Q69994: Using argv and envp Variables in a LAN Manager 2.00 Service

Article: Q69994
Product(s): Microsoft LAN Manager
Version(s): 
Operating System(s): 
Keyword(s): 
Last Modified: 30-JUL-2001

Question:

I have written a LAN Manager version 2.00 service that tries to launch
a second process (that is, run another .EXE file). However, the
DosExecPgm() call keeps returning ERROR_FILE_NOT_FOUND, even though
the .EXE I'm trying to start exists in the same directory as my service
.EXE. Why isn't my second .EXE being found?

Response:

When LAN Manager 2.00 launches a service (for example, in response to
the Net Start command), it passes to the service no explicit arguments
and no environment variables [the argument and environment pointers in
the DosExecPgm() call are both set to NULL]. This results in the new
process inheriting the environment established by CONFIG.SYS. If the
.EXE for your new process cannot be found in the PATH listed in
CONFIG.SYS, your DosExecPgm() call will fail. The following are four
possible solutions:

1. Insist that your users place your .EXEs in the same directory and hard code
  the full pathname.

2. As part of the installation of your service, have the user add the location
  of your .EXEs to the CONFIG.SYS PATH variable.

3. Extract from the argv[0] variable, passed to your service by OS/2, the path
  of your first .EXE and use it to build the full pathname for the .EXE you're
  attempting to launch. This will only work if all of your .EXEs exist in the
  same directory.

4. Add a keyword to LANMAN.INI for your service that supplies the necessary
  path.

Of these three solutions, solutions 1 and 2 place unreasonable
restrictions on the user. The second solution can also cause problems
if there are other .EXEs with the same name as yours in the path. The
fourth solution is good if your service needs to create temporary
files or other files that the user may not want in the same directory
as the .EXEs (since the user may have read/execute-only privileges on
that directory). Although it is probably best to keep all of your
.EXEs together, it is not the best solution when attempting to start
child processes.

The third solution is the best and is used for standard LAN Manager
2.00 services to launch child processes. Argv[0] can be safely used to
determine your services "home" directory, since it always contains the
full pathname of the .EXE that was started. This is guaranteed by how
LAN Manager issues the DosExecPgm() call. Because the user must keep
all of his or her .EXEs in a single directory, this also places the
least number of restrictions on the user.

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