Linux Format - UK (2019-12)

http://www.techradar.com/pro/linux December 2019 LXF257 13

ANSWERS

However, there is a much simpler

solution. It sounds like you have bought

this Pi and are looking for something to use

it for; this is not it. The simple solution is to

buy a USB OTG (On The Go) cable which

will enable you to connect a normal SD

card reader to your phone’s microUSB

port. It is also possible to get an OTG

card reader, avoiding the separate reader

and cable.

You may need to enable OTG in the

phone’s settings (matthew did let us know

his phone doesn’t support OTG. DOH!–ED)

in order to be able to mount the SD card,

then you can access its contents through

your preferred file manager and upload

them to your cloud service using the

phone’s wireless connection. If you really

want to involve the Pi in this process, leave

it at home running Nextcloud. You will have

your own private cloud service and all your

photos will be waiting for you at home

when you return.

Q

Slax on USB

I have a problem with Slax on a

USB drive. When this month’s Linux

Format arrived I decided to try running

Slax from a USB drive because I had

never tried to run an OS from USB. I put

the ISO onto a 1GB drive using:

$ sudo dd if=slax-32bit-9.9.1.iso of=/dev/

sdb

The code was written to the USB

drive. Then I altered the computer boot

sequence to read USB first. After putting

the USB into the computer, I started the

computer and I could see it reading the

USB first. However, Slax did not start.

To test the validity of the code, I

repeated the process with a DVD disk.

That did start Slax but took a long time

to do so. Next I reformatted the USB

drive and started again. But Slax would

not start the computer. Where am I

going wrong, please?

Bryan Mitchell

A

You cannot simply dump an ISO

filesystem for an optical drive onto a

USB stick, or hard drive, and boot from it.

The two types of media use different boot

processes, the main difference being that

on a USB stick or hard drive the system

expects to find a partition table, whereas

optical discs have none.

At this point readers will be shouting

“I can boot Ubuntu/Mint/whatever ISO

images from a USB stick”, and they are

correct, as there is a way to make an ISO

image bootable from a USB stick, using

what is known as a hybrid format ISO

image. The Slax ISO has not been

processed in this way, but it is easy enough

to do yourself. This applies to any bootable

ISO, not just Slax, so the first step is to

check whether the ISO is hybrid, using

fdisk. Open a terminal and run:

$ sudo fdisk -l /path/to/slax.iso

If all it shows is something like

Disk slax-64bit-9.11.0.iso: 264.86 MiB,

277708800 bytes, 542400 sectors

Units: sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes /

512 bytes

I/O size (minimum/optimal): 512 bytes /

512 bytes

then there is no partition table and the

image is not (yet) USB-bootable. If this is

followed by partition information, you can

dd the image to a USB stick. To add that

partition information, install the syslinux

package from your distro’s package

manager, then you can go back to your

terminal and run:

$ isohybrid /path/to/slax.iso

This modifies the ISO image by writing

partition information to an otherwise

unused area at the start of the image,

which means you have to copy the ISO file

from the DVD to your hard disk

beforehand. Running fdisk again should

now reveal some extra information – the

partition table – and you can now dd it to

your USB stick and boot from it.

Q

Binary chop

I need to feed a program the

ending part of a binary data file whose

first x bytes have to be ignored. Basically

I have to strip a binary data file of its

initial part and read it starting from an

offset value.

I have a hunch that a program like tail

or head should be used, but being a

newbie I can’t understand how to do this.

Could you please provide a command

Some distros have ISO images that

will boot fine from a USB stick. Others,

like Slax, need a little massaging first.

GET HELP NOW!

We’d love to try and answer any questions

you send to [email protected],

no matter what the level. We’ve all been

stuck before, so don’t be shy. However, we’re

only human (although many suspect Jonni

is a robot), so it’s important that you include

as much information as you can. If

something works on one distro but not

another, then tell us. If you get an error

message, please tell us the exact message

and precisely what you did to invoke it.

If you have, or suspect, a hardware

problem, let us know about the hardware.

Consider installing hardinfo or lshw. These

programs list the hardware on your

machine, so send us their output. If you’re

unwilling, or unable, to install these, run the

following commands in a root terminal and

send us the system.txt file too.

uname -a > system.txt

lspci >> system.txt

lspci -vv >> system.txt

line telling me how to feed (using piping,

I suppose) the file BinaryData.bin

starting from an offset value OFFSET, as

if it was the first byte, to the program

Program?

Grabby

A

You can do this with tail (you would

use head to output the first part of

the file). You can also do it with dd and

split. There are probably others too, but we

will just look at how to use these three.

Using tail:

$ tail --bytes=+X BinaryData.bin | <program>

Tail (and head) normally work in a line-

based mode as they are usually used on

1112Decmbr rb2c09Gob0Gtauni December 2019 LXF257 13

ANSWERS

However, there is a much simpler
solution. It sounds like you have bought
this Pi and are looking for something to use
it for; this is not it. The simple solution is to
buy a USB OTG (On The Go) cable which
will enable you to connect a normal SD
card reader to your phone’s microUSB
port. It is also possible to get an OTG
card reader, avoiding the separate reader
and cable.
You may need to enable OTG in the
phone’s settings (matthew did let us know
his phone doesn’t support OTG. DOH!–ED)
in order to be able to mount the SD card,
then you can access its contents through
your preferred file manager and upload
them to your cloud service using the
phone’s wireless connection. If you really
want to involve the Pi in this process, leave
it at home running Nextcloud. You will have
your own private cloud service and all your
photos will be waiting for you at home
whenyoureturn.

Q

Slax on USB
I have a problem with Slax on a
USB drive. When this month’s Linux
Format arrived I decided to try running
Slax from a USB drive because I had
never tried to run an OS from USB. I put
the ISO onto a 1GB drive using:
$ sudo dd if=slax-32bit-9.9.1.iso of=/dev/
sdb
The code was written to the USB
drive. Then I altered the computer boot
sequence to read USB first. After putting
the USB into the computer, I started the
computer and I could see it reading the
USB first. However, Slax did not start.
To test the validity of the code, I
repeated the process with a DVD disk.
That did start Slax but took a long time
to do so. Next I reformatted the USB
drive and started again. But Slax would
not start the computer. Where am I
going wrong, please?
BryanMitchell

A

You cannot simply dump an ISO
filesystem for an optical drive onto a
USB stick, or hard drive, and boot from it.
The two types of media use different boot
processes, the main difference being that
on a USB stick or hard drive the system
expects to find a partition table, whereas
optical discs have none.
At this point readers will be shouting
“I can boot Ubuntu/Mint/whatever ISO
images from a USB stick”, and they are
correct, as there is a way to make an ISO
image bootable from a USB stick, using
what is known as a hybrid format ISO
image. The Slax ISO has not been
processed in this way, but it is easy enough
to do yourself. This applies to any bootable

ISO, not just Slax, so the first step is to

check whether the ISO is hybrid, using

fdisk. Open a terminal and run:

$ sudo fdisk -l /path/to/slax.iso

If all it shows is something like

Disk slax-64bit-9.11.0.iso: 264.86 MiB,

277708800 bytes, 542400 sectors

Units: sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes /

512 bytes

I/O size (minimum/optimal): 512 bytes /

512 bytes

then there is no partition table and the

image is not (yet) USB-bootable. If this is

followed by partition information, you can

dd the image to a USB stick. To add that

partition information, install the syslinux

package from your distro’s package

manager, then you can go back to your

terminal and run:

$ isohybrid /path/to/slax.iso

This modifies the ISO image by writing

partition information to an otherwise

unused area at the start of the image,

which means you have to copy the ISO file

from the DVD to your hard disk

beforehand. Running fdisk again should

now reveal some extra information – the

partition table – and you can now dd it to

yourUSBstickandbootfromit.

Q

Binary chop

I need to feed a program the

ending part of a binary data file whose

first x bytes have to be ignored. Basically

I have to strip a binary data file of its

initial part and read it starting from an

offset value.

I have a hunch that a program like tail

or head should be used, but being a

newbie I can’t understand how to do this.

Could you please provide a command

Some distros have ISO images that

will boot fine from a USB stick. Others,

like Slax, need a little massaging first.

GETHELPNOW!

We’d love to try and answer any questions

you send to [email protected],

no matter what the level. We’ve all been

stuck before, so don’t be shy. However, we’re

only human (although many suspect Jonni

is a robot), so it’s important that you include

as much information as you can. If

something works on one distro but not

another, then tell us. If you get an error

message, please tell us the exact message

and precisely what you did to invoke it.

If you have, or suspect, a hardware

problem, let us know about the hardware.

Consider installing hardinfo or lshw. These

programs list the hardware on your

machine, so send us their output. If you’re

unwilling, or unable, to install these, run the

following commands in a root terminal and

send us the system.txt file too.

uname -a > system.txt

lspci >> system.txt

lspci -vv >> system.txt

line telling me how to feed (using piping,

I suppose) the file BinaryData.bin

starting from an offset value OFFSET, as

if it was the first byte, to the program

Program?

Grabby

A

You can do this with tail (you would

use head to output the first part of

the file). You can also do it with dd and

split. There are probably others too, but we

will just look at how to use these three.

Using tail:

$ tail --bytes=+X BinaryData.bin | <program>

Tail (and head) normally work in a line-

based mode as they are usually used on