MyComputingArt

Hard disk suspension in an Antec SLK3000B

The main problem of the Antec SLK3000B case is it converts hard disk vibrations to noise, and this is the most annoying noise coming from my pc when the fans are set at the lowest speed. In the SLK3000B the hard disks lay in a cage with grommets that are supposed to dampen the vibrations of the 7200 and more rpm hard disks.
The trend spreading amongst silencing modders is to suspend the hard disks in the air to avoid contact between the case and the hard disks.

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Posted by: z24 | Sun, Aug 12 2012 | Category: /hardware | Permanent link | home
Tagged as: case, cooling, disk suspension, hardware, silencing

Accessing and changing the registry from outside Windows

Problem: I got myself locked out of my pc
Solution: access the registry from outside Windows and change the account lockout settings

After enabling Remote Desktop access to access from my notebook to my pc through my wireless LAN, I was playing around with account locking settings to defend from possible brute force attacks coming through the WLAN (supposing the attacker cracked the WPA-PSK password): I set the lock so that after two failed attempts to login the account would be locked until the administrator (me) unlocks it manually.
I wanted to adopt such a security measure for RDP access only, but unfortunately the account lockout policy is valid for any login attempt, being it local or remote.
Then, as a slight security measure, I also disabled the administrator user (my user is already an administrator and an attacker should also find a valid username).
I mistyped the password twice and I got myself stuck: administrator and guest were disabled and my account was locked.
After rebooting, at the logon screen there were no more users, so that the "To begin, click your username" sentence on the left sounded like a joke, having absolutely nothing on the right.

The solution was obvious:

try to access and change the registry from linux (I have dual boot)
manually restore a previous version of the registry

I solved using Offline NTPassword & Registry Editor, an offline regitry editor on a boot disk; I made the floppy, rebooted and then I started looking in the registry the affecting keys, but it was not necessary: there's a feature to edit the accounts, and that allowed me to enable the administrator.

I also found dumphive, a useful program to dump the registry hives to text files.

Instead on www.beginningtoseethelight.org there's plenty of Windows NT, 2000 and XP low level settings and hacks, I would say "all about the registry": for instance, where and how users and passwords, including account statistics and policies, are stored and encoded in the SAM hive of the registry, and a schematic explanation of the registry structure; and don't miss the other sections of the site, they're enlightening too.
About the second option, there's a Microsoft article that explains how to manually restore the registry to a previous state.

Posted by: Z24 | Wed, May 04 2011 | Category: /windows | Permanent link | home
Tagged as: system recover, windows, xp

Ubuntu 6.06 Dapper Drake 32 bit on Windows XP with Qemu, Qemu networking, Linux applications in Windows using X server

With this little tutorial I will explain what I did to:

install Qemu and its accelerator kqemu
create an image file where the guest operating system will be installed
install and then run Ubuntu 6.06 Dapper Drake 32 bit as a guest operating system
connect from Windows host to Linux guest with qemu redir option
connect from Windows host to Linux guest and connect from Linux guest to Windows host using tap driver
run seamless Linux applications in the Windows graphical environment using an X server

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Posted by: Z24 | Wed, May 04 2011 | Category: /windows | Permanent link | home
Tagged as: client-server, linux, qemu, virtualization, windows, xp

Recover "Logical sector size is 0" with dd

A few hours ago while I was using my pc suddenly Windows froze completely (mouse was stuck and Ctrl+Alt+Del did nothing). It's not astonishing but I was quite surprised because such a freeze never happened since I began using Windows XP on my new pc.
The problem appeared at the reboot: grub, the bootloader on /dev/sda, showed this error message:

13 : Invalid or unsupported executable format

I have a dual boot configuration with Windows XP booting from a EIDE disk and Ubuntu booting from a SATA disk, so I entered Ubuntu, successfully; /dev/hda1 (the Windows partition) was not mounted while /dev/hda5 and /dev/hda6 were; attempting to mount it resulted in

Special device /dev/hda1 does not exist

At reboot I started Windows XP Recovery Console from the Windows CD and tried CHKDSK.EXE, and this was the outcome:

The volume appears to contain one or more unrecoverable problems

I booted again linux to launch fsck and see it fail:

Logical sector size is zero.

Then I found the solution in ubuntu forum:

root@am2:/home/z24# dd if=/dev/hda1 of=/defmedia/bkup_fat32_hda1.img bs=512 count=2048000 conv=noerror,sync
2048000+0 records in
2048000+0 records out
1048576000 bytes (1.0 GB) copied, 43.61 seconds, 24.0 MB/s

root@am2:/home/z24# dd if=/defmedia/bkup_fat32_hda1.img of=/home/z24/sector6.bin bs=512 count=1 skip=6 conv=noerror,sync
1+0 records in
1+0 records out
512 bytes (512 B) copied, 0.011544 seconds, 44.4 kB/s

root@am2:/home/z24# dd if=/home/z24/sector6.bin of=/dev/hda1 bs=512 count=1 conv=noerror,sync,notrunc
1+0 records in
1+0 records out
512 bytes (512 B) copied, 0.030644 seconds, 16.7 kB/s

Explanation:

the first dd makes a backup of the first gigabyte of the Windows partition: I copied 1 GB only because I didn't have enough space on a ext2fs to backup all the 28 GB of /dev/hda1.
the second dd extracts the sixth sector to a temporary file: as reported by Microsoft KB247575, "The backup FAT32 boot sector is located at sector 6 of the logical drive".
the third dd copies the extracted sector 6 to sector 0 of /dev/hda1.

In the original post the partition that was just backupped with dd was also checked with losetup and mount. Thanks a lot to the ubuntuforums user Onlymee for his post!

Update 13.09.2008

The same problem happened again today and gave me the opportunity to complete the series of error messages :)
The first, at boot time, was the same:

grub: 13 : Invalid or unsupported executable format

Mounting the partition (mount -t vfat /dev/sda1 /mnt):

mount: wrong fs type, bad option, bad superblock on /dev/sda1, missing codepage or other error

dmesg | grep sda1

VFS: Can't find a valid FAT filesystem on dev sda1

But fdisk -l /dev/sda shows the partition table.
fsck.vfat /dev/sda1 (executed from Ubuntu 8.04 alternate cd)

Cluster size is zero

The solution was exactly the same: copy the sixth sector back to the first. And voilà, it booted.

Posted by: z24 | Wed, May 04 2011 | Category: /hardware | Permanent link | home
Tagged as: error, grub, hardware, linux, system recover

Mounting a second fan on the back of the case (Antec SLK3000B)

With the summer approaching, I am making some experiments trying to cool my pc as much as possible while keeping it quiet. Now, airflow in the case is made by 2 fans: the intake fan, a Papst 4412 F/2GLL, pulls air inside the case from the front, the exhaust fan, a Antec Tricool coming with the SLK3000B, pushes air out to the back; in addition, the psu fan pulls air from the top of the motherboard through the psu to the back.
Since I bought a second Papst 4412 F/2GLL, I tried positioning this fan in different locations to see which one conributes the best to the cooling. One of these is the back of the case, in the bottom, where there would be additional cards: it pushes air out of the case through the back slots.

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Posted by: z24 | Wed, May 04 2011 | Category: /hardware | Permanent link | home
Tagged as: case, cooling, fan, hardware, silencing

How to force Firefox to open in a new tab a link that tries to open a new window

Type about:config in the address bar, read the warning and confirm.
Then change the value of browser.link.open_newwindow.restriction to 0.
Done.

See mozillazine about:config FAQ for a detailed description of the variables and values.