XEmacs

To get rid of that annoying flashing when making a mistake in XEmacs:

M-x

set-variable

visible-bell

Value: nil

rpm -qpl packagename.rpm 

Renaming a large number of hidden files

The following command searches the current directory, recursively, for all hidden mp3 files, renaming them with a .blah suffix:

find . | egrep "/\..*mp3$" | while read e ; do mv "$e" "$e.blah"; done

Filenames can have spaces in them!

Prolong the life of your external USB drive

I have an external usb powered hard drive (one of these) connected to my server permanently, as part of my backup solution. To prolong the life of the disk, I spin it down after my overnight using the following command:

sdparm --command=stop /dev/sda

Note: your device might be mounted somewhere other than /dev/sda.

du

Lists the size of each directory/file in the current directory, and prints the sizes in human readable form:

du -h  --max-depth=1

psrinfo -v

lists the processors on a box

Vim

Setting a text file to unix format from DOS using vim:

:set ff=unix

To find out what format a files is:

:set ff?

RPM

To check the version of an installed rpm package, use the following command (this example looks at procps, which includes the ps command):

rpm -qa | grep procps

returns:

procps-2.0.7-11.21AS.4

awk

To print a timestamp (UTC) in a locale readable string do the following:

echo "1136211843" | awk '{print strftime("%c", $1)}'

prints:

Mon Jan  2 09:24:03 2006

• From the server (in my case a Powerbook) login into the linux box (but make sure you do this from an xterm session), using ssh (don't forget the -X): ssh -X linuxhostname. From the client (debian ssh prompt) run an app: xcalc, ddd etc. The window should appear on the server (Powerbook).

• From the server (in my case a Powerbook) login into the linux box (but make sure you this from an xterm session), using ssh (don't forget the -X): ssh -X linuxhostname. From the client (debian ssh prompt) run an app: xcalc, ddd etc. The window should appear on the server (Powerbook).

• Enable X11 forwarding on the client (in my case a debian distro). To do this reconfigure the sshd daemon, by changing the line X11Forwarding no in /etc/sshd_config to X11Forwarding yes. Then restart the sshd daemon: /etc/init.d/ssh restart.
• From the server (in my case a Powerbook) login into the linux box, using ssh (don't forget the -X): ssh -X linuxhostname. From the client (debian ssh prompt) run an app: xcalc, ddd etc. The window should appear on the server (Powerbook).

X11

I'm going to explain how I run x windows applications on my linux box (x client), displayed on my powerbook (x server), via X11 forwarding.

• I enabled X11 forwarding on the client (linux box, which btw is a debian install). To do this I reconfigured the sshd daemon, by changing the line X11Forwarding no in /etc/sshd_config to X11Forwarding yes. Then I restarted the sshd daemon: /etc/init.d/ssh restart.
• From the Powerbook I'm now able to login into the linux box, using -X to ssh: ssh -X linuxhostname. From linux I run the app of my choice, xcalc, ddd etc. The window pops up on my Powerbook.

Note, no need to use xhost +. The above solution is much more secure, both for client and server. All communication is authenticated and encrypted.

I created an image file from the corrupt disk using dd -> dd if=/dev/hdd of=imagename.img conv=noerror

I wanted to use an image file so that I could mess around without harming the data on the original corrupt disk.

I used testdisk to restore the image file's partition information (follow interactive menu system).

I was then able to mount the disk:

mount -t ntfs imagename.img /mnt/restoredntfs -o loop,offset=32256

Becasue I was mounting from an image file, I had to mount to a loop device. Thanks NASA, apparently.

According to testdisk my partition was situated at the 63rd cylinder -> 63 * 512 (assuming 512 bytes per block) = 32256 bytes.

Here goes...

Re-format external USB hard-drive

Motive: I wanted a backup solution that preserved file permissions when using rsync with the -a option.

My Western Digital usb drive had a vfat file system - which doesn't preserve file permissions.

This is what you'll need to do in order to convert to an ext3 file system:

When you plug the drive in check dmesg to find out which /dev device it's been mapped to. I found mine under /dev/sda1.

Then you'll need to partition the disk:

fdisk /dev/sda1

This will give you a command prompt interface. Type p to get a list of the current partitions.

I had 4 partitions, so I deleted them all using the d command.

Then create a your partition(s). I created 1 great big extended partition using the n command. It asks you a few questions about block sizes etc, I chose the defaults.

Then I typed w to write the partition data to the disk. Then I quit fdisk.

Then I created the filesystem:

mkfs.ext3 /dev/sda1

It asked me a few questions, I excepted all the defaults.

Then you're ready to mount the device:

mount /dev/sda1 /mnt/usbdrive

You'll have to create the folder /mnt/usbdrive yourself.

So that the disk gets mounted on reboot add the following line to /etc/fstab:

/dev/sda1 /mnt/usbdrive ext3 defaults 0 0

This also means you can simply type:

mount /dev/sda1

when mounting the disk from the command line.

dd if=/dev/urandom bs=1 count=128 | od -x