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I have setup a new environment - it's a chroot containing Ubuntu 14.04 (trusty) in a Chromebook (Asus flip C100P - ARM based). I've got gcc and g++ installed. I created a simple "hello, world" program (test.c) and compiled it via:

 gcc -o t.exe test.c

When I go to run ./t1.exe, I get the following:

bash: ./t.exe: Permission denied

Note that I was executing as root and the permissions on ./t.exe is set wide open (chmod 777, verified via ls -l).

So I tried determining what's wrong - here's what I've tried:

% file ./t.exe

./t.exe: ELF 32-bit LSB  executable, ARM, EABI5 version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.32, BuildID[sha1]=82a6c6227e0f7171a68c71a74c6e6396e37e6675, not stripped

% ldd ./t.exe

not a dynamic executable

% readelf -d ./t.exe | grep NEEDED

0x00000001 (NEEDED)                     Shared library: [libc.so.6]

% dpkg -l libc6

Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name           Version      Architecture Description
+++-==============-============-============-=================================
ii  libc6:armhf    2.19-0ubuntu armhf        Embedded GNU C Library: Shared li

% cat /etc/ld.so.conf.d/*

# Multiarch support
/lib/arm-linux-gnueabihf
/usr/lib/arm-linux-gnueabihf
/usr/lib/arm-linux-gnueabihf/mesa-egl
/usr/lib/arm-linux-gnueabihf/mesa
/usr/lib/arm-linux-gnueabihf/libfakeroot
# libc default configuration
/usr/local/lib

% ls -l libc.so.6

lrwxrwxrwx 1 root root 14 Aug 12 19:37 libc.so.6 -> /lib/libc.so.6

% ls -l /usr/local/lib/libc.so.6

lrwxrwxrwx 1 root root 14 Aug 12 18:21 /usr/local/lib/libc.so.6 -> /lib/libc.so.6

% ls -l /usr/lib/libc.so.6

lrwxrwxrwx 1 root root 14 Aug 12 19:37 /usr/lib/libc.so.6 -> /lib/libc.so.6

% ls -l /lib/libc.so.6

lrwxrwxrwx 1 root root 34 Aug 12 18:11 /lib/libc.so.6 -> /lib/arm-linux-gnueabihf/libc.so.6

% ls -l /lib/arm-linux-gnueabihf/libc.so.6

lrwxrwxrwx 1 root root 12 May 26 07:55 /lib/arm-linux-gnueabihf/libc.so.6 -> libc-2.19.so

% ls -l /lib/arm-linux-gnueabihf/libc-2.19.so 

-rwxr-xr-x 1 root root 902876 May 26 07:56 /lib/arm-linux-gnueabihf/libc-2.19.so

% objdump -a /lib/arm-linux-gnueabihf/libc-2.19.so 

/lib/arm-linux-gnueabihf/libc-2.19.so:     file format elf32-littlearm

/lib/arm-linux-gnueabihf/libc-2.19.so

% objdump -a ./t.exe

./t.exe:     file format elf32-littlearm

./t.exe

% uname -a 

Linux localhost 3.14.0 #1 SMP PREEMPT Tue Aug 2 21:07:06 PDT 2016 armv7l armv7l armv7l GNU/Linux

I suspect that I've got a borked toolchain, but I'm truly stumped at this point.
Does anyone have any ideas on what's going on here or how to proceed in finding the problem?

youngmj
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  • wow, I'm saving this Q for the amazing list of cmds to check with... But, try `printf "#!/bin/bash\necho Hello Scripting!\n" > ./myTest.sh ; chmod 755 myTest.sh ; ./myTest.sh` . (I may have missed a `;` or `'` etc, but hopefully you get the idea). If this fails, then there is something wrong with permissions on you `./` dir OR one of the directories "above" that. See http://stackoverflow.com/a/26718467/620097 for some ideas. Good luck. – shellter Aug 13 '16 at 04:16
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    Have you tried compiling with something like `-march=i686` ? It seems your binary is being generated for the Chromebook and not for the Ubuntu (you can try copying the executable to your Chromebook and it should run there, which confirms this). – Daniel Aug 13 '16 at 05:16
  • @Mondkin - wrong architecture. This is on an ARM. Even if I specified the option for the ARM I'm on, I don't think it'll make a difference. I don't understand your comment - "generated for the Chromebook and not for the Ubuntu"; I'm not using a cross-toolset. I'm running Ubuntu in crouton on the Chromebook, and I execute gcc from inside the chroot running Ubuntu. – youngmj Aug 15 '16 at 14:01
  • @shelter - I confess that I grimaced a bit when I read your suggestion, because I really thought I had shown this was not a permissions/privs issue. However, I tried it anyway (just to be thorough)... and, lo and behold, I can't even execute that simple bash script! So I'm digging deeper. Thank you! – youngmj Aug 15 '16 at 14:03
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    Further investigation shows that I can actually mv the generated executable to my home directory, and it executes fine from there. So it appears that there's something about the location (permissions somewhere in the directory tree?) where I originally built the executable that's problematic. But because the executable image runs without problems, it looks like my toolchain is fine - this seems to be an environment issue. I'll update again, if / when I find the root cause, in case anyone runs into this in the future and finds this in a search. – youngmj Aug 15 '16 at 16:46

3 Answers3

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So it turns out that I was originally using a directory on a removable SD card, and I had used that card to house my encrypted chroot as well. (Not recommended BTW - very slow.) This directory was therefore visible and reachable by ChromeOS and Ubuntu, without explicitly setting up a share.

Looking online for an answer, I stumbled across the following: https://ubuntuforums.org/showthread.php?t=1956802. It turns out that my /etc/fstab file was effectively empty - containing only "# UNCONFIGURED FSTAB FOR BASE SYSTEM" in it.

Looking at the output from 'mount', it appears that the file system on the SD card is mounted with 'noexec'. I believe this is the source of my problems - I think I could add an fstab entry for this filesystem with the 'exec' flag instead, and everything should work.

Thinking about this further, however, I decided not to do this - after all, I only need items in the encrypted file systems (which are container files on the SD card) to allow execution of files, and making the files on the SD card file system directly executable may be slightly less secure. Therefore, I decided to simply change the directory tree I use for development work to be under my user home directory (which is in the encrypted file system used by Ubuntu in the chroot, and is apparently located on the SD card in a container file, but not directly in the file system on the SD card partition itself). I forego the immediate access to files from both my chroot and ChromeOS environments, but, if I really need this in the future, I can set up a share - probably on a separate device/partition (USB flash drive).

youngmj
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I am running Linux on a Chromebook via crouton. I am learning the go programming language and was able to get go to interpret my "Hello, World!" program, but when I had it compile the code, I couldn't run the resulting binary. I'd forgotten about this noexec problem. All I had to do was to remount the SD card with exec and the permissions were resolved.

For me it was:

sudo mount -o remount,exec /media/removable/SD\ Card

CameraCarryingCoder
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sudo mount -o remount,exec /dev/sdXY

This works on my chromebook. I had the same issue.

Samuel Philipp
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whatyouwill
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