The CHECKSUM utility calculates file, image, or object checksums for an
OpenVMS file. For a file checksum the algorithm used determines if the
internal record structure of the file is followed or not. For an image
or object checksum, the utility always follows the image or object
structure.
The /FILE, /IMAGE, and /OBJECT qualifiers determine which kind of
checksum is calculated. They imply a default file type (.DAT, .EXE or
.OBJ) and determine the amount of information displayed. The default,
/FILE, results in an XOR file checksum, according to the file's record
structure. It implies a default file type .DAT and determines that no
information is output to SYS$OUTPUT.
For file checksums, you can specify which algorithm CHECKSUM will use
to perform calculations. By default, the Alpha and VAX XOR record-based
algorithm is used. Optionally, you can select either the CRC algorithm
or the MD5 algorithm, each using the whole content of the file to
calculate the checksum. The CRC algorithm is the same as the algorithm
used for ELF-64 files and is used by popular compression tools like
PKZIP. (That is, a file checksum in a ZIP file can be compared with the
file checksum obtained by the CHECKSUM utility.) The MD5 algorithm is
the MD5 digest, which can be obtained using public domain tools such as
MD5.EXE and md5sum.
Image checksums differ between the Alpha/VAX platforms and the I64
platform. Object checksums are only available for the I64 platform.
With the platform qualifiers, /ALPHA, /I64 or /VAX non-native images or
objects can be checksummed.
For all ELF-64 image and object checksums, CHECKSUM uses a CRC-32
algorithm. The CRC, known as AUTODIN II, Ethernet, or FDDI CRC, is
documented as part of the VAX CRC instructions. The image or object
checksum follows the ELF-64 data structures that are used for OpenVMS
I64 object and image files. For these checksums, only the invariant
data is used for the calculation. Variant data, such as timestamps and
versions, are excluded from the checksum calculation in order to
compare results from different compile and link operations.
For Alpha and VAX images, CHECKSUM uses an XOR algorithm. The image
checksum follows the Alpha and VAX image structure and only uses
invariant data for the calculation. Variant data, such as timestamps
are excluded in order to compare results from different link
operations. Note that on Alpha and VAX systems, object files cannot be
checksummed based on object invariant data.
/ALGORITHM=option
/ALGORITHM=XOR (default)
Selects the algorithm used for file checksums. The default is the XOR
algorithm for data within records, as used by the previous Checksum
utilities on OpenVMS Alpha and VAX systems. Options include:
- CRC --- A CRC-32 algorithm for all bytes within the file (possible
record structures are ignored); this algorithm is also known as AUTODIN
II, Ethernet, or FDDI CRC.
- MD5 --- The MD5 digest, as published by Ronald L. Rivest (RFC
1321), for all bytes within the file (possible record structures are
ignored).
- XOR --- An XOR algorithm for all data, according to the record
structure of the file.
/ALPHA
Calculates an Alpha-type checksum and is only useful with the /IMAGE
qualifier on I64 systems (that is, it checksums Alpha images on I64
systems). It is set by default on Alpha platforms and invalid on VAX
platforms.
/FILE (default)
Calculates a file checksum.
By default, the XOR algorithm (/ALGORITHM=XOR) is used for the
checksum. The /FILE qualifier also implies a default file type of .DAT.
By default, unsigned decimal checksum value is saved in the DCL symbol
CHECKSUM$CHECKSUM and not output to the screen. By specifying
/SHOW=DATA, the full filename of the specified input file is output in
addition to the file checksum, an unsigned decimal value.
The /ALPHA, /I64, or /VAX platform qualifiers do not influence the file
checksum result. However, /ALPHA and /VAX prohibit the /SHOW qualifier
because these qualifiers were not available on the original Checksum
utility for Alpha and VAX systems.
/I64
Calculates an I64-type checksum and is only useful on Alpha systems
with /IMAGE or /OBJECT (that is, it checksums I64 images or objects on
Alpha systems). The /I64 qualifier is set by default on I64 platforms
and invalid on VAX platforms.
/IMAGE
Calculates a checksum of all image bytes. The image structure is
followed to include only the image bytes into the checksum. Invariant
data, such as the linker version and the link date, are omitted.
For I64 images (that is, I64 formatted files), a CRC checksum is
calculated and additional information is output to SYS$OUTPUT,
including the following:
- The resulting full filename and checksums for the image segments
- The header checksums and the overall image checksum
The output values are shown in hexadecimal notation. The DCL symbol,
CHECKSUM$CHECKSUM, shows the result in hexadecimal notation.
For Alpha and VAX images, an XOR checksum is calculated and additional
information is output to SYS$OUTPUT:
- The resulting full filename and checksums for the image sections
- The header checksum and the overall image checksum
The output checksum values are in hexadecimal notation. However, the
result in the DCL symbol CHECKSUM$CHECKSUM is in unsigned decimal
notation.
Note
For Alpha and VAX images, the unsigned decimal notation of the checksum
value in the DCL symbol CHECKSUM$CHECKSUM retains compatiblity with the
previous checksum tool.
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The /IMAGE qualifier implies the default file type of .EXE. For I64
images, this qualifier also implies the default keyword values HEADERS
and SEGMENTS for the /SHOW qualifier.
/OBJECT
Calculates a CRC checksum of all I64 object bytes.
The /OBJECT qualifier follows the ELF-64 object structure to include
only the object bytes into the checksum. Invariant data, as the
language processor version and the generation date, are omitted.
Additional information is output to SYS$OUTPUT, including the following:
- The resulting full filename of the specified input file
- The checksums for the object sections, headers, and the overall
object checksum
The output checksum values are in hexadecimal notation. The result
provided in the DCL symbol, CHECKSUM$CHECKSUM, is in hexadecimal
notation.
The /OBJECT qualifier implies the default file type of .OBJ. This
qualifier also implies the default keyword values HEADERS and SECTIONS
for the /SHOW qualifier.
This qualifier is invalid on the VAX platform. On Alpha platforms, it
it is only applicable with the /I64 qualifier.
/OUTPUT[=filespec]
/NOOUTPUT
The /OUTPUT qualifier controls where the output of the command is sent.
The /NOOUTPUT qualifier supresses output.
If you specify /OUTPUT and a file specification (/OUTPUT=filespec), the
output is sent to the specified file, rather than to the current output
device, SYS$OUTPUT. If you do not enter the qualifier, or if you enter
the /OUTPUT qualifier without a file specification, the output is sent
to SYS$OUTPUT.
Using the /OUTPUT qualifier does not affect the result (that is, the
DCL symbol CHECKSUM$CHECKSUM).
/SHOW=(option[,...])
Controls which checksum and additional information is output to the
device.
Options for this qualifier are as follows:
- ALL --- Sets all of the applicable options, with the following
restrictions:
- For file checksums, only the DATA keyword is allowed.
- For image checksums, all keywords are allowed.
- For object checksums, the SEGMENT keyword is not allowed.
- DATA --- Outputs the full file name and the file checksum. For
compatibility, this option is available for /FILE.
- EXCLUDED --- Formats the data excluded from the image or object
checksums.
- HEADERS --- Output checksums of all I64 headers. This option is set
by default for /IMAGE and /OBJECT.
- SECTIONS --- Output checksums of all ELF-64 sections. This option
is set by default for /OBJECT.
- SEGMENTS --- Output checksums of all ELF-64 program segments. This
option is set by default for /IMAGE.
The /SHOW qualifier is invalid on the VAX platform.
/VAX
Calculates a VAX-type checksum and is only useful on I64 or Alpha
systmes with /IMAGE to checksum VAX images on non-VAX systems. This
qualifier is invalid on VAX platforms.
