Re: [Freedos-user] Presenting: SUDO for DOS

[E. C. M. <pu...@ul...>]

On at 2026-03-18 10:54 +0100, Sijmen J. Mulder via Freedos-user wrote:
> Hi all,
> 
> Thought someone might get a chuckle out of this:
> 
> https://codeberg.org/sjmulder/sudo.com
> 
>> An implementation of sudo for DOS, to run the given command with full privileges.
> 
> Was a good DOS and x86-16 learning experience though!

I have several programs with similar tasks:

* The lMS-DOS "comloader" [1], setting up an embedded (flat-format or 
MZ) executable as if that executable itself was loaded rather than the 
comloader. This involves cutting the command name out of the PSP command 
line tail, then setting up the two default FCBs in the PSP and the "FCB 
drives valid" flags in AL and AH.

* The lRxDOS comloader [2] which is the base for the lMS-DOS one.

* Eric Auer's callver with some patches by me [3], this passes a command 
to a child process running a "%COMSPEC% /C " command.

* The Comspec Load Utility (or Codified Likeness Utility) [4], a command 
shell launcher for the Multiple Command Payload (or Master Control 
Program). The MCP contains a (patched) copy of FreeCOM [5] in its lDOS 
comloader, but this requires the "COMMAND" command name be specified. 
That isn't expected for %COMSPEC% so clu.exe can be used for %COMSPEC%. 
It will find ldosmcp.com and load it, telling it to pass control to the 
FreeCOM executable. CLU can relocate its PSP to the top of the Low 
Memory Area [6], and will then load the MCP application executable using 
int 21h function 4B01h [7] and chain the current process to terminate 
into the loaded MCP [8].

The MCP comloader in turn can relocate the FreeCOM process that it 
builds into the Upper Memory Area [9], where the comloader itself cannot 
fit due to the many commands that it contains.

Regards,
ecm


[1]: https://hg.pushbx.org/ecm/msdos4/file/5d7ba07e2e21/comload.asm
[2]: https://hg.pushbx.org/ecm/ldos/file/4091fac59e21/comload.asm
[3]: https://hg.pushbx.org/ecm/callver/file/fd67af5c53ee/callver.asm
[4]: https://hg.pushbx.org/ecm/mcp/file/f885328d4bdf/clu.asm
[5]: https://github.com/FDOS/freecom/issues/184
[6]: https://hg.pushbx.org/ecm/mcp/file/f885328d4bdf/clu.asm#l118
[7]: https://hg.pushbx.org/ecm/mcp/file/f885328d4bdf/clu.asm#l534
[8]: https://hg.pushbx.org/ecm/mcp/file/f885328d4bdf/clu.asm#l582
[9]: https://hg.pushbx.org/ecm/msdos4/file/5d7ba07e2e21/comload.asm#l483