One source of error which I’ve observed, was even recommended in the old ‘linpopup’ package documentation.
ICYMI, “Linpopup” was a Linux extension to the Samba server, meant to allow messages to be passed directly from one computer to another on a LAN. It was based on the old “WinPopup” feature, which Microsoft discontinued with Windows XP (Service Pack 2 ? )
I think that one of the problems with the original WinPopup was, that its messages were allowed to be rich text, including URLs, which users were tricked into clicking on, because users did not recognize that pop-up windows they were getting, were in fact intended as a feature, but that these messages were eventually sent out to blocks of IP addresses as a form of spam, sometimes carrying a payload of malware.
Unlike its Windows predecessor, LinPopup only allows Plain Old Text to be sent. But this posting is not meant to describe this, as a feature of Samba. I’m intending to showcase this as an example of a type of mistake, which modern-day thinkers make when creating configuration files. In order to ready a Samba server to receive these messages, a Linux user is given the suggestion to put the following into their /etc/samba/smb.conf, near the end of their [global] section:
message command = /usr/local/bin/LinPopUp "%f" "%m" %s; rm %s
I know this, because I custom-compiled the old package, and this was stated in the documentation.
Now, it is possible to configure some other program to receive the message, which Samba leaves in the temporary file ‘%s’, as long as we remember that any message command which Samba runs, will be run as user ‘nobody’, with the privileges of user ‘nobody’. That’s not a problem. But there is a problem with this configuration line, which users ran in to, and which users had trouble pinpointing.
This is meant for a configuration file, but the above syntax would be suitable for a shell script. A configuration file will often allow for an executable program to be specified, and will even go so far as to allow command-line parameters to be passed in. But a configuration file will not go so far, as to allow two programs to be executed in sequence. That is a luxury which too many modern coders take for granted, apparently.
The two programs referred to above are
In fact, this configuration mistake will pass in the semicolon, as part of the parameters to /usr/local/bin/LinPopUp , thereby mangling the ability of this program to identify the file the message is in. And then it will pass in the string “rm” as well…
What I had to do myself, was something like
message command = bash -c '/usr/local/bin/linpopup "%f" "%m" %s ; rm %s' &
The one program I’m telling Samba to run, is ‘bash’. It, in turn, can run several other programs synchronously, asynchronously, etc..
Also, it should be noted that the ‘&’ at the end of my line, is not equivalent to its use in shell scripts, where it tells a running instance of ‘bash’, to disconnect the child process immediately, and to continue running the rest of the script. My ‘&’ does not assume that ‘bash’ is already running, and appears as a parameter to ‘bash’ itself.
For all I know, ‘bash’ could simply ignore this. But I do know, that this ‘&’ does not interfere in my message command working…
(Edit : ) And, It is up to the way the Samba server parses its configuration file, whether it expands the variables, which begin with ‘%’ , inside single quotes. It doesn’t matter that ‘bash’ would not do so.