Tuesday, July 27, 2010

Linux File Formats

The syntax of each line in this file is:minute, hour, day of month, Month, day of week, (user name), command
Columns are: device file to mount, directory to mount on, filesystem type, options, backup frequency, and fsck pass number (To specify the order in which filesystems should be checked on boot; 0 means no check.) The noauto option stops this mount from being done automatically on boot. Below is a detailed list of what is on each column.
  1. The name of the device such as "/dev/hda1"
  2. The mount point. Use "/" for root. Other typical mount points are "/dos" for DOS, "swap" or "none" for the swap partition, and "/mnt/floppy" for "/dev/fd0" (the floppy drive).
  3. The type of filesystem. They are: mini, ext, ext2(linux native), xiafs, msdos, hpfs, ntfs, fat32, iso9660(CD-ROM), NFS, swap (for swap space).
  4. The mount options for use with the filesystem. Each filesystem type has different mount options. Read the mount man page to see possible options. ro= read only, user- allows normal users to mount the device.
  5. The frequency the filesystem needs to be dumped (backed up) by the dump command. For ext2, normally make it 1, for others make it 0. 0 or nothing means it is not dumped. If 1, it is backed up during a system backup.
  6. A number telling the order in which the filesystems should be checked at reboot time by the fsck program. Your root should be 1, others are in ascending order or 0 to not be checked.
Sets up host address information for local use. The format is:
IPaddress name1 name2...
Sets the services under the inetd daemon. The fields of this file are:
  1. service name
  2. socket type
  3. protocol
  4. wait or nowait
  5. user
  6. server program name
  7. server program command line arguments

Sets the init configuration. An entry in the inittab file has the following format:
Tells LILO how to boot The lilo.conf file below is for a system which has a Linux root partition on /dev/hda1 and a MS-DOS partition on /dev/hda2. See the "How Linux Works" guide and the "Linux User's Guidel" for more information.

boot = /dev/hda
# Tell LILO to install the boot loader on the /dev/hda disk boot record
vga = normal
# Set a normal video mode
delay = 60
# The time in tenths of seconds to press to get the LILO prompt

# Equivalent would be "prompt" on one line, and "timeout=60" on

# another line.
# Sets the default boot to DOS, Without this line, the default is the first stanza
install = /boot/boot.b
# The file containing the boot sector to use
# Have LILO perform some optimization.
map = /boot/map
#Specifies the map file LILO creates when installed

# Section for Linux root partition on /dev/hda2.
image = /vmlinuz
# Location of kernel
label = linux
# Name of the OS that is displayed in the LILO boot menu
root = /dev/hda1
# Location of root partition, if this isn't here the kernel image must have

# this set using the rdev command
# Mount read only on startup, Can also be set by rdev

# Section for MSDOS partition on /dev/hda1.
other = /dev/hda2
# Location of partition
table = /dev/hda
# Location of partition table for /dev/hda2
label = msdos
# Name of OS (for boot menu)
if the command "vga= ask" is given, LILO will prompt the user for a video mode at boot time.
The file has one line per username, and is divided into seven colon-delimited fields:
  1. Username.
  2. Password, in an encrypted form.
  3. Numeric user id.
  4. Numeric group id.
  5. Full name or other description of account. This is called gecos.
  6. The user's home directory.
  7. The user's login shell (program to run at login).
The format is explained in more detail on the passwd manual page.
The main XFree86 configuration file. Type "man XF86Config"
  • The first section is "Files"
    Sets the path to the X11R6 RGB color database
    Sets the path to a directory containing X11 fonts
  • The second section is "ServerFlags", all lines are commented out
  • The third section is "Keyboard"
  • The fourth section is "Pointer"
    Specifies the mouse protocol
    Specifies the device file by which the mouse can be accessed.
  • The fifth section is "Monitor" which specifies the characteristics of your monitor
    Specifies resolution modes for your monitor
    The file, VideoModes.doc describes in detail how to determine the ModeLine values for each resolution mode. Two files, modeDB.txt and Monitors,may have ModeLine information for your monitor. They are located in /usr/X11R6/lib/X11/doc.
  • The sixth section is "Screen" describing the video/monitor card configuration for the particular server.
    The Driver line specifies the X server that you will be using. Valid Driver values are:_ Accel: For the XF86 S3, XF86 Mach32, XF86 Mach8, XF86 8514,
    XF86 P9000, XF86 AGX,and XF86 W32 servers;
    _ SVGA: For the XF86 SVGA server;
    _ VGA16: For the XF86 VGA16 server;
    _ VGA2: For the XF86 Mono server;
    _ Mono: For the non-VGA monochrome drivers in the XF86 Mono and XF86 VGA16 servers.
    Be sure that /usr/X11R6/bin/X is a symbolic link to this server.
    The Device line specifies the Identifier of the Device section that corresponds to the video card to use for this server. Above, we created a Device section with the line Identifier "#9 GXE 64"
    Therefore, we use "#9 GXE 64" on the Device line here. Similarly, the Monitor line specifies the name of the Monitor section to be used with this server. Here, "CTX 5468 NI" is the Identifier used in the Monitor section described above.
  • Subsection "Display" defines several properties of the XFree86 server corre-sponding to your monitor/video card combination. The XF86Config file describes all of these options in detail. Most of them are not necessary to get the system working.
    The options that you should know about are:
    • _ Depth. Defines the number of color planes; that is, the number of bits per pixel. Usually, Depth is set to 16. For the VGA16 server, you would use a depth of 4, and for the monochrome server a depth of 1. If you use an accelerated video card with enough memory to support more bits per pixel, you can set Depth to 24, or 32.
    • _ Modes. This is the list of mode names that have been defined using the ModeLine directive(s) in the Monitor section. In the above section, we used ModeLines named "1024x768", "800x600",and "640x48"0. Therefore, we use a Modes line ofModes "1024x768" "800x600" "640x480"
      The first mode listed on this line is the default when XFree86 starts. After XFree86 is running, you can switch between the modes listed here using the keys Ctrl - Alt –Numeric + and Ctrl - Alt - Numeric - .
      It might be best, when you initially configure XFree86, to use lower resolution video modes like 640x480, which tend to work with most systems. Once you have the basic configuration working, you can modify XF86Config to support higher resolutions.
    • _ Virtual. Set the virtual desktop size. XFree86 can use additional memory on your video card to extend the size of the desktop. When you move the mouse pointer to the edge of the display, the desktop scrolls, bringing the additional space into view. Even if you run the server at a lower video resolution like 800x600, you can set Virtual to the total resolution that your video card can support. A 1-megabyte video card can support 1024x768 at a depth of 8 bits per pixel; a 2-megabyte card 1280x1024 at depth 8, or 1024x768 at depth 16. Of course, the entire area will not be visible at once, but it can still be used. The Virtual feature is rather limited. If you want to use a true virtual desktop, fvwm and similar window managers allow you to have large, virtual desktops by hiding windows and using other techniques, instead of storing the entire desktop in video memory. See the manual pages for fvwm for more details about this. Some Linux systems use fvwm by default.
    • _ ViewPort. If you are using the Virtual option that is described above, ViewPort sets the coordinates of the upper-left-hand corner of the virtual desktop when XFree86 starts up. Virtual 0 is often used. If this is unspecified, then the desktop is centered on the virtual desktop display, which may be undesirable to you.