chroot cannot find command

Angel Tsankov · External Since: May 04, 2006 Posts: 66

I checked that /bin/ls exists, then I ran the following command

chroot /bin /bin/ls

and I got this:

chroot: cannot run command `/bin/ls`: No such file or directory

What is wrong?!

Angel Tsankov · External Since: May 04, 2006 Posts: 66

>> I checked that /bin/ls exists, then I ran the following command
>>
>> chroot /bin /bin/ls
>>
>> and I got this:
>>
>> chroot: cannot run command `/bin/ls`: No such file or directory
>>
>> What is wrong?!
>
> Because in the chroot'd environment, it's not /bin/ls, it's /ls.
>
> Note that this is not likely to work either, since /bin/ls will probably
> require libraries in /lib, which will be inaccessible from the chroot'd
> environment.

Neither the above chroot command, neither the following work:

chroot /bin /ls

They both fail with exactly the same error message: chroot: cannot run command `/bin/ls`: No such file or directory

I also compiled a simple C program and put it in /bin (/bin/a.out):

int main( )
{
return 0;
}

Then I executed
chroot /bin /bin/a.out
chroot /bin /a.out

Both failed with chroot: cannot run command `...`: No such file or directory

Vilmos Soti · External Since: May 03, 2005 Posts: 140

"Angel Tsankov" <fn42551 DeleteThis @fmi.uni-sofia.bg> writes:

>>> I checked that /bin/ls exists, then I ran the following command
>>> chroot /bin /bin/ls
>>> and I got this:
>>> chroot: cannot run command `/bin/ls`: No such file or directory
>>> What is wrong?!
>> Because in the chroot'd environment, it's not /bin/ls, it's /ls.
>> Note that this is not likely to work either, since /bin/ls will
>> probably require libraries in /lib, which will be inaccessible from
>> the chroot'd environment.
>
> Neither the above chroot command, neither the following work:
>
> chroot /bin /ls
>
> They both fail with exactly the same error message: chroot: cannot
> run command `/bin/ls`: No such file or directory
>
> I also compiled a simple C program and put it in /bin (/bin/a.out):
>
> int main( )
> {
> return 0;
> }
>
> Then I executed
> chroot /bin /bin/a.out
> chroot /bin /a.out
>
> Both failed with chroot: cannot run command `...`:
> No such file or directory

That's seems right. That error message "No such file or directory"
doesn't mean that your program is "missing", but that the dynamic
loader, and later the libraries, are not present.

Link your program statically, and it will (hopefully) work. This is
actual output, I just edited (threw out the invariant stuff) from
the output of "file":

# cat a.c
int main (void);

int main (void)
{
return 0;
}

# gcc -static -o a.static a.c
# gcc -o a.dynamic a.c
# file a.static
a.static: 80386, statically linked, not stripped
# file a.dynamic
a.dynamic: 80386, dynamically linked (uses shared libs), not stripped
# chroot /tmp/ /a.dynamic
chroot: cannot run command `/a.dynamic': No such file or directory
# chroot /tmp/ /a.static
#

Vilmos

Douglas Mayne · External Since: Feb 13, 2006 Posts: 269

On Fri, 05 May 2006 23:04:47 +0300, Angel Tsankov wrote:

>>> I checked that /bin/ls exists, then I ran the following command
>>>
>>> chroot /bin /bin/ls
>>>
>>> and I got this:
>>>
>>> chroot: cannot run command `/bin/ls`: No such file or directory
>>>
>>> What is wrong?!
>>
>> Because in the chroot'd environment, it's not /bin/ls, it's /ls.
>>
>> Note that this is not likely to work either, since /bin/ls will probably
>> require libraries in /lib, which will be inaccessible from the chroot'd
>> environment.
>
> Neither the above chroot command, neither the following work:
>
> chroot /bin /ls
>
> They both fail with exactly the same error message:
> chroot: cannot run command `/bin/ls`: No such file or directory
>
> I also compiled a simple C program and put it in /bin (/bin/a.out):
>
> int main( )
> {
> return 0;
> }
>
> Then I executed
> chroot /bin /bin/a.out
> chroot /bin /a.out
>
> Both failed with chroot: cannot run command `...`: No such file or directory
>
Erik Max Francis tried to tell you that libraries are required. chroot is
non-trivial because the "root" filesystem is a fundamental element of
unix design. If you break it, you get to keep both pieces.

I compiled "Hello World" using the defaults. The resulting executable
includes these library dependancies:

$ ldd a.out
libstdc++.so.5 => /usr/lib/libstdc++.so.5 (0x40027000)
libm.so.6 => /lib/libm.so.6 (0x400df000)
libgcc_s.so.1 => /usr/lib/libgcc_s.so.1 (0x40103000)
libc.so.6 => /lib/libc.so.6 (0x4010c000)
/lib/ld-linux.so.2 (0x40000000)

If any of the links are broken in the chroot'ed environment, then the
command won't run. The application's library links must resolve
_relative_ to the chroot environment. Most likely, /bin is not appropriate
for these links to resolve.

--
Douglas Mayne

John-Paul Stewart · External Since: Mar 29, 2005 Posts: 1520

Angel Tsankov wrote:
>>>I checked that /bin/ls exists, then I ran the following command
>>>
>>>chroot /bin /bin/ls
>>>
>>>and I got this:
>>>
>>>chroot: cannot run command `/bin/ls`: No such file or directory
>>>
>>>What is wrong?!
>>
>>Because in the chroot'd environment, it's not /bin/ls, it's /ls.
>>
>>Note that this is not likely to work either, since /bin/ls will probably
>>require libraries in /lib, which will be inaccessible from the chroot'd
>>environment.
>
>
> Neither the above chroot command, neither the following work:
>
> chroot /bin /ls
>
> They both fail with exactly the same error message: chroot: cannot run command `/bin/ls`: No such file or directory

Of course.

The error message is probably coming from 'ldd' (the dynamic linker)
when it can't find libraries under /lib (as the previous poster
mentioned). Do an 'ldd /bin/ls' and you'll get a list of all the
libraries that it requies. (The list is surprisingly long on this
system.) You'll need *all* of those libraries to appear under /lib *in
the chroot environment*.

Which brings us to the question: why are you trying to chroot to /bin?
That makes no sense. Build a full chroot environment someplace else
(/var/chroot or /home/chroot or ...) with copies of /bin and /lib (and
possibly bits of /dev and /etc and ...) and chroot to *that*. You
cannot just chroot to random points and you almost certainly don't want
the chroot environment cluttering up your /bin.

If you really don't want to have a copy of (parts of) /lib in your
chroot environment, you'll have to re-build all of the necessary
binaries using static linking. That's probably more work and would
likely take up more disk space than a proper chroot environment.