Command: fdshield
The FreeDOS FDSHIELD malware shield monitors DOS sessions and helps
block dangerous activity typical of trojan horses, viruses, malware,
and human error. It is not a virus scanner like Clamscan and does not
check known virus signatures, but only monitors for known risky
behavior.
Syntax:
FDSHIELD [/v][/t][/T][/x][/X][/b][/B][/w][/W]
Options:
Basic protection when called without options. Halts the system if
a program attempts to disable certain other common anti-virus
monitors, and blocks certain potentially dangerous FCB based
deletes with wildcards in the file name extension. If you use
FDSHIELD in a DOS box, only the DOS in the box is stopped, not
the whole system.
/v Makes verbose. Verbose gives additional information on why an
action was prohibited, and when FDSHIELD halts the system, it will
wait 20 seconds before automatically rebooting or closing the DOS
box.
/t Prohibits TSR. When this is selected, FDSHIELD will print a system
halted message and reboot or close the session if a program
attempts to terminate and stay resident. This may help stop trojans
and some resident file infectors and multipartite viruses. The DOS
extenders CWSDPMI and RTM are explicitly allowed to load in this
mode. Note that viruses tend to go resident without using the DOS
functions for that, which allows them to bypass FDSHIELD.
This option makes sense as many programs like DOSFSCK, BZIP2, UPX,
WGET and others originally come from UNIX and are ported to DOS by
compilertools like DJGPP and need CWSDPMI.
/T Prohibits TSR. When this is selected, FDSHIELD will print a system
halted message and reboot or close the session if a program
attempts to terminate and stay resident. This option works pretty
much like the /t option. The CWSDPMI and RTM DOS extenders are not
allowed to load in this mode. In OS/2 DOS box and similar, CWSDPMI
is not needed anyway. Some other DOS extenders are not TSR at all
and therefore work without problems with FDSHIELD /T.
/x Write protects program files with the com, exe, and sys suffix.
When you select this option, FDSHIELD prevents most attempts to
write to system files, but does allow creating new program files in
ways which explicitly avoid overwriting existing files. Many tools
like compilers or archivers use other, unsafe, ways to create
files, so they will get blocked by FDSHIELD. You should boot
without the FDSHIELD /x protection if you plan to install or
compile programs. If you do have /x protection on, however, many
viruses will not be able to infect program files.
/X Write protects system files with bat, com, exe, and sys suffix.
This option does not permit creating system files at all. Batch
files are no common target for viruses, but there are situations
where you do not want them to be modified anyway. Neither the /x
nor the /X protection prevent long file name based access to
program files. This affects only DOS versions which support long
file names in some way.
/b Write protects floppy disk BOOT areas. This can prevent boot sector
and multipartite viruses from spreading to diskettes in plain DOS.
However, the protection does not work in OS/2 and Win NT DOS boxes.
As these sectors are usually only written by tools like FORMAT,
SYS and FDISK /b and /B should not be used when running
these tools.
/B Write protects hard disk BOOT areas. This may prevent multipartite
viruses from spreading to the hard drive partitions. It may not
work in OS/2 and Win NT DOS boxes, but they have built in
protection against boot sector modifications.
/w Write protects floppy (/w) disks. Pipes do not work if the temp
directory (if none set: current directory) is on a read-only disk.
This protection does not work in OS/2 or NT DOS boxes.
/W Write protects hard disks and all other non-diskette drives with
FAT filesystem, like RAMDISKs. If DOS tries to write to a "fixed"
disk, it can get stuck at a prompt which only lets you retry but
not abort the write attempt. If you use both /w and /W at the same
time, FDSHIELD will make all files look as if they are readonly,
which usually prevents DOS from trying to write to disk. The same
warning about pipes and DOS boxes as for the /w protection holds
for the /W protection.
/? Shows the help.
Comments:
Load FDSHIELD as early as possible (after TSR programs like keyboard
and CD-ROM drivers) to get its protection as all actions before
loading FDSHIELD can damage your system.
For this reason you should change the boot order in the BIOS to C:
instead of A: first. Many new machines offer a manual change of the
boot order when starting the computer if you need it.
As FDSHIELD offers no function to unload you have to reboot the
computer if some programs are blocked by its functions. For this
reason it is recommended to add a boot menu (see example) for
different purposes.
For more information see:
https://gitlab.com/FreeDOS/util/fdshield section DOC.
Examples:
In CONFIG.SYS / FDCONFIG.SYS:
MENU 0. FreeDOS system
MENU 1. minimal virus protection
MENU 2. medium protection (1.-TSR +HD bootsector write prtoection)
MENU 3. medium protection (recommended) (2.+program write protection)
MENU 4. maximum protection (3.-all TSR+write protection all)
and in AUTOEXEC.BAT:
IF "%CONFIG%"=="0" echo The system is not protected by FDSHIELD
IF "%CONFIG%"=="1" LH FDSHIELD /v
IF "%CONFIG%"=="2" LH FDSHIELD /v /t /B
IF "%CONFIG%"=="3" LH FDSHIELD /v /t /B /x
IF "%CONFIG%"=="4" LH FDSHIELD /v /T /B /b /X /w /W
See also:
autoexec.bat/fdauto.bat
config.sys/fdconfig.sys
dosfsck
doslfn
fcbs
fdisk
format
menu
set
sys
Copyright © 2005 Eric Auer, Walt Gregg, updated 2008 by W. Spiegl.
This file is derived from the FreeDOS Spec Command HOWTO.
See the file H2Cpying for copying conditions.