xorg Xinerama / Dual Screen 
The hard work with xinerama / dual screen was:

* set the monitor sync/refresh rate (it won't start without for an old crt not supporting ddc)

* set Option "NoAccel" "true" (screen distortions)

* touchpad only works with dual screen

* instabilities with two different cards (via / ati - resolved by using only ati card that has two VGA connectors)

Testing with: #> X -config /absolutepath/xorg.conf -verbose

xinerama xorg.conf:
Section "Files"
FontPath "/usr/share/X11/fonts/misc"
FontPath "/usr/share/X11/fonts/75dpi/:unscaled"
FontPath "/usr/share/X11/fonts/75dpi"
EndSection

Section "Module"
Load "i2c"
Load "bitmap"
Load "ddc"
Load "dri"
Load "extmod"
SubSection "extmod"
Option "omit xfree86-dga"
EndSubSection
Load "int10"
Load "vbe"
Load "dbe"
EndSection

Section "InputDevice"
Identifier "Generic Keyboard"
Driver "kbd"
Option "CoreKeyboard"
Option "XkbRules" "xorg"
Option "XkbModel" "pc105"
Option "XkbLayout" "ru,us"
Option "XkbOptions" "grp:caps_toggle"
EndSection

Section "InputDevice"
Identifier "Generic Mouse"
Driver "mouse"
Option "CorePointer"
Option "Device" "/dev/input/mice"
Option "Protocol" "ExplorerPS/2"
Option "ZAxisMapping" "4 5"
Option "Emulate3Buttons" "true"
EndSection

Section "Device"
Identifier "dev0"
Driver "via"
BusID "PCI:1:0:0"
Screen 0
EndSection

Section "Device"
Identifier "dev1"
Driver "mga"
BusID "PCI:0:20:0"
Screen 1
EndSection

Section "Monitor"
Identifier "monitor0"
Option "DPMS"
EndSection

Section "Monitor"
Identifier "monitor1"
Option "DPMS"
HorizSync 28-50
VertRefresh 60-85
EndSection

Section "Screen"
Identifier "screen0"
Device "dev0"
Monitor "monitor0"
DefaultDepth 16
SubSection "Display"
Depth 16
Modes "1024x768"
EndSubSection
EndSection

Section "Screen"
Identifier "screen1"
Device "dev1"
Monitor "monitor1"
DefaultDepth 16
SubSection "Display"
Depth 16
Modes "1024x768"
EndSubSection
EndSection

Section "ServerLayout"
Identifier "Default Layout"
InputDevice "Generic Keyboard"
InputDevice "Generic Mouse"
Screen "screen0"
Screen "screen1" RightOf "screen0"
EndSection

Section "DRI"
Mode 0666
EndSection

Section "ServerFlags"
Option "Xinerama" "on"
EndSection
dual head xorg.conf:
Section "ServerLayout"
Identifier "X.org Configured"
Screen 0 "Screen0" 0 0
Screen 1 "Screen1" RightOf "Screen0"
InputDevice "Mouse0" "CorePointer"
InputDevice "Keyboard0" "CoreKeyboard"
EndSection

Section "Files"
RgbPath "/etc/X11/rgb"
ModulePath "/usr/lib/xorg/modules"
FontPath "/usr/share/fonts/X11/misc"
FontPath "/usr/X11R6/lib/X11/fonts/misc"
FontPath "/usr/share/fonts/X11/cyrillic"
FontPath "/usr/share/fonts/X11/100dpi/:unscaled"
FontPath "/usr/share/fonts/X11/75dpi/:unscaled"
FontPath "/usr/share/fonts/X11/Type1"
FontPath "/usr/X11R6/lib/X11/fonts/Type1"
FontPath "/usr/share/fonts/X11/100dpi"
FontPath "/usr/share/fonts/X11/75dpi"
FontPath "/var/lib/defoma/x-ttcidfont-conf.d/dirs/TrueType"
EndSection

Section "Module"
Load "extmod"
Load "GLcore"
Load "dbe"
Load "dri"
EndSection

Section "InputDevice"
Identifier "Keyboard0"
Driver "kbd"
Option "CoreKeyboard"
Option "XkbRules" "xorg"
Option "XkbModel" "pc105"
Option "XkbLayout" "ru,us"
Option "XkbOptions" "grp:caps_toggle"
EndSection

Section "InputDevice"
Identifier "Mouse0"
Driver "mouse"
Option "Protocol" "auto"
Option "Device" "/dev/input/mice"
Option "ZAxisMapping" "4 5 6 7"
EndSection

Section "InputDevice"
Identifier "Mouse0"
Driver "mouse"
Option "Protocol" "auto"
Option "Device" "/dev/input/mice"
Option "ZAxisMapping" "4 5 6 7"
EndSection

Section "Monitor"
Identifier "Monitor0"
VendorName "PHL"
ModelName "PHILIPS 107E"
HorizSync 30.0 - 70.0
VertRefresh 50.0 - 160.0
Option "DPMS"
EndSection

Section "Monitor"
Identifier "Monitor1"
VendorName "Monitor Vendor"
ModelName "Monitor Model"
EndSection

Section "Device"
Option "NoAccel" "true"
Identifier "Card0"
Driver "ati"
VendorName "ATI Technologies Inc"
BoardName "Radeon RV100 QY [Radeon 7000/VE]"
BusID "PCI:0:20:0"
Screen 0
EndSection

Section "Device"
Option "NoAccel" "true"
Identifier "Card1"
Driver "ati"
VendorName "ATI Technologies Inc"
BoardName "Radeon RV100 QY [Radeon 7000/VE]"
BusID "PCI:0:20:0"
Screen 1
EndSection

Section "Screen"
Identifier "Screen0"
Device "Card0"
Monitor "Monitor0"
DefaultDepth 16
SubSection "Display"
Depth 16
Modes "1024x768"
EndSubSection
EndSection

Section "Screen"
Identifier "Screen1"
Device "Card1"
Monitor "Monitor1"
DefaultDepth 16
SubSection "Display"
Depth 16
Modes "1024x768"
EndSubSection
EndSection

Section "ServerFlags"
Option "AllowMouseOpenFail" "true"
Option "DontVTSwitch" "true"
Option "DontZap" "true"
Option "DontZoom" "true"
Option "BlankTime" "0"
Option "StandbyTime" "0"
Option "SuspendTime" "0"
Option "OffTime" "0"
EndSection


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xorg ati ES1000 with DRI 
xorg ati/radeon video driver for ES1000 has DRI disabled :-(

As a workaraound i changed ChipID in xorg.conf to "0x515a"

suggested by http://ubuntuforums.org/showpost.php?p= ... stcount=15
Section "Device"
Identifier "ATI Technologies Inc ES1000"
Driver "ati"
ChipID 0x515a
EndSection


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udev - usb add / remove 
Because udev didn't know anything of idVendor or idProduct if you remove a device i use ENV{PRODUCT} to match for my unplugged device:


ACTION=="add", KERNEL=="event*", SUBSYSTEM=="input", \
SYSFS{idVendor}=="1234", SYSFS{idProduct}=="5678", \
SYMLINK+="input/myevent"

ACTION=="remove", SUBSYSTEM=="usb", \
ENV{PRODUCT}=="1234/5678/100", \
RUN+="/usr/bin/killall myprog"


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Permissions 

File Permissions


Action --- r-- -w- --x rw- r-x -wx rwx r-s
read - cat file no yes no no yes yes no yes
write - ls /tmp >> file no no yes no yes no yes yes
write - ls /tmp > file no no yes no yes no yes yes
remove file yes* yes* yes yes* yes yes* yes yes
executing a script no no no no no yes no yes yes**

yes*: These files gave a "rm: remove write-protected file 'filename'?" error. Saying "yes" removes these files. Also performing a "rm -rf" file removes the file without any warning. The ability to remove a file is controlled at the directory level.
yes**: execute a file with permission of owner or group

Directory Permissions


Action --- r-- -w- --x rw- r-x -wx rwx
cd into directory no no no yes no yes yes yes
ls directory no yes* no no yes* yes no yes
file name completion no yes no no yes yes no yes
create new file in dir. no no no no no no yes yes
read file in dir. no no no yes no yes yes yes
modify file in dir. no no no yes no yes yes yes
remove files no no no no no no yes yes
execute script no no no yes no yes yes yes

ls = yes* - Only the files are listed with error. No other file attributes are able to be listed. File name completion works in these cases as well.

t - Save text attribute (sticky bit): The user may delete or modify only those files in the directory that they own or have write permission for (/tmp).

s - Set group ID: files in that directory will have the group ownership as the directory, instead of than the group of the user that created the file


If you want to have full access to a directory with 2 different users in different groups make a new group and add both users.

addgroup newgroup
adduser user1 newgroup
adduser user2 newgroup

chown root:newgroup /directory
chmod 775 /directory

You do not need to use group ID (s-Flag).


You can use these commands to set 755 on directories and 644 on files

find -type f -exec chmod 644 {} \;
find -type d -exec chmod 755 {} \;


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Monitoring filesystem activity under Linux with block_dump 
sudo sysctl vm.block_dump=1

or

echo 1 > /proc/sys/vm/block_dump


tail -f /var/log/kern.log

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