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 Clamscanand 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 an 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 an 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.
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:
dosfsck
doslfn
fcbs
fdisk
format
set
sys
File:
Please read this command's lsm file also.
You will find the updated version (internet) here and
the version described in this manual page here.
The lsm file contains information about the name of the programmer,
the download site, and some other command related information.
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.