My disks and motherboard AFAIK were not hot-swap-compatible, but with some SCSI/SATA commands I was able to have a behavior very similar to that.

The first part of hot-swapping of course is the hardware – I used mobile racks for this purpose (something like this, but with a separate power switch), but you can simply unplug/plug your disks as well in case you are brave enough to do so. I think the mobile rack is far more safe (I have seen dead hard drives because of an improperly connected power connector).

The magic behind the hot-swapping is basically two SCSI commands: remove-single-device and add-single-device. With these you are able to tell the SCSI driver to release and to grab the disks again.

Be sure to unmount and to have the drive absolutely unused when you tell the driver to release the devices – it will not check if the drives are in use or not and your kernel may get confused about the disappearing drives. (Believe me, I tried :)

One more thing you need to know before using those commands: the host, channel, ID, LUN numbers of your drives. You can find these numbers easily, simply cat /proc/scsi/scsi, or ls /dev/disks/by-path/*.

Okay, enough of chattering, here is the Bash script (assuming you have a proper fstab entry for /mnt/swaptest, and the SCSI id of 0:0:1:0):


# unmount the file system
umount /mnt/swaptest || exit 1

echo "Swap was succesful."


Basically that’s all.

You might use mdadm to have a RAID-1 array, and have a copy of your system in a safe place, you can handle this easily as well:

# mark the disk as faulty for further remove from the array
mdadm /dev/md0 --fail /dev/sdb1

echo "Swap was succesful."


Of course these swaps can become more complex, using more disks, more RAID arrays, LVM volumes, but these are the basics – I assume you can figure out the rest :)

Oh, and the disclaimer: always have a backup of your data before trying these steps/commands, and I have read not all the drives are capable of doing such things, I personally do not think this can lead to hardware failure but I cannot be certain about it. Please try anything at your own risk.

This had been happening in console and under X too. I thought it might be a kernel-related issue, some kind of a timer or interrupt problem, maybe timeout.

All in all this turned out to be an APIC problem, and the machine is working perfectly with a noapic boot parameter.

This is the few lines of default initramfs script which is responsible for the behaviour described above:

/usr/share/initramfs-tools/scripts/local-top, from line 40:

# Make sure that we have a d-m path
vg=${vg#/dev/mapper/}
if [ "$vg" = "$1" ]; then
    return 1
fi


And it wouldn’t be enough to remove this check, because there is an another one for the format:

# Make sure that the device includes at least one dash
if [ "$(echo -n "$vg" | tr -d -)" = "$vg" ]; then
    return 1
fi


So you have to use the /dev/mapper/[vg_name]-[lv_name] format in GRUB’s menu.lst (or LILO’s lilo.conf) to boot from an LVM device. Unless you change the script above, of course :)

Source: https://code.ticketmaster.com/trac/browser/spine/trunk/lib/Spine/Plugin/SystemInfo.pm?rev=123#L225

ORA-19502: write error on file "/path/to/datafile.dbf", blockno 1669073 (blocksize=8192)
ORA-27072: File I/O error
Linux Error: 2: No such file or directory


ORA-19502: write error on file "/path/to/datafile.dbf", blockno 1831475 (blocksize=8192)
ORA-27072: File I/O error
Linux Error: 13: Permission denied


Long story short, these messages are exotic forms of the boring “Out of disk space” message.

And even if you have enough space for the restore, you may need ~+20% spare space. Don’t know exactly why, but that was needed in my case.

Oracle loves disk space and strange messages – lesson learned.

http://dev.kakaopor.hu/stuffs/bootsplash-3.1.6a-2.6.32.diff


sudo apt-get install apache2 apache2-mod-php4


Note: you can also have PHP5 installed as module and PHP4 as CGI, everything works the same way with swapping the versions in commands.

First of all you will need the php5-cgi package, and enable the Actions module:


sudo apt-get install php5-cgi
a2enmod actions


Add a ScriptAlias directive to your apache2.conf - if you have not done this already - like this:


ScriptAlias /cgi-bin /cgi-bin


Now create the /cgi-bin directory and symlink the php5-cgi binary to /cgi-bin/php5-cgi:


mkdir /cgi-bin
ln -s /usr/bin/php5-cgi /cgi-bin/php5-cgi


Finally in every VirtualHost where you need PHP5 support put these lines:


AddHandler php5-script .php
Action php5-script /cgi-bin/php5-cgi


All you have to do is restart the apache to take changes effect and you’re done.

First you have to shut down the MySQL server, next you need to start it in safe mode with no priviliges table loaded, update the password to a new one, and restart the database server just as before.

Step by step

1. Stop the database server:
$ sudo /etc/init.d/mysql stop
Stopping MySQL database server: mysqld.

2. Start in safe mode in the background (remember the PID! (29789 in my case as you can see)):
$ sudo mysqld_safe --skip-grant-tables &
[1] 29752
Starting mysqld daemon with databases from /var/lib/mysql
mysqld_safe[29789]: started

3. Now you can log in with the root user without password.
   $ mysql -u root
   Welcome to the MySQL monitor. Commands end with ; or \g.
   Your MySQL connection id is 39
   Server version: 5.0.51a-6 (Debian)

   Type 'help;' or '\h' for help. Type '\c' to clear the buffer.


4. Set a new password, flush the privileges, and quit:
   mysql> UPDATE mysql.user SET password=PASSWORD('your-new-password') WHERE User='root';
   Query OK, 0 rows affected (0.00 sec)
   Rows matched: 3 Changed: 3 Warnings: 0

   mysql> FLUSH PRIVILEGES;
   Query OK, 0 rows affected (0.00 sec)

   mysql> QUIT
Bye


5. Now shut down the mysqld_safe what you have used (kill its PID):
$ sudo kill 29752
STOPPING server from pid file /var/run/mysqld/mysqld.pid
mysqld_safe[29869]: ended
[1]+ Done sudo mysqld_safe --skip-grant-tables

6. And you can start your mysql server normally again:
$ sudo /etc/init.d/mysql start
Starting MySQL database server: mysqld.


Original source is the Locked Out of MySQL topic on CentOS.org.

You can download the new version from http://dev.kakaopor.hu/early-ssh/

• unlocking crypto devices – even your root can be an encrypted filesystem
• assembling/altering mdadm RAID arrays
• checking the root filesystem in read-write mode, taking action in case of errors
• and so on… (if you have anything you wish to see here, please share it in a comment)

You can download the source code, and debian package here:
http://dev.kakaopor.hu/early-ssh/