10:27 a.m.
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I've been volunteered to try to build a boot image for a Nitrogen 6x
Freescale SOM board using whatever OS I can make work. I chose
Fedora's ARM image since I'm more comfortable with using Fedora. In
the process of trying to using xzcat to dump the image to the microSD
card I noticed something strange. When I tried:
sudo xzcat Fedora-Minimal-armhfp-20-1-sda.raw.xz > /dev/sdb
I would get a 'Permission denied' error.
But when I ran the same command as root directly, it worked just fine.
I'm not sure I've ever encountered a situation where sudo wouldn't
work like this before. Is there a particular reason for this? Or is
this a bug? For the record, I changed nothing on the device between
attempts to xzcat the image.
- --
Mark Haney
Network/Systems Administrator
Practichem
W: (919) 714-8428
Fedora release 20 (Heisenbug) 3.13.6-200.fc20.x86_64
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2:04 p.m.
On Apr 1, 2014 9:47 AM, "Mark Haney" <mhaney(a)practichem.com> wrote:
...
Well, someone on the Fedora team needs to fix the documentation then.
But now it makes sense. I didn't stop to think about the redirect,
since my boss isn't giving me time to think. Apologies for spamming
the list.
- --
Mark Haney
...
You're referring to a wiki page, right? If so, you're part of the team!
IIRC, wiki access requires only a FAS account and the Contributor Agreement
( basically you're saying yes, you can edit my wiki edits, in this case .)
Seemingly minor contributions like this add up. Communicate for big
changes, of course, but if you find something like this where the issue is
clear, we all benefit.
--Pete
1:24 p.m.
On 04/01/2014 08:47 AM, Mark Haney issued this missive:
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On 04/01/14 11:33, Chris Adams wrote:
> Once upon a time, Mark Haney <mhaney(a)practichem.com> said:
>> sudo xzcat Fedora-Minimal-armhfp-20-1-sda.raw.xz > /dev/sdb
>>
>> I would get a 'Permission denied' error.
>
> That's because the "> /dev/sdb" was parsed and handled by your
> user shell (redirection is handled by the shell before running the
> command). sudo only got "xzcat
> Fedora-Minimal-armhfp-20-1-sda.raw.xz" as arguments. You should be
> able to quote what you want actually passed to sudo:
>
> sudo "xzcat Fedora-Minimal-armhfp-20-1-sda.raw.xz > /dev/sdb"
>
Well, someone on the Fedora team needs to fix the documentation then.
But now it makes sense. I didn't stop to think about the redirect,
since my boss isn't giving me time to think. Apologies for spamming
the list.
In general, if you're asking a command (in this case sudo) to run
another command (xzcat) and the argument list to that second command
contains spaces, then the entire command should be enclosed by quotes
to keep the shell from processing the arguments and command. Again, this
is standard operation.
This is not Fedora-specific. You'd hit the exact same thing on any Linux
system using the bash shell (I think the other shells would also do
this). Even BSD-derived systems (FreeBSD, Mac OSX) would do this.
----------------------------------------------------------------------
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- AIM/Skype: therps2 ICQ: 22643734 Yahoo: origrps2 -
- -
- Beware of programmers who carry screwdrivers -
----------------------------------------------------------------------
10:50 a.m.
On 1 April 2014 16:45, Markus Schönhaber
<fedora-users(a)list-post.mks-mail.de> wrote:
01.04.2014 17:33, Chris Adams:
> Once upon a time, Mark Haney <mhaney(a)practichem.com> said:
>> sudo xzcat Fedora-Minimal-armhfp-20-1-sda.raw.xz > /dev/sdb
>>
>> I would get a 'Permission denied' error.
>
> That's because the "> /dev/sdb" was parsed and handled by your user
> shell (redirection is handled by the shell before running the command).
> sudo only got "xzcat Fedora-Minimal-armhfp-20-1-sda.raw.xz" as
> arguments. You should be able to quote what you want actually passed to
> sudo:
>
> sudo "xzcat Fedora-Minimal-armhfp-20-1-sda.raw.xz > /dev/sdb"
... which would give a "command not found" error.
Something like
sudo bash -c "xzcat Fedora-Minimal-armhfp-20-1-sda.raw.xz > /dev/sdb"
should work though, since the shell which is started with elevated
rights is doing the output redirection now.
xzcat Fedora-Minimal-armhfp-20-1-sda.raw.xz | sudo dd of=/dev/sdb
Will also work, using sudo to grant write permissions, but not read permissions.
Less flexible than specifying a command to a sudoed shell command, but
also more granular control (if you can call dd as root granular).
--
imalone
http://ibmalone.blogspot.co.uk
10:47 a.m.
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On 04/01/14 11:33, Chris Adams wrote:
Once upon a time, Mark Haney <mhaney(a)practichem.com> said:
> sudo xzcat Fedora-Minimal-armhfp-20-1-sda.raw.xz > /dev/sdb
>
> I would get a 'Permission denied' error.
That's because the "> /dev/sdb" was parsed and handled by your
user shell (redirection is handled by the shell before running the
command). sudo only got "xzcat
Fedora-Minimal-armhfp-20-1-sda.raw.xz" as arguments. You should be
able to quote what you want actually passed to sudo:
sudo "xzcat Fedora-Minimal-armhfp-20-1-sda.raw.xz > /dev/sdb"
Well, someone on the Fedora team needs to fix the documentation then.
But now it makes sense. I didn't stop to think about the redirect,
since my boss isn't giving me time to think. Apologies for spamming
the list.
- --
Mark Haney
Network/Systems Administrator
Practichem
W: (919) 714-8428
Fedora release 20 (Heisenbug) 3.13.6-200.fc20.x86_64
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10:45 a.m.
01.04.2014 17:33, Chris Adams:
Once upon a time, Mark Haney <mhaney(a)practichem.com> said:
> sudo xzcat Fedora-Minimal-armhfp-20-1-sda.raw.xz > /dev/sdb
>
> I would get a 'Permission denied' error.
That's because the "> /dev/sdb" was parsed and handled by your user
shell (redirection is handled by the shell before running the command).
sudo only got "xzcat Fedora-Minimal-armhfp-20-1-sda.raw.xz" as
arguments. You should be able to quote what you want actually passed to
sudo:
sudo "xzcat Fedora-Minimal-armhfp-20-1-sda.raw.xz > /dev/sdb"
... which would give a "command not found" error.
Something like
sudo bash -c "xzcat Fedora-Minimal-armhfp-20-1-sda.raw.xz > /dev/sdb"
should work though, since the shell which is started with elevated
rights is doing the output redirection now.
--
Regards
mks
10:33 a.m.
Once upon a time, Mark Haney <mhaney(a)practichem.com> said:
sudo xzcat Fedora-Minimal-armhfp-20-1-sda.raw.xz > /dev/sdb
I would get a 'Permission denied' error.
That's because the "> /dev/sdb" was parsed and handled by your user
shell (redirection is handled by the shell before running the command).
sudo only got "xzcat Fedora-Minimal-armhfp-20-1-sda.raw.xz" as
arguments. You should be able to quote what you want actually passed to
sudo:
sudo "xzcat Fedora-Minimal-armhfp-20-1-sda.raw.xz > /dev/sdb"
--
Chris Adams <linux(a)cmadams.net>
10:35 a.m.
01.04.2014 17:27, Mark Haney:
I've been volunteered to try to build a boot image for a Nitrogen
6x
Freescale SOM board using whatever OS I can make work. I chose
Fedora's ARM image since I'm more comfortable with using Fedora. In
the process of trying to using xzcat to dump the image to the microSD
card I noticed something strange. When I tried:
sudo xzcat Fedora-Minimal-armhfp-20-1-sda.raw.xz > /dev/sdb
I would get a 'Permission denied' error.
But when I ran the same command as root directly, it worked just fine.
I'm not sure I've ever encountered a situation where sudo wouldn't
work like this before. Is there a particular reason for this? Or is
this a bug? For the record, I changed nothing on the device between
attempts to xzcat the image.
There's nothing strange or weird with that. While xzcat is run via sudo
with elevated rights, the output redirection is done by the user's shell
(i. e. *not* with elevated rights).
Do, for example, something like
sudo date > output.file
and look who's output.file's owner.
--
Regards
mks
1:58 p.m.
On 04/01/2014 08:47 AM, Mark Haney wrote:
Well, someone on the Fedora team needs to fix the documentation
then.
But now it makes sense. I didn't stop to think about the redirect,
since my boss isn't giving me time to think. Apologies for spamming
the list.
No apologies needed, as you were simply asking a simple question.
3688
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3688
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8 comments
7 participants
participants (7)
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Chris Adams -
Ian Malone -
Joe Zeff -
Mark Haney -
Markus Schönhaber -
Pete Travis -
Rick Stevens