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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sudo sysctl vm.block_dump=1

or

echo 1 > /proc/sys/vm/block_dump


tail -f /var/log/kern.log

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apt-get install ntfs-g3

/etc/group
+fuse:x:100:users

vol_id /dev/sda1

/etc/fstab

UUID=5EFC7B02FC7AD42D   /media/usbhdd ntfs-3g rw,users,uid=1000,guid=1000,umask=007,locale=de_AT.utf8,force   0    0

user can mount but not unmount
https://bugs.launchpad.net/ubuntu/+source/util-linux/+bug/71609/comments/7

wget http://launchpadlibrarian.net/7435949/u ... ount.patch

$ sudo apt-get update
$ sudo apt-get install build-essential
$ sudo apt-get build-dep mount
$ cd /tmp
$ apt-get source mount
$ cd util-linux-2.12r
$ ./debian/rules patch
$ patch -Np1 -i ../util-linux_user_mount.patch
$ ./configure
$ make lib
$ make -C mount
$ sudo chown root:root mount/umount
$ sudo chmod 4755 mount/umount
$ sudo mv mount/umount /bin

automount with udev:

06-usbsticks.rules

BUS=="usb", KERNEL=="sd*", SYSFS{serial}=="DEF10000CC2DAB6", NAME="%k", run+="/bin/mount /media/usbhdd"

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First computer where to redirect serial via TCP:

stty -F /dev/ttyS0 raw 9600 -echo
nc 192.168.0.1 1111  >/dev/ttyS0 </dev/ttyS0

Second computer receiving needs 2 serial's

stty -F /dev/ttyS0 raw 9600 -echo
stty -F /dev/ttyS1 raw 9600 -echo

nc -l -p 1111  >/dev/ttyS1 </dev/ttyS1

Now a programm can connect to /dev/ttyS0 and talks to out first computer.


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What i want from a raid1:

notiy if a disk fails

This is done by mdadm

boot degraded with only one disk

boot degraded does not work with ubuntu, because mdadm does not start a degraded raid

my workaround is to add a bootmenue entry in grub

title           Ubuntu, kernel 2.6.20-16-generic (raid defect)
root            (hd0,1)
kernel          /boot/vmlinuz-2.6.20-16-generic root=/dev/md1 ro raid_degraded
initrd          /boot/initrd.img-2.6.20-16-generic

and make an initrd (update-innitramfs -u) with /etc/initramfs-tools/scripts/init-premount/raid_degraded

#!/bin/sh

set -eu

PREREQ="udev"

prereqs()
{
        echo "$PREREQ"
}

case ${1:-} in
  prereqs)
    prereqs
    exit 0
    ;;
  *)
    . /scripts/functions
    ;;
esac

if [ -e /scripts/local-top/md ]; then
  log_warning_msg "old md initialisation script found, getting out of its way..."
  exit 1
fi

MDADM=$(command -v mdadm)
[ -x $MDADM ] || exit 0

if grep raid_degraded /proc/cmdline 2>/dev/null; then
  echo "MD_DEGRADED_ARGS=' '" >> /conf/md.conf
fi

exit 0

reported to ubuntu https://bugs.launchpad.net/ubuntu/+source/mdadm/+bug/120375

easy change disk if one disk fails

Threrefore i made a script doing partitioning, adding to raid and installing bootloader of the new disk

#!/bin/sh

if grep -q sda /proc/mdstat; then
  SRC_DISK=/dev/sda
  DST_DISK=/dev/sdb
else
  SRC_DISK=/dev/sdb
  DST_DISK=/dev/sda
fi

if ! sfdisk -l 2>/dev/null | grep -q $SRC_DISK; then
  echo $SRC_DISK not found
  exit 1
fi

if ! sfdisk -l 2>/dev/null | grep -q $DST_DISK; then
  echo $DST_DISK not found
  exit 1
fi

sfdisk -d $SRC_DISK | sfdisk $DST_DISK

mdadm /dev/md0 -a ${DST_DISK}1
mdadm /dev/md1 -a ${DST_DISK}2

cat /proc/mdstat

/usr/sbin/grub --batch --device-map=/dev/null <<EOF
device (hd0) $DST_DISK
root (hd0,1)
setup (hd0)
quit
EOF

exit 0

set uuid

ubuntu cannot boot if any uuid of any disk is different - solution set uuid:

mdadm --stop /dev/md0
madmd --assemble --verbose /dev/md0 /dev/hda1 /dev/hdb1 \
--update=uuid --uuid=xxxxxxxx:xxxxxxxx:xxxxxxxx:xxxxxxxx

newer versions of mdadm should be able to set uuid with --create

why is my raid1 so slow ?

Reading from my raid1 is as fast as a single sata disc:

hdparm -t /dev/sda1

/dev/sda1:
Timing buffered disk reads: 172 MB in 3.00 seconds = 57.27 MB/sec

hdparm -t /dev/sdb1

/dev/sdb1:
Timing buffered disk reads: 172 MB in 3.01 seconds = 57.20 MB/sec

hdparm -t /dev/md0

/dev/md0:
Timing buffered disk reads: 172 MB in 3.00 seconds = 57.29 MB/sec

i tried

* different motherboard with a different sata onboard controller but also the same results

* different ubuntu kernels: 2.6.17, 2.60.20 and from gutsy 2.6.22rc

* different images:
linux-image-2.6.20-16-generic 2.6.20-16.29
linux-image-2.6.20-16-lowlatency 2.6.20-16.29
linux-image-2.6.20-16-server 2.6.20-16.29

* also a raid1 with PATA Disks

reported to ubuntu https://bugs.launchpad.net/ubuntu/+source/mdadm/+bug/120378

can anybody explain me why?


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