[users@httpd] Script behaving differently when run by Apache and when run from a shell by user www-data?

[EML <sa...@cyconix.com>]

The CGI Howto page contains some basic information on how Apache 
actually runs a program, but is there any more detailed information 
anywhere?

Specifically, I have a problem where a bash script runs as expected when 
run from an interactive shell by user www-data (this is Ubuntu). 
However, the script behaves differently when run via Apache from a web 
client. This is nothing to do with PATH or envvar differences: when run 
by Apache, an operation to unmount a disk appears to succeed, but 
actually doesn't unmount the disk. When run from the interactive shell, 
as the same user, the operation unmounts the disk.

This is a basic Apache install on Ubuntu 22.04 - no suexec, no chroot, 
plain CGI, etc. I've been running scripts via Apache this way for years, 
but this is the first script which attempts to carry out disk 
operations. All these scripts appear in the sudoers file to allow Apache 
to carry out specific privileged operations.

I asked this question <https://unix.stackexchange.com/q/767587/212513> 
today on StackExchange (https://unix.stackexchange.com/q/767587/212513, 
if the link is scrubbed), with much more detail, but I think that was 
probably the wrong place to ask.

  Thanks.

Re: [users@httpd] Script behaving differently when run by Apache and when run from a shell by user www-data?

[Frank Gingras <th...@apache.org>]

On Tue, Jan 23, 2024 at 2:02 PM EML <sa...@cyconix.com> wrote:

> The CGI Howto page contains some basic information on how Apache actually
> runs a program, but is there any more detailed information anywhere?
>
> Specifically, I have a problem where a bash script runs as expected when
> run from an interactive shell by user www-data (this is Ubuntu). However,
> the script behaves differently when run via Apache from a web client. This
> is nothing to do with PATH or envvar differences: when run by Apache, an
> operation to unmount a disk appears to succeed, but actually doesn't
> unmount the disk. When run from the interactive shell, as the same user,
> the operation unmounts the disk.
>
> This is a basic Apache install on Ubuntu 22.04 - no suexec, no chroot,
> plain CGI, etc. I've been running scripts via Apache this way for years,
> but this is the first script which attempts to carry out disk operations.
> All these scripts appear in the sudoers file to allow Apache to carry out
> specific privileged operations.
>
> I asked this question <https://unix.stackexchange.com/q/767587/212513>
> today on StackExchange (https://unix.stackexchange.com/q/767587/212513,
> if the link is scrubbed), with much more detail, but I think that was
> probably the wrong place to ask.
>
>  Thanks.
>

Let's take a step back - why are you unmounting from a cgi script?