Category: linux

Last night I was reading a data sheet about the ICH10 I/O Controller Hub (Section 13.7.5) and got a little more insight on the workings of the Reset Control Register (port 0xcf9).

Bits 1 and 3 determine the type of reset being requested and bit 2 initiates the reset.   When bit 2 (SYS_RST) transitions from 0 to 1 a reset is initiated as determined by the policy of bits 1 and 3.

Bit 1, System Reset (SYS_RST) determines a soft reset (0) or hard reset (1).
Bit 3, Full Reset (FULL_RST) if set to 1 causes a full power cycle.

On some systems, the ACPI FACP RESET_REG and RESET_VALUE are set 0xcf9 and 0x06 respectively which essentially triggers a hard system reset when doing a reboot using the reboot=acpi kernel option.

The kernel also has a reboot=pci option that will force a reset via the Reset Control Register and does this in three stages. First it sets bit 1 (SYS_RST=hard reset), waits 50 microseconds and then transitions SYS_RST from 0 to 1 to initiate the reset.

However, a full system reset can be initiated by also setting bit three by writing 0x0e to port 0xcf9.  I’ve noticed that some newer laptops on the market seem to be doing a full system reset on reboot, so I wonder if this is the mechanism they are using nowadays.

The beauty of Linux is that one can string a bunch of commands together to do this from user space:

echo -e ‘\xe’ | sudo dd of=/dev/port bs=1 seek=3321

..so make sure you data is sync’d before hand as this is destructive as power cycling the machine while it’s on.

From Canonical

From Bash Pocket Reference and Advanced Bash−Scripting Guide

When you’re working with variations of a file—like backups or different file types—it can get tedious typing out the same commands with small tweaks. Using the brace symbols ({}), you can easily perform batch operations on multiple versions of a file.

Say you want to rename just part of a filename. Instead of typing out mv /path/to/file.txt /path/to/file.xml, you could just run:

mv /path/to/file.{txt,xml}

This runs the command with the same arguments, only with the parts inside the brace changed—the first part corresponding to the first argument, the second part corresponding to the second argument.

The most common example of this is when you’re backing up a file that you’re making changes to. For example, if you are tweaking your rc.conf, you’ll want to make a backup in case the new one doesn’t work. So, to do so, you can just run:

sudo cp /etc/rc.conf{,-old}

Putting nothing before the comma will just append -old to the filename after copying it with cp. If your new file doesn’t work out and you want to restore the backed up file to its original location, you can just use:

sudo mv /etc/rc.conf{-old,}

Moving the comma to the other end of the brace will remove -old from the end of the file and restore it to its original name.

The braces can also work when moving or creating multiple files at once. For example, if you wanted to create three numbered directories, you could just run:

mkdir myfolder{1,2,3}

This will create three folders: myfolder1, myfolder2, and myfolder3.