In Chrome OS, Bash won't execute my script. How do I get Bash to run my script?

Question

I have a foo.sh file in my current directory. If I try to run ./foo.sh, I get:

-bash: ./foo.sh: /bin/sh: bad interpreter: Permission denied

But if I run /bin/sh ./foo.sh then it runs fine.

How can I fix this so I can just run ./foo.sh and it automatically runs it with /bin/sh?

Edit: Okay, this is Chrome OS and this particular folder is mounted with noexec. Apparently that foils the ability to just run ./foo.sh; but why? Why can I still run sh foo.sh to achieve the exact same thing? What security, then, does noexec give?

Answer 1

The noexec flag will appropriately apply to scripts, because that would be the "expected" behavior.

However, setting noexec only stops people who don't know enough about what they're doing. When you run sh foo.sh you're actually running sh from its default location (probably /bin) which is not on a filesystem mounted with noexec.

You can even get around noexec for regular binary files by invoking ld directly.

cp /bin/bash $HOME
/lib/ld-2.7.so $HOME/bash

This will run bash, regardless of whether or not it's on a filesystem mounted with noexec.

Answer 2

You can also get this error (or a very, very similar message) if you try to execute a file with MS-DOS 2-byte (carriage-return linefeed) line endings.

Vim is so smart these days, that it doesn't neccessarily show you the carriage returns as '^M'. So you can get fooled if you don't check what Vim thinks the "file format" is and just rely on the on-screen-appearance.

In this case the "#!/bin/sh^M" causes the kernel to try to find "/bin/sh^M", which it can't. Bad interpreter, indeed.

Answer 3

If you have the option to run the script or program from a USB stick (or other removable media), you can try unmounting and manually re-mounting it:

1. Plug in USB stick

2. Find USB stick device with $ mount

3. Take note of it; let's assume it is /dev/sdb1

4. Unmount USB stick:

   $ cd /media/removable
   
   $ sudo umount mountpoint
   

Finally, re-mount USB stick:

$ sudo mount /dev/sdb1 mountpoint

With mountpoint the USB stick's mount name

Answer 4

I had the same question. My problem was with the SD card. This worked for me, and it's much simpler than the other answers here. I learned it from Crouton issue #928.

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

Note that you have to use the mount point, not the device (/dev/mmcblk1p1). Same thing for USB (/dev/sdb1) in your case. Only the mount point is different:

$ sudo mount -o remount,exec /media/removable/USB\ Drive

You'll know it had the desired effect because "noexec" will disappear from the mount options when you query.

Answer 5

For system security reasons on ChromeOS/ChromiumOS certain folders are marked noexec and you either need to remount with the command below, or use an alternate path that doesn't have noexec set, like the second example.

These commands assume you are at least in developer mode and have access to the shell with chronos@localhost / $ and not just crosh> and know the sudo password.

sudo mount -i -o remount,exec /home/chronos/user/

The more sustainable method that should survive an upgrade because Google reserves most of /usr/local for developers:

sudo mkdir -p /usr/local/bin/ && sudo chown -R chronos: /usr/local/bin/
cp ${HOME}/Downloads/foo.sh /usr/local/bin/

The additional benefit of putting things here is that it is in the $PATH already (try echo $PATH to confirm this) so you don't need to use the full path to run scripts or binaries that are in /usr/local/bin and have had chmod +x run on them.