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This page last modified: Jul 14 2008
description:How to get checksum fingerprints
title:Examples of Linux checksum fingerprints for files: md5, sha.

Table of contents
Quick example
Additional notes

Quick example

Two computers:,
User id: mst3k

Back up /home/mst3k from to to
directory /home/mst3k/zeus_backup. Use cron. Below is the crontab
entry. Put this text into a file crontab.txt and run the crontab
loading command:

crontab crontab.txt

Below is crontab.txt:

# field          allowed values
# -----          --------------
# minute         0-59
# hour           0-23
# day of month   1-31
# month          1-12 (or names, see below)
# day of week    0-7 (0 or 7 is Sun, or use names)

0 3 * * * /bin/date >> rsync-out.txt ; /bin/nice /usr/bin/rsync -avz --delete -e ssh /home/mst3k mst3k\ >> rsync-out.txt 2>&1

Now you have a backup, but how to verify that the files in the backup
are identical to the originals? Frequently backup are created without
errors or warnings, but the files are not readable for whatever
reason. This is a common occurance with tape systems, but can happen
when backing up to hard drive or optical media. You can check the file
checksums. This isn't complete (that would require a full restore, and
some way to test the restore). However, checksums will reveal some of
the more common failures.

Login to hera. 

cd /home/mst3k/zeus_backup/mst3k

find ./ -type f -exec sha1sum {} \; > ~/zeus_sums.txt

Login to zeus.

scp hera:zeus_sums.txt .

sha1sum -c anubis_sums.txt

Here is a portion of the output:

./.kde/Autostart/.directory: OK
./.ssh/authorized_keys: OK
./.ssh/id_dsa: OK
./.ssh/ OK
./.ssh/known_hosts: OK
./.ssh/known_hosts~: OK
./.xemacs/custom.el: OK
./.xemacs/custom.el~: OK
./.xemacs/init.el: OK
./.xemacs/init.el~: OK
./crontab.txt: OK
./crontab.txt~: OK
./public_html/cowpea/CVS/Repository: OK
./public_html/cowpea/CVS/Entries: OK
./public_html/cowpea/CVS/Root: OK
./error.txt: OK
./rsync-out.txt: FAILED
./tmp.txt: OK
./tmp.txt~: OK
./ OK
./ OK
sha1sum: WARNING: 1 of 667 computed checksums did NOT match

All the files on zeus match the backup on hera except rsync-out.txt
which is fine because that is the rsync log file and it should be out
of date.

If you delete some files from zeus, you'll get a warning like this:
sha1sum: WARNING: 1155 of 1822 listed files could not be read

Additional notes

As input we'll use the date command with nanoseconds. This is not
random and it would be far more clever to figure out how to get a few
bytes from /dev/random.

See this online page:

The various checksum digest commands have more or less the same
format, except openssl.

md5sum file

openssl dgst -type_of_checksum file

md5sum and similar programs print the checksum and the file name. If
the source was stdin, then the file name is -

Man pages have descriptions, although as of Fedora 8 in 2008, the
openssl has several digests not mentioned in the man page.

Available checksums from openssl seem to be:

md5, md4, md2, sha1, sha, mdc2, ripemd160,

as well as these undocumented digests:

sha256, sha384, sha512

Tab-complete from bash tells me these executables exist:
sha1sum    sha224sum  sha256sum  sha384sum  sha512sum

as well as the classic md5sum, and the older (?) cksum and sum.

[zeus ~]$ date --rfc-3339=ns
2008-03-26 10:30:12.586033647-04:00
[zeus ~]$ echo -n "2008-03-26 10:30:12.586033647-04:00" | openssl dgst -md5
[zeus ~]$ echo -n "2008-03-26 10:30:12.586033647-04:00" | md5sum
66eb0dd85a05053ded4e4b94cfa51b26  -
[zeus ~]$ echo -n "2008-03-26 10:30:12.586033647-04:00" | openssl dgst -sha1
[zeus ~]$ echo -n "2008-03-26 10:30:12.586033647-04:00" | sha1sum
b2e4c38153a14517a8290569ea860634001d4de3  -
[zeus ~]$ echo -n "2008-03-26 10:30:12.586033647-04:00" | openssl dgst -sha512
[zeus ~]$ echo -n "2008-03-26 10:30:12.586033647-04:00" | sha512sum
1b79e25e115affa870d7aeef06990b01b4df4a343f22b3a52cd1050a95da10839f60ce1a1475e6d6c9d8831b471a489c98d82e0a09b3632d7b68a3dff78402cc -
[zeus ~]$ echo -n "2008-03-26 10:30:12.586033647-04:00" | cksum
467202395 35
[zeus ~]$ echo -n "2008-03-26 10:30:12.586033647-04:00" | sum
02721     1
[zeus ~]$

I'm not entirely clear about cksum and sum, but they seem to be rarely used.

Several utilities such as md5sum have a mode to verify files. To run
the check you (or someone giving you files) runs md5sum and gives you
the file of the results. The check is performed by running md5sum in
--check mode using the file of the results. Here is a somewhat trivial
example. I've made a new directory, copied some Perl scripts into the
new directory. I ran md5sum on the originals, then cd'd to the
copy_dir and checked the copies.

[zeus ~]$ mkdir copy_dir
[zeus ~]$ cp -av *.pl ./copy_dir/
`' -> `./copy_dir/'
`' -> `./copy_dir/'
`' -> `./copy_dir/'
`' -> `./copy_dir/'
`' -> `./copy_dir/'
`' -> `./copy_dir/'
[zeus ~]$ md5sum *.pl > check_us.txt
[zeus ~]$ cd copy_dir/
[zeus copy_dir]$ md5sum --check ../check_us.txt OK OK OK OK OK OK
[zeus copy_dir]$