cat hello.c
#include <stdio.h>
int main(void)
printf("Hello World!\n");
return 0;
A simple, standard, C program. Compiling and running it shouldn't
produce any surprises... except when it does.
./hello
bash: ./hello: No such file or directory
The first time I got that, it was quite confusing. So, strace to the
rescue -- I thought. But nope:
strace ./hello
execve("./hello", ["./hello"], [/* 14 vars */]) = -1 ENOENT (No such file or directory)
(output trimmed)
No luck there. What's going on? No, it's not some race condition whereby
the file is being removed. A simple
ls -l will show it's there, and
that it's executable. So what? When I first encountered this, I was at a
loss. Eventually, after searching for several hours, I figured it out
and filed it under "surprising things with an easy fix". And didn't
think of it anymore for a while, because once you understand what's
going on, it's not that complicated. But I recently realized that it's
not that obvious, and I've met several people who were at a loss when
encountering this, and who
didn't figure it out. So, here goes:
If you tell the kernel to run some application (i.e., if you run one of
the
exec system calls), it will open the binary and try to figure out
what
kind of application it's dealing with. It may be a script with a
shebang line (in which case the kernel calls the appropriate
interpreter), or it may be an ELF binary, or whatever.
If it is an ELF binary, the kernel checks if the architecture of the
binary matches the CPU we're running on. If that's the case, it will
just execute the instructions in the binary. If it's not an ELF binary,
or if the architecture doesn't match, it will fall back on some other
mechanism (e.g., the
binfmt_misc subsystem could have some emulator
set up to run binaries for the architecture in question, or may have
been set up to run java on jar files, etc). Eventually, if all else
fails, the kernel will return an error:
./hello: cannot execute binary file: Exec format error
"Exec format error" is the error message for ENOEXEC, the error code
which the kernel returns if it determines that it cannot run the given
binary. This makes it fairly obvious what's wrong, and why.
Now assume the kernel is biarch -- that is, it runs on an architecture
which can run binaries for two CPU
ISAs; e.g., this may be
the case for an x86-64 machine, where the CPU can run binaries for that
architecture as well as binaries for the i386 architecture (and its
32-bit decendants) without emulation. If the kernel has the option to
run 32-bit x86 binaries enabled at compile time (which most binary
distributions do, these days), then running i386 ELF binaries is
possible, in theory. As far as the kernel is concerned, at least.
So, the kernel maps the i386 binary into memory, and jumps to the
binary's entry point. And here is where it gets interesting: When the
binary in question uses shared libraries, the kernel not only needs to
open this binary itself, but also the runtime dynamic linker (RTDL). It
is then the job of the RTDL to map the shared libraries into memory for
the process to use, before jumping to its code.
But what if the RTDL isn't installed? Well, then the kernel won't find
it. The RTDL is just this file, so that means it will produce an ENOENT
error code -- the error message for which is "No such file or
directory".
And there you have it. The solution is simple, and the explanation too;
but still, even so, it can be a bit baffling: the system tells you "the
file isn't there", without telling you
which file it's missing. Since
you passed it only one file, it's reasonable for you to believe the
missing file is the binary you're asking the system to execute. But
usually, that's not the problem: the problem is that the file containing
the
RTDL is not installed, which is just a result of you not having
enabled multiarch.
Solution:
dpkg --add-architecture <target architecture>
apt update
apt install libc6:<target architecture>
Obviously you might need to add some more libraries, too, but that's not
usually a problem.
A constant demand for creativity is raising from every corner of the Western world, from any business sector or professional activity, by individual or communities. This term is used everywhere, even in advertising to attract the attention of consumers: as a thirsty wanderer lost in the desert sand, the need for creativity seems to be the source of an oasis of salvation.
Julien Ries anthropological research showed us that, already more than two million years ago, Homo Habilis looks like Symbolicus, with aesthetic sensibility, sense of symmetry and consciousness of creativity. Gilbert Durand confirms that the specific activity of man, the identity card of Homo Sapiens, is the symbolic activity, an essential part of his creativity. Then, man is creative at the moment when his first activates his imaginative feature.
So we can ask ourselves, how did we miss the creativity of man, of which so much we feel the need, or at least where is it hiding now? But above all which kind of creativity are we talking about?
<Read More >
I'm in London for 
Earlier this morning, 
Like 
I noticed that libfuse maintainer has changed last year.
What happened in the 
After almost six months of development 
As a follow up to 
which highlights another nice feature: the 
I was first contacted to talk about women participation in Debian, which I kindly refused, but I said I would maybe talk about motivating new contributors, possibly with some more friends that would maybe join me at the stage. I need to confess that at that moment I had no idea (ok, a vague idea ) about what I was going to talk. So I promptly emailed some Debian friends, shared the invitation, shared some thoughts, got feedbacks, got encouragement, and we finally made it!
