Simple hello world snap builds but fails to run (Permission denied)

snap
1

I have simple hello world snap which builds fine but gets permission denied on running.

O/P from device:

bot@localhost:/tmp$ helloapp.helloapp
/snap/helloapp/x8/command-helloapp.wrapper: 2: exec: /snap/helloapp/x8/bin/hello: Permission denied
bot@localhost:/tmp$

===

hello.c

#include <stdio.h>
#include <stdlib.h>

void main (void) {
printf ("\nSIMPLIFIED HELLO WORLD !!!\n");
}

Makefile:

hello: hello.c
gcc -c hello.c -o hello

snapcraft.yaml:

apps:
helloapp:
command: bin/hello
parts:
gnu-hello:
plugin: autotools
source: simplehello
source-subdir: .
override-build: |
make
mkdir -p $SNAPCRAFT_PART_INSTALL/bin
cp hello $SNAPCRAFT_PART_INSTALL/bin

2

What are the permissions on that binary you create? It seems you simply don’t have the right permissions to execute it. Is it readable and executable for all/others?

I would also suggest using base: core18. This will build the snap in a clean environment, making sure that there is nothing funky going on with your install.

3

Thanks @galgalesh missed +x permission on the binary. With +x added, no ‘permission denied’ error.

But now this is what I get:

bot@localhost:~$ helloapp.helloapps
/snap/helloapp/x9/command-helloapps.wrapper: 2: exec: /snap/helloapp/x9/bin/hellobin: Exec format error

bot@localhost:~$ ls -l /snap/bin/helloapp.helloapps
lrwxrwxrwx 1 root root 13 Dec 26 10:28 /snap/bin/helloapp.helloapps -> /usr/bin/snap
aruba-iotadmin@localhost:~$

4

Can you run that compiled C program outside of it being snapped? It doesn’t work here, so I don’t believe this is snap at fault.

alan@KinkPad-K450:~/Temp/forum$ cat hello.c
#include <stdio.h>
#include <stdlib.h>

void main (void) {
printf ("\nSIMPLIFIED HELLO WORLD !!!\n");
}
alan@KinkPad-K450:~/Temp/forum$ gcc -c hello.c -o hello
alan@KinkPad-K450:~/Temp/forum$ file hello
hello: ELF 64-bit LSB relocatable, x86-64, version 1 (SYSV), not stripped
alan@KinkPad-K450:~/Temp/forum$ chmod +x hello
alan@KinkPad-K450:~/Temp/forum$ ./hello 
bash: ./hello: cannot execute binary file: Exec format error
5

You are right. It fails to run where it is built.

O/p of file shows this:
parts/gnu-hello/install/bin/hellobin: ELF 64-bit LSB relocatable, x86-64, version 1 (SYSV), not stripped

Both host and device are x86_64, still the binary fails to run on host as well as device.

dev:~/helloworld/snap$ uname -a
Linux dev 4.15.0-72-generic #81-Ubuntu SMP Tue Nov 26 12:20:02 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
dev:~/helloworld/snap$

6

This works:

#include <stdio.h>
#include <stdlib.h>

void main (void) {
printf ("\nSIMPLIFIED HELLO WORLD !!!\n");
}


$ g++ hello.c -o hello
$ ./hello 

SIMPLIFIED HELLO WORLD !!!
7

What does o/p of file on hello looks like?

8 
$ file hello
hello: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=f4c7c5c0bbef5d5d2b7196c3f1874506ba445a84, for GNU/Linux 3.2.0, not stripped