'Permission denied' executing .sh from mounted vfat USB

jodib · 08-06-2013, 07:57 PM

Upgraded my Linux distro. and encountering (?permission?) problems running scripts on mounted USB drives. For example:

Code:

root@me:~# mkdir /mmm
root@me:~# mount /dev/sdc1 /mmm
root@me:~# echo "echo hi" > /mmm/try.sh
root@me:~# chmod 777 /mmm
root@me:~# chmod 777 /mmm/try.sh
root@me:~# /mmm/try.sh

root@me:~# /mmm/try.sh
bash: /mmm/try.sh: Permission denied

root@me:~# /bin/sh /mmm/try.sh 
hi

root@me:~# cp /mmm/try.sh /root/try.sh
root@me:~# chmod 777 /root/try.sh
root@me:~# /root/try.sh

In other words, no matter what I do with chmod and/or chgrp doesn't help. But if I copy the same script from the USB to a local filesystem then it works.

Puzzled, not sure where to look. SELinux doesn't seem to be on.

Mount shows:
/dev/sdc1 on /mmm type vfat (rw,relatime,fmask=0022,dmask=0077,codepage=cp437,iocharset=utf8,shortname=mixed,showexec,utf8,flush ,errors=remount-ro)

MS3FGX · 08-06-2013, 08:14 PM

FAT doesn't support the extended Unix permissions, so you can't set it as executable, and thus it can't be executed.

As a workaround you should be able to mount the whole partition with the "exec" option, but that will make all files executable so be careful.

Firerat · 08-06-2013, 08:21 PM

well, seeing as it is a shell script, just point at it..

Code:

bash /mmm/try.sh

Sydney · 08-06-2013, 08:22 PM

It also looks like you are able to launch the script if you specify the interpreter. Is the #! line of your script tainted with a DOS EOL or the path maybe wrong on it? If it is a DOS EOL you could run

Code:

sed -i -e 's/.$//g' try.sh

to remove it.

Firerat · 08-06-2013, 08:26 PM

ahh, good point Sydney

try this

Code:

cat > /mmm/try.sh << "EOF"
#!/bin/bash
echo "Hello World!"
EOF
chod 700 ./mmm/try.sh # never 777, unless you really, *really* need it
./mmm/try.sh

jodib · 08-06-2013, 08:41 PM

@MS3FGX: I've tried specifying 'exec' option when I mount, no difference

Code:

mount -t vfat -o rw,auto,user,fmask=0022,dmask=0000,exec /dev/sdc1 /mmm

@Firerat: yes prefixing it with /bin/bash (or /bin/sh) works - but I'm not sure why I didn't need this before

@Sydney and Firerat: adding the first line #!/bin/bash doesn't make a difference - still get "Permission denied"

One more item I noticed is that the chmod 777 doesn't affect the file permissions. I suspect MS3FGX's point about FAT is the reason - but why did all this work before? What's changed?

jodib · 08-06-2013, 08:46 PM

Aha Found the problem!

The USB drive was mounted twice - the 1st by the OS (some automatic) as /media/Lexar and the 2nd by me. That 1st/auto had "showexec" flag which I suspect was the problem or overriding whatever I specified during my mount. Once I umounted /media/Lexar, then my mount flags would work.

Thanks all!

Firerat · 08-06-2013, 08:51 PM

Quote:

Originally Posted by jodib

@Firerat: yes prefixing it with /bin/bash (or /bin/sh) works - but I'm not sure why I didn't need this before

Yeah, my fault I totally missed that in your OP