xinit (startx). Its usage is of course overridden by a .xinitrc file located in the home directory of a user.

/etc/adduser.conf

'adduser' configuration. The adduser command can create new users, groups and add existing users to existing groups. Adding users with adduser is much easier than adding them by hand. Adduser will choose appropriate UID and GID values, create a home directory, copy skeletal user configuration from /etc/skel, allow you to set an initial password and the GECOS field. Optionally a custom script can be executed after this commands. See adduser(8) and adduser.conf(5) for full documentation.

/etc/adjtime

Has parameters to help adjust the software (kernel) time so that it matches the RTC.

/etc/aliases

This is the aliases file – it says who gets mail for whom. It was originally generated by `eximconfig', part of the exim package distributed with Debian, but it may edited by the mail system administrator. See exim info section for details of the things that can be configured here. An aliases database file (aliases.db) is built from the entries in the aliases files by the newaliases utility.

/etc/alternatives

It is possible for several programs fulfilling the same or similar functions to be installed on a single system at the same time. For example, many systems have several text editors installed at once. This gives choice to the users of a system, allowing each to use a different editor, if desired, but makes it difficult for a program to make a good choice of editor to invoke if the user has not specified a particular preference.

The alternatives system aims to solve this problem. A generic name in the filesystem is shared by all files providing interchangeable functionality. The alternatives system and the system administrator together determine which actual file is referenced by this generic name. For example, if the text editors ed(1) and nvi(1) are both installed on the system, the alternatives system will cause the generic name /usr/bin/editor to refer to /usr/bin/nvi by default. The system administrator can override this and cause it to refer to /usr/bin/ed instead, and the alternatives system will not alter this setting until explicitly requested to do so.

The generic name is not a direct symbolic link to the selected alternative. Instead, it is a symbolic link to a name in the alternatives directory, which in turn is a symbolic link to the actual file referenced. This is done so that the system administrator's changes can be confined within the /etc directory.

/etc/apt

This is Debian's next generation front-end for the dpkg package manager. It provides the apt-get utility and APT dselect method that provides a simpler, safer way to install and upgrade packages. APT features complete installation ordering, multiple source capability and several other unique features, see the Users Guide in /usr/share/doc/apt/guide.text.gz

/etc/apt/sources.list
 

/etc/asound.conf

ALSA (Advanced Linux Sound Architecture) configuration file. It is normally created via alsactl or other third-party sound configuration utilities that may be specific to a distribution such as sndconfig from Redhat.

/etc/at.deny

Users denied access to the at daemon. The 'at' command allows user to execute programs at an arbitrary time.

/etc/autoconf

Configuration files for autoconf. 'autoconf' creates scripts to configure source code packages using templates. To create configure from configure.in, run the autoconf program with no arguments. autoconf processes configure.ac with the m4 macro processor, using the Autoconf macros. If you give autoconf an argument, it reads that file instead of configure.ac and writes the configuration script to the standard output instead of to configure. If you give autoconf the argument -, it reads the standard input instead of configure.ac and writes the configuration script on the standard output.

The Autoconf macros are defined in several files. Some of the files are distributed with Autoconf; autoconf reads them first. Then it looks for the optional file acsite.m4 in the directory that contains the distributed Autoconf macro files, and for the optional file aclocal.m4 in the current directory. Those files can contain your site's or the package's own Autoconf macro definitions. If a macro is defined in more than one of the files that autoconf reads, the last definition it reads overrides the earlier ones.

/etc/bash.bashrc

System wide functions and aliases' file for interactive bash shells.
 

/etc/cron.d, /etc/cron.daily, /etc/cron.weekly, /etc/cron.monthly

These directories contain scripts to be executed on a regular basis by the cron daemon.

/etc/crontab

'cron' configuration file. This file is for the cron table to setup the automatic running of system routines. A cron table can also be established for individual users. The location of these user cron table files will be explained later on.

# /etc/crontab: system-wide crontab
# Unlike any other crontab you don't have to run the `crontab'
# command to install the new version when you edit this file.
# This file also has a username field, that none of the other crontabs do.

SHELL=/bin/sh
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin

# m h dom mon dow user command
25 6 * * * root test -e /usr/sbin/anacron || run-parts --report /etc/cron.daily
47 6 * * 7 root test -e /usr/sbin/anacron || run-parts --report /etc/cron.weekly
52 6 1 * * root test -e /usr/sbin/anacron || run-parts --report /etc/cron.monthly
#

/etc/cups

Configuration files for the Common UNIX Printing System (CUPS). Files here are used to define client-specific parameters, such as the default server or default encryption settings.

/etc/deluser.conf

'deluser' configuration files. The deluser command can remove users and groups and remove users from a given group. Deluser can optionally remove and backup the user's home directory and mail spool or all files on the system owned by him. Optionally a custom script can also be executed after each of the commands.

/etc/devfs

This daemon sets up the /dev filesystem for use. It creates required symbolic links in /dev and also creates (if so configured, as is the default) symbolic links to the "old" names for devices.

/etc/devfs/conf.d/

'devfsd' configuration files. This daemon sets up the /dev filesystem for use. It creates required symbolic links in /dev and also creates (if so configured, as is the default) symbolic links to the "old" names for devices.

/etc/dhclient.conf, /etc/dhclient-script

'dhclient' configuration file and 'dhclient' script files respectively. It configures your system so that it may act as a client on a DHCP based network. It is essential to connect to the Internet nowadays.
 

/etc/fstab

The configuration file for 'mount' and now 'supermount'. It lists the filesystems mounted automatically at startup by the mount -a command (in /etc/rc or equivalent startup file). Under Linux, also contains information about swap areas used automatically by swapon -a.

 

  # /etc/fstab: static file system information.
  #
  # The following is an example. Please see fstab(5) for further details.
  # Please refer to mount(1) for a complete description of mount options.
  #
  # Format:
  # <file system> <mount point> <type> <options> <dump> <pass>
  #
  # dump(8) uses the <dump> field to determine which file systems need
  # to be dumped. fsck(8) uses the <pass> column to determine which file
  # systems need to be checked--the root file system should have a 1 in 
  # this field, other file systems a 2, and any file systems that should
  # not be checked (such as MS-DOS or NFS file systems) a 0.
  #
  # The `sw' option indicates that the swap partition is to be activated
  # with `swapon -a'.
  /dev/hda2 none swap sw 0 0
  # The `bsdgroups' option indicates that the file system is to be mounted
  # with BSD semantics (files inherit the group ownership of the directory
  # in which they live). `ro' can be used to mount a file system read-only.
  /dev/hda3 / ext2 defaults 0 1 
  /dev/hda5 /home ext2 defaults 0 2
  /dev/hda6 /var ext2 defaults 0 2
  /dev/hda7 /usr ext2 defaults,ro 0 2
  /dev/hda8 /usr/local ext2 defaults,bsdgroups 0 2
  # The `noauto' option indicates that the file system should not be mounted
  # with `mount -a'. `user' indicates that normal users are allowed to mount
  # the file system.
  /dev/cdrom /cdrom iso9660 defaults,noauto,ro,user 0 0
  /dev/fd0 /floppy minix defaults,noauto,user 0 0
  /dev/fd1 /floppy minix defaults,noauto,user 0 0
  # NFS file systems: server:
  /export/usr /usr nfs defaults 0 0
  # proc file system:
  proc /proc proc defaults 0 0

/etc/ftpaccess

Determines who might get ftp-access to your machine.

/etc/ftpchroot

List of ftp users that need to be chrooted.

/etc/ftpuser

List of disallowed ftp users.

/etc/gateways

Lists gateways for 'routed'.

/etc/gettydefs

Configures console-logins.

/etc/gnome-vfs-mime-magic

MIME magic patterns as used by the Gnome VFS library.

/etc/group

Similar to /etc/passwd. It lists the configured user groups and who belongs to them.

/etc/group-

Old /etc/group file.

/etc/gshadow

Contains encrypted forms of group passwords.

/etc/gshadow-

Old /etc/gshadow file.

/etc/hostname

Contains the hostname of your machine (can be fully qualified or not).

/etc/host.conf

Determines the search order for look-ups (usually hosts bind, i.e. "check /etc/hosts first and then look for a DNS").

/etc/hosts

This file is used to define a system name and domain combination with a specific IP address. This file needs to always contain an entry for an IP address, if the machine is connected to the network.
 

/etc/hosts.allow

Part of the tcp-wrappers system to control access to your machine's services. It lists hosts that are allowed to access the system and specific daemons.
 

/etc/hosts.deny

part of the tcp-wrappers system to control access to your machine's services. It lists hosts that are not allowed to access the system.
 

/etc/httpd

Apache configuration files. Apache is a versatile, high-performance HTTP server. The most popular server in the world, Apache features a modular design and supports dynamic selection of extension modules at runtime. Its strong points are its range of possible customization, dynamic adjustment of the number of server processes, and a whole range of available modules including many authentication mechanisms, server-parsed HTML, server-side includes, access control, CERN httpd metafiles emulation, proxy caching, etc. Apache also supports multiple virtual homing.

/etc/identd.conf

TCP/IP IDENT protocol server. It implements the TCP/IP proposed standard IDENT user identification protocol (RFC 1413). identd operates by looking up specific TCP/IP connections and returning the username of the process owning the connection. It can also return other information besides the username.
 

/etc/inetd.conf

Configuration of services that are started by the INETD TCP/IP super server. 'inetd' is now deprecated. 'xinetd' has taken its place. See /etc/xinet.conf for further details.

  # /etc/inetd.conf:  see inetd(8) for further information.
  #
  # Internet server configuration database
  #
  #
  # Lines starting with "#:LABEL:" or "#<off>#" should not
  # be changed unless you know what you are doing!
  #
  # If you want to disable an entry so it isn't touched during
  # package updates just comment it out with a single '#' character.
  #
  # Packages should modify this file by using update-inetd(8)
  #

/etc/init.d

Order of scripts run in /etc/rc?.d
==================================

0. Overview.

   All scripts executed by the init system are located in /etc/init.d.
   The directories /etc/rc?.d (? = S, 0 .. 6) contain relative links to
   those scripts. These links are named S<2-digit-number><
   original-name> or K<2-digit-number><original-name>.

   If a scripts has the ".sh" suffix it is a bourne shell script and
   MAY be handled in an optimized manner. The behaviour of executing the
   script in an optimized way will not differ in any way from it being
   forked and executed in the regular way.

   The following runlevels are defined:

   N       System bootup (NONE).
   S       Single user mode (not to be switched to directly)
   0       halt
   1       single user mode
   2 .. 5  multi user mode
   6       reboot

1. Boot.

   When the systems boots, the /etc/init.d/rcS script is executed. It
   in turn executes all the S* scripts in /etc/rcS.d in alphabetical
   (and thus numerical) order. The first argument passed to the
   executed scripts is "start". The runlevel at this point is
   "N" (none).

   Only things that need to be run once to get the system in a consistent
   state are to be run. The rcS.d directory is NOT meant to replace rc.local.
   One should not start daemons in this runlevel unless absolutely
   necessary. Eg, NFS might need the portmapper, so it is OK to start it
   early in the boot process. But this is not the time to start the
   squid proxy server.

2. Going multiuser.

   After the rcS.d scripts have been executed, init switches to the
   default runlevel as specified in /etc/inittab, usually "2".

   Init then executes the /etc/init.d/rc script which takes care of
   starting the services in /etc/rc2.d.

   Because the previous runlevel is "N" (none) the /etc/rc2.d/KXXxxxx
   scripts will NOT be executed - there is nothing to stop yet,
   the system is busy coming up.

   If for example there is a service that wants to run in runlevel 4
   and ONLY in that level, it will place a KXXxxxx script in
   /etc/rc{2,3,5}.d to stop the service when switching out of runlevel 4.
   We do not need to run that script at this point.
   
   The /etc.rc2.d/SXXxxxx scripts will be executed in alphabetical
   order, with the first argument set to "start".

3. Switching runlevels.

   When one switches from (for example) runlevel 2 to runlevel 3,
   /etc/init.d/rc will first execute in alphabetical order all K
   scripts for runlevel 3 (/etc/rc3.d/KXXxxxx) with as first argument
   "stop" and then all S scripts for runlevel 3 (/etc/rc3.d/SXXxxxx)
   with as first argument "start".

   As an optimization, a check is made for each "service" to see if
   it was already running in the previous runlevel. If it was, and there
   is no K (stop) script present for it in the new runlevel, there is
   no need to start it a second time so that will not be done.

   On the other hand, if there was a K script present, it is assumed the
   service was stopped on purpose first and so needs to be restarted.

   We MIGHT make the same optimization for stop scripts as well-
   if no S script was present in the previous runlevel, we can assume
   that service was not running and we don't need to stop it either.
   In that case we can remove the "coming from level N" special case
   mentioned above in 2). But right now that has not been implemented.

4. Single user mode.

   Switching to single user mode is done by switching to runlevel 1.
   That will cause all services to be stopped (assuming they all have
   a K script in /etc/rc1.d). The runlevel 1 scripts will then switch
   to runlevel "S" which has no scripts - all it does is spawn
   a shell directly on /dev/console for maintenance.

5. Halt/reboot

   Going to runlevel 0 or 6 will cause the system to be halted or rebooted,
   respectively. For example, if we go to runlevel 6 (reboot) first
   all /etc/rc6.d/KXXxxxx scripts will be executed alphabetically with
   "stop" as the first argument.

   Then the /etc/rc6.d/SXXxxxx scripts will be executed alphabetically
   with "stop" as the first argument as well. The reason is that there
   is nothing to start any more at this point - all scripts that are
   run are meant to bring the system down.

   In the future, the /etc/rc6.d/SXXxxxx scripts MIGHT be moved to
   /etc/rc6.d/K1XXxxxx for clarity.

/etc/inittab

Boot-time system configuration/initialization script. Tells init how to handle runlevels. It sets the default runlevel. This is run first except when booting in emergency (-b) mode. It also enables a user to startup a getty session on an external device such as the serial ports. To add terminals or dial-in modem lines to a system, just add more lines to /etc/inittab, one for each terminal or dial-in line. For more details, see the manual pages init, inittab, and getty. If a command fails when it starts, and init is configured to restart it, it will use a lot of system resources: init starts it, it fails, init starts it, it fails, and so on. To prevent this, init will keep track of how often it restarts a command, and if the frequency grows to high, it will delay for five minutes before restarting again. /etc/inittab also has some special features that allow init to react to special circumstances. powerwait Allows init to shut the system down, when the power fails. This assumes the use of a UPS, and software that watches the UPS and informs init that the power is off. ctrlaltdel Allows init to reboot the system, when the user presses ctrl-alt-del on the console keyboard. Note that the system administrator can configure the reaction to ctrl-alt-del to be something else instead, e.g., to be ignored, if the system is in a public location. sysinit Command to be run when the system is booted. This command usually cleans up /tmp, for example. The list above is not exhaustive. See your inittab manual page for all possibilities, and for details on how to use the ones above. To set (or reset) initial terminal colours. The following shell script should work for VGA consoles: for n in 1 2 4 5 6 7 8; do setterm -fore yellow -bold on -back blue -store > /dev/tty$n done Substitute your favorite colors, and use /dev/ttyS$n for serial terminals. To make sure they are reset when people log out (if they've been changed) replace the references to getty (or mingetty or uugetty or whatever) in /etc/inittab with references to /sbin/mygetty. #!/bin/sh setterm -fore yellow -bold on -back blue -store > $1 exec /sbin/mingetty $@ An example /etc/inittab is provided below.

  # /etc/inittab: init(8) configuration.
  # $Id: etc.xml,v 1.10 2004/02/03 21:42:57 binh Exp $
  # The default runlevel. id:2:initdefault:
  # Boot-time system configuration/initialization script.
  # This is run first except when booting in emergency (-b) mode.
  si::sysinit:/etc/init.d/rcS
  # What to do in single-user mode.
  ~~:S:wait:/sbin/sulogin
  # /etc/init.d executes the S and K scripts upon change
  # of runlevel.
  #
  # Runlevel 0 is halt.
  # Runlevel 1 is single-user.
  # Runlevels 2-5 are multi-user.
  # Runlevel 6 is reboot.

/usr/X11R6/lib

X libraries.

/usr/local/lib

Local libraries.

/etc/lilo.conf

Configuration file for the Linux boot loader 'lilo'. 'lilo' is the original OS loader and can load Linux and others. The 'lilo' package normally contains lilo (the installer) and boot-record-images to install Linux, OS/2, DOS and generic Boot Sectors of other Oses. You can use Lilo to manage your Master Boot Record (with a simple text screen, text menu or colorful splash graphics) or call 'lilo' from other boot-loaders to jump-start the Linux kernel.
 

/etc/mime.types

MIME-TYPES and the extensions that represent them. This file is part of the "mime-support" package. Note: Compression schemes like "gzip", "bzip", and "compress" are not actually "mime-types". They are "encodings" and hence must _not_ have entries in this file to map their extensions. The "mime-type" of an encoded file refers to the type of data that has been encoded, not the type of the encoding.

/etc/minicom

'minicom' configuration files. 'minicom' is a communication program which somewhat resembles the shareware program TELIX but is free with source code and runs under most unices. Features include dialling directory with auto-redial, support for UUCP-style lock files on serial devices, a separate script language interpreter, capture to file, multiple users with individual configurations, and more.

/etc/modules

List of modules to be loaded at startup.
 

/etc/modules.conf

  ### This file is automatically generated by update-modules"
  #
  # Please do not edit this file directly. If you want to change or add
  # anything please take a look at the files in /etc/modutils and read
  # the manpage for update-modules.
  #
  ### update-modules: start processing /etc/modutils/0keep
  # DO NOT MODIFY THIS FILE!
  # This file is not marked as conffile to make sure if you upgrade modutils
  # it will be restored in case some modifications have been made.
  #
  # The keep command is necessary to prevent insmod and friends from ignoring
  # the builtin defaults of a path-statement is encountered. Until all other
  # packages use the new `add path'-statement this keep-statement is essential
  # to keep your system working
  keep

/etc/motd

The message of the day, automatically output after a successful login. Contents are up to the system administrator. Often used for getting information to every user, such as warnings about planned downtimes. Linux debian.localdomain.com 2.4.18 #1 Sat Mar 15 00:17:39 EST 2003 i686 unknown Most of the programs included with the Debian GNU/Linux system are freely redistributable; the exact distribution terms for each program are described in the individual files in /usr/share/doc/*/copyright Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent permitted by applicable law.

/etc/mtab

List of currently mounted filesystems. Initially set up by the bootup scripts, and updated automatically by the mount command. Used when a list of mounted filesystems is needed, e.g., by the df command. This file is sometimes a symbolic link to /proc/mounts.

/etc/networks

List of networks that the system is currently located on. For example, 192.168.0.0.
 

/etc/ppp/

The place where your dial-up configuration files are placed. More than likely to be created by the text menu based pppconfig or other GUI based ppp configuration utilities such as kppp or gnome-ppp.

/etc/pam.conf

Most programs use a file under the /etc/pam.d/ directory to setup their PAM service modules. This file is and can be used, but is not recommended.
 

/etc/passwd

This is the 'old' password file, It is kept for compatibility and contains the user database, with fields giving the username, real name, home directory, encrypted password, and other information about each user. The format is documented in the passwd man(ual) page.
 

/etc/profile

Files and commands to be executed at login or startup time by the Bourne or C shells. These allow the system administrator to set global defaults for all users.

/etc/profile.d

Shells scripts to be executed upon login to the Bourne or C shells. These scripts are normally called from the /etc/profile file.

/etc/protocols

Protocols definitions file. It describes the various DARPA Internet protocols that are available from the TCP/IP subsystem. It should be consulted instead of using the numbers in the ARPA include files or resorting to guesstimation. This file should be left untouched since changes could result in incorrect IP packages.

/etc/pcmcia

Configuration files for PCMCIA devices. Generally only useful to laptop users.
 

/etc/rc.boot or /etc/rc?.d

These directories contain all the files necessary to control system services and configure runlevels. A skeleton file is provided in /etc/init.d/skeleton

/etc/rcS.d

The scripts in this directory are executed once when booting the system, even when booting directly into single user mode. The files are all symbolic links, the real files are located in /etc/init.d/. For a more general discussion of this technique, see /etc/init.d/README.

/etc/resolv.conf

Configuration of how DNS is to occur is defined in this file. It tells the name resolver libraries where they need to go to find information not found in the /etc/hosts file. This always has at least one nameserver line, but preferably three. The resolver uses each in turn. More than the first three can be included but anything beyond the first three will be ignored. Two lines that appear in the /etc/resolv.conf file are domain and search. Both of these are mutually exclusive options, and where both show up, the last one wins. Other entries beyond the three discussed here are listed in the man pages but aren't often used.
 

/etc/samba

Samba configuration files. A 'LanManager' like file and printer server for Unix. The Samba software suite is a collection of programs that implements the SMB protocol for unix systems, allowing you to serve files and printers to Windows, NT, OS/2 and DOS clients. This protocol is sometimes also referred to as the LanManager or NetBIOS protocol.

/etc/sane.d

Sane configuration files. SANE stands for "Scanner Access Now Easy" and is an application programming interface (API) that provides standardized access to any raster image scanner hardware (flatbed scanner, hand-held scanner, video- and still-cameras, frame-grabbers, etc.). The SANE API is public domain and its discussion and development is open to everybody. The current source code is written for UNIX (including GNU/Linux) and is available under the GNU General Public License (the SANE API is available to proprietary applications and backends as well, however).

SANE is a universal scanner interface. The value of such a universal interface is that it allows writing just one driver per image acquisition device rather than one driver for each device and application. So, if you have three applications and four devices, traditionally you'd have had to write 12 different programs. With SANE, this number is reduced to seven: the three applications plus the four drivers. Of course, the savings get even bigger as more and more drivers and/or applications are added.

Not only does SANE reduce development time and code duplication, it also raises the level at which applications can work. As such, it will enable applications that were previously unheard of in the UNIX world. While SANE is primarily targeted at a UNIX environment, the standard has been carefully designed to make it possible to implement the API on virtually any hardware or operating system.

While SANE is an acronym for “Scanner Access Now Easy'' the hope is of course that SANE is indeed sane in the sense that it will allow easy implementation of the API while accommodating all features required by today's scanner hardware and applications. Specifically, SANE should be broad enough to accommodate devices such as scanners, digital still and video cameras, as well as virtual devices like image file filters.

If you're familiar with TWAIN, you may wonder why there is a need for SANE. Simply put, TWAIN does not separate the user-interface from the driver of a device. This, unfortunately, makes it difficult, if not impossible, to provide network transparent access to image acquisition devices (which is useful if you have a LAN full of machines, but scanners connected to only one or two machines; it's obviously also useful for remote-controlled cameras and such). It also means that any particular TWAIN driver is pretty much married to a particular GUI API (be it Win32 or the Mac API). In contrast, SANE cleanly separates device controls from their representation in a user-interface. As a result, SANE has no difficulty supporting command-line driven interfaces or network-transparent scanning. For these reasons, it is unlikely that there will ever be a SANE backend that can talk to a TWAIN driver. The converse is no problem though: it would be pretty straight forward to access SANE devices through a TWAIN source. In summary, if TWAIN had been just a little better designed, there would have been no reason for SANE to exist, but things being the way they are, TWAIN simply isn't SANE.

/etc/securetty
 

/etc/sudoers

Sudoers file. This file must be edited with the 'visudo' command as root. The sudo command allows an authenticated user to execute an authorized command as root. Both the effective UID and GID are set to 0 (you are basically root). It determines which users are authorized and which commands they are authorized to use. Configuration of this command is via this file.

/etc/shadow

Shadow password file on systems with shadow password software installed (PAMs). Shadow passwords move the encrypted password from /etc/passwd into /etc/shadow; the latter is not readable by anyone except root. This makes it more difficult to crack passwords.
 

/etc/security

Essential to security. This subdirectory allows administrators to impose quota limits, access limits and also to configure PAM environments.

/etc/serial.conf

Serial port configuration. Changeable parameters include speed, baud rate, port, irq and type.

/etc/services

A definition of the networks, services and the associated port for each protocol that are available on this system. For example, web services (http) are assigned to port 80 by default. # /etc/services: # $Id: etc.xml,v 1.10 2004/02/03 21:42:57 binh Exp $ # # Network services, Internet style # # Note that it is presently the policy of IANA to assign a single # well-known port number for both TCP and UDP; hence, most entries # here have two entries even if the protocol doesn't support UDP # operations. Updated from RFC 1700, “Assigned Numbers'' (October # 1994). Not all ports are included, only the more common ones. echo 7/tcp echo 7/udp discard 9/tcp sink null discard 9/udp sink null systat 11/tcp users daytime 13/tcp daytime 13/udp netstat 15/tcp qotd 17/tcp quote msp 18/tcp # message send protocol msp 18/udp # message send protocol chargen 19/tcp ttytst source chargen 19/udp ttytst source ftp-data 20/tcp ftp 21/tcp fsp 21/udp fspd ssh 22/tcp # SSH Remote Login Protocol ssh 22/udp # SSH Remote Login Protocol telnet 23/tcp # 24 – private smtp 25/tcp mail # 26 – unassigned time 37/tcp timserver time 37/udp timserver rlp 39/udp resource # resource location nameserver 42/tcp name # IEN 116 whois 43/tcp nicname re-mail-ck 50/tcp # Remote Mail Checking Protocol re-mail-ck 50/udp # Remote Mail Checking Protocol domain 53/tcp nameserver # name-domain server domain 53/udp nameserver netbios-ns 137/tcp # NETBIOS Name Service netbios-ns 137/udp netbios-dgm 138/tcp # NETBIOS Datagram Service netbios-dgm 138/udp netbios-ssn 139/tcp # NETBIOS session service netbios-ssn 139/udp x11 6000/tcp x11-0 # X windows system x11 6000/udp x11-0 # X windows system

/etc/shells

Lists trusted shells.
 

/etc/sysconfig/

This directory contains configuration files and subdirectories for the setup of system configuration specifics and for the boot process, like 'clock', which sets the timezone, or 'keyboard' which controls the keyboard map. The contents may vary drastically depending on which distribution and what utilities you have installed. For example, on a Redhat or Mandrake based system it is possible to alter an endless array of attributes from the default desktop to whether DMA should be enabled for your IDE devices. On our Debian reference system though this folder is almost expedient containing only two files hwconf and soundcard which are both configured by the Redhat utilities hwconf and sndconfig respectively.

/etc/slip

Configuration files for the setup and operation of SLIP (serial line IP) interface. Generally unused nowadays. This protocol has been superceded by the faster and more efficient PPP protocol.

/etc/screenrc
 

/etc/ssh

'ssh' configuration files. 'ssh' is a secure rlogin/rsh/rcp replacement (OpenSSH). This is the portable version of OpenSSH, a free implementation of the Secure Shell protocol as specified by the IETF secsh working group. 'ssh' (Secure Shell) is a program for logging into a remote machine and for executing commands on a remote machine. It provides secure encrypted communications between two untrusted hosts over an insecure network. X11 connections and arbitrary TCP/IP ports can also be forwarded over the secure channel. It is intended as a replacement for rlogin, rsh and rcp, and can be used to provide applications with a secure communication channel. It should be noted that in some countries, particularly Iraq, and Pakistan, it may be illegal to use any encryption at all without a special permit.

/etc/syslog.conf

Lists where log files should go, what messages are written to them and the level of verbosity. It is also now possible to filter based on message content, message integrity, message encryption (near future), portability and better network forwarding.
 

/etc/timezone

local timezone.

/etc/updatedb.conf

Sets environment variables that are used by updatedb which therefore configures the database for 'locate', a utility that locates a pattern in a database of filenames and returns the filenames that match.
 

/etc/vga

The configuration file for the svgalib is stored in this directory. svgalib provides graphics capabilities to programs running on the system console, without going through the X Window System. It uses direct access to the video hardware to provide low-level access to the standard VGA and SVGA graphics modes. It only works with some video hardware; so use with caution.

/etc/vim

Contains configuration files for both vim and its X based counterpart gvim. A wide range of options can be accessed though these two files such as automatic indentation, syntax highlighting, etc….

/etc/xinetd.d/

The original 'inetd' daemon has now been superceded by the much improved 'xinetd'. 'inetd' should be run at boot time by /etc/init.d/inetd (or /etc/rc.local on some systems). It then listens for connections on certain Internet sockets. When a connection is found on one of its sockets, it decides what service the socket corresponds to, and invokes a program to service the request. After the program is finished, it continues to listen on the socket (except in some cases). Essentially, inetd allows running one daemon to invoke several others, reducing load on the system. Services controlled via xinetd put their configuration files here.