LeRoy on 10 Mar 2013 10:06:37 -0700

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Re: [PLUG] File ownership under Linux

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On 03/10/2013 11:04 AM, Eric H. Johnson wrote:
> Hi all,
> I am running into a problem running an executable cross compiled on
> Ubuntu for X86 and targeting an Arm7. I suspect the problem may
> have to do with ownership. I am using Ubuntu 12.04 on an X86 to
> target to an Arm7. I have successfully compiled a patched kernel
> which successfully boots to it and a Debian Wheezy image. I am now
> trying to port some utilities which I have successfully compiled on
> the x86 with the same tool chain. There is no packaging system in
> place so I am just copying files.
> The file I want to run is an executable, so if I try the fully
> qualified path, running as root on arm7: /usr/bin/xenomai/latency
> I get an error to the effect that there is no file or directory by
> that name.
> Here is what I need clarification on. Everything on the Arm7 runs
> on an SD card, so at the moment I just plug the SD into the x86
> computer and copy the files I need. When I copy I am running as
> root on the x86. After I boot to the SD from the Arm7 and check the
> file ownership and attributes they are:
> root:root and -xrw-xr-xr respectively.

What file system are you running on the SD chip?

If the SD chip is using a Windows file system then all files are
automatically root:root ownership.  Also how is the SD chip mounted?
You can see this by issuing a mount command.

There are some distributions that mount FAT and NTFS file systems as
ro (read only) and noexec (non executable).

> But even so I have used chmod and chown to force the ownership and 
> attributes, but see no discernible difference.

As stated above FAT and NTFS file systems cannot have ownership and
permissions changed.

When I mount /windows on my dual boot laptop mount shows:
/dev/sda1 on /windows type fuseblk

On my Debian system a NTFS file system mounts with setting the user_id
and group_id which cannot be changed with chown.  Also if the file
system is mounted with noexec then you cannot run even a script.

To change this you need to run
mount -o remount,etc

Read the man page for mount to check on all of the options available.

ls -lh /windows
drwxrwxrwx 1 root root 4.0K May 22  2009 Temp
drwxrwxrwx 1 root root 4.0K Oct 10  2008 Users
- -rwxrwxrwx 1 root root 1.4M Nov  7  2007 VC_RED.cab
- -rwxrwxrwx 1 root root 5.6K Nov  7  2007 vcredist.bmp
- -rwxrwxrwx 1 root root 228K Nov  7  2007 VC_RED.MSI
drwxrwxrwx 1 root root  28K Mar  3 10:06 Windows

If you are putting linux on a SD chip first I would make the
filesystem either ext3 or ext4 or any other UNIX type filesystem.

Personally I create SD chips as encrypted chips which require
cryptsetup LuksOpen /dev/sdc1 sandisk

Then I can mount /dev/mapper/sandisk /mnt/sandisk

I hope that this helps :-)

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